Accepted Manuscript Prevention of Cerebral Palsy, Autism Spectrum Disorder, and Attention Deficit - Hyperactivity Disorder Alan D. Strickland PII: DOI: Reference:
S0306-9877(14)00049-8 http://dx.doi.org/10.1016/j.mehy.2014.02.003 YMEHY 7501
To appear in:
Medical Hypotheses
Received Date: Accepted Date:
21 October 2013 3 February 2014
Please cite this article as: A.D. Strickland, Prevention of Cerebral Palsy, Autism Spectrum Disorder, and Attention Deficit - Hyperactivity Disorder, Medical Hypotheses (2014), doi: http://dx.doi.org/10.1016/j.mehy.2014.02.003
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Prevention of Cerebral Palsy, Autism Spectrum Disorder, and Attention Deficit - Hyperactivity Disorder
Alan D. Strickland, MD, DChem
Alan D. Strickland, MD, DChem 101 Waterlily Lake Jackson, TX 77566
Correspondence to: Alan D. Strickland, MD, DChem 101 Waterlily Lake Jackson, TX 77566 Telephone 979-373-4012 [email protected]
No grant support was used.
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ABSTRACT This hypothesis states that cerebral palsy (CP), autism spectrum disorder (ASD), and attention-deficit /hyperactivity disorder (ADHD) are all caused by an exaggerated central nervous system inflammatory response to a prenatal insult. This prenatal insult may be one or more episodes of ischemia–reperfusion, an infectious disease of the mother or the fetus, or other causes of maternal inflammation such as allergy or autoimmune disease. The resultant fetal inflammatory hyper-response injures susceptible neurons in the developing white matter of the brain in specific areas at specific gestational ages. The exaggerated neuroinflammatory response is theorized to occur between about 19 and 34 post-conception weeks for CP, about 32 and 40 weeks for ADHD, and about 36 and 48 weeks (i. e. 2 months after delivery) for ASD. The exaggerated inflammatory response is hypothesized to occur because present diets limit intake of effective antioxidants and omega-3 polyunsaturated fatty acids while increasing intake of omega6 polyunsaturated fatty acids. Oxidation products of the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) limit neuroinflammation while oxidation products of the omega-6 fatty acid arachidonic acid exacerbate inflammation. Preventative treatment should begin in all pregnant women during the first trimester and should include both DHA and an effective antioxidant for prevention of neuroinflammation. The suggested antioxidant would be N-acetylcysteine, though melatonin could be chosen instead. Combined DHA and NAC therapy is theorized to decrease the incidence of the three disorders by more than 75 percent.
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INTRODUCTION Cerebral palsy (CP) is the most common static motor disorder in children, currently affecting 3.3 children for every 1,000 live births in the United States. [1] The incidence appears to be rising. [2] There is no treatment for CP itself, so therapy is supportive and attempts to relieve problems caused by spastic muscles and lack of muscle coordination. Formerly, it was believed that CP resulted from anoxia during labor and delivery. In 1986, Nelson and Ellenberg reported on 45,559 children born at 12 academic centers. [3] They reviewed the mother’s health before pregnancy, the pregnancy records, the labor and delivery records, and the nursery records to determine which factors were associated with each child. They then obtained data from physical examinations until the children reached 7 years of age to determine which children had CP. They found that the factors associated with CP were determined before or during pregnancy and that labor and delivery added very little, if anything, to the cause of CP. Nelson’s conclusion is that CP cannot be prevented. [4] Known clinical correlates of CP include multiple gestation, male gender, intrauterine infections, maternal thyroid disease, maternal autoimmune disease, maternal coagulation disorders, premature birth, and fetal infections. [1, 5]
Autism Spectrum Disorder (ASD) is a family of neurological diagnoses (autism, Asperger’s syndrome, and pervasive developmental disorder) in which symptoms are first noticed after about 12 months of age, although retrospective analysis usually can identify symptoms by a few months of age. The affected children display difficulty with social interactions, varying degrees of language difficulty, and unusual behaviors such
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as rocking, becoming extremely upset over minor changes in the environment, or extreme reactions to odors, sounds, tastes, or the feel of objects. [6] The incidence of ASD is increasing rapidly with the latest estimate of incidence being 1 in every 88 children. [7] Because these disorders seem to appear during late infancy and early toddlerhood, many different causes have been postulated. Postulates that have been rejected include poor parenting skills, infant vaccinations, and various viral infections during infancy. About 10% of children with ASD have genetic abnormalities such as Down’s syndrome, fragile X syndrome, or tuberous sclerosis, so much effort is currently being expended to find a genetic basis for ASD. A recent review article suggests a combination of genetic and epigenetic factors (particularly suggesting brain-derived neurotropic factor, which is important in synaptic connections during learning and the synaptic pruning that occurs during late teenage years) in conjunction with environmental factors may be implicated in autism since older patients with autism show difficulty with synaptic plasticity. [8] Identified perinatal correlates with ASD include male gender (almost 5 to 1 ratio), prematurity, uterine bleeding (“threatened abortion”), older parents, fetal distress, C-section delivery, induced labor, 1 minute Apgar score below 7, and epidural anesthesia. [7, 9] By 7 years of life, children with ASD tend to have more problems than control children with constipation and diarrhea and to have different colonic flora, but these changes are probably due to specialized diets and the increased use of probiotics and fish oil in these children with ASD. [10] No medications are helpful and therapy is aimed at early intervention in training children to control symptoms as much as possible while training parents to encourage this symptom reduction.
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Attention deficit – hyperactivity disorder (ADHD) is a neurological malady in which children are quite distractible and/or have difficulty remaining still and quiet for normal lengths of time. [11] The degree to which a particular child is affected with either problem varies and the response to medications also varies. The prevalence of ADHD is also increasing and is currently calculated, using combined data from studies using DSM-IV criteria, at 13 children per every 100 children in the United States and 11 per 100 in other developed nations, though estimates vary from 2 to 20 per 100 children in various reports. [11] Poor parental discipline of the children was initially thought to be the etiology, and parental training in how to handle the children is still a major type of therapy. However, since treatment with amphetamine, atomoxetine, tricyclic antidepressants, and clonidine were found to improve the symptoms, ADHD was accepted as a neurological disorder and alterations of the central nervous system were sought. Factors associated with developing ADHD include maternal smoking during pregnancy, male gender, maternal urinary tract infection, and uterine bleeding (“threatened abortion”). [12] There seems to be some increase of ADHD in premature infants. The cause has not been proven, and genetic associations are being sought.
These disorders are currently understood as separate disorders with separate unknown etiologies – presumably genetic in ASD and ADHD and possibly with a genetic component in some cases of CP. As such, there is thought to be little hope of preventing these disorders other than through genetic counseling for pregnancies subsequent to an affected child.
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HYPOTHESIS This hypothesis states that CP, ASD, and ADHD are all the result of an exaggerated fetal central nervous system inflammatory response to a prenatal/perinatal insult (such as hypoxia, a maternal infection, a fetal infection, or a maternal inflammatory disease) with suggested timing of the insult to post-conception weeks 19 to 34 for CP, 32 to 40 for ADHD, and 36 to 48 (i. e. 2 months post delivery) for ASD. The hypothesis further states that deficiencies of dietary omega-3 fatty acids and antioxidants is the cause of the vigorous neuroinflammatory damage and that the increasing incidence of the disorders results from progressive decreases in the dietary supply of these nutrients. This single etiology would explain similarities in the prevalence of the disorders such as the increasing incidence of all three disorders, the male predominance in all three disorders, and the higher risk of all three disorders in prematurely born infants. The hypothesis states that substantial prevention of the three disorders should be possible by treating all pregnant women with docosahexaenoic acid and N-acetylcysteine (or possibly melatonin) starting in the first trimester.
Fetal Brain Formation in the Disorders The architecture and the major connections of the central nervous system develop in the fetal brain in a sequential fashion starting within the first few weeks of gestation and continuing through the first six months of post-natal life. [13, 14] Cerebral development continues, of course, after six months of post-natal life, but the emphasis changes around two months post-delivery from cellular proliferation and myelination to formation
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of synaptic networks. In addition to the vascular tissue of the central nervous system [15], five other cell types are involved in this development [13, 14]. The neurons are cells that will produce neurotransmitters and respond to the reception of neurotransmitters. The remaining four cell types are collectively named glial cells and are not part of the neurotransmission of nerve signals. Ependymal cells line the ventricles of the brain and the inner canal of the spinal cord as a protective layer, participate in the blood-brain barrier, circulate cerebrospinal fluid by their cilia, and form the choroid plexus producing cerebrospinal fluid. Astrocytes, noted for their fibrous processes, provide scaffolding, directional aide for migrating neurons, cushioning, and transport of nutrients from the blood vessels to the other central nervous system cells. This transport function allows the astrocytes to participate in the blood-brain barrier excluding certain substances and cells from the central nervous system. Microglial cells provide the innate immune system of the central nervous system. They produce and release cytokines and also phagocytize dead neural cells and foreign organisms. Oligodendrocytes produce myelin that is used to insulate nerve fibers and allow efficient transmission of electrical impulses without loss of energy to surrounding cells. The neurons, microglia, astrocytes, ependyma, and oligodendrocytes have different sensitivities and responses to intrauterine or perinatal events such as hyperbilirubinemia or hypoxia. [16, 17]
These five cell types do not, however, proliferate to the same degree during the stages of development of the central nervous system. Thus, during the first half of gestation, proliferation focuses on neurons and astrocytes as the neural plate, neural tube, and the
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folding of the caudal neural tube take place and expand. During these periods, neurons are being formed in germinal centers in the basal plate and then migrating radially along the fibrous processes of the astrocytes to reach the top layer of cells where horizontal migration may then occur to get the cell body to specific locations in various nuclei. [13, 14] This “inside out” formation can leave tracks of cell projections to connect different nuclei and allow nuclei with different neurotransmitters (serotonin, dopamine, glutamine, GABA, etc) to form and be connected with other nuclei. In a slightly delayed time period, angioneogenesis brings blood vessels to the fetal brain with the vessels penetrating in an “outside in” fashion. [15, 18] Thus, the deeper layers, the white matter of the brain, are supplied by smaller, higher pressure, terminal portions of the arteries while the gray matter is supplied by more proximal portions of arteries. [18, 19] Thus, the white matter is more exposed to ischemia from hypotension, stroke, or dehydration. Deeper structures in the white matter, such as the lenticular-capsular area and the basal ganglia are particularly vulnerable to these insults since they are supplied with very narrow, end-arteriolar vessels. [19, 20, 21] Microglial cells first appear as ameboid cells at 4.5 weeks gestation from the meninges, choroid plexus, and ventricles moving into the white matter of the telencephalon and diencephalon, especially concentrating in areas of junctions of white matter pathways. [22] The ameboid form of microglial cells are CD68 positive and are activated so that they can rapidly react immunologically. [22, 23, 24] By 10 to 12 weeks of gestation, these ameboid microglia accumulate at the interface between the subplate and cortical plate in the white matter of the subplate which contains the thalamocortical fibers. Another invasion of microglial cells occurs from 12 to 13 weeks of gestation, with the microglia apparently coming through the vascular
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system and remaining confined to white matter. [22] During 19 to 30 weeks of gestation, activated microglial cells are present in high concentrations in laminar regions of the white matter, particularly in three bands located in the lower subplate (thalamocortical tracts), subventricular zone and corpus callosum, and the periventricular zone. [22, 25] There is also microglial concentration in the tracts to the visual cortex. Microglia regulate the numbers of neurons in these areas due to their ability to phagocytize neurons as well as foreign cells. [26] Oligodendrocytes become more prominent during the final trimester and the first few months after birth when myelination of the neuronal axons is occurring. [25] The glutaminergic system, an excitatory system, develops during the last trimester. [27] The GABAergic system and nuclei serve as the chief inhibitory neurotransmission system and also develop later in gestation with their rapid proliferation occurring between 30 and 40 weeks of gestation. [28] Extensive modification of the GABAergic system continues until about 2 years postnatally.
Histopathology and Neuroimaging Studies in the Disorders
CP has been studied extensively by histopathology and by neuroimaging. MRI studies have found characteristic damage to specific areas of the white matter. In one report where 351 children with CP had MRI examinations, the most common white matter damage visible on MRI (over 40% of cases) was to the periventricular area with either leukomalacia or hemorrhage. [29] This periventricular white matter damage was present in 71% of infants having spastic diplegia, 35% of infants having spastic quadriplegia, and 34% of infants having spastic hemiplegia. The second most common area of
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damage was the basal ganglia and thalamus, accounting for about 13% of the cases of CP. Damage to these areas was present in 76% of children with dystonic CP, 12% of children with spastic quadriplegia, and 3% of children with spastic diplegia. Damage to the cortical or subcortical area (the striatum) was the third most common white matter damage seen on MRI at 9% of the cases. All types of CP except ataxic CP were seen in these children. Focal infarctions were present in 7% of the cases accounting for 27% of the spastic hemiplegia cases and 2% of the spastic quadriplegia cases. Malformations of the brain or other damage such as viral infections accounted for 16% of the cases of CP with a scatter of the types of CP. About 12% of the cases of CP had structurally normal MRI studies with over 50% of ataxic CP being associated with normal MRI. Ataxic CP has been related to genetic abnormalities. [30] Dyskinetic CP has been related to neonatal hyperbilirubinemia rather than MRI changes. [31]
Histopathology of human fetuses has shown that activated microglia are at high concentrations in the periventricular white matter during the 24th to 34th weeks of gestation. [32] These microglia are capable of causing cell death through free radical damage, cytokines, phagocytosis, and excitotoxicity. Post mortem examinations of CP patients have shown microglia and high concentrations of pro-inflammatory cytokines such as TNF-α and IL-1b in periventricular areas. [33] Other studies have also shown that the tissue has high levels of the cytokines interferon-gamma, tumor necrosis factoralpha, interleukin 2, and interleukin 6. [32] Immature, premyelinating oligodendrocytes are also present in high numbers in the periventricular white matter during these weeks
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and appear to be killed by the activated microglia. [25] Excitotoxicity through the glutamate transporters appears to occur and cause the death of neurons.
ASD has also been studied with histopathology and neuroimaging modalities, although not as extensively as CP. MRI studies show that even before 6 months of age, ASD patients have a significantly increased volume of cerebrospinal fluid in the subarachnoid space and a significantly increased cerebral volume compared to normal infants. Both of these abnormalities worsen through 24 months of postnatal age (when the study ended). [34] In spite of the increased cerebral volume, there are focal areas of decreased volume of gray matter in the fronto-striatal and parietal networks and reduction of white matter volume in the cerebellum, the left internal capsule, and the fornices. [35] Enlarged white matter volumes in certain areas such as the dorsolateral prefrontal cortex were investigated in 3 to 40 year old autism subjects and found to have increased volume secondary to excessive presence of microglial cells with their cell processes surrounding and enveloping neurons. This gliosis, though present early in life, worsens with age causing increasing neuronal disorganization. [36, 37] The presence of gliosis in these areas suggests that the enlarged white matter volumes are the result of neuroinflammation present early in life and continuing through at least age 40 years. Disrupted white matter could explain the decreases in gray matter because, since “white matter myelinated axons provide communication between different gray matter sites, disruptions in their integrity may also lead to gray matter alterations and changes in functional connectivity.” [38] No areas of gray matter were increased in volume in ASD patients. Many functional connectivity studies have shown problems with
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the fronto-parietal network and the temporo-parietal network, areas showing gliosis. [35, 38, 39] This immune dysfunction is correlated with increased behavioral problems in ASD and can persist from the perinatal period into adult life. [6, 40]
ADHD has also been the target of neuroimaging studies that have consistently shown abnormalities in the structure and function of the fronto-striatal network as well as dysfunction and decreased size of the basal ganglia. [41, 42, 43, 44, 45, 46] Other white matter tracts are also implicated in ADHD including the cerebellum (in the cerebellothalamo-striato-cortico network), corpus callosum, inferior parietal, occipito-parietal, inferior frontal, and inferior temporal areas. Since ADHD is not diagnosed typically until after 5 years of age, no human data about perinatal neuroinflammation or cytokines is available. Indeed, none of the five published post mortem examinations of ADHD patients report on neuropathology, focusing instead on the deaths due to toxic effects of the medications used to treat ADHD. However, since the neuroimaging studies show similar findings to those of CP in the fronto-striatal area and basal ganglia and to ASD in the cerebellar connections, it is reasonable to assume that similar events with microglial cytokine production and phagocytosis occurred at similar gestational times to cause those neural lesions. Additional evidence for a prenatal neuroinflammatory cause of ADHD comes from a study that identified 190 pairs of same-sex children discordant for ADHD. [47] Bacterial lipopolysaccharide was present in the ADHD affected twin and not in the unaffected twin with a p = 0.04 statistical significance
Neuroinflammation
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Thus, the literature evidence suggests that CP, ASD, and ADHD all have white matter structural and functional defects in areas that are at higher risk of ischemia due to smaller, high-pressure arteries and that correspond to prenatal concentrations of activated microglia that are capable of causing cell death, preventing myelination, and causing continued inflammation in response to either ischemia or an initial inflammatory insult. Cell membranes store polyunsaturated long chain fatty acids as phosphoglycerolipids. During inflammatory events, the cell membranes release these phosphoglycerolipids. Phospholipases (such as phospholipase A2 in the brain) hydrolyze the phospholipids to release these long chain polyunsaturated fatty acids. Reactive oxygen and reactive nitrogen species that are present due to initial microglial inflammatory responses can then be used by cyclooxygenases, lipoxidases, prostacyclin synthetase, and thromboxane synthetase to produce locally active ecosanoids such as prostaglandins, thromboxanes, and lipoxins. There is also some production of racemic ecosanoids, suggesting that the reactive oxygen species and reactive nitrogen species released in the inflammatory process can directly oxidize the long chain polyunsaturated fatty acids to produce inflammatory ecosanoids. [48, 49, 50] When the fatty acid utilized by these enzymes is arachidonic acid, produced from the dietary n-6 fatty acid linoleic acid, the resultant ecosanoids promote inflammation and lead to production of pro-inflammatory cytokines such as those mentioned above in CP. [51] When the fatty acids used by the enzymes are derived from the n-3 fatty acid family, the ecosanoids are generally anti-inflammatory and prevent generation of the cytokines mentioned above in CP. [51] The dietary source of n-3 fatty acids is gammalinolenic acid. It is processed by the same enzymes that are used to convert linoleic acid
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to arachidonic acid in a competitive manner to produce eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from the gamma-linolenic acid. A high ratio of linoleic acid to gamma-linolenic acid in the diet therefore results in abundant production of arachidonic acid and the diverting of gamma-linolenic acid into the oxidative pathway to produce energy.
Dietary Changes Causing Changes in Inflammatory Responses of the Fetus
Diets have been changing at the same time that the incidences of CP, ASD, and ADHD have been increasing. The United States Department of Agriculture has performed nation-wide nutritional surveys for several decades. These surveys have found that women of child-bearing age in the 21st century consume foods and supplements that only provide about half of the Vitamin E required for good nutrition so that over 97% of these women are getting inadequate amounts of this antioxidant that can penetrate the blood-brain barrier. [52] The surveys also show that these women of child-bearing age generally get 15 g of linoleic acid (omega 6 fatty acid precursor to arachidonic acid) and 1.5 g of gamma-linolenic acid (omega 3 precursor of EPA and DHA). The dietary ratio of omega 6 to omega 3 fatty acids formerly was much lower, probably close to 1 to 1. [53] The change in the omega 6 to omega 3 ratio in the diet began in the 1920s when costefficient methods of extracting vegetable oils were developed and intake of the resulting high-linoleic acid corn oil, safflower oil, and soybean oil began increasing. Partial hydrogenation to produce solid forms of vegetable oil selectively depletes omega 3 fatty acids, further increasing the ratio of omega 6 to omega 3 fatty acids. The practice of
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feeding grain rather than straw or grass to livestock to speed weight gain and protein storage further increases the omega 6 to omega 3 ratio in the human diet. Grains are high in omega 6 which then is stored in the chickens, cattle, and other livestock, replacing the omega 3 fatty acids that were present in livestock fed straw and leafy plant material, the plant parts richer in omega-3 fatty acids. Due to fears of probable mercury contamination of fatty fish, pregnant women and women who might become pregnant have been advised to avoid fatty fish, a good source of pre-formed EPA and DHA. Thus, another source of omega 3 fatty acids is missing from the maternal diet. These dietary changes have accelerated through the end of the 20th century as medical sources stressed changing to polyunsaturated vegetable oils, which are high in omega6 fatty acids, to avoid saturated fats and heart disease. Nuts, the usual source of vitamin E, were also discouraged in favor of a low fat diet. The fetal brain requires and stores large amounts of DHA during gestation. [54, 55] In the absence of adequate sources of DHA, arachidonic acid is stored instead. Thus, the combination of low vitamin E intake and an excess of omega 6 over omega 3 fatty acids in the diets of women who are bearing children would be producing fetuses that have an overabundance of central nervous system arachidonic acid with a paucity of DHA, a paucity of neurologic antioxidants, and microglia that are activated and ready to produce pro-inflammatory cytokines. These cytokines produce exaggerated inflammatory responses following either exposure to inflammatory lipopolysaccharides or to ischemiareperfusion episodes such as kinking of the umbilical cord, maternal hypotension, positional compromise of uterine blood flow, or inadequate uterine blood flow for multiple fetuses, especially triplets or more. The high incidence of CP, ASD, and ADHD
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in older mothers, threatened abortions (intrauterine bleeding), and mothers who smoke would reflect fetal hypoxia caused by compromised placentas and placental oxygenated blood flow. The degree to which ischemia causes fetal neuroinflammation would be expected to vary with gestational age as the oxygen requirement of the fetus increased throughout pregnancy and as the concentration of activated microglia changed in various portions of the brain. Premature birth is known to cause frequent episodes of hypoxia with reperfusion/hyperoxia following increased respiratory support. Inflammatory responses could also result from maternal or fetal infections or maternal allergic reactions or immunological disorders. [33, 56, 57] The male predominance in CP, ASD, and ADHD would be explained by this inflammatory etiology through the protective effect of estradiol on the fetal inflammatory response to reactive oxygen species, which would decrease the neuronal injury. [58]
Based on the knowledge of histopathology and neuroimaging in the three disorders and on the information about the timing and location of activated microglia, it is hypothesized that CP results from inflammatory insults between about 19 and about 34 weeks of gestation [32] while ADHD results from inflammatory insults from about 32 weeks to term (involving thalamic white matter tracts as well as glutaminergic and GABAergic tracts) and ASD results from inflammatory insults from about 36 weeks to several months after delivery (involving glutaminergic and GABAergic tracts). The importance of the GABAergic system in inhibition of excitation by neurons with other neurotransmitters would suggest the later time frame for inflammatory insults in ASD and ADHD. The lack of motor problems (spasticity or ataxia) in these two disorders would also suggest a
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later time of insult. Thus, treatment of pregnant women beginning before 13 weeks of gestation with DHA and NAC should substantially prevent the disorders in a similar fashion to the prevention of neural tube defects by administration of folic acid starting before pregnancy.
Animal studies in several species have shown that either a significant ischemic episode or exposure to bacterial lipopolysaccharide at gestational times representing 30 to 32 weeks in human gestation is capable of inducing neuroinflammatory responses in fetuses with resultant histological damage similar to that found in human CP. [59, 60, 61, 62, 63] In rabbits, prenatal ischemia also results in motor problems similar to human CP. [64] NAC protected fetal rabbits from lipopolysaccharide-induced inflammatory injury to the brain. [65] Prenatal hypoxia has also been shown to cause hyperactivity in rats similar to human ADHD, and antioxidants reduced or eliminated the hyperactivity. [63] Thus, animal data support the hypothesis that neuroinflammation is the cause of CP, ASD, and ADHD and that administration of antioxidants such as NAC during pregnancy could possibly prevent these disorders by controlling reactive oxidation and nitration species that cause the production of ecosanoids from arachidonic acid and result in the neuroinflammation. The addition of DHA to decrease the proinflammatory effect of excess arachidonic acid would be expected to improve the treatment.
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EVALUATION OF THE HYPOTHESIS The hypothesis that CP, ASD, and ADHD are the result of hyper-inflammatory responses in the fetal white matter (in different spatial locations at differing gestational ages) caused by the lack of both the antioxidant vitamin E and the anti-inflammatory omega 3 fatty acids in the maternal diet suggests that all three disorders could be prevented by proper administration of an anti-oxidant capable of reaching the fetal central nervous system and the administration of DHA. Animal models have been tested and support this hypothesis in CP and, in one study, in ADHD. Thus, it would seem that a human trial would be warranted as long as the safety of administering an anti-oxidant and DHA was established. DHA has been administered in studies of maternal depression at doses of 1 g per day accompanied by 1 gram EPA per day throughout pregnancy with no reported problems. [66]. Since laboratory studies have suggested that vitamin E is not adequate to prevent damage from reactive oxygen species, the use of N-acetylcysteine is suggested. It is effective in animal studies of fetal oxidative insult and is listed as having FDA approval for use in pregnancy with a class B status. [65, 67] Melatonin, another potent antioxidant which can penetrate the blood-brain barrier, has also been investigated in pregnant rats and found to prevent excessive inflammatory response to ischemia-reperfusion in the rat, so it could be used instead of NAC. [68, 69] Thus, a clinical trial should be performed with four cohorts – a cohort receiving both 1 g DHA per day and 600 mg NAC twice each day, a DHA group receiving 1 g DHA per day and Placebo N, an NAC group receiving Placebo D and 600 mg NAC twice each day, and a control cohort receiving Placebo D and Placebo N. The use of four groups would allow evaluation of the effectiveness of DHA and NAC individually and would allow
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determination of any synergy between the two treatments. Since development of the central nervous system, particularly the GABAergic system, continues after birth, the infants would be continued until six months of age on the same medications that the mothers took. The suggested postnatal dosage of DHA would be 200 mg per day and of NAC would be 100 mg twice per day for the infants. It might be reasonable to substitute vitamin E for the NAC after delivery, but continuing the same medication would prevent adding another variable to the study. Physical and neuropsychiatric examinations of the children would then be performed frequently until they reached seven years of age.
Using Chi-square contingency tables allows estimation of the size of human clinical trials that would be needed to test the hypothesis. Using the definitions: N = number of patients in each group p = prevalence (or incidence since this will involve newborns) of the disease expressed as number of cases per 1 live birth. This would mean that p is 1/88 = 0.011364 for ASD, p is 0.1 for ADHD (choosing a prevalence below the 11% and 13% from the article by Faraone [11]) , and p is 0.0033 for CP. dD = decimal decrease in prevalence of disease due to DHA dN = decimal decrease in prevalence of disease due to NAC y = decimal decrease in prevalence due to synergy of DHA and NAC where (dD + dN + y) must be less than or equal to 1 (since a 1 would imply eradication of the disorder). The contingency table is then:
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Table If There Is No Effect of Drugs
No DHA DHA
No Disease No NAC N-pN N-pN
No Disease NAC N-pN N-pN
Disease No NAC pN pN
Disease NAC pN pN
No Disease NAC N – (1-dN)pN N – (1-dD-dN-y)pN
Disease No NAC pN (1-dD)pN
Disease NAC (1-dN)pN (1-dD-dN-y)pN
Table Showing Drug Effect:
No DHA DHA
No Disease No NAC N-pN N - (1-dD)pN
Writing the equation for chi square, simplifying, and solving for N results in the formula: N = χ2 [(1-p)/p] / [dD2 + dN2 + (dD + dN + y)2] For four degrees of freedom and α = 0.05 the χ2 would be 9.488 and the values for p are given above for the three disorders. It remains to make estimates of dD, dN, and y to be able to estimate the number of participants needed for each cohort in the trial. Laboratory studies in rats suggest that the values of dN and dD could be very close to 1 individually. [68, 70, 71] For calculation of N, the assumption is made that dN = 0.65 and dD = 0.1 with y assumed to be zero – corresponding to the 75% reduction assumed above. With this assumption, the cohort size for CP would be 2881 (total trial 11,524 participants), the cohort size for ASD would be 830 (total trial 3,320 participants), and the cohort size for ADHD would be 86 (total trial 344 participants). With the assumption of dN = 0.8 and dD = 0.1 the cohort sizes become 1963 for CP (7852 total), 566 for ASD (2264 total), and 59 for ADHD (236 total). These are large trials that would probably require a multi-center study. With the inevitable loss to follow-up over a 5 to 7 year period of trying to follow the children, a dropout rate of at least 20% should be
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anticipated. It would be reasonable to suggest a study with cohort sizes 710 participants (total study size 2840, allowing for a 25% rate of dropout or loss to follow-up) to provide data at the α 0.05 level for ASD and at an α below 0.0001 for ADHD. These 2840 infants would have also been evaluated for CP. Thus, if the findings for ASD and/or ADHD were promising, the study could be extended to 10,000 pregnancies to obtain enough participants to examine the effects of the drugs on CP prevention.
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Consequences of the Hypothesis and Discussion If the hypothesis is correct that CP, ASD, and ADHD are three manifestations of prenatal or early postnatal neuroinflammatory hyper-response and that the dietary deficiency of DHA and effective central nervous system antioxidants seen in western society is allowing this to occur, treatment of all pregnant women with docosahexaenoic acid and an effective antioxidant such as N-acetylcysteine or melatonin would stop the current scourge of these disorders. From laboratory studies, a drop of 75% to 90% could be possible. If it is found that there are side effects to either of the treatments, evaluation of each woman for DHA status and antioxidant status could be used to identify the pregnancies at greatest risk and treat them selectively. Preventing CP, ASD, and ADHD would greatly benefit society in both economic savings and societal improvement. Schools would not be disrupted by the children with ASD and ADHD. The children would no longer require various compensations and treatments throughout their lives while falling short of their potentials. Parents would not have to endure the hardships involved in raising and providing for these individuals with many special needs. Much suffering would be prevented.
Conflict of Interest Statement The author states that he has no conflict of interest with relation to anything discussed in this article.
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Conflict of Interest Statement The author states that he has no conflict of interest with relation to anything discussed in this article.
S0306-9877(14)00049-8 http://dx.doi.org/10.1016/j.mehy.2014.02.003 YMEHY 7501
To appear in:
Medical Hypotheses
Received Date: Accepted Date:
21 October 2013 3 February 2014
Please cite this article as: A.D. Strickland, Prevention of Cerebral Palsy, Autism Spectrum Disorder, and Attention Deficit - Hyperactivity Disorder, Medical Hypotheses (2014), doi: http://dx.doi.org/10.1016/j.mehy.2014.02.003
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Prevention of Cerebral Palsy, Autism Spectrum Disorder, and Attention Deficit - Hyperactivity Disorder
Alan D. Strickland, MD, DChem
Alan D. Strickland, MD, DChem 101 Waterlily Lake Jackson, TX 77566
Correspondence to: Alan D. Strickland, MD, DChem 101 Waterlily Lake Jackson, TX 77566 Telephone 979-373-4012 [email protected]
No grant support was used.
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ABSTRACT This hypothesis states that cerebral palsy (CP), autism spectrum disorder (ASD), and attention-deficit /hyperactivity disorder (ADHD) are all caused by an exaggerated central nervous system inflammatory response to a prenatal insult. This prenatal insult may be one or more episodes of ischemia–reperfusion, an infectious disease of the mother or the fetus, or other causes of maternal inflammation such as allergy or autoimmune disease. The resultant fetal inflammatory hyper-response injures susceptible neurons in the developing white matter of the brain in specific areas at specific gestational ages. The exaggerated neuroinflammatory response is theorized to occur between about 19 and 34 post-conception weeks for CP, about 32 and 40 weeks for ADHD, and about 36 and 48 weeks (i. e. 2 months after delivery) for ASD. The exaggerated inflammatory response is hypothesized to occur because present diets limit intake of effective antioxidants and omega-3 polyunsaturated fatty acids while increasing intake of omega6 polyunsaturated fatty acids. Oxidation products of the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) limit neuroinflammation while oxidation products of the omega-6 fatty acid arachidonic acid exacerbate inflammation. Preventative treatment should begin in all pregnant women during the first trimester and should include both DHA and an effective antioxidant for prevention of neuroinflammation. The suggested antioxidant would be N-acetylcysteine, though melatonin could be chosen instead. Combined DHA and NAC therapy is theorized to decrease the incidence of the three disorders by more than 75 percent.
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INTRODUCTION Cerebral palsy (CP) is the most common static motor disorder in children, currently affecting 3.3 children for every 1,000 live births in the United States. [1] The incidence appears to be rising. [2] There is no treatment for CP itself, so therapy is supportive and attempts to relieve problems caused by spastic muscles and lack of muscle coordination. Formerly, it was believed that CP resulted from anoxia during labor and delivery. In 1986, Nelson and Ellenberg reported on 45,559 children born at 12 academic centers. [3] They reviewed the mother’s health before pregnancy, the pregnancy records, the labor and delivery records, and the nursery records to determine which factors were associated with each child. They then obtained data from physical examinations until the children reached 7 years of age to determine which children had CP. They found that the factors associated with CP were determined before or during pregnancy and that labor and delivery added very little, if anything, to the cause of CP. Nelson’s conclusion is that CP cannot be prevented. [4] Known clinical correlates of CP include multiple gestation, male gender, intrauterine infections, maternal thyroid disease, maternal autoimmune disease, maternal coagulation disorders, premature birth, and fetal infections. [1, 5]
Autism Spectrum Disorder (ASD) is a family of neurological diagnoses (autism, Asperger’s syndrome, and pervasive developmental disorder) in which symptoms are first noticed after about 12 months of age, although retrospective analysis usually can identify symptoms by a few months of age. The affected children display difficulty with social interactions, varying degrees of language difficulty, and unusual behaviors such
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as rocking, becoming extremely upset over minor changes in the environment, or extreme reactions to odors, sounds, tastes, or the feel of objects. [6] The incidence of ASD is increasing rapidly with the latest estimate of incidence being 1 in every 88 children. [7] Because these disorders seem to appear during late infancy and early toddlerhood, many different causes have been postulated. Postulates that have been rejected include poor parenting skills, infant vaccinations, and various viral infections during infancy. About 10% of children with ASD have genetic abnormalities such as Down’s syndrome, fragile X syndrome, or tuberous sclerosis, so much effort is currently being expended to find a genetic basis for ASD. A recent review article suggests a combination of genetic and epigenetic factors (particularly suggesting brain-derived neurotropic factor, which is important in synaptic connections during learning and the synaptic pruning that occurs during late teenage years) in conjunction with environmental factors may be implicated in autism since older patients with autism show difficulty with synaptic plasticity. [8] Identified perinatal correlates with ASD include male gender (almost 5 to 1 ratio), prematurity, uterine bleeding (“threatened abortion”), older parents, fetal distress, C-section delivery, induced labor, 1 minute Apgar score below 7, and epidural anesthesia. [7, 9] By 7 years of life, children with ASD tend to have more problems than control children with constipation and diarrhea and to have different colonic flora, but these changes are probably due to specialized diets and the increased use of probiotics and fish oil in these children with ASD. [10] No medications are helpful and therapy is aimed at early intervention in training children to control symptoms as much as possible while training parents to encourage this symptom reduction.
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Attention deficit – hyperactivity disorder (ADHD) is a neurological malady in which children are quite distractible and/or have difficulty remaining still and quiet for normal lengths of time. [11] The degree to which a particular child is affected with either problem varies and the response to medications also varies. The prevalence of ADHD is also increasing and is currently calculated, using combined data from studies using DSM-IV criteria, at 13 children per every 100 children in the United States and 11 per 100 in other developed nations, though estimates vary from 2 to 20 per 100 children in various reports. [11] Poor parental discipline of the children was initially thought to be the etiology, and parental training in how to handle the children is still a major type of therapy. However, since treatment with amphetamine, atomoxetine, tricyclic antidepressants, and clonidine were found to improve the symptoms, ADHD was accepted as a neurological disorder and alterations of the central nervous system were sought. Factors associated with developing ADHD include maternal smoking during pregnancy, male gender, maternal urinary tract infection, and uterine bleeding (“threatened abortion”). [12] There seems to be some increase of ADHD in premature infants. The cause has not been proven, and genetic associations are being sought.
These disorders are currently understood as separate disorders with separate unknown etiologies – presumably genetic in ASD and ADHD and possibly with a genetic component in some cases of CP. As such, there is thought to be little hope of preventing these disorders other than through genetic counseling for pregnancies subsequent to an affected child.
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HYPOTHESIS This hypothesis states that CP, ASD, and ADHD are all the result of an exaggerated fetal central nervous system inflammatory response to a prenatal/perinatal insult (such as hypoxia, a maternal infection, a fetal infection, or a maternal inflammatory disease) with suggested timing of the insult to post-conception weeks 19 to 34 for CP, 32 to 40 for ADHD, and 36 to 48 (i. e. 2 months post delivery) for ASD. The hypothesis further states that deficiencies of dietary omega-3 fatty acids and antioxidants is the cause of the vigorous neuroinflammatory damage and that the increasing incidence of the disorders results from progressive decreases in the dietary supply of these nutrients. This single etiology would explain similarities in the prevalence of the disorders such as the increasing incidence of all three disorders, the male predominance in all three disorders, and the higher risk of all three disorders in prematurely born infants. The hypothesis states that substantial prevention of the three disorders should be possible by treating all pregnant women with docosahexaenoic acid and N-acetylcysteine (or possibly melatonin) starting in the first trimester.
Fetal Brain Formation in the Disorders The architecture and the major connections of the central nervous system develop in the fetal brain in a sequential fashion starting within the first few weeks of gestation and continuing through the first six months of post-natal life. [13, 14] Cerebral development continues, of course, after six months of post-natal life, but the emphasis changes around two months post-delivery from cellular proliferation and myelination to formation
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of synaptic networks. In addition to the vascular tissue of the central nervous system [15], five other cell types are involved in this development [13, 14]. The neurons are cells that will produce neurotransmitters and respond to the reception of neurotransmitters. The remaining four cell types are collectively named glial cells and are not part of the neurotransmission of nerve signals. Ependymal cells line the ventricles of the brain and the inner canal of the spinal cord as a protective layer, participate in the blood-brain barrier, circulate cerebrospinal fluid by their cilia, and form the choroid plexus producing cerebrospinal fluid. Astrocytes, noted for their fibrous processes, provide scaffolding, directional aide for migrating neurons, cushioning, and transport of nutrients from the blood vessels to the other central nervous system cells. This transport function allows the astrocytes to participate in the blood-brain barrier excluding certain substances and cells from the central nervous system. Microglial cells provide the innate immune system of the central nervous system. They produce and release cytokines and also phagocytize dead neural cells and foreign organisms. Oligodendrocytes produce myelin that is used to insulate nerve fibers and allow efficient transmission of electrical impulses without loss of energy to surrounding cells. The neurons, microglia, astrocytes, ependyma, and oligodendrocytes have different sensitivities and responses to intrauterine or perinatal events such as hyperbilirubinemia or hypoxia. [16, 17]
These five cell types do not, however, proliferate to the same degree during the stages of development of the central nervous system. Thus, during the first half of gestation, proliferation focuses on neurons and astrocytes as the neural plate, neural tube, and the
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folding of the caudal neural tube take place and expand. During these periods, neurons are being formed in germinal centers in the basal plate and then migrating radially along the fibrous processes of the astrocytes to reach the top layer of cells where horizontal migration may then occur to get the cell body to specific locations in various nuclei. [13, 14] This “inside out” formation can leave tracks of cell projections to connect different nuclei and allow nuclei with different neurotransmitters (serotonin, dopamine, glutamine, GABA, etc) to form and be connected with other nuclei. In a slightly delayed time period, angioneogenesis brings blood vessels to the fetal brain with the vessels penetrating in an “outside in” fashion. [15, 18] Thus, the deeper layers, the white matter of the brain, are supplied by smaller, higher pressure, terminal portions of the arteries while the gray matter is supplied by more proximal portions of arteries. [18, 19] Thus, the white matter is more exposed to ischemia from hypotension, stroke, or dehydration. Deeper structures in the white matter, such as the lenticular-capsular area and the basal ganglia are particularly vulnerable to these insults since they are supplied with very narrow, end-arteriolar vessels. [19, 20, 21] Microglial cells first appear as ameboid cells at 4.5 weeks gestation from the meninges, choroid plexus, and ventricles moving into the white matter of the telencephalon and diencephalon, especially concentrating in areas of junctions of white matter pathways. [22] The ameboid form of microglial cells are CD68 positive and are activated so that they can rapidly react immunologically. [22, 23, 24] By 10 to 12 weeks of gestation, these ameboid microglia accumulate at the interface between the subplate and cortical plate in the white matter of the subplate which contains the thalamocortical fibers. Another invasion of microglial cells occurs from 12 to 13 weeks of gestation, with the microglia apparently coming through the vascular
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system and remaining confined to white matter. [22] During 19 to 30 weeks of gestation, activated microglial cells are present in high concentrations in laminar regions of the white matter, particularly in three bands located in the lower subplate (thalamocortical tracts), subventricular zone and corpus callosum, and the periventricular zone. [22, 25] There is also microglial concentration in the tracts to the visual cortex. Microglia regulate the numbers of neurons in these areas due to their ability to phagocytize neurons as well as foreign cells. [26] Oligodendrocytes become more prominent during the final trimester and the first few months after birth when myelination of the neuronal axons is occurring. [25] The glutaminergic system, an excitatory system, develops during the last trimester. [27] The GABAergic system and nuclei serve as the chief inhibitory neurotransmission system and also develop later in gestation with their rapid proliferation occurring between 30 and 40 weeks of gestation. [28] Extensive modification of the GABAergic system continues until about 2 years postnatally.
Histopathology and Neuroimaging Studies in the Disorders
CP has been studied extensively by histopathology and by neuroimaging. MRI studies have found characteristic damage to specific areas of the white matter. In one report where 351 children with CP had MRI examinations, the most common white matter damage visible on MRI (over 40% of cases) was to the periventricular area with either leukomalacia or hemorrhage. [29] This periventricular white matter damage was present in 71% of infants having spastic diplegia, 35% of infants having spastic quadriplegia, and 34% of infants having spastic hemiplegia. The second most common area of
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damage was the basal ganglia and thalamus, accounting for about 13% of the cases of CP. Damage to these areas was present in 76% of children with dystonic CP, 12% of children with spastic quadriplegia, and 3% of children with spastic diplegia. Damage to the cortical or subcortical area (the striatum) was the third most common white matter damage seen on MRI at 9% of the cases. All types of CP except ataxic CP were seen in these children. Focal infarctions were present in 7% of the cases accounting for 27% of the spastic hemiplegia cases and 2% of the spastic quadriplegia cases. Malformations of the brain or other damage such as viral infections accounted for 16% of the cases of CP with a scatter of the types of CP. About 12% of the cases of CP had structurally normal MRI studies with over 50% of ataxic CP being associated with normal MRI. Ataxic CP has been related to genetic abnormalities. [30] Dyskinetic CP has been related to neonatal hyperbilirubinemia rather than MRI changes. [31]
Histopathology of human fetuses has shown that activated microglia are at high concentrations in the periventricular white matter during the 24th to 34th weeks of gestation. [32] These microglia are capable of causing cell death through free radical damage, cytokines, phagocytosis, and excitotoxicity. Post mortem examinations of CP patients have shown microglia and high concentrations of pro-inflammatory cytokines such as TNF-α and IL-1b in periventricular areas. [33] Other studies have also shown that the tissue has high levels of the cytokines interferon-gamma, tumor necrosis factoralpha, interleukin 2, and interleukin 6. [32] Immature, premyelinating oligodendrocytes are also present in high numbers in the periventricular white matter during these weeks
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and appear to be killed by the activated microglia. [25] Excitotoxicity through the glutamate transporters appears to occur and cause the death of neurons.
ASD has also been studied with histopathology and neuroimaging modalities, although not as extensively as CP. MRI studies show that even before 6 months of age, ASD patients have a significantly increased volume of cerebrospinal fluid in the subarachnoid space and a significantly increased cerebral volume compared to normal infants. Both of these abnormalities worsen through 24 months of postnatal age (when the study ended). [34] In spite of the increased cerebral volume, there are focal areas of decreased volume of gray matter in the fronto-striatal and parietal networks and reduction of white matter volume in the cerebellum, the left internal capsule, and the fornices. [35] Enlarged white matter volumes in certain areas such as the dorsolateral prefrontal cortex were investigated in 3 to 40 year old autism subjects and found to have increased volume secondary to excessive presence of microglial cells with their cell processes surrounding and enveloping neurons. This gliosis, though present early in life, worsens with age causing increasing neuronal disorganization. [36, 37] The presence of gliosis in these areas suggests that the enlarged white matter volumes are the result of neuroinflammation present early in life and continuing through at least age 40 years. Disrupted white matter could explain the decreases in gray matter because, since “white matter myelinated axons provide communication between different gray matter sites, disruptions in their integrity may also lead to gray matter alterations and changes in functional connectivity.” [38] No areas of gray matter were increased in volume in ASD patients. Many functional connectivity studies have shown problems with
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the fronto-parietal network and the temporo-parietal network, areas showing gliosis. [35, 38, 39] This immune dysfunction is correlated with increased behavioral problems in ASD and can persist from the perinatal period into adult life. [6, 40]
ADHD has also been the target of neuroimaging studies that have consistently shown abnormalities in the structure and function of the fronto-striatal network as well as dysfunction and decreased size of the basal ganglia. [41, 42, 43, 44, 45, 46] Other white matter tracts are also implicated in ADHD including the cerebellum (in the cerebellothalamo-striato-cortico network), corpus callosum, inferior parietal, occipito-parietal, inferior frontal, and inferior temporal areas. Since ADHD is not diagnosed typically until after 5 years of age, no human data about perinatal neuroinflammation or cytokines is available. Indeed, none of the five published post mortem examinations of ADHD patients report on neuropathology, focusing instead on the deaths due to toxic effects of the medications used to treat ADHD. However, since the neuroimaging studies show similar findings to those of CP in the fronto-striatal area and basal ganglia and to ASD in the cerebellar connections, it is reasonable to assume that similar events with microglial cytokine production and phagocytosis occurred at similar gestational times to cause those neural lesions. Additional evidence for a prenatal neuroinflammatory cause of ADHD comes from a study that identified 190 pairs of same-sex children discordant for ADHD. [47] Bacterial lipopolysaccharide was present in the ADHD affected twin and not in the unaffected twin with a p = 0.04 statistical significance
Neuroinflammation
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Thus, the literature evidence suggests that CP, ASD, and ADHD all have white matter structural and functional defects in areas that are at higher risk of ischemia due to smaller, high-pressure arteries and that correspond to prenatal concentrations of activated microglia that are capable of causing cell death, preventing myelination, and causing continued inflammation in response to either ischemia or an initial inflammatory insult. Cell membranes store polyunsaturated long chain fatty acids as phosphoglycerolipids. During inflammatory events, the cell membranes release these phosphoglycerolipids. Phospholipases (such as phospholipase A2 in the brain) hydrolyze the phospholipids to release these long chain polyunsaturated fatty acids. Reactive oxygen and reactive nitrogen species that are present due to initial microglial inflammatory responses can then be used by cyclooxygenases, lipoxidases, prostacyclin synthetase, and thromboxane synthetase to produce locally active ecosanoids such as prostaglandins, thromboxanes, and lipoxins. There is also some production of racemic ecosanoids, suggesting that the reactive oxygen species and reactive nitrogen species released in the inflammatory process can directly oxidize the long chain polyunsaturated fatty acids to produce inflammatory ecosanoids. [48, 49, 50] When the fatty acid utilized by these enzymes is arachidonic acid, produced from the dietary n-6 fatty acid linoleic acid, the resultant ecosanoids promote inflammation and lead to production of pro-inflammatory cytokines such as those mentioned above in CP. [51] When the fatty acids used by the enzymes are derived from the n-3 fatty acid family, the ecosanoids are generally anti-inflammatory and prevent generation of the cytokines mentioned above in CP. [51] The dietary source of n-3 fatty acids is gammalinolenic acid. It is processed by the same enzymes that are used to convert linoleic acid
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to arachidonic acid in a competitive manner to produce eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) from the gamma-linolenic acid. A high ratio of linoleic acid to gamma-linolenic acid in the diet therefore results in abundant production of arachidonic acid and the diverting of gamma-linolenic acid into the oxidative pathway to produce energy.
Dietary Changes Causing Changes in Inflammatory Responses of the Fetus
Diets have been changing at the same time that the incidences of CP, ASD, and ADHD have been increasing. The United States Department of Agriculture has performed nation-wide nutritional surveys for several decades. These surveys have found that women of child-bearing age in the 21st century consume foods and supplements that only provide about half of the Vitamin E required for good nutrition so that over 97% of these women are getting inadequate amounts of this antioxidant that can penetrate the blood-brain barrier. [52] The surveys also show that these women of child-bearing age generally get 15 g of linoleic acid (omega 6 fatty acid precursor to arachidonic acid) and 1.5 g of gamma-linolenic acid (omega 3 precursor of EPA and DHA). The dietary ratio of omega 6 to omega 3 fatty acids formerly was much lower, probably close to 1 to 1. [53] The change in the omega 6 to omega 3 ratio in the diet began in the 1920s when costefficient methods of extracting vegetable oils were developed and intake of the resulting high-linoleic acid corn oil, safflower oil, and soybean oil began increasing. Partial hydrogenation to produce solid forms of vegetable oil selectively depletes omega 3 fatty acids, further increasing the ratio of omega 6 to omega 3 fatty acids. The practice of
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feeding grain rather than straw or grass to livestock to speed weight gain and protein storage further increases the omega 6 to omega 3 ratio in the human diet. Grains are high in omega 6 which then is stored in the chickens, cattle, and other livestock, replacing the omega 3 fatty acids that were present in livestock fed straw and leafy plant material, the plant parts richer in omega-3 fatty acids. Due to fears of probable mercury contamination of fatty fish, pregnant women and women who might become pregnant have been advised to avoid fatty fish, a good source of pre-formed EPA and DHA. Thus, another source of omega 3 fatty acids is missing from the maternal diet. These dietary changes have accelerated through the end of the 20th century as medical sources stressed changing to polyunsaturated vegetable oils, which are high in omega6 fatty acids, to avoid saturated fats and heart disease. Nuts, the usual source of vitamin E, were also discouraged in favor of a low fat diet. The fetal brain requires and stores large amounts of DHA during gestation. [54, 55] In the absence of adequate sources of DHA, arachidonic acid is stored instead. Thus, the combination of low vitamin E intake and an excess of omega 6 over omega 3 fatty acids in the diets of women who are bearing children would be producing fetuses that have an overabundance of central nervous system arachidonic acid with a paucity of DHA, a paucity of neurologic antioxidants, and microglia that are activated and ready to produce pro-inflammatory cytokines. These cytokines produce exaggerated inflammatory responses following either exposure to inflammatory lipopolysaccharides or to ischemiareperfusion episodes such as kinking of the umbilical cord, maternal hypotension, positional compromise of uterine blood flow, or inadequate uterine blood flow for multiple fetuses, especially triplets or more. The high incidence of CP, ASD, and ADHD
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in older mothers, threatened abortions (intrauterine bleeding), and mothers who smoke would reflect fetal hypoxia caused by compromised placentas and placental oxygenated blood flow. The degree to which ischemia causes fetal neuroinflammation would be expected to vary with gestational age as the oxygen requirement of the fetus increased throughout pregnancy and as the concentration of activated microglia changed in various portions of the brain. Premature birth is known to cause frequent episodes of hypoxia with reperfusion/hyperoxia following increased respiratory support. Inflammatory responses could also result from maternal or fetal infections or maternal allergic reactions or immunological disorders. [33, 56, 57] The male predominance in CP, ASD, and ADHD would be explained by this inflammatory etiology through the protective effect of estradiol on the fetal inflammatory response to reactive oxygen species, which would decrease the neuronal injury. [58]
Based on the knowledge of histopathology and neuroimaging in the three disorders and on the information about the timing and location of activated microglia, it is hypothesized that CP results from inflammatory insults between about 19 and about 34 weeks of gestation [32] while ADHD results from inflammatory insults from about 32 weeks to term (involving thalamic white matter tracts as well as glutaminergic and GABAergic tracts) and ASD results from inflammatory insults from about 36 weeks to several months after delivery (involving glutaminergic and GABAergic tracts). The importance of the GABAergic system in inhibition of excitation by neurons with other neurotransmitters would suggest the later time frame for inflammatory insults in ASD and ADHD. The lack of motor problems (spasticity or ataxia) in these two disorders would also suggest a
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later time of insult. Thus, treatment of pregnant women beginning before 13 weeks of gestation with DHA and NAC should substantially prevent the disorders in a similar fashion to the prevention of neural tube defects by administration of folic acid starting before pregnancy.
Animal studies in several species have shown that either a significant ischemic episode or exposure to bacterial lipopolysaccharide at gestational times representing 30 to 32 weeks in human gestation is capable of inducing neuroinflammatory responses in fetuses with resultant histological damage similar to that found in human CP. [59, 60, 61, 62, 63] In rabbits, prenatal ischemia also results in motor problems similar to human CP. [64] NAC protected fetal rabbits from lipopolysaccharide-induced inflammatory injury to the brain. [65] Prenatal hypoxia has also been shown to cause hyperactivity in rats similar to human ADHD, and antioxidants reduced or eliminated the hyperactivity. [63] Thus, animal data support the hypothesis that neuroinflammation is the cause of CP, ASD, and ADHD and that administration of antioxidants such as NAC during pregnancy could possibly prevent these disorders by controlling reactive oxidation and nitration species that cause the production of ecosanoids from arachidonic acid and result in the neuroinflammation. The addition of DHA to decrease the proinflammatory effect of excess arachidonic acid would be expected to improve the treatment.
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EVALUATION OF THE HYPOTHESIS The hypothesis that CP, ASD, and ADHD are the result of hyper-inflammatory responses in the fetal white matter (in different spatial locations at differing gestational ages) caused by the lack of both the antioxidant vitamin E and the anti-inflammatory omega 3 fatty acids in the maternal diet suggests that all three disorders could be prevented by proper administration of an anti-oxidant capable of reaching the fetal central nervous system and the administration of DHA. Animal models have been tested and support this hypothesis in CP and, in one study, in ADHD. Thus, it would seem that a human trial would be warranted as long as the safety of administering an anti-oxidant and DHA was established. DHA has been administered in studies of maternal depression at doses of 1 g per day accompanied by 1 gram EPA per day throughout pregnancy with no reported problems. [66]. Since laboratory studies have suggested that vitamin E is not adequate to prevent damage from reactive oxygen species, the use of N-acetylcysteine is suggested. It is effective in animal studies of fetal oxidative insult and is listed as having FDA approval for use in pregnancy with a class B status. [65, 67] Melatonin, another potent antioxidant which can penetrate the blood-brain barrier, has also been investigated in pregnant rats and found to prevent excessive inflammatory response to ischemia-reperfusion in the rat, so it could be used instead of NAC. [68, 69] Thus, a clinical trial should be performed with four cohorts – a cohort receiving both 1 g DHA per day and 600 mg NAC twice each day, a DHA group receiving 1 g DHA per day and Placebo N, an NAC group receiving Placebo D and 600 mg NAC twice each day, and a control cohort receiving Placebo D and Placebo N. The use of four groups would allow evaluation of the effectiveness of DHA and NAC individually and would allow
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determination of any synergy between the two treatments. Since development of the central nervous system, particularly the GABAergic system, continues after birth, the infants would be continued until six months of age on the same medications that the mothers took. The suggested postnatal dosage of DHA would be 200 mg per day and of NAC would be 100 mg twice per day for the infants. It might be reasonable to substitute vitamin E for the NAC after delivery, but continuing the same medication would prevent adding another variable to the study. Physical and neuropsychiatric examinations of the children would then be performed frequently until they reached seven years of age.
Using Chi-square contingency tables allows estimation of the size of human clinical trials that would be needed to test the hypothesis. Using the definitions: N = number of patients in each group p = prevalence (or incidence since this will involve newborns) of the disease expressed as number of cases per 1 live birth. This would mean that p is 1/88 = 0.011364 for ASD, p is 0.1 for ADHD (choosing a prevalence below the 11% and 13% from the article by Faraone [11]) , and p is 0.0033 for CP. dD = decimal decrease in prevalence of disease due to DHA dN = decimal decrease in prevalence of disease due to NAC y = decimal decrease in prevalence due to synergy of DHA and NAC where (dD + dN + y) must be less than or equal to 1 (since a 1 would imply eradication of the disorder). The contingency table is then:
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Table If There Is No Effect of Drugs
No DHA DHA
No Disease No NAC N-pN N-pN
No Disease NAC N-pN N-pN
Disease No NAC pN pN
Disease NAC pN pN
No Disease NAC N – (1-dN)pN N – (1-dD-dN-y)pN
Disease No NAC pN (1-dD)pN
Disease NAC (1-dN)pN (1-dD-dN-y)pN
Table Showing Drug Effect:
No DHA DHA
No Disease No NAC N-pN N - (1-dD)pN
Writing the equation for chi square, simplifying, and solving for N results in the formula: N = χ2 [(1-p)/p] / [dD2 + dN2 + (dD + dN + y)2] For four degrees of freedom and α = 0.05 the χ2 would be 9.488 and the values for p are given above for the three disorders. It remains to make estimates of dD, dN, and y to be able to estimate the number of participants needed for each cohort in the trial. Laboratory studies in rats suggest that the values of dN and dD could be very close to 1 individually. [68, 70, 71] For calculation of N, the assumption is made that dN = 0.65 and dD = 0.1 with y assumed to be zero – corresponding to the 75% reduction assumed above. With this assumption, the cohort size for CP would be 2881 (total trial 11,524 participants), the cohort size for ASD would be 830 (total trial 3,320 participants), and the cohort size for ADHD would be 86 (total trial 344 participants). With the assumption of dN = 0.8 and dD = 0.1 the cohort sizes become 1963 for CP (7852 total), 566 for ASD (2264 total), and 59 for ADHD (236 total). These are large trials that would probably require a multi-center study. With the inevitable loss to follow-up over a 5 to 7 year period of trying to follow the children, a dropout rate of at least 20% should be
20
anticipated. It would be reasonable to suggest a study with cohort sizes 710 participants (total study size 2840, allowing for a 25% rate of dropout or loss to follow-up) to provide data at the α 0.05 level for ASD and at an α below 0.0001 for ADHD. These 2840 infants would have also been evaluated for CP. Thus, if the findings for ASD and/or ADHD were promising, the study could be extended to 10,000 pregnancies to obtain enough participants to examine the effects of the drugs on CP prevention.
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Consequences of the Hypothesis and Discussion If the hypothesis is correct that CP, ASD, and ADHD are three manifestations of prenatal or early postnatal neuroinflammatory hyper-response and that the dietary deficiency of DHA and effective central nervous system antioxidants seen in western society is allowing this to occur, treatment of all pregnant women with docosahexaenoic acid and an effective antioxidant such as N-acetylcysteine or melatonin would stop the current scourge of these disorders. From laboratory studies, a drop of 75% to 90% could be possible. If it is found that there are side effects to either of the treatments, evaluation of each woman for DHA status and antioxidant status could be used to identify the pregnancies at greatest risk and treat them selectively. Preventing CP, ASD, and ADHD would greatly benefit society in both economic savings and societal improvement. Schools would not be disrupted by the children with ASD and ADHD. The children would no longer require various compensations and treatments throughout their lives while falling short of their potentials. Parents would not have to endure the hardships involved in raising and providing for these individuals with many special needs. Much suffering would be prevented.
Conflict of Interest Statement The author states that he has no conflict of interest with relation to anything discussed in this article.
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Conflict of Interest Statement The author states that he has no conflict of interest with relation to anything discussed in this article.
