Adriana Ochoa

Mutations in EFHC1 cause juvenile myoclonic epilepsy

Juvenile myoclonic epilepsy (JME) is the most frequent cause of hereditary grand mal seizures. We previously mapped and narrowed a region associated with JME on chromosome 6p12–p11 (EJM1). Here, we describe a new gene in this region, EFHC1, which encodes a protein with an EF-hand motif. Mutation analyses identified five missense mutations in EFHC1 that cosegregated with epilepsy or EEG polyspike wave in affected members of six unrelated families with JME and did not occur in 382 control individuals. Overexpression of EFHC1 in mouse hippocampal primary culture neurons induced apoptosis that was significantly lowered by the mutations. Apoptosis was specifically suppressed by SNX-482, an antagonist of R-type voltage-dependent Ca2+ channel (Cav2.3). EFHC1 and Cav2.3 immunomaterials overlapped in mouse brain, and EFHC1 coimmunoprecipitated with the Cav2.3 C terminus. In patch-clamp analysis, EFHC1 specifically increased R-type Ca2+ currents that were reversed by the mutations associated with JME.

Hyperglycosylation and Reduced GABA Currents of Mutated GABRB3 Polypeptide in Remitting Childhood Absence Epilepsy

Childhood absence epilepsy (CAE) accounts for 10% to 12% of epilepsy in children under 16 years of age. We screened for mutations in the GABA(A) receptor (GABAR) beta 3 subunit gene (GABRB3) in 48 probands and families with remitting CAE. We found that four out of 48 families (8%) had mutations in GABRB3. One heterozygous missense mutation (P11S) in exon 1a segregated with four CAE-affected persons in one multiplex, two-generation Mexican family. P11S was also found in a singleton from Mexico. Another heterozygous missense mutation (S15F) was present in a singleton from Honduras. An exon 2 heterozygous missense mutation (G32R) was present in two CAE-affected persons and two persons affected with EEG-recorded spike and/or sharp wave in a two-generation Honduran family. All mutations were absent in 630 controls. We studied functions and possible pathogenicity by expressing mutations in HeLa cells with the use of Western blots and an in vitro translation and translocation system. Expression levels did not differ from those of controls, but all mutations showed hyperglycosylation in the in vitro translation and translocation system with canine microsomes. Functional analysis of human GABA(A) receptors (alpha 1 beta 3-v2 gamma 2S, alpha 1 beta 3-v2[P11S]gamma 2S, alpha 1 beta 3-v2[S15F]gamma 2S, and alpha 1 beta 3-v2[G32R]gamma 2S) transiently expressed in HEK293T cells with the use of rapid agonist application showed that each amino acid transversion in the beta 3-v2 subunit (P11S, S15F, and G32R) reduced GABA-evoked current density from whole cells. Mutated beta 3 subunit protein could thus cause absence seizures through a gain in glycosylation of mutated exon 1a and exon 2, affecting maturation and trafficking of GABAR from endoplasmic reticulum to cell surface and resulting in reduced GABA-evoked currents.

Novel mutations in Myoclonin1/EFHC1 in sporadic and familial juvenile myoclonic epilepsy

Background: Juvenile myoclonic epilepsy (JME) accounts for 3 to 12% of all epilepsies. In 2004, the GENESS Consortium demonstrated four missense mutations in Myoclonin1/EFHC1 of chromosome 6p12.1 segregating in 20% of Hispanic families with JME. Objective: To examine what percentage of consecutive JME clinic cases have mutations in Myoclonin1/EFHC1. Methods: We screened 44 consecutive patients from Mexico and Honduras and 67 patients from Japan using heteroduplex analysis and direct sequencing. Results: We found five novel mutations in transcripts A and B of Myoclonin1/EFHC1. Two novel heterozygous missense mutations (c.755C>A and c.1523C>G) in transcript A occurred in both a singleton from Mexico and another singleton from Japan. A deletion/frameshift (C.789del.AV264fsx280) in transcript B was present in a mother and daughter from Mexico. A nonsense mutation (c.829C>T) in transcript B segregated in four clinically and seven epileptiform-EEG affected members of a large Honduran family. The same nonsense mutation (c.829C>T) occurred as a de novo mutation in a sporadic case. Finally, we found a three-base deletion (−364○%–362del.GAT) in the promoter region in a family from Japan. Conclusion: Nine percent of consecutive juvenile myoclonic epilepsy cases from Mexico and Honduras clinics and 3% of clinic patients from Japan carry mutations in Myoclonin1/EFCH1. These results represent the highest number and percentage of mutations found for a juvenile myoclonic epilepsy causing gene of any population group. GLOSSARY: CAE = childhood absence epilepsy; FS = febrile seizures in infancy/childhood; GM = grand mal tonic clonic seizure; JME = Juvenile myoclonic epilepsy; PSW = 3–6 Hz polyspike and slow wave complexes; SW = single spike and slow wave complex.

Normal prism adaptation but reduced after-effect in basal ganglia disorders using a throwing task

Prism adaptation is a form of visuomotor learning in which the visual and motor systems need to be adjusted because a visual perturbation is produced by horizontally displacing prisms. Despite being known for over two centuries, the neuronal substrates of this phenomenon are not yet completely understood. In this article the possible role of the basal ganglia in this kind of learning was analysed through a study of Huntingtons and Parkinsons disease patients. A throwing technique requiring the use of open loop feedback was used. The variables analysed were visuomotor performance, adaptation rate and magnitude, and the after‐effect. The results clearly showed that both Huntingtons and Parkinsons disease groups learned at the same rate as control subjects. In addition, despite having a disturbed visuomotor performance, both experimental groups showed the same adaptation magnitude as the control group. Finally, the after‐effect, which is measured after removing the prisms, is reduced in both patients groups. This reduction leads to a disruption in the normal adaptation–after‐effect correlation found in normal volunteers. These results suggest that basal ganglia are not involved in this type of open‐looped visuomotor learning. The large number of patients studied as well as the similarity of the findings between both populations support this hypothesis. By contrast, there is an impairment in the after‐effect on both basal ganglia patient populations. This impairment may be the result of the deterioration of the perceptual recalibration process involved in visuomotor learning.

Distinct distribution of autosomal dominant spinocerebellar ataxia in the Mexican population

Dominant ataxias show wide geographic variation. We analyzed 108 dominant families and 123 sporadic ataxia patients from Mexico for mutations causing SCA1–3, 6–8, 10, 12, 17 and DRPLA. Only 18.5% of dominant families remained undiagnosed; SCA2 accounted for half (45.4%), followed by SCA10 (13.9%), SCA3 (12%), SCA7 (7.4%), and SCA17 (2.8%). None had SCA1, 6, 8, 12 or DRPLA. Among sporadic cases, 6 had SCA2 (4.9%), and 2 had SCA17 (1.6%). In the SCA2 patients we identified 6 individuals with the rare (CAG)33 allele, 2 of whom showed early onset ataxia. The distribution of dominant ataxia mutations in Mexicans is distinct from other populations.

Olfactory dysfunction in hereditary ataxia and basal ganglia disorders.

&NA; In the present study the olfactory system of hereditary ataxia patients was tested using the smell identification test. Two previous findings suggested a possible olfactory impairment in these patients. First, an olfactory dysfunction has been found in different neurodegenerative diseases, and second, human functional imaging has shown cerebellar activation during olfaction. As an initial approach to determine if cerebellar ataxia impairs the olfactory process, cerebellar ataxia patients, along with basal ganglia patients, were tested. The results show an olfactory deficit in both basal ganglia and hereditary ataxia patients. Further exploration of the olfactory capacities in hereditary ataxia is necessary to elucidate the specific nature of the deficits. NeuroReport 14:1339–1341

Clinical and genetic characteristics of Mexican Huntington's disease patients.

We report the characteristics of 691 Mexican patients with Huntingtons disease (HD). These patients, representing 401 families, constitute the largest series of Mexican HD cases as yet described in the literature. We found the clinical characteristics of these patients to be similar to those of other populations, but we observed a higher frequency of infantile cases, a shorter disease duration and a lower suicide rate. In 626 cases, for which molecular analyses were available, CAG‐trinucleotide expansion size ranged from 37–106 repeats. The large number of CAG repeats (19.04 ± 3.02) in normal alleles and the presence of new mutations suggest that the overall prevalence of HD in the Mexican population could be expected to be within range of, or higher than, that reported for Europeans.

Disruption of visual and motor connectivity in spinocerebellar ataxia type 7

Spinocerebellar ataxia type 7 (SCA7) is an autosomal‐dominant neurodegenerative disorder characterized by progressive ataxia and retinal dystrophy. It is caused by a CAG trinucleotide expansion in the ataxin7 gene. Anatomical studies have shown severe cerebellar degeneration and region‐specific neocortical atrophy in SCA7 patients. However, the impact of the neurodegeneration on the functional integration of the remaining tissue is still unknown. The aim of this study was to examine functional connectivity abnormalities in areas with significant gray matter atrophy in SCA7 patients and their relationship with number of CAG repeats. Using a combination of voxel‐based morphometry and resting‐state fMRI, we studied 26 genetically confirmed SCA7 patients and aged‐matched healthy controls. In SCA7 patients we found reduced functional interaction between the cerebellum and the middle and superior frontal gyri, disrupted functional connectivity between the visual and motor cortices, and increased functional coordination between atrophied areas of the cerebellum and a range of visual cortical areas compared with healthy controls. The degree of mutation expansion showed a negative effect on both the functional interaction between the right anterior cerebellum and the left superior frontal gyrus and the connectivity between the right anterior cerebellum and left parahippocampal gyrus. We found abnormal functional connectivity patterns, including both hypo‐ and hyperconnectivity, compared with controls. These abnormal patterns show reasonable association with the severity of gene mutation. Our findings suggest that aberrant changes are prevalent in both motor and visual systems, adding significantly to our understanding of the pathophysiology of SCA7.

Analysis of the (CAG)n repeat causing Huntington's disease in a Mexican population

We investigated the allele distribution of the polymorphic (CAG)n repeat in the IT15 gene in 96 normal subjects from the Mexican population and 83 unrelated patients with Huntingtons disease. Our results show that the size distributions of normal and affected alleles do not overlap. Normal alleles range from 13 to 32 triplets, with 18 being the most frequent allele, while HD alleles contain 37 to 76 repeats with 42 being the most frequent. One allele in the range of intermediate alleles was found (32 repeats) in a normal subject. The juvenile onset cases in this study are associated with an expansion greater than 49 repeats. In the available parent‐offspring pairs, paternal alleles show instability with an expansion of 28 repeats in one case.

Repeat interruptions in spinocerebellar ataxia type 10 expansions are strongly associated with epileptic seizures

Spinocerebellar ataxia type 10 (SCA10), an autosomal dominant neurodegenerative disorder, is the result of a non-coding, pentanucleotide repeat expansion within intron 9 of the Ataxin 10 gene. SCA10 patients present with pure cerebellar ataxia; yet, some families also have a high incidence of epilepsy. SCA10 expansions containing penta- and heptanucleotide interruption motifs, termed “ATCCT interruptions,” experience large contractions during germline transmission, particularly in paternal lineages. At the same time, these alleles confer an earlier age at onset which contradicts traditional rules of genetic anticipation in repeat expansions. Previously, ATCCT interruptions have been associated with a higher prevalence of epileptic seizures in one Mexican-American SCA10 family. In a large cohort of SCA10 families, we analyzed whether ATCCT interruptions confer a greater risk for developing seizures in these families. Notably, we find that the presence of repeat interruptions within the SCA10 expansion confers a 6.3-fold increase in the risk of an SCA10 patient developing epilepsy (6.2-fold when considering patients of Mexican ancestry only) and a 13.7-fold increase in having a positive family history of epilepsy (10.5-fold when considering patients of Mexican ancestry only). We conclude that the presence of repeat interruptions in SCA10 repeat expansion indicates a significant risk for the epilepsy phenotype and should be considered during genetic counseling.