FULL-LENGTH ORIGINAL RESEARCH
Spinal muscular atrophy associated with progressive myoclonic epilepsy: A rare condition caused by mutations in ASAH1 *†Guido Rubboli, ‡Pierangelo Veggiotti, §Antonella Pini, ¶Angela Berardinelli, #Gaetano Cantalupo, **Enrico Bertini, ††Francesco Danilo Tiziano, **Adele D’Amico, ¶Elena Piazza, ††Emanuela Abiusi, ††Stefania Fiori, †Elena Pasini, #Francesca Darra, §Giuseppe Gobbi, and †Roberto Michelucci Epilepsia, 56(5):692–698, 2015 doi: 10.1111/epi.12977
SUMMARY
Guido Rubboli is professor of clinical epileptology at Filadelfia/University of Copenhagen
Objective: To present the clinical features and the results of laboratory investigations in three patients with spinal muscular atrophy associated with progressive myoclonic epilepsy (SMA-PME), a rare condition caused by mutations in the N-acylsphingosine amidohydrosilase 1 (ASAH1) gene. Methods: The patients were submitted to clinical evaluation, neurophysiologic investigations (that included wakefulness and sleep electroencephalography [EEG], videopolygraphic recording with jerk-locked back-averaging, multimodal evoked potentials, and electromyography), brain magnetic resonance imaging (MRI), biochemical screening, muscle and skin biopsies, and molecular genetic analysis. Results: The main clinical features were onset in childhood with proximal muscular weakness, generalized epilepsy with absences and myoclonic seizures, cognitive impairment of variable degree; the course was progressive with muscle wasting and uncontrolled epileptic seizures. In one patient, earlier onset before the age of 2 years was associated with a more complex clinical picture, with abnormal eye movements, progressive cognitive impairment, and a more rapid and severe course. EEG/polygraphic data were consistent with PME, demonstrating generalized spike-and-wave discharges, evidence of positive and negative myoclonia, and prominent photosensitivity. In one patient, transcranial magnetic stimulation showed a hyperexcitable motor cortex, whereas somatosensory evoked potentials were unaffected. Possible involvement of the central acoustic and visual pathways was suggested by abnormal auditory and visual evoked potentials. Muscle biopsies showed typical signs of neurogenic damage. Molecular genetic analysis showed mutations of the ASAH1 gene. Significance: Our data indicate that SMA-PME associated with ASAH1 mutations is a genetically distinct condition with specific clinical and neurophysiologic features. Further studies are warranted to explore the role of the ASAH1 gene in muscle and brain function. KEY WORDS: Progressive myoclonus epilepsy, Spinal muscular atrophy, ASAH1 mutations, Myoclonus, Polygraphy.
Accepted February 24, 2015; Early View publication April 3, 2015. *Danish Epilepsy Center, Filadelfia/University of Copenhagen, Dianalund, Denmark; †Neurology Unit, Bellaria Hospital, IRCCS Institute of Neurological Sciences, Bologna, Italy; ‡Department of Brain and Behavioral Sciences, Child Neuropsychiatry Unit, IRCCS C. Mondino National Neurological Institute, University of Pavia, Pavia, Italy; §Child Neurology Unit, Bellaria Hospital, IRCCS Institute of Neurological Sciences, Bologna, Italy; ¶Child Neuropsychiatry Unit, IRCCS C. Mondino National Neurological Institute, Pavia, Italy; #Department of Life and Reproduction Sciences, University of Verona, Verona, Italy; **IRCCS Laboratory of Molecular Medicine, Bambino Gesu’ Children’s Research Hospital, Rome, Italy; and ††Medical Genetics Institute, Catholic University, Rome, Italy Address correspondence to Guido Rubboli, Danish Epilepsy Center, Filadelfia/University of Copenhagen, Kolonivej 1, 4293 Dianalund, Denmark. E-mail: [email protected] Wiley Periodicals, Inc. © 2015 International League Against Epilepsy
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693 SMA-PME Linked to ASAH1 Mutations A peculiar clinical picture characterized by the association of spinal muscular atrophy (SMA) and progressive myoclonic epilepsy (PME) was reported for the first time by Jankovic and Rivera,1 who described three subjects showing slight mental retardation, adult-onset myoclonic epilepsy, and predominantly distal signs of SMA. Only a few individuals with a similar condition, inherited as an autosomal recessive trait, were published afterward.2–8 In most of these cases, SMN1 mutations were ruled out, suggesting that the association between SMA and PME (SMA-PME) represented a separate clinical and genetic entity. Recently, the genetic cause of SMA-PME was identified by Zhou et al.,9 who discovered a homozygous missense mutation (c.125C>T [p.Thr42Met]) in exon 2 of the N-acylsphingosine amidohydrosilase 1 (ASAH1) gene in three unrelated SMA-PME-affected families, two of them of Italian origin. An additional patient with two new mutations (c.850G>T [p.Gly284X] and c.456A>C [p.Lys152Asn]) was reported afterward by Dyment et al.10 In this article, we describe the clinical findings and the results of laboratory investigations in three additional patients with SMA-PME linked to mutations in ASAH1, unrelated to those previously reported, with the aim to further contribute to the definition of the phenotype of this rare condition.
Cases Histories Case 1 An 18-year-old girl was born after an uneventful pregnancy (two previous pregnancies had ended at the III and IX month of gestation with death of the fetus due to placental displacement); an older sister was in healthy condition, and no familial antecedents for neuromuscular disorders were reported. Early developmental milestones were normal. At the age of 6 years, the patient started to show slowness of gait and difficulties in standing from the sitting position. At 8 years of age, brief episodes of impairment of consciousness associated with “jerks” at the upper limbs were noticed. Valproic acid was started at the age of 10 years without improvement. In the following years, seizure frequency and muscular weakness increased progressively, significantly impairing her motor skills (she became unable to ride the bicycle and started to show extreme difficulties in walking up the stairs). At age 13 years, clonazepam was associated with valproic acid, with some improvement of myoclonia. At this age, when she first came to our observation, the patient’s neurologic examination showed mild scoliosis, fasciculations at the tongue, diffuse muscular weakness and hypotrophy that was more pronounced to the limb girdles, abundant asynchronous myoclonia that were more evident in the upper limbs proximally, fine postural “tremor” in the hands, and ataxia with “anserine” gait (see Video S1). Neuropsychological assessment showed IQ slightly below normal values. Over the years, myoclonia increased and
neurologic impairment progressed to the point of requiring assistance for standing and walking. She also started to manifest myoclonic seizures, mainly in the morning, occasionally preceded by visual phenomena; convulsive seizures rarely occurred, usually favored by sleep deprivation. No further neuropsychological deterioration was detected. At the age of 18 years, she had an episode of prolonged myoclonic status that required admission to the intensive care unit and tracheostomy. Her neurologic state progressively worsened after the status and she died at the age of 19 years of systemic complications. Case 2 An 8-year, 6-month-old girl, born from unrelated parents, presented with a delayed and clumsy deambulation that was acquired at 17 months of life. At the age of 2 years, 6 months she started to present with falls to the ground and subtle limb “tremor.” At 3 years of age, epileptic seizures characterized by staring and myoclonic jerks appeared. At this age, a febrile episode, associated with a transitory increment of seizures (up to 50/day), left neurologic sequelae such as worsening of the gait disorder, abnormal eye movements, (horizontal pendular nystagmus and propensity to upward gaze), limb tremor at rest accentuated by movement, and occasionally involuntary distal choreoathetoid movements (fine finger movements of flexion-extension type). At the age of 4 years, 11 months, seizures occurred daily. Neurologic examination showed the persistence of abnormal eye movements, a “tremorlike” disorder at the head and the upper limbs, diffuse hypotonia and proximal muscular weakness at the lower limbs with normal tendon reflexes, and ataxic gait and dyskinetic movements (chorea-like). The patient had difficulty in walking up the stairs and sitting up from the supine position (see Video S2). The cognitive status was mildly impaired (IQ was 66 on the Griffiths Mental Development scale). In the following years, the course was characterized by increment of the seizure frequency, worsening of the dyskinesias, and dramatic progression of the muscular weakness at the lower limbs with inability to stand up from the floor; in addition, mild weakness appeared also at the upper limbs. At the age of 7 years, 8 months, neurologic examination revealed cyclo-rotatory nystagmus, profound weakness and hypotonia, diffuse muscle atrophy involving both upper and lower limbs, no head control, inability to sit unsupported and to roll on her back; abundant fasciculations at the tongue, and limb “tremor” at rest. Cognitive functions were significantly impaired. Various combinations of antiepileptic drugs (lamotrigine, zonisamide, levetiracetam, felbamate, lorazepam, valproate, clonazepam, and ethosuximide) poorly controlled the seizures that occurred several times per day. Hydrocortisone was ineffective; ketogenic diet was not tolerated. Because of recurrent episodes of lung infections due to respiratory muscle impairment and dysphagia, Epilepsia, 56(5):692–698, 2015 doi: 10.1111/epi.12977
694 G. Rubboli et al. tracheostomy and percutaneous endoscopic gastrostomy were performed. Case 3 A 3-year-old girl was referred to us for difficulty with walking. Neurologic examination showed mild proximal weakness, normal tendon reflexes, and hand tremor at rest. Over the years, muscular weakness progressed, with increasing difficulty in walking up the stairs, and her voice acquired a nasal tone. At 8 years, falls to the ground started to occur, and at the age of 12 years, action myoclonus, myoclonic seizures, absences associated with head drop or postural lapses at the upper limbs (see Video S3), and rare generalized tonic–clonic seizures appeared. Severe action myoclonus and myoclonic seizures caused a rapidly progressive decline in motor function and marked impairment of speech. Cognitive functions were relatively spared. At age 14 years she was wheelchair-bound and because of dysphagia and abundant bronchial secretions, she underwent tracheostomy and percutaneous gastrostomy. She was treated with barbiturates, clonazepam, levetiracetam, valproate, and high doses of piracetam, with only a mild decrease of myoclonus and epileptic seizures.
A
B
Laboratory Investigations Biochemical screening was unremarkable in all cases, but for elevation of creatine kinase (up to 389 U/L; normal value T); patient 2 was a compound heterozygote for a frame-shift mutation (c.223insC) and the “classical” c.125C>T mutation. A TaqMan gene expression assay for leukocyte expression of ASAH1 gene showed 70% of decrease in transcript level. Patient 3 showed a heterozygous nonsense mutation c.177C>G.mat in exon 3 and a missense mutation (c.456A>C.pat) in exon 6, recently described by Dyment et al.10 The bi-parental segregation of the mutations found in the three patients has been confirmed.
Discussion SMA-PME is a rare condition that has been demonstrated recently to be linked to mutations in the ASAH1 gene.9,10 An overview of all patients reported in the literature,1–10 including those described before the discovery of the genetic cause, identifies as distinctive features: onset usually with proximal muscular weakness, later appearance of a generalized epilepsy with absences and myoclonic seizures, cognitive impairment of variable degree, and a progressive course. Epilepsy as first symptom, with early drug refractoriness and rapidly disabling, followed some years later by subtle muscular compromise was observed only in one patient.10 Age of onset can range from childhood (around the age of 3–4 years) to adolescence, or even adulthood. Childhood onset is characterized by a course with severe muscle wasting, uncontrolled epileptic seizures, and a dismal evolution, with death occurring at a juvenile age, often because of respiratory complications.5–7,9 Conversely, subjects with juvenile/adult onset1,8 show a slower and benign evolution, without cognitive impairment, and with epilepsy and myoclonus responding to antiepileptic drugs. The main clinical features of our patients, that is, proximal muscular weakness appearing in childhood, followed afterward by generalized epilepsy, mild-to-moderate cogni-
697 SMA-PME Linked to ASAH1 Mutations tive impairment, and a progressive evolution with severe muscular damage and drug-resistant epilepsy, are similar to those described previously in other subjects with childhood onset SMA-PME.5–7,9 Of interest, our patient 2, with onset at the age of 2 years, showed a more complex clinical picture with abnormal eye movements, more pronounced cognitive impairment, and a more severe evolution to the point of requiring tracheostomy and PEG because of recurrent lung infections, resembling similar early onset cases described by Haliloglu et al.6 In our patients, the epilepsy presented with the typical clinical and EEG/polygraphic characteristics of progressive myoclonic epilepsies, whereas the muscular disorder had the features of a lower motor neuron disease with fasciculations, generalized atrophy, and proximal weakness. Notably, in the more severely affected patient 2, muscle tissue analysis revealed both cytochrome c oxidase deficiency and mitochondrial DNA depletion. Severe depletion of mitochondrial DNA has been reported in muscles from patients with SMA related to mutations in SMN1, and this was interpreted as a consequence of the severe neurogenic muscle atrophy.11 Similarly a defect in cytochrome c oxidase deficiency has also been reported in the muscle biopsy of patients affected by amyotrophic lateral sclerosis.12 Whether a defect in ASAH1 disease pathogenesis is involved in a secondary defect of cytochrome c oxidase deficiency or in addition has an impact on mtDNA maintenance remains to be explained. The restraint of COX deficiency to atrophic fibers, the lack of ragged red fibers, and the absence of mitochondriarelated nuclear gene alterations are in favor for the hypothesis that mtDNA depletion is related to the severe neurogenic muscle fiber atrophy.11 Concerning the ultrastructure results of two skin biopsies in patient 2, we consider the presence of “zebra bodies” as unspecific. Slowing of the EEG background activity with generalized spike-and-wave discharges, polygraphic evidence of positive and negative myoclonia either related or unrelated to the epileptic EEG paroxysms, consistent with cortical and subcortical myoclonus respectively, and photic reflex myoclonia have been described in various forms of PME.13–16 Of interest, the study of cortical excitability by motor-evoked potential analysis showed an hyperexcitable motor cortex, whereas SEPs appeared unaffected, indicating that the sensory cortex might be unable, or might have lost the capability, to produce exaggerated responses to incoming stimuli, as observed also in other rare forms of PME.17 We observed also a fine postural “tremor” at both hands that in polygraphic recordings was associated with recurrent myoclonic potentials in the forearm muscles. This phenomenon, reported also in other patients with SMA-PME,6,7,9,10 might be a cortical myoclonic phenomenon, as demonstrated in other PMEs.17,18 Further support for a cortical involvement has been provided by the evidence of giant SEPs and enhanced C-reflex in a patient with juvenile-onset SMA-PME.8
In our patient 1, abnormal auditory evoked potentials suggested a possible dysfunction of the central acoustic pathway, in keeping with some previous reports that described an overt sensorineural deafness.2,7,10 In SMA-PME, linkage analysis, homozygosity mapping, and exome sequencing identified a homozygous missense mutation (c.125C>T [p.Thr42Met]) in exon 2 of ASAH1 in the affected children of two families; the same mutation, associated with a deletion of the whole gene, was found also in a third family.9 Therefore, available data support a pathogenetic hypothesis based on a defective ceramidase function. The Thr42Met mutant protein was expressed in various patient tissues and showed a decreased enzymatic activity. By investigating the ASAH1 function in vivo with a knockdown model, Zhou et al.9 demonstrated that ASAH1 missense mutations decrease acid-ceramidase activity causing a marked defect of motor-axonal branching associated with a significant increase in apoptosis in the spinal cord, supporting the pathogenetic role of ASAH1 mutations in SMA-PME. Of interest, mutations in the same gene also cause Farber disease, a rare and severe autosomal-recessive pathologic entity caused by a striking reduction or absence of lysosomal acid-ceramidase activity.19 Farber disease is clinically characterized by onset before 4 months of age, painful and progressively deformed joints, subcutaneous nodules (lipogranulomata), particularly at the wrist or in areas subject to trauma, progressive laryngeal involvement with hoarse cry, and death usually by 2 years of age. Although accumulation of ceramides and gangliosides in the brain and spinal cord of patients with Farber disease has been reported,19 its clinical presentation is significantly different from SMA-PME. Indeed, in the latter condition, the onset is in childhood, death occurs in adolescence or juvenile age, and symptomatology is restricted to the central nervous system. These phenotypic differences have been postulated to depend on the residual levels of ASAH1 activity, suggesting that a milder reduction of enzymatic activity as in SMA-PME may result in a later-onset phenotype involving only the spinal cord motoneurons and other areas of the central nervous system.9 However, the observation of severely reduced levels of ceramidase activity in one SMAPME patient with subtle muscular involvement suggests that additional factors may affect the clinical expression.10 This pathogenetic hypothesis, based on a defective ceramidase function, may open interesting future therapeutic perspectives for patients with SMA-PME, which may include both gene and enzymatic replacement therapies, with the aim of correcting the enzymatic deficits, as has been already undertaken for Farber disease.20,21
Disclosure None of the authors has any conflict of interest to disclose. We confirm that we have read the Journal’s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines. Epilepsia, 56(5):692–698, 2015 doi: 10.1111/epi.12977
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References 1. Jankovic J, Rivera VM. Hereditary myoclonus and progressive distal muscular atrophy. Ann Neurol 1979;6:227–231. 2. Lance WJ, Evans WA. Progressive myoclonic epilepsy. Clin Exp Neurol 1984;20:141–151. 3. D’Ecclesia G, Scorrano V, Bernardini C, et al. Unusual familial association of epilepsy, myoclonus and muscular atrophy. Case report [in Italian]. Riv Neurol 1985;55:313–316. 4. Taglioli M, Bartolini S, Volpi G, et al. Progressive familial myoclonic epilepsy with bulbo-spinal amyotrophy. Clinical, electrophysiological study and biopsy of a case [in Italian]. Riv Neurol 1990;60:201–206. 5. Marjanovic B, Todorovic S, Dozic S. Association of progressive myoclonic epilepsy and spinal muscular atrophy. Paediatr Neurol 1993;9:147–150. 6. Haliloglu G, Chattopadhyay A, Skorodis L, et al. Spinal muscular atrophy with progressive myoclonic epilepsy: new cases and review of literature. Neuropediatrics 2002;33:314–319. 7. Striano P, Boccella P, Sarappa C, et al. Spinal muscular atrophy and progressive myoclonic epilepsy: one case report and characteristics of the epileptic syndrome. Seizure 2004;1:582–586. 8. Temucin CM, Buyukserbetci G, Ozdamar SE, et al. A rare phenotype: progressive myoclonic epilepsy with lower motor neuron involvement. Epilepsia 2008;49:1809–1812. 9. Zhou J, Tawk M, Tiziano FD, et al. Spinal muscular atrophy associated with progressive myoclonic epilepsy is caused by mutations in ASAH1. Am J Hum Genet 2012;91:5–14. 10. Dyment DA, Sell E, Vanstone MR, et al. Evidence for clinical, genetic and biochemical variability in spinal muscular atrophy with progressive myoclonic epilepsy. Clin Genet 2014;86:558–563. 11. Berger A, Mayr JA, Meierhofer D, et al. Severe depletion of mitochondrial DNA in spinal muscular atrophy. Acta Neuropathol 2003;105:245–251. 12. Crugnola V, Lamperti C, Lucchini V, et al. Mitochondrial respiratory chain dysfunction in muscle from patients with amyotrophic lateral sclerosis. Arch Neurol 2010;67:849–854. 13. Tassinari CA, Bureau-Paillas M, Dalla Bernardina B, et al. Etude electroencephalographique de la dyssinergie cerebelleuse myoclonique avec epilepsie (sindrome de Ramsay-Hunt). Rev Electroencephalogr Neurophysiol Clin 1974;4:407–428.
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14. Tassinari CA, Bureau-Paillas M, Dalla Bernardina B, et al. Lafora disease (author’s transl). Rev Electroencephalogr Neurophysiol Clin 1978;8:107–122. 15. Rubboli G, Meletti S, Gardella E, et al. Photic reflex myoclonus: a neurophysiological study in progressive myoclonus epilepsies. Epilepsia 1999;40(Suppl. 4):50–58. 16. Berkovic SF. Progressive myoclonus epilepsies. In Engel J, Pedley TA (Eds) Epilepsy. A comprehensive textbook. 2nd Ed. Philadelphia, PA: Walters Kluwer-Lippincott Williams & Wilkins, 2008:2525–2535. 17. Rubboli G, Franceschetti S, Berkovic SF, et al. Clinical and neurophysiologic features of progressive myoclonus epilepsy without renal failure caused by SCARB2 mutations. Epilepsia 2011;52:2356– 2363. 18. Regragui W, Gerdelat-Mas A, Simonetta-Moreau M. Cortical tremor (FCMTE: familial cortical myoclonic tremor with epilepsy). Neurophysiol Clin 2006;36:345–349. 19. Levade T, Sandhoff K, Schulze H, et al. Acid ceramidase deficiency: farber lipogranulomatosis. In Valle D, Beaudet AL, Vogelstein B, et al. (Eds) Scriver’s OMMBID (The online metabolic & molecular bases of inherited disease), New York: McGraw-Hill; 2009. Available at:http:// www.ommbid.com. Accessed September 17, 2014. 20. Yeager AM, Uhas KA, Coles CD, et al. Bone marrow transplantation for infantile ceramidase deficiency (Farber disease). Bone Marrow Transplant 2000;26:357–363. 21. Walia J, Neschadim A, Lopez-Perez O, et al. Autologous transplantation of lentivector/acid ceramidase-transduced hematopoietic cells in nonhuman primates. Hum Gene Ther 2011;22:679–687.
Supporting Information Additional Supporting Information may be found in the online version of this article: Video S1. Patient 1 at the age of 13 years. Video S2. Patient 2 at the age of 4 years, 6 months. Video S3. Patient 3 at the age of 12 years.
Spinal muscular atrophy associated with progressive myoclonic epilepsy: A rare condition caused by mutations in ASAH1 *†Guido Rubboli, ‡Pierangelo Veggiotti, §Antonella Pini, ¶Angela Berardinelli, #Gaetano Cantalupo, **Enrico Bertini, ††Francesco Danilo Tiziano, **Adele D’Amico, ¶Elena Piazza, ††Emanuela Abiusi, ††Stefania Fiori, †Elena Pasini, #Francesca Darra, §Giuseppe Gobbi, and †Roberto Michelucci Epilepsia, 56(5):692–698, 2015 doi: 10.1111/epi.12977
SUMMARY
Guido Rubboli is professor of clinical epileptology at Filadelfia/University of Copenhagen
Objective: To present the clinical features and the results of laboratory investigations in three patients with spinal muscular atrophy associated with progressive myoclonic epilepsy (SMA-PME), a rare condition caused by mutations in the N-acylsphingosine amidohydrosilase 1 (ASAH1) gene. Methods: The patients were submitted to clinical evaluation, neurophysiologic investigations (that included wakefulness and sleep electroencephalography [EEG], videopolygraphic recording with jerk-locked back-averaging, multimodal evoked potentials, and electromyography), brain magnetic resonance imaging (MRI), biochemical screening, muscle and skin biopsies, and molecular genetic analysis. Results: The main clinical features were onset in childhood with proximal muscular weakness, generalized epilepsy with absences and myoclonic seizures, cognitive impairment of variable degree; the course was progressive with muscle wasting and uncontrolled epileptic seizures. In one patient, earlier onset before the age of 2 years was associated with a more complex clinical picture, with abnormal eye movements, progressive cognitive impairment, and a more rapid and severe course. EEG/polygraphic data were consistent with PME, demonstrating generalized spike-and-wave discharges, evidence of positive and negative myoclonia, and prominent photosensitivity. In one patient, transcranial magnetic stimulation showed a hyperexcitable motor cortex, whereas somatosensory evoked potentials were unaffected. Possible involvement of the central acoustic and visual pathways was suggested by abnormal auditory and visual evoked potentials. Muscle biopsies showed typical signs of neurogenic damage. Molecular genetic analysis showed mutations of the ASAH1 gene. Significance: Our data indicate that SMA-PME associated with ASAH1 mutations is a genetically distinct condition with specific clinical and neurophysiologic features. Further studies are warranted to explore the role of the ASAH1 gene in muscle and brain function. KEY WORDS: Progressive myoclonus epilepsy, Spinal muscular atrophy, ASAH1 mutations, Myoclonus, Polygraphy.
Accepted February 24, 2015; Early View publication April 3, 2015. *Danish Epilepsy Center, Filadelfia/University of Copenhagen, Dianalund, Denmark; †Neurology Unit, Bellaria Hospital, IRCCS Institute of Neurological Sciences, Bologna, Italy; ‡Department of Brain and Behavioral Sciences, Child Neuropsychiatry Unit, IRCCS C. Mondino National Neurological Institute, University of Pavia, Pavia, Italy; §Child Neurology Unit, Bellaria Hospital, IRCCS Institute of Neurological Sciences, Bologna, Italy; ¶Child Neuropsychiatry Unit, IRCCS C. Mondino National Neurological Institute, Pavia, Italy; #Department of Life and Reproduction Sciences, University of Verona, Verona, Italy; **IRCCS Laboratory of Molecular Medicine, Bambino Gesu’ Children’s Research Hospital, Rome, Italy; and ††Medical Genetics Institute, Catholic University, Rome, Italy Address correspondence to Guido Rubboli, Danish Epilepsy Center, Filadelfia/University of Copenhagen, Kolonivej 1, 4293 Dianalund, Denmark. E-mail: [email protected] Wiley Periodicals, Inc. © 2015 International League Against Epilepsy
692
693 SMA-PME Linked to ASAH1 Mutations A peculiar clinical picture characterized by the association of spinal muscular atrophy (SMA) and progressive myoclonic epilepsy (PME) was reported for the first time by Jankovic and Rivera,1 who described three subjects showing slight mental retardation, adult-onset myoclonic epilepsy, and predominantly distal signs of SMA. Only a few individuals with a similar condition, inherited as an autosomal recessive trait, were published afterward.2–8 In most of these cases, SMN1 mutations were ruled out, suggesting that the association between SMA and PME (SMA-PME) represented a separate clinical and genetic entity. Recently, the genetic cause of SMA-PME was identified by Zhou et al.,9 who discovered a homozygous missense mutation (c.125C>T [p.Thr42Met]) in exon 2 of the N-acylsphingosine amidohydrosilase 1 (ASAH1) gene in three unrelated SMA-PME-affected families, two of them of Italian origin. An additional patient with two new mutations (c.850G>T [p.Gly284X] and c.456A>C [p.Lys152Asn]) was reported afterward by Dyment et al.10 In this article, we describe the clinical findings and the results of laboratory investigations in three additional patients with SMA-PME linked to mutations in ASAH1, unrelated to those previously reported, with the aim to further contribute to the definition of the phenotype of this rare condition.
Cases Histories Case 1 An 18-year-old girl was born after an uneventful pregnancy (two previous pregnancies had ended at the III and IX month of gestation with death of the fetus due to placental displacement); an older sister was in healthy condition, and no familial antecedents for neuromuscular disorders were reported. Early developmental milestones were normal. At the age of 6 years, the patient started to show slowness of gait and difficulties in standing from the sitting position. At 8 years of age, brief episodes of impairment of consciousness associated with “jerks” at the upper limbs were noticed. Valproic acid was started at the age of 10 years without improvement. In the following years, seizure frequency and muscular weakness increased progressively, significantly impairing her motor skills (she became unable to ride the bicycle and started to show extreme difficulties in walking up the stairs). At age 13 years, clonazepam was associated with valproic acid, with some improvement of myoclonia. At this age, when she first came to our observation, the patient’s neurologic examination showed mild scoliosis, fasciculations at the tongue, diffuse muscular weakness and hypotrophy that was more pronounced to the limb girdles, abundant asynchronous myoclonia that were more evident in the upper limbs proximally, fine postural “tremor” in the hands, and ataxia with “anserine” gait (see Video S1). Neuropsychological assessment showed IQ slightly below normal values. Over the years, myoclonia increased and
neurologic impairment progressed to the point of requiring assistance for standing and walking. She also started to manifest myoclonic seizures, mainly in the morning, occasionally preceded by visual phenomena; convulsive seizures rarely occurred, usually favored by sleep deprivation. No further neuropsychological deterioration was detected. At the age of 18 years, she had an episode of prolonged myoclonic status that required admission to the intensive care unit and tracheostomy. Her neurologic state progressively worsened after the status and she died at the age of 19 years of systemic complications. Case 2 An 8-year, 6-month-old girl, born from unrelated parents, presented with a delayed and clumsy deambulation that was acquired at 17 months of life. At the age of 2 years, 6 months she started to present with falls to the ground and subtle limb “tremor.” At 3 years of age, epileptic seizures characterized by staring and myoclonic jerks appeared. At this age, a febrile episode, associated with a transitory increment of seizures (up to 50/day), left neurologic sequelae such as worsening of the gait disorder, abnormal eye movements, (horizontal pendular nystagmus and propensity to upward gaze), limb tremor at rest accentuated by movement, and occasionally involuntary distal choreoathetoid movements (fine finger movements of flexion-extension type). At the age of 4 years, 11 months, seizures occurred daily. Neurologic examination showed the persistence of abnormal eye movements, a “tremorlike” disorder at the head and the upper limbs, diffuse hypotonia and proximal muscular weakness at the lower limbs with normal tendon reflexes, and ataxic gait and dyskinetic movements (chorea-like). The patient had difficulty in walking up the stairs and sitting up from the supine position (see Video S2). The cognitive status was mildly impaired (IQ was 66 on the Griffiths Mental Development scale). In the following years, the course was characterized by increment of the seizure frequency, worsening of the dyskinesias, and dramatic progression of the muscular weakness at the lower limbs with inability to stand up from the floor; in addition, mild weakness appeared also at the upper limbs. At the age of 7 years, 8 months, neurologic examination revealed cyclo-rotatory nystagmus, profound weakness and hypotonia, diffuse muscle atrophy involving both upper and lower limbs, no head control, inability to sit unsupported and to roll on her back; abundant fasciculations at the tongue, and limb “tremor” at rest. Cognitive functions were significantly impaired. Various combinations of antiepileptic drugs (lamotrigine, zonisamide, levetiracetam, felbamate, lorazepam, valproate, clonazepam, and ethosuximide) poorly controlled the seizures that occurred several times per day. Hydrocortisone was ineffective; ketogenic diet was not tolerated. Because of recurrent episodes of lung infections due to respiratory muscle impairment and dysphagia, Epilepsia, 56(5):692–698, 2015 doi: 10.1111/epi.12977
694 G. Rubboli et al. tracheostomy and percutaneous endoscopic gastrostomy were performed. Case 3 A 3-year-old girl was referred to us for difficulty with walking. Neurologic examination showed mild proximal weakness, normal tendon reflexes, and hand tremor at rest. Over the years, muscular weakness progressed, with increasing difficulty in walking up the stairs, and her voice acquired a nasal tone. At 8 years, falls to the ground started to occur, and at the age of 12 years, action myoclonus, myoclonic seizures, absences associated with head drop or postural lapses at the upper limbs (see Video S3), and rare generalized tonic–clonic seizures appeared. Severe action myoclonus and myoclonic seizures caused a rapidly progressive decline in motor function and marked impairment of speech. Cognitive functions were relatively spared. At age 14 years she was wheelchair-bound and because of dysphagia and abundant bronchial secretions, she underwent tracheostomy and percutaneous gastrostomy. She was treated with barbiturates, clonazepam, levetiracetam, valproate, and high doses of piracetam, with only a mild decrease of myoclonus and epileptic seizures.
A
B
Laboratory Investigations Biochemical screening was unremarkable in all cases, but for elevation of creatine kinase (up to 389 U/L; normal value T); patient 2 was a compound heterozygote for a frame-shift mutation (c.223insC) and the “classical” c.125C>T mutation. A TaqMan gene expression assay for leukocyte expression of ASAH1 gene showed 70% of decrease in transcript level. Patient 3 showed a heterozygous nonsense mutation c.177C>G.mat in exon 3 and a missense mutation (c.456A>C.pat) in exon 6, recently described by Dyment et al.10 The bi-parental segregation of the mutations found in the three patients has been confirmed.
Discussion SMA-PME is a rare condition that has been demonstrated recently to be linked to mutations in the ASAH1 gene.9,10 An overview of all patients reported in the literature,1–10 including those described before the discovery of the genetic cause, identifies as distinctive features: onset usually with proximal muscular weakness, later appearance of a generalized epilepsy with absences and myoclonic seizures, cognitive impairment of variable degree, and a progressive course. Epilepsy as first symptom, with early drug refractoriness and rapidly disabling, followed some years later by subtle muscular compromise was observed only in one patient.10 Age of onset can range from childhood (around the age of 3–4 years) to adolescence, or even adulthood. Childhood onset is characterized by a course with severe muscle wasting, uncontrolled epileptic seizures, and a dismal evolution, with death occurring at a juvenile age, often because of respiratory complications.5–7,9 Conversely, subjects with juvenile/adult onset1,8 show a slower and benign evolution, without cognitive impairment, and with epilepsy and myoclonus responding to antiepileptic drugs. The main clinical features of our patients, that is, proximal muscular weakness appearing in childhood, followed afterward by generalized epilepsy, mild-to-moderate cogni-
697 SMA-PME Linked to ASAH1 Mutations tive impairment, and a progressive evolution with severe muscular damage and drug-resistant epilepsy, are similar to those described previously in other subjects with childhood onset SMA-PME.5–7,9 Of interest, our patient 2, with onset at the age of 2 years, showed a more complex clinical picture with abnormal eye movements, more pronounced cognitive impairment, and a more severe evolution to the point of requiring tracheostomy and PEG because of recurrent lung infections, resembling similar early onset cases described by Haliloglu et al.6 In our patients, the epilepsy presented with the typical clinical and EEG/polygraphic characteristics of progressive myoclonic epilepsies, whereas the muscular disorder had the features of a lower motor neuron disease with fasciculations, generalized atrophy, and proximal weakness. Notably, in the more severely affected patient 2, muscle tissue analysis revealed both cytochrome c oxidase deficiency and mitochondrial DNA depletion. Severe depletion of mitochondrial DNA has been reported in muscles from patients with SMA related to mutations in SMN1, and this was interpreted as a consequence of the severe neurogenic muscle atrophy.11 Similarly a defect in cytochrome c oxidase deficiency has also been reported in the muscle biopsy of patients affected by amyotrophic lateral sclerosis.12 Whether a defect in ASAH1 disease pathogenesis is involved in a secondary defect of cytochrome c oxidase deficiency or in addition has an impact on mtDNA maintenance remains to be explained. The restraint of COX deficiency to atrophic fibers, the lack of ragged red fibers, and the absence of mitochondriarelated nuclear gene alterations are in favor for the hypothesis that mtDNA depletion is related to the severe neurogenic muscle fiber atrophy.11 Concerning the ultrastructure results of two skin biopsies in patient 2, we consider the presence of “zebra bodies” as unspecific. Slowing of the EEG background activity with generalized spike-and-wave discharges, polygraphic evidence of positive and negative myoclonia either related or unrelated to the epileptic EEG paroxysms, consistent with cortical and subcortical myoclonus respectively, and photic reflex myoclonia have been described in various forms of PME.13–16 Of interest, the study of cortical excitability by motor-evoked potential analysis showed an hyperexcitable motor cortex, whereas SEPs appeared unaffected, indicating that the sensory cortex might be unable, or might have lost the capability, to produce exaggerated responses to incoming stimuli, as observed also in other rare forms of PME.17 We observed also a fine postural “tremor” at both hands that in polygraphic recordings was associated with recurrent myoclonic potentials in the forearm muscles. This phenomenon, reported also in other patients with SMA-PME,6,7,9,10 might be a cortical myoclonic phenomenon, as demonstrated in other PMEs.17,18 Further support for a cortical involvement has been provided by the evidence of giant SEPs and enhanced C-reflex in a patient with juvenile-onset SMA-PME.8
In our patient 1, abnormal auditory evoked potentials suggested a possible dysfunction of the central acoustic pathway, in keeping with some previous reports that described an overt sensorineural deafness.2,7,10 In SMA-PME, linkage analysis, homozygosity mapping, and exome sequencing identified a homozygous missense mutation (c.125C>T [p.Thr42Met]) in exon 2 of ASAH1 in the affected children of two families; the same mutation, associated with a deletion of the whole gene, was found also in a third family.9 Therefore, available data support a pathogenetic hypothesis based on a defective ceramidase function. The Thr42Met mutant protein was expressed in various patient tissues and showed a decreased enzymatic activity. By investigating the ASAH1 function in vivo with a knockdown model, Zhou et al.9 demonstrated that ASAH1 missense mutations decrease acid-ceramidase activity causing a marked defect of motor-axonal branching associated with a significant increase in apoptosis in the spinal cord, supporting the pathogenetic role of ASAH1 mutations in SMA-PME. Of interest, mutations in the same gene also cause Farber disease, a rare and severe autosomal-recessive pathologic entity caused by a striking reduction or absence of lysosomal acid-ceramidase activity.19 Farber disease is clinically characterized by onset before 4 months of age, painful and progressively deformed joints, subcutaneous nodules (lipogranulomata), particularly at the wrist or in areas subject to trauma, progressive laryngeal involvement with hoarse cry, and death usually by 2 years of age. Although accumulation of ceramides and gangliosides in the brain and spinal cord of patients with Farber disease has been reported,19 its clinical presentation is significantly different from SMA-PME. Indeed, in the latter condition, the onset is in childhood, death occurs in adolescence or juvenile age, and symptomatology is restricted to the central nervous system. These phenotypic differences have been postulated to depend on the residual levels of ASAH1 activity, suggesting that a milder reduction of enzymatic activity as in SMA-PME may result in a later-onset phenotype involving only the spinal cord motoneurons and other areas of the central nervous system.9 However, the observation of severely reduced levels of ceramidase activity in one SMAPME patient with subtle muscular involvement suggests that additional factors may affect the clinical expression.10 This pathogenetic hypothesis, based on a defective ceramidase function, may open interesting future therapeutic perspectives for patients with SMA-PME, which may include both gene and enzymatic replacement therapies, with the aim of correcting the enzymatic deficits, as has been already undertaken for Farber disease.20,21
Disclosure None of the authors has any conflict of interest to disclose. We confirm that we have read the Journal’s position on issues involved in ethical publication and affirm that this report is consistent with those guidelines. Epilepsia, 56(5):692–698, 2015 doi: 10.1111/epi.12977
698 G. Rubboli et al.
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Supporting Information Additional Supporting Information may be found in the online version of this article: Video S1. Patient 1 at the age of 13 years. Video S2. Patient 2 at the age of 4 years, 6 months. Video S3. Patient 3 at the age of 12 years.
