Alternating hemiplegia of childhood: no mutations in the glutamate transporter EAAT1

Clinical profile of patients with ATP1A3 mutations in Alternating Hemiplegia of Childhood-a study of 155 patients

BACKGROUND

Mutations in the gene ATP1A3 have recently been identified to be prevalent in patients with alternating hemiplegia of childhood (AHC2). Based on a large series of patients with AHC, we set out to identify the spectrum of different mutations within the ATP1A3 gene and further establish any correlation with phenotype.

METHODS

Clinical data from an international cohort of 155 AHC patients (84 females, 71 males; between 3 months and 52 years) were gathered using a specifically formulated questionnaire and analysed relative to the mutational ATP1A3 gene data for each patient.

RESULTS

In total, 34 different ATP1A3 mutations were detected in 85 % (132/155) patients, seven of which were novel. In general, mutations were found to cluster into five different regions. The most frequent mutations included: p.Asp801Asn (43 %; 57/132), p.Glu815Lys (16 %; 22/132), and p.Gly947Arg (11 %; 15/132). Of these, p.Glu815Lys was associated with a severe phenotype, with more severe intellectual and motor disability. p.Asp801Asn appeared to confer a milder phenotypic expression, and p.Gly947Arg appeared to correlate with the most favourable prognosis, compared to the other two frequent mutations. Overall, the comparison of the clinical profiles suggested a gradient of severity between the three major mutations with differences in intellectual (p = 0.029) and motor (p = 0.039) disabilities being statistically significant. For patients with epilepsy, age at onset of seizures was earlier for patients with either p.Glu815Lys or p.Gly947Arg mutation, compared to those with p.Asp801Asn mutation (p < 0.001). With regards to the five mutation clusters, some clusters appeared to correlate with certain clinical phenotypes. No statistically significant clinical correlations were found between patients with and without ATP1A3 mutations.

CONCLUSIONS

Our results, demonstrate a highly variable clinical phenotype in patients with AHC2 that correlates with certain mutations and possibly clusters within the ATP1A3 gene. Our description of the clinical profile of patients with the most frequent mutations and the clinical picture of those with less common mutations confirms the results from previous studies, and further expands the spectrum of genotype-phenotype correlations. Our results may be useful to confirm diagnosis and may influence decisions to ensure appropriate early medical intervention in patients with AHC. They provide a stronger basis for the constitution of more homogeneous groups to be included in clinical trials.

Alternating Hemiplegia of Childhood: Retrospective Genetic Study and Genotype-Phenotype Correlations in 187 Subjects from the US AHCF Registry

Mutations in ATP1A3 cause Alternating Hemiplegia of Childhood (AHC) by disrupting function of the neuronal Na+/K+ ATPase. Published studies to date indicate 2 recurrent mutations, D801N and E815K, and a more severe phenotype in the E815K cohort. We performed mutation analysis and retrospective genotype-phenotype correlations in all eligible patients with AHC enrolled in the US AHC Foundation registry from 1997-2012. Clinical data were abstracted from standardized caregivers’ questionnaires and medical records and confirmed by expert clinicians. We identified ATP1A3 mutations by Sanger and whole genome sequencing, and compared phenotypes within and between 4 groups of subjects, those with D801N, E815K, other ATP1A3 or no ATP1A3 mutations. We identified heterozygous ATP1A3 mutations in 154 of 187 (82%) AHC patients. Of 34 unique mutations, 31 (91%) are missense, and 16 (47%) had not been previously reported. Concordant with prior studies, more than 2/3 of all mutations are clustered in exons 17 and 18. Of 143 simplex occurrences, 58 had D801N (40%), 38 had E815K (26%) and 11 had G937R (8%) mutations. Patients with an E815K mutation demonstrate an earlier age of onset, more severe motor impairment and a higher prevalence of status epilepticus. This study further expands the number and spectrum of ATP1A3 mutations associated with AHC and confirms a more deleterious effect of the E815K mutation on selected neurologic outcomes. However, the complexity of the disorder and the extensive phenotypic variability among subgroups merits caution and emphasizes the need for further studies.

ATP1A3 mutations and genotype-phenotype correlation of alternating hemiplegia of childhood in Chinese patients

Alternating hemiplegia of childhood (AHC) is a rare and severe neurological disorder. ATP1A3 was recently identified as the causative gene. Here we report the first genetic study in Chinese AHC cohort. We performed whole-exome sequencing on three trios and three unrelated patients, and screened additional 41 typical cases and 100 controls by PCR-Sanger sequencing. ATP1A3 mutations were detected in 95.7% of typical AHC patients. At least 93.3% were de novo. Four late onset, atypical AHC patients were also mutation positive, suggesting the need for testing ATP1A3 mutations in atypical cases. Totally, 13 novel missense mutations (T370N, G706R, L770R, T771N, T771I, S772R, L802P, D805H, M806K, P808L, I810N, L839P and G893R) were identified in our study. By homology modeling of the mutant protein structures and calculation of an extensive list of molecular features, we identified two statistically significant molecular features, solvent accessibility and distance to metal ion, that distinguished disease-associated mutations from neutral variants. A logistic regression classifier achieved 92.9% accuracy by the average of 100 times of five-fold cross validations. Genotype-phenotype correlation analysis showed that patients with epilepsy were more likely to carry E815K mutation. In summary, ATP1A3 is the major pathogenic gene of AHC in Chinese patients; mutations have distinctive molecular features that discriminate them from neutral variants and are correlated with phenotypes.

A novel SLC2A1 mutation linking hemiplegic migraine with alternating hemiplegia of childhood

BACKGROUND

Hemiplegic migraine (HM) and alternating hemiplegia of childhood (AHC) are rare episodic neurological brain disorders with partial clinical and genetic overlap. Recently, ATP1A3 mutations were shown to account for the majority of AHC patients. In addition, a mutation in the SLC2A1 gene was reported in a patient with atypical AHC. We therefore investigated whether mutations in these genes may also be involved in HM. Furthermore, we studied the role of SLC2A1 mutations in a small set of AHC patients without ATP1A3 mutations.

METHODS

We screened 42 HM patients (21 familial and 21 sporadic patients) for ATP1A3 and SLC2A1 mutations. In addition, four typical AHC patients and one atypical patient with overlapping symptoms of both disorders were screened for SLC2A1 mutations.

RESULTS

A pathogenic de novo SLC2A1 mutation (p.Gly18Arg) was found in the atypical patient with overlapping symptoms of AHC and hemiplegic migraine. No mutations were found in the HM and the other AHC patients.

CONCLUSION

Screening for a mutation in the SLC2A1 gene should be considered in patients with a complex phenotype with overlapping symptoms of hemiplegic migraine and AHC.

Lack of SLC2A1 (glucose transporter 1) mutations in 30 Italian patients with alternating hemiplegia of childhood

Alternating hemiplegia of childhood is a rare, predominantly sporadic disorder. Diagnosis is clinical, and little is known about genetics. Glucose transporter 1 deficiency syndrome shares with alternating hemiplegia of childhood paroxysmal and nonparoxysmal symptoms. The aim of the study was to investigate glucose transporter 1 mutations in 30 Italian patients. Genetic material was analyzed by DNA amplification and glucose transporter 1 region sequencing. Mutational analysis findings of the SLC2A1 gene were negative in all patients. The pattern of movement disorders was reviewed. Interictal dystonia and multiple paroxysmal events were typical of alternating hemiplegia of childhood. In conclusion, alternating hemiplegia of childhood is a heterogeneous clinical condition, and although glucose transporter 1 deficiency can represent an undiagnosed cause of this disorder, mutational analysis is not routinely recommended. Alternatively, a careful clinical analysis and the 3-O-methyl-D-glucose uptake test can allow prompt identification of a subgroup of patients with alternating hemiplegia of childhood treatable with a ketogenic diet.

Alternating hemiplegia of childhood: metabolic studies in the largest European series of patients

Alternating hemiplegia of childhood (AHC) is a rare disorder with diagnosis based on clinical criteria, as no laboratory, neuroradiological or genetic markers are currently available. The pathogenic mechanisms are still an enigma. Some hypotheses have been proposed such as hemiplegic migraine variant, epileptic mechanism, channelopathy and mitochondrial disorder, but none of these has been confirmed. Our aim was to analyze the results of metabolic studies performed on a series of 157 European patients who fulfilled diagnostic criteria for AHC. We tried to find a common metabolic abnormality, related with AHC. We did not find significant abnormalities in basic metabolic screening, at different ages. Neurotransmitters in cerebrospinal fluid (n = 26) were normal in all of the patients. Mitochondrial respiratory chain enzyme activities were analyzed in 19 muscle biopsies; in 4 cases, different MRC enzyme deficiencies were demonstrated, ranging from mild-unspecific deficiencies to more profound and probably primary defects. Although we did not find specific metabolic markers in our series, some metabolic disorders such as pyruvate dehydrogenase deficiency, MELAS, cerebral glucose transporter defect and neurotransmitter deficiency can exhibit symptoms similar to those of AHC and need to be ruled out before a diagnosis of AHC can be established. Further studies including high-throughput diagnostic technologies seem necessary to elucidate the etiology of this severe and enigmatic disorder.

Evidence of a non-progressive course of alternating hemiplegia of childhood: study of a large cohort of children and adults

Alternating hemiplegia of childhood is a neurological disorder characterized by episodes of hemiplegia, various non-epileptic paroxysmal events and global neurological impairment. Characterization of the evolution and outcome into adulthood has not been sufficiently investigated. The goal of this study was to elucidate the natural history of alternating hemiplegia within a large cohort of 157 patients, as part of the European Network for Research on Alternating Hemiplegia project. A questionnaire was formulated to determine the severity of both paroxysmal and global neurological impairment and address progression of the disorder by allocating data to specific age epochs up to and over 24 years of age. Patients in early age groups were consistently present in subsequent later age groups and for each patient, data were collected for each corresponding age epoch. The study was based on predominantly retrospective and, for a period of 2 years, prospective data. At inclusion, patients were aged from 9 months to 52 years. The median age at diagnosis was 20 months. All patients experienced hemiplegic attacks; 86.5% reported episodes of bilateral weakness, 88% dystonic attacks, 53% epileptic seizures, 72% developed chorea and/or dystonia and 92% mental retardation. When data over the course of the illness were examined for the whole cohort, the severity of symptoms did not appear to change, with the exception of abnormal ocular movements and hypotonia that regressed, but did not disappear into adulthood (from 86 to 36% and 76 to 36%, respectively). No statistically significant correlation between a history of severe paroxysmal hemiplegic/dystonic episodes and a worse neurological outcome was identified. Seven patients died, some of whom experienced severe plegic attacks or epileptic seizures at the time of death. History of severe plegic/dystonic attacks was not found to be an aggravating factor for deceased patients. Our results provide evidence that the natural history of alternating hemiplegia is highly variable and unpredictable for individual patients. However, we did not find evidence to support a steadily progressive and degenerative course of the disorder when patients were analysed as a group. For a minority of patients, a risk of sudden death was associated with more severe neurological impairment. The European Network for Research on Alternating Hemiplegia Registry, validated by our study, includes all major neurological signs and symptoms of alternating hemiplegia and may thus be used as a precedent for the progressive inclusion and follow-up of patients as well as a reference for genetic studies and treatment trials.

CACNA1A Mutation Linking Hemiplegic Migraine and Alternating Hemiplegia of Childhood

Familial hemiplegic migraine (FHM) and alternating hemiplegia of childhood (AHC) are severe neurological disorders that share clinical features. Therefore, FHM genes are candidates for AHC. We performed mutation analysis in the CACNA1A gene in a monozygotic twin pair with clinical features overlapping with both AHC and FHM and identified a novel de novo CACNA1A mutation. We provide the first evidence that a CACNA1A mutation can cause atypical AHC, indicating an overlap of molecular mechanisms causing AHC and FHM. These results also suggest that CACNA1A mutation scanning is indicated in patients with a severe neurological phenotype that includes paroxysmal (alternating) hemiplegia.

[Alternating hemiplegia of childhood in Spanish population. Study of a series of 17 patients]

BACKGROUND AND OBJECTIVE

Alternating hemiplegia of childhood (AHC) is a rare disease of unknown etiology characterized by early onset of recurrent episodes of hemiplegia, tonic or dystonic attacks and abnormal ocular movements with a fatal outcome to severe encephalopathy. Our aim was to describe the clinical manifestations, precipitating factors, complementary studies results, long-term outcome and response to treatment in a series of AHC patients.

PATIENTS AND METHOD

Descriptive, retrospective and multicenter study in 17 Spanish patients aged between 1-24 years who fulfilled diagnostic criteria of AHC.

RESULTS

Twelve cases fulfilled criteria of typical AHC and 5 were atypical. Mean age at diagnosis was 26 months and 47% cases had a family history of migraine. Mean age at onset of hemiplegic attacks was 9.3 months. Symptoms disappeared during sleep and precipitating factors were present in 94% cases. Most patients developed mental retardation with ataxia and dysarthria. Work-up tests (metabolic, neurophysiologic and radiologic) were normal or nonspecific. In 3 patients mutations in CACNA1A, ATP1A2 were ruled out. Positive responses to flunarizine was observed in 81%.

CONCLUSIONS

The characteristic clinical symptoms are still the clue to make the diagnosis of this disease, with a lack of genetic, biochemical or radiological specific studies. Early diagnosis avoids invasive tests, repeating procedures, using ineffective and potentially toxic treatments, and allows to start treatment with flunarizine without delay. More genetic studies are needed in broader series of patients.