British lournul of Hu~mutology.1992. 80, 1 1 7-120
The neurologic aspects of transcobalamin I1 deficiency CHARLESA. H A I , I , t Stratton Veterans Affairs Medical Center, Albany, New York
Received 4 June 1 9 9 1 ; accepted for publication 23 August 1991
Summary. Thirty-four symptomatic cases of inherited transcobalamin I1 (TCII) deficiency were analysed in order to determine the frequency and nature of neurologic manifestations. In no instance was there definite evidence of a neurologic disorder at the time of presentation as a young infant. One child of 24 years transiently lost deep tendon reflexes at a time of suboptimal treatment. A syndrome of
mental retardation and other neurologic manifestations was observed in three cases, all with the following in common: ( 1 ) a n extended duration of illness of 2-1 7 years: (2) inadequate or no treatment with Cbl; (3) treatment with folic or folinic acid. TCII deficiency rarely if ever presents with neurologic manifestations. However, neurologic disorders can be produced subsequently by improper treatment.
Acquired cobalamin (Cbl, vitamin B, *) deficiency of all types and age groups may cause symptoms, malfunction and anatomical lesions of the central nervous system (CNS)(Beck, 1988; Green & Jacobsen, 1990: Hall, 1990). The CNS is invariably involved in a congenital form of Cbl deficiency, methylcobalamin deficiency (Hall, 1990). The frequency of involvement of the CNS in another congenital disorder which results in tissue deficiency of Cbl, deficiency of the transport protein transcobalamin I1 (TCII),has neither been studied nor reported. TCII is a trace protein in plasma that binds Cbl as it is released from intrinsic factor within the enterocyte and binds Cbl released by tissues as it recycles, although it is not known whether this recycled Cbl binds to TCII within cells or in the circulation (Fig 1). TCII-Cbl is taken up by specific, high affinity receptors which have been observed in several human cells and this process is the means by which all tissues studied to date obtain their Cbl (Hall, 1989). Therefore, the individual with an inherited inability to synthesize a functional TCII cannot absorb Cbl nor transfer it into tissues and has. in effect, a systemic Cbl deficiency. Once internalized by endocytosis, the Cbl is split from the TCII-Cbl in the lysosomes and becomes available for the Cbl metabolism of the cell (Fig 1 ). TCII is not reutilized after giving up Cbl to tissue. Threequarters of the Cbl in plasma is carried by another carrier protein, haptocorrin (Hc) or K-binder, of unknown function. However, as will be discussed in more detail below, there could be a transport function ofHc in TCII deficiency. It might appear to be difficult to justify studying and reporting a single
facet of such a rare disorder but there are good reasons. The differential diagnosis among the several intracellular defects of Cbl metabolism, acquired Cbl deficiency and TCII deficiency in a very young infant can be exceedingly difficult. Any feature of the clinical presentation that will guide the subsequent evaluation in the right direction will assist in a prompt and correct diagnosis. The precise basis for the effect of any type of Cbl deficiency on the CNS remains unknown. Inherited defects affect a single point in Cbl metabolism and, as will be demonstrated here, the correlation between a point lesion and clinical expression can guide the direction of future basic research. PATIENT POPULATION AND METHODS The present analysis is based on 36 cases of the genotype TC2*SEA/TC2*SEA (Hall, 1 9 8 9 ) known to the author. Thirteen cases have been published as full papers and two cases as abstracts. Data of another 1 3 cases were obtained by personal communications with the physicians. The author was personally involved in the evaluation of the remaining eight cases. Seventeen out of 3 6 infants were symptomatic by age 1 month and another 11 by age 3 months. In those cases where sufficient data existed to make a positive or negative classification. almost all had weight loss and/or failure to thrive (2 1/22), vomiting and/or diarrhoea ( 2 0 / 2 0 ) ,lesions of the mouth (17119) and poor resistance to infections (18 / 2 2 ) . One infant was anaemic, whereas 23/27 had pancytopenia. The bone marrow was megaloblastic in 29 of the cases where there was sufficient information. The marrows of two infants were reported as hypoplastic without further comment. In 26 patients where serum Cbl levels were available, 19 were normal, two were low and five increased. The analysis of symptoms was based on 34 cases. Excluded
t Deceased. Correspondence: Dr Richard C. Chu, The Nutrition Laboratory for Clinical Assessment and Research ( 1 51E), Stratton Veterans Affairs Medical Center, 1 1 3 Holland Avenue, Albany, NY 12208. U.S.A. 117
118
Charles A. Hall
were a set of twins diagnosed at delivery and treated 3 weeks later without developing symptoms. There was specific information, positive or negative, about the CNS for 21/34 cases. There was insufficient data for the remaining 1 3 although had there been prominent CNS involvement, a comment would have been likely. RESULTS Two patients possibly had CNS manifestations at presentation. The information about both cases came from limited personal communication only. A 5-month-old child who presented with severe megaloblastic anaemia and a staphylococcal septicaemia had seizures.There is no mention of other symptoms referable to the CNS. A second infant presented at 6-7 months of age with failure to thrive, vomiting and anaemia. Possible truncal hypotonia. ataxia, and a delay in walking and talking were mentioned but there was no formal evaluation. At age 3 years he had achieved a normal psychomotor development. Both infants were older at presentation than the typical TCII deficient infant. The head circumference of a third child, who presented at 6 weeks in the classical way, was below the second percentile, although height and weight were at the 25th percentile. The neurological examination was normal and the child subsequently developed normally. Microcephaly is characteristic of infants of comparable age with other forms of Cbl deficiency (Hall, 1990) but there are virtually no data for TCII deficiency.
TC
There was clear evidence of CNS involvement during the course of their illness in the following four cases but none presented with CNS manifestations. K.C. (Zeitlin et al, 1985) became ill at age 10 d with vomiting, diarrhoea and fever with a response to a multiple vitamin preparation which supplied 12.5 pg of CN-Cbl per day. For the next 6 months there were relapses and remissions when the medication was stopped and restarted. At age 7 months megaloblastic anaemia was recognized and high-dose treatment with hydroxocobalamin (OH-Cbl),plus folic acid, was initiated. Developmental milestones were normal at the time. The diagnosis of TCII deficiency was not made for another 5 months and during the interval the clinical status fluctuated with changes in treatment. Between the ages of 1 and 2; years an attempt was made to maintain the child on oral OH-Cbl but the amount was clearly suboptimal and she lost the deep tendon reflexes in her legs. These were restored by an increase in dose. At age 6 years she was neurologically normal and doing well at school. V.P. (Mane etal, 1977; Gimferrer etal, 1981)was found to have megaloblastic anaemia at age 1 month but free of CNS symptoms. Her problem for 16 years was considered to be related to folate and not Cbl metabolism. Folic acid was the principal component of her treatment, although some Cbl was given intermittently and occasionally folinic acid. Over the years there were many interruptions in treatment with relapses. At age 1 3 years some loss of vision and mental retardation were first recorded. The diagnosis of TCII defi-
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+ H, +
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Methylmalonyl CoA Mutase
I
1
Neurology of TCZZ Deficiency ciency was made at age 16 years and appropriate amounts of Cbl given, although folic acid was not discontinued. The loss of vision and mild mental retardation stabilized. The family moved out of the country and the case was lost to follow-up. M.N. (Burman et al, 1979) presented at age 5 weeks with vomiting, diarrhoea and megaloblastic anaemia but no neurologic manifestations. He responded to a combination of folic acid and Cbl. There was a relapse at 1 year when treatment was stopped which was followed by 1 6 months of folic acid only. He then developed neurologic disease which consisted of a delay in walking until 2 years, a wide unsteady gait, inability to sit or speak and seizures. There are no details of treatment for the next 24 years when mental retardation and ataxia were noted. Between ages 8 and 1 6 years he received daily folic acid with Cbl every 4-6 weeks. His IQ was 60. speech was slurred, there was mild ataxia, he had choreiform movements of his hands and suffered severe seizures. The diagnosis of TCII deficiency was made at age 1 7 years and appropriate treatment with Cbl was initiated. A.F. (Tauro etal, 1976)presented at age4 weeks with poor feeding, pancytopenia and a megaloblastic bone marrow. There were no neurologic manifestations. The diagnosis of dihydrofolate reductase deficiency was made and he was treated for the next 2 years with folinic acid only. Normal physical and mental development were noted at age 6 months. He sat at 9 months and walked with help at 1 year. However, between 1 and 2 years there was severe neurologic regression with microcephaly, inability to sit, hypotonia, loss of some deep tendon reflexes, ataxia of arms, tonic seizures, and cerebral atrophy and ventricular dilatation by CT scan. The correct diagnosis of TCII deficiency was subsequently made (Thomas et a/, 1982; Hoffbrand et al, 1984) and the therapy changed from folic acid to OH-Cbl. At age 6 years he showed microcephaly. severe retardation, clumsy finger movements, unsteady gait, and exterior plantar reflexes. Speech comprehension was adequate but he could speak only about 1 2 single words. The CT scan was still abnormal but improved. The neurologic disorder in this child resembled closely that of MeCbl deficiency and acquired Cbl deficiency in infants of comparable age (Hall, 1990). DISCUSSION In summary, no infant with TCII deficiency has expressed definite neurologic manifestations at presentation. There was a transient loss of reflexes in one child after age 2+years when treatment became suboptimal. The three cases with definite and permanent neurologic injury had three factors in common: (1) a long duration of disease from 2 to 1 7 years: (2) inadequate or no treatment with Cbl, ( 3 ) treatment with folic or folinic acid. The relative significance of these factors is unknown. The need for Cbl is obvious. Folic acid in the absence of Cbl induces or aggravates the CNS manifestations of Cbl deficiency (Vilter u t a / , 1947). When neurologic manifestations accompany megaloblastic anaemia in the very young infant, congenital MeCbl deficiency or acquired Cbl deficiency are more likely than TCII deficiency. The absence of CNS manifestations at the initial presentation of TCII deficiency may be a factor of time. The dividing cells of
119
the gut, bone marrow and immune system which are severely affected by TCII deficiency as it typically presents prior to age 2 months may be dependent on a constant and immediate supply of TCII-Cbl. Other tissues, including brain and liver, may store Cbl from intrauterine life and be able to ride out the early weeks until the infant is treated. This is an unlikely explanation since the CNS is not affected in those infants diagnosed at age 2-6 months, a time when the CNS of infants with acquired Cbl deficiency and MeCbl deficiency is profoundly affected (Hall, 1990). Moreover, there are no late sequelae in properly treated cases of TCII deficiency,whereas in adequately treated MeCbl deficiency and acquired Cbl deficiency of infancy late CNS impairment is common (Hall, 1990). It must be noted that the clinical recognition of neurologic abnormalities may be most difficult in these very young and very sick infants. Is it possible that the CNS is not dependent on TCII for delivery of Cbl? Virtually all that is known about transport to the human CNS is from a study by Lazar & Carmel (1981). They observed small amounts of Cbl in the cerebrospinal fluid, most of it carried by TCII. Homogenates of human brain and spinal cord took up Cbl bound to TCII but not Cbl bound to R-binder (Hc). A continuation of this work with a determination of the actual mode of entry under physiological conditions is much needed. Endothelial cells contain receptors for TCII-Cbl (Quadros & Rothenberg, 1990) and possibly cells of the choroid plexus will take up TCII-Cbl. There is no free Cbl in the circulation except when Cbl is injected in large amounts (Hall et al. 1979) and uptake ofHcCbl by the CNS is most unlikely. It would appear. thus, that somehow the CNS does get Cbl from TCII, a hypothesis supported by the studies of Bhatt & Linnell (1990). Is it possible that the CNS depends less on intracellular Cbl than do some other tissues? An analysis of the CNS expression of MeCbl deficiency suggests that it is the lack of MeCbl, required as a methyl donor in methionine synthase activity, that is responsible for the CNS lesions (Hall, 1990). Methionine (Met) is a product of this reaction and possibly Met synthesized in other tissues can supply the needs of the CNS. Nitrous oxide (N20) inactivates MeCbl in the monkey, fruit bat and pig (Weir et al, 1988, 1990; Vieira-Makings et al, 1990). Met in the diet, to a large degree, ameliorated the development of spinal cord lesions induced by N 2 0 in these species. Thus, Met or a product of Met appears to enter the CNS and compensate for the loss of MeCbl. Van der Westhuyzen et al(198 5) showed N20to depress Met in the liver, brain and spinal cord of fruit bats and Met in the diet to restore it. Spector et al(1980)observed Met to enter rat brain as well as the synthesis of Met by the cells via the MeCbl-dependent Met synthase. If in TCII deficiency the CNS is protected by exogenous Met, where could this Met come from? The most likely source is the liver and, as noted above, slowly turning over Cbl that accumulates in the liver in utero could provide the CNS with enough Met to meet its needs until the infant IS either treated or dies. The liver may also get Cbl via Hc. Burger et al(19 7 5) showed that the liver of the rabbit took up Hc-Cbl by the receptor system responsive to asialoglycoproteins in general. Whereas we observed the uptake of Hc-Cbl by human
120
Charles A. Hall
hepatocytes to be inefficient as compared to uptake by the receptor system for TCII and subject to other limiting factors, Hc-Cbl can enter hepatocytes (Hall et al, 1989). Possibly through the combination of retained Cbl, small amounts of Cbl uptake from Hc and betaine dependent Met synthesis, enough Met can be supplied by the liver to protect the CNS. There is almost no data on Met status in TCII deficiency but we recently observed a case (unpublished) with normal serum Met and normal serum homocysteine (Hcy). These observations contrast with MeCbl deficiency where Cbldependent Met synthesis is depressed in all tissues and serum Met is low while serum Hcy is much increased (Hall, 1990). The body Hcy is increased and the plasma Met low in acquired Cbl deficiency of infancy as well (Higginbottom et al, 1978). The data from this one case of TCII deficiency suggest that substantial Met synthesis was taking place in some tissue. ACKNOWLEDGMENT The author’s work was supported by the Research Service of the Department of Veterans Affairs. KEFERENCES Beck, W.S. (1988) Cobalamin and the nervous system. New England journal of Medicine, 318, 1752-1 754. Burger. R.L., Schneider, R.J.. Mehlman. C.S. & Allen, R.H. (1975) Human plasma K-type vitamin B12-binding proteins. Journal of Biological Chemistry. 250, 7707-771 3. Bhatt, H.R. & Linnell, J.C. (1990) Cobalamin influx into the brain of the rat in vivo. Biomedicine and Physiology q/Vitamin B12 (ed. by J. C. Linnell and H. R . Bhatt). p. 97. The Children’s Medical Charity. London. Burman. J.F., Mollin, D.L., Sourial, N.A. & Sladden, R.A. (1979) Inherited lack of transcobalamin 11 in serum and megaloblastic anaemia: a further patient. British journal qfHaematology. 43.2 738.
Gimferrer. E.. Mane, J. Vives. Baiget, M.. Vives-Corrons, 1.L.. Barcelo. M.J.. Fabrega, J,, Hall, C.A. & Begley, J.A. (1981) Inherited deficiency of transcobolamin I1 in a Spanish woman. Biologia y Clinica Hematologica, 3, 267-270. Green, R. & Jacobsen. D.W. (1990) The role of cobalamins in the nervous system. Biomedicine and Physiologg of Vitamin B 1 2 (ed. by J. C. Linnell and H. R. Bhatt), p. 107. The Children’sMedical Charity, London. Hall, C.A. (1989) The proteins of transport of the cobalamins. Folutes and Cobalamins (ed. by J. A. Zittoun and B. A. Cooper), p. 53. Springer, Berlin. Hall, C.A. (1990) Function of vitamin Blz in the central nervous system as revealed by congenital defects. American journal of Hematology. 34, 121-127. Hall, C.A..Hitzig, W.H., Green, P.D. &Begley,J.A. (1979) Transport
of therapeutic cyanocobalamin in the congenital deficiency of transcobalamin I1 (TCII). Blood, 53, 251-263. Higginbottom, M.C., Sweetman, L. & Nyhan. W.L. (1978) A syndrome of methylmalonic aciduria. homocystinuria. megaloblastic anemia and neurologic abnormalities in a vitamin BIZdeficient breast-fed infant of a strict vegetarian. New England journal of Medicine, 299, 3 17-323. Hoffbrand. A.V., Tripp, E., Jackson, B.F.A. & Luck, W.E. (1984) Hereditary abnormal transcobalamin 11 previously diagnosed as congenital dihydrofolate reductase deficiency. New England journal of Medicine. 310, 789-790. Lazar. G.S. & Carmel, R. (1981) Cobalamin binding and uptake in vitro in the human central nervous system. journal of Laboratory arid Clinical Medicine. 97, 123-1 33. Mane, J. Vives, Vives-Corrons, J.L. & Roxman, D. ( 1 977) Congenital folatc-depcndcnt mcgaloblastic anaemia of unknown aetiology. Lancet, i, 262-263. Quadros, E.V. & Rothenberg, S.P. (1990) The structure and biosynthesis of human transcobalamin 11. Biomedicine and Physiology of Vitamin B l 2 (ed. by J. C. Linnell and H. R. Bhatt). p. 281. The Children’s Medical Charity, London. Spector. R.. Coakley, G. & Blakely. R. (198U) Methioninc recycling in brain: A role for folates and vitamin B, L. journal ofhieurochetnistry. 34, 132-1 37. Tauro. G.P.. Danks. D.M.. Row, P.B., Van der Weyden, M.B., Schwarz. M.A., Collins, V.L. & Neal, B.W. (1976) Dihydrofolate reductase deficiency causing megaloblastic anemia in two families. New England journal of Medicine. 294, 466-470. Thomas, P.K.. Hofirand, A.V. & Smith, 1,s. (1982) Neurological involvement in hereditary transcobalamin I1 deficiency. Journal of Neurology, Neurosurgery, and Psychiatry. 45, 74-77. Van der Westhuyzen. J.. Van Tonder, S.V., Gibson, J.E.. Kilroe-Smith. T.A. & Metz, j. (1 98 5) Plasma amino acids and tissue methionine levels in fruit bats (Rousettus aegyptiacus) with nitrous oxidcinduced vitamin Bll deficiency. British journal of Nutrition. 5 3 , 657-662.
Vilter, C.F.. Vilter, R.W. & Spies, T.D. (1947) The treatment of pernicious and related anemias with synthetic folic acid. Journal of I d m a t o r y and Clinical Medicine. 32, 262-273. Viera-Makings, E., Metz. J., Van der Westhuyxen, J., Bottiglieri, T. & Chanarin. I. (1990) Cobalamin neuropathy. Is S-adenosylhomocysteine toxicity a factor? Biochemistry Journal, 266, 707-71 1. Weir, D.G., Keating, S., Molloy. A,. McPartlin. J.. Kennedy, S., Blanchflower, J., Kennedy. D.G., Rice, D. & Scott. J.M. (1988) Methylation deficiency causes vitamin BI2-associatedneuropathy in the pig. journal of Neurochrmistry, 5 1 , 1949-1952. Weir, D.G., Molloy. A,, Keating, J.N.. McPartlin, J., Kennedy, S., Blanchflower. J., Rice, D. & Scott, J.M. (1 990) Hypomethylation produces vitamin B12 associated neuropath in the pig. Biomedicine and Physiology of Vitamin B11 (ed. by J. C. Linnell and H. R. Bhatt), p. 129. The Children’s Medical Charity, London. Zeitlin, H.C., Sheppard, K.. Baum, J.D., Bolton, F.G. & Hall, C.A. ( 1 985) HomoLygous transcobalamin I1 deficiency maintained on oral hydroxocobalamin. Blood, 66, 1022-1 027.
The neurologic aspects of transcobalamin I1 deficiency CHARLESA. H A I , I , t Stratton Veterans Affairs Medical Center, Albany, New York
Received 4 June 1 9 9 1 ; accepted for publication 23 August 1991
Summary. Thirty-four symptomatic cases of inherited transcobalamin I1 (TCII) deficiency were analysed in order to determine the frequency and nature of neurologic manifestations. In no instance was there definite evidence of a neurologic disorder at the time of presentation as a young infant. One child of 24 years transiently lost deep tendon reflexes at a time of suboptimal treatment. A syndrome of
mental retardation and other neurologic manifestations was observed in three cases, all with the following in common: ( 1 ) a n extended duration of illness of 2-1 7 years: (2) inadequate or no treatment with Cbl; (3) treatment with folic or folinic acid. TCII deficiency rarely if ever presents with neurologic manifestations. However, neurologic disorders can be produced subsequently by improper treatment.
Acquired cobalamin (Cbl, vitamin B, *) deficiency of all types and age groups may cause symptoms, malfunction and anatomical lesions of the central nervous system (CNS)(Beck, 1988; Green & Jacobsen, 1990: Hall, 1990). The CNS is invariably involved in a congenital form of Cbl deficiency, methylcobalamin deficiency (Hall, 1990). The frequency of involvement of the CNS in another congenital disorder which results in tissue deficiency of Cbl, deficiency of the transport protein transcobalamin I1 (TCII),has neither been studied nor reported. TCII is a trace protein in plasma that binds Cbl as it is released from intrinsic factor within the enterocyte and binds Cbl released by tissues as it recycles, although it is not known whether this recycled Cbl binds to TCII within cells or in the circulation (Fig 1). TCII-Cbl is taken up by specific, high affinity receptors which have been observed in several human cells and this process is the means by which all tissues studied to date obtain their Cbl (Hall, 1989). Therefore, the individual with an inherited inability to synthesize a functional TCII cannot absorb Cbl nor transfer it into tissues and has. in effect, a systemic Cbl deficiency. Once internalized by endocytosis, the Cbl is split from the TCII-Cbl in the lysosomes and becomes available for the Cbl metabolism of the cell (Fig 1 ). TCII is not reutilized after giving up Cbl to tissue. Threequarters of the Cbl in plasma is carried by another carrier protein, haptocorrin (Hc) or K-binder, of unknown function. However, as will be discussed in more detail below, there could be a transport function ofHc in TCII deficiency. It might appear to be difficult to justify studying and reporting a single
facet of such a rare disorder but there are good reasons. The differential diagnosis among the several intracellular defects of Cbl metabolism, acquired Cbl deficiency and TCII deficiency in a very young infant can be exceedingly difficult. Any feature of the clinical presentation that will guide the subsequent evaluation in the right direction will assist in a prompt and correct diagnosis. The precise basis for the effect of any type of Cbl deficiency on the CNS remains unknown. Inherited defects affect a single point in Cbl metabolism and, as will be demonstrated here, the correlation between a point lesion and clinical expression can guide the direction of future basic research. PATIENT POPULATION AND METHODS The present analysis is based on 36 cases of the genotype TC2*SEA/TC2*SEA (Hall, 1 9 8 9 ) known to the author. Thirteen cases have been published as full papers and two cases as abstracts. Data of another 1 3 cases were obtained by personal communications with the physicians. The author was personally involved in the evaluation of the remaining eight cases. Seventeen out of 3 6 infants were symptomatic by age 1 month and another 11 by age 3 months. In those cases where sufficient data existed to make a positive or negative classification. almost all had weight loss and/or failure to thrive (2 1/22), vomiting and/or diarrhoea ( 2 0 / 2 0 ) ,lesions of the mouth (17119) and poor resistance to infections (18 / 2 2 ) . One infant was anaemic, whereas 23/27 had pancytopenia. The bone marrow was megaloblastic in 29 of the cases where there was sufficient information. The marrows of two infants were reported as hypoplastic without further comment. In 26 patients where serum Cbl levels were available, 19 were normal, two were low and five increased. The analysis of symptoms was based on 34 cases. Excluded
t Deceased. Correspondence: Dr Richard C. Chu, The Nutrition Laboratory for Clinical Assessment and Research ( 1 51E), Stratton Veterans Affairs Medical Center, 1 1 3 Holland Avenue, Albany, NY 12208. U.S.A. 117
118
Charles A. Hall
were a set of twins diagnosed at delivery and treated 3 weeks later without developing symptoms. There was specific information, positive or negative, about the CNS for 21/34 cases. There was insufficient data for the remaining 1 3 although had there been prominent CNS involvement, a comment would have been likely. RESULTS Two patients possibly had CNS manifestations at presentation. The information about both cases came from limited personal communication only. A 5-month-old child who presented with severe megaloblastic anaemia and a staphylococcal septicaemia had seizures.There is no mention of other symptoms referable to the CNS. A second infant presented at 6-7 months of age with failure to thrive, vomiting and anaemia. Possible truncal hypotonia. ataxia, and a delay in walking and talking were mentioned but there was no formal evaluation. At age 3 years he had achieved a normal psychomotor development. Both infants were older at presentation than the typical TCII deficient infant. The head circumference of a third child, who presented at 6 weeks in the classical way, was below the second percentile, although height and weight were at the 25th percentile. The neurological examination was normal and the child subsequently developed normally. Microcephaly is characteristic of infants of comparable age with other forms of Cbl deficiency (Hall, 1990) but there are virtually no data for TCII deficiency.
TC
There was clear evidence of CNS involvement during the course of their illness in the following four cases but none presented with CNS manifestations. K.C. (Zeitlin et al, 1985) became ill at age 10 d with vomiting, diarrhoea and fever with a response to a multiple vitamin preparation which supplied 12.5 pg of CN-Cbl per day. For the next 6 months there were relapses and remissions when the medication was stopped and restarted. At age 7 months megaloblastic anaemia was recognized and high-dose treatment with hydroxocobalamin (OH-Cbl),plus folic acid, was initiated. Developmental milestones were normal at the time. The diagnosis of TCII deficiency was not made for another 5 months and during the interval the clinical status fluctuated with changes in treatment. Between the ages of 1 and 2; years an attempt was made to maintain the child on oral OH-Cbl but the amount was clearly suboptimal and she lost the deep tendon reflexes in her legs. These were restored by an increase in dose. At age 6 years she was neurologically normal and doing well at school. V.P. (Mane etal, 1977; Gimferrer etal, 1981)was found to have megaloblastic anaemia at age 1 month but free of CNS symptoms. Her problem for 16 years was considered to be related to folate and not Cbl metabolism. Folic acid was the principal component of her treatment, although some Cbl was given intermittently and occasionally folinic acid. Over the years there were many interruptions in treatment with relapses. At age 1 3 years some loss of vision and mental retardation were first recorded. The diagnosis of TCII defi-
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Methylmalonyl CoA Mutase
I
1
Neurology of TCZZ Deficiency ciency was made at age 16 years and appropriate amounts of Cbl given, although folic acid was not discontinued. The loss of vision and mild mental retardation stabilized. The family moved out of the country and the case was lost to follow-up. M.N. (Burman et al, 1979) presented at age 5 weeks with vomiting, diarrhoea and megaloblastic anaemia but no neurologic manifestations. He responded to a combination of folic acid and Cbl. There was a relapse at 1 year when treatment was stopped which was followed by 1 6 months of folic acid only. He then developed neurologic disease which consisted of a delay in walking until 2 years, a wide unsteady gait, inability to sit or speak and seizures. There are no details of treatment for the next 24 years when mental retardation and ataxia were noted. Between ages 8 and 1 6 years he received daily folic acid with Cbl every 4-6 weeks. His IQ was 60. speech was slurred, there was mild ataxia, he had choreiform movements of his hands and suffered severe seizures. The diagnosis of TCII deficiency was made at age 1 7 years and appropriate treatment with Cbl was initiated. A.F. (Tauro etal, 1976)presented at age4 weeks with poor feeding, pancytopenia and a megaloblastic bone marrow. There were no neurologic manifestations. The diagnosis of dihydrofolate reductase deficiency was made and he was treated for the next 2 years with folinic acid only. Normal physical and mental development were noted at age 6 months. He sat at 9 months and walked with help at 1 year. However, between 1 and 2 years there was severe neurologic regression with microcephaly, inability to sit, hypotonia, loss of some deep tendon reflexes, ataxia of arms, tonic seizures, and cerebral atrophy and ventricular dilatation by CT scan. The correct diagnosis of TCII deficiency was subsequently made (Thomas et a/, 1982; Hoffbrand et al, 1984) and the therapy changed from folic acid to OH-Cbl. At age 6 years he showed microcephaly. severe retardation, clumsy finger movements, unsteady gait, and exterior plantar reflexes. Speech comprehension was adequate but he could speak only about 1 2 single words. The CT scan was still abnormal but improved. The neurologic disorder in this child resembled closely that of MeCbl deficiency and acquired Cbl deficiency in infants of comparable age (Hall, 1990). DISCUSSION In summary, no infant with TCII deficiency has expressed definite neurologic manifestations at presentation. There was a transient loss of reflexes in one child after age 2+years when treatment became suboptimal. The three cases with definite and permanent neurologic injury had three factors in common: (1) a long duration of disease from 2 to 1 7 years: (2) inadequate or no treatment with Cbl, ( 3 ) treatment with folic or folinic acid. The relative significance of these factors is unknown. The need for Cbl is obvious. Folic acid in the absence of Cbl induces or aggravates the CNS manifestations of Cbl deficiency (Vilter u t a / , 1947). When neurologic manifestations accompany megaloblastic anaemia in the very young infant, congenital MeCbl deficiency or acquired Cbl deficiency are more likely than TCII deficiency. The absence of CNS manifestations at the initial presentation of TCII deficiency may be a factor of time. The dividing cells of
119
the gut, bone marrow and immune system which are severely affected by TCII deficiency as it typically presents prior to age 2 months may be dependent on a constant and immediate supply of TCII-Cbl. Other tissues, including brain and liver, may store Cbl from intrauterine life and be able to ride out the early weeks until the infant is treated. This is an unlikely explanation since the CNS is not affected in those infants diagnosed at age 2-6 months, a time when the CNS of infants with acquired Cbl deficiency and MeCbl deficiency is profoundly affected (Hall, 1990). Moreover, there are no late sequelae in properly treated cases of TCII deficiency,whereas in adequately treated MeCbl deficiency and acquired Cbl deficiency of infancy late CNS impairment is common (Hall, 1990). It must be noted that the clinical recognition of neurologic abnormalities may be most difficult in these very young and very sick infants. Is it possible that the CNS is not dependent on TCII for delivery of Cbl? Virtually all that is known about transport to the human CNS is from a study by Lazar & Carmel (1981). They observed small amounts of Cbl in the cerebrospinal fluid, most of it carried by TCII. Homogenates of human brain and spinal cord took up Cbl bound to TCII but not Cbl bound to R-binder (Hc). A continuation of this work with a determination of the actual mode of entry under physiological conditions is much needed. Endothelial cells contain receptors for TCII-Cbl (Quadros & Rothenberg, 1990) and possibly cells of the choroid plexus will take up TCII-Cbl. There is no free Cbl in the circulation except when Cbl is injected in large amounts (Hall et al. 1979) and uptake ofHcCbl by the CNS is most unlikely. It would appear. thus, that somehow the CNS does get Cbl from TCII, a hypothesis supported by the studies of Bhatt & Linnell (1990). Is it possible that the CNS depends less on intracellular Cbl than do some other tissues? An analysis of the CNS expression of MeCbl deficiency suggests that it is the lack of MeCbl, required as a methyl donor in methionine synthase activity, that is responsible for the CNS lesions (Hall, 1990). Methionine (Met) is a product of this reaction and possibly Met synthesized in other tissues can supply the needs of the CNS. Nitrous oxide (N20) inactivates MeCbl in the monkey, fruit bat and pig (Weir et al, 1988, 1990; Vieira-Makings et al, 1990). Met in the diet, to a large degree, ameliorated the development of spinal cord lesions induced by N 2 0 in these species. Thus, Met or a product of Met appears to enter the CNS and compensate for the loss of MeCbl. Van der Westhuyzen et al(198 5) showed N20to depress Met in the liver, brain and spinal cord of fruit bats and Met in the diet to restore it. Spector et al(1980)observed Met to enter rat brain as well as the synthesis of Met by the cells via the MeCbl-dependent Met synthase. If in TCII deficiency the CNS is protected by exogenous Met, where could this Met come from? The most likely source is the liver and, as noted above, slowly turning over Cbl that accumulates in the liver in utero could provide the CNS with enough Met to meet its needs until the infant IS either treated or dies. The liver may also get Cbl via Hc. Burger et al(19 7 5) showed that the liver of the rabbit took up Hc-Cbl by the receptor system responsive to asialoglycoproteins in general. Whereas we observed the uptake of Hc-Cbl by human
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hepatocytes to be inefficient as compared to uptake by the receptor system for TCII and subject to other limiting factors, Hc-Cbl can enter hepatocytes (Hall et al, 1989). Possibly through the combination of retained Cbl, small amounts of Cbl uptake from Hc and betaine dependent Met synthesis, enough Met can be supplied by the liver to protect the CNS. There is almost no data on Met status in TCII deficiency but we recently observed a case (unpublished) with normal serum Met and normal serum homocysteine (Hcy). These observations contrast with MeCbl deficiency where Cbldependent Met synthesis is depressed in all tissues and serum Met is low while serum Hcy is much increased (Hall, 1990). The body Hcy is increased and the plasma Met low in acquired Cbl deficiency of infancy as well (Higginbottom et al, 1978). The data from this one case of TCII deficiency suggest that substantial Met synthesis was taking place in some tissue. ACKNOWLEDGMENT The author’s work was supported by the Research Service of the Department of Veterans Affairs. KEFERENCES Beck, W.S. (1988) Cobalamin and the nervous system. New England journal of Medicine, 318, 1752-1 754. Burger. R.L., Schneider, R.J.. Mehlman. C.S. & Allen, R.H. (1975) Human plasma K-type vitamin B12-binding proteins. Journal of Biological Chemistry. 250, 7707-771 3. Bhatt, H.R. & Linnell, J.C. (1990) Cobalamin influx into the brain of the rat in vivo. Biomedicine and Physiology q/Vitamin B12 (ed. by J. C. Linnell and H. R . Bhatt). p. 97. The Children’s Medical Charity. London. Burman. J.F., Mollin, D.L., Sourial, N.A. & Sladden, R.A. (1979) Inherited lack of transcobalamin 11 in serum and megaloblastic anaemia: a further patient. British journal qfHaematology. 43.2 738.
Gimferrer. E.. Mane, J. Vives. Baiget, M.. Vives-Corrons, 1.L.. Barcelo. M.J.. Fabrega, J,, Hall, C.A. & Begley, J.A. (1981) Inherited deficiency of transcobolamin I1 in a Spanish woman. Biologia y Clinica Hematologica, 3, 267-270. Green, R. & Jacobsen. D.W. (1990) The role of cobalamins in the nervous system. Biomedicine and Physiologg of Vitamin B 1 2 (ed. by J. C. Linnell and H. R. Bhatt), p. 107. The Children’sMedical Charity, London. Hall, C.A. (1989) The proteins of transport of the cobalamins. Folutes and Cobalamins (ed. by J. A. Zittoun and B. A. Cooper), p. 53. Springer, Berlin. Hall, C.A. (1990) Function of vitamin Blz in the central nervous system as revealed by congenital defects. American journal of Hematology. 34, 121-127. Hall, C.A..Hitzig, W.H., Green, P.D. &Begley,J.A. (1979) Transport
of therapeutic cyanocobalamin in the congenital deficiency of transcobalamin I1 (TCII). Blood, 53, 251-263. Higginbottom, M.C., Sweetman, L. & Nyhan. W.L. (1978) A syndrome of methylmalonic aciduria. homocystinuria. megaloblastic anemia and neurologic abnormalities in a vitamin BIZdeficient breast-fed infant of a strict vegetarian. New England journal of Medicine, 299, 3 17-323. Hoffbrand. A.V., Tripp, E., Jackson, B.F.A. & Luck, W.E. (1984) Hereditary abnormal transcobalamin 11 previously diagnosed as congenital dihydrofolate reductase deficiency. New England journal of Medicine. 310, 789-790. Lazar. G.S. & Carmel, R. (1981) Cobalamin binding and uptake in vitro in the human central nervous system. journal of Laboratory arid Clinical Medicine. 97, 123-1 33. Mane, J. Vives, Vives-Corrons, J.L. & Roxman, D. ( 1 977) Congenital folatc-depcndcnt mcgaloblastic anaemia of unknown aetiology. Lancet, i, 262-263. Quadros, E.V. & Rothenberg, S.P. (1990) The structure and biosynthesis of human transcobalamin 11. Biomedicine and Physiology of Vitamin B l 2 (ed. by J. C. Linnell and H. R. Bhatt). p. 281. The Children’s Medical Charity, London. Spector. R.. Coakley, G. & Blakely. R. (198U) Methioninc recycling in brain: A role for folates and vitamin B, L. journal ofhieurochetnistry. 34, 132-1 37. Tauro. G.P.. Danks. D.M.. Row, P.B., Van der Weyden, M.B., Schwarz. M.A., Collins, V.L. & Neal, B.W. (1976) Dihydrofolate reductase deficiency causing megaloblastic anemia in two families. New England journal of Medicine. 294, 466-470. Thomas, P.K.. Hofirand, A.V. & Smith, 1,s. (1982) Neurological involvement in hereditary transcobalamin I1 deficiency. Journal of Neurology, Neurosurgery, and Psychiatry. 45, 74-77. Van der Westhuyzen. J.. Van Tonder, S.V., Gibson, J.E.. Kilroe-Smith. T.A. & Metz, j. (1 98 5) Plasma amino acids and tissue methionine levels in fruit bats (Rousettus aegyptiacus) with nitrous oxidcinduced vitamin Bll deficiency. British journal of Nutrition. 5 3 , 657-662.
Vilter, C.F.. Vilter, R.W. & Spies, T.D. (1947) The treatment of pernicious and related anemias with synthetic folic acid. Journal of I d m a t o r y and Clinical Medicine. 32, 262-273. Viera-Makings, E., Metz. J., Van der Westhuyxen, J., Bottiglieri, T. & Chanarin. I. (1990) Cobalamin neuropathy. Is S-adenosylhomocysteine toxicity a factor? Biochemistry Journal, 266, 707-71 1. Weir, D.G., Keating, S., Molloy. A,. McPartlin. J.. Kennedy, S., Blanchflower, J., Kennedy. D.G., Rice, D. & Scott. J.M. (1988) Methylation deficiency causes vitamin BI2-associatedneuropathy in the pig. journal of Neurochrmistry, 5 1 , 1949-1952. Weir, D.G., Molloy. A,, Keating, J.N.. McPartlin, J., Kennedy, S., Blanchflower. J., Rice, D. & Scott, J.M. (1 990) Hypomethylation produces vitamin B12 associated neuropath in the pig. Biomedicine and Physiology of Vitamin B11 (ed. by J. C. Linnell and H. R. Bhatt), p. 129. The Children’s Medical Charity, London. Zeitlin, H.C., Sheppard, K.. Baum, J.D., Bolton, F.G. & Hall, C.A. ( 1 985) HomoLygous transcobalamin I1 deficiency maintained on oral hydroxocobalamin. Blood, 66, 1022-1 027.
