Predisposing chromosome for spinocerebellar ataxia type 6 (SCA6) in Japanese

Spinocerebellar [corrected] Ataxia Type 6: Molecular Mechanisms and Calcium Channel Genetics

Spinocerebellar ataxia (SCA) type 6 is an autosomal dominant disease affecting cerebellar degeneration. Clinically, it is characterized by pure cerebellar dysfunction, slowly progressive unsteadiness of gait and stance, slurred speech, and abnormal eye movements with late onset. Pathological findings of SCA6 include a diffuse loss of Purkinje cells, predominantly in the cerebellar vermis. Genetically, SCA6 is caused by expansion of a trinucleotide CAG repeat in the last exon of longest isoform CACNA1A gene on chromosome 19p13.1-p13.2. Normal alleles have 4-18 repeats, while alleles causing disease contain 19-33 repeats. Due to presence of a novel internal ribosomal entry site (IRES) with the mRNA, CACNA1A encodes two structurally unrelated proteins with distinct functions within an overlapping open reading frame (ORF) of the same mRNA: (1) α1A subunit of P/Q-type voltage gated calcium channel; (2) α1ACT, a newly recognized transcription factor, with polyglutamine repeat at C-terminal end. Understanding the function of α1ACT in physiological and pathological conditions may elucidate the pathogenesis of SCA6. More importantly, the IRES, as the translational control element of α1ACT, provides a potential therapeutic target for the treatment of SCA6.

Mutation analysis of CACNA1A gene in Iranian migrainous and review literatures

BACKGROUND

There are contrary results about the role of CACNA1A gene in the causation of common migraine in different populations. However, migraine may be genetically heterogeneous and more studies in different families and populations are required for a definite conclusion. The aim of this study was to surveyed leukocyte genomic DNA mutation of CACNA1A in Iranian migraine patients with [MA] and without aura [MO] who has family history of migraine and we performed a narrative review of all studies that evaluated CACNA1A gene, non-hemiplegic migraine [MA and MO] and FHM [familial hemiplegic migraine].

MATERIALS AND METHODS

The 30 patients with family history of migraine were selected for mutations analysis for CACNA1A gene by PCR method. For review, we searched MEDLINE-PUBMED, ISI, Scopus and Cochrane databases up to December 2012.

RESULTS

Mutation analysis of the 4 exons of the CACNA1A gene in these patients revealed no mutations in this gene. Direct sequencing revealed a polymorphism previously reported G to A transition in the exon 16 [nt2369, G→A] in 9 patients. In review, the correlation of FHM loci [CACNA1A gene] with MA and MO has been showed in different population and only small population from Caucasians presented this correlation.

CONCLUSION

CACNA1A is most likely not a major susceptibility gene for common migraine in Iranian maigrainous. It's essential to study more on larger series and covering all 47 exons of the CACNA1A gene to confirm this hypothesis.

Thr698Thr (nt2369) polymorphism on CACNA1A gene and head pain severity in familial migraine

BACKGROUND

Migraine is a common neurological disorder with a significant genetic component. Less information is known about the contribution of minor genetic variations, such as single nucleotide polymorphism (SNP) on the migraine process. In the present study, we aim to investigate the role of CACNA1A gene polymorphism on severity and related factors in family positive migraine patients.

MATERIALS AND METHODS

We included 74 common migraine patients consequently. Headache severity was evaluated according to Headache Impact Test (HIT6) questionnaire and quality of life of patients was investigated according to MSQ (Migraine-Specific Quality of Life Questionnaire v2.1) questionnaire. Thirty patients with positive family history of migraine were selected and sequencing analysis after DNA extraction was performed.

RESULTS

Direct sequencing revealed a known SNP G to A transition in the exon 16 (nt2369, G → A) in 9 patients. There was no significantly correlation between polymorphism and type of migraine, severity, frequency, duration and quality of life in family positive migraine. Evaluated migraine severity by HIT6 questioner couldn't act as a risk factor for this polymorphism (OR: 0.93, CI%95 0.82-1.06 P = 0.3).

CONCLUSION

In Iranian population no significant association was seen between Thr698Thr (nt2369) polymorphism and head pain severity in familial migraine. Confirmation of this hypothesis needs further investigation.

Molecular epidemiology of spinocerebellar ataxia type 6

We performed a population-based clinical and molecular genetic study of spinocerebellar ataxia type 6 (SCA6) in the northeast of England. The minimum point prevalence of SCA6 was 1.59 in 100,000 (95% confidence interval [CI], 1.04-2.14), and the number of individuals who either had SCA6 or are at risk of developing SCA6 was at least 5.21 in 100,000 (95% CI, 4.31-6.10), or 1 in 19,210. Microsatellite analysis of the CACNA1A gene indicated a founder effect for SCA6 within this region.

A novel haplotype of spinocerebellar ataxia type 6 contributes to the highest prevalence in Western Japan

The highest prevalence rate of spinocerebellar ataxia type 6 (SCA6) in the worldwide population is in the Chugoku and Kansai areas of Western Japan, but the reason of this geographic characteristics is unclear. We investigated the predisposing haplotypes and their geographic distribution. Genotyping of five microsatellite markers and three single nucleotide polymorphisms linked to the CACNA1A gene in 150 Japanese SCA6 patients from unrelated 118 families revealed three major haplotypes, carrying a pool of one common haplotype core. A founder chromosome was thought to have historically diverged into at least three types. One of the major haplotypes newly identified showed a strong geographical cluster around the Seto Inland Sea in the Chugoku and Kansai areas of Western Japan, whereas the others were widely distributed throughout Japan. The distribution of predisposing haplotypes contributes to the geographical differences in prevalence of SCA6.

Meiotic instability of the CAG repeats in the SCA6/CACNA1A gene in two Japanese SCA6 families

Intergenerational stability of the CAG repeat number has been considered to be a specific molecular feature of SCA6 compared with other CAG repeat diseases. Nevertheless, we showed meiotic instability of the CAG repeats in the SCA6/CACNL1A gene in two Japanese SCA6 families, including de novo expansion. In one family, the CAG20 allele expanded to the CAG26 one during paternal transmission, and in the other family, the CAG19 allele expanded to the CAG20 one during maternal transmission. Although it is controversial as to whether the CAG20 allele is pathological or not, this is the first case of haplotype analysis-proven de novo expansion in SCA6, confirming the derivation of an expanded allele from one normal allele. We should carefully follow up the individuals carrying the CAG20 allele in our family who show normal neurological and radiological findings at present.