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T. Takeuchi, T. Hayashi, S. Goto–Omoto, T. Gekka, H. Yamada, A. Kurita, K. Inoue, K. Kitahara; Two Patients With Spinocerebellar Ataxia Type 7 (SCA7) in a Japanese Family: Ophthalmic and Genetic Features . Invest. Ophthalmol. Vis. Sci. 2006;47(13):4624.
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Spinocerebellar ataxia type 7 (SCA7) is a rare autosomal dominant neuro–degenerative disease with macular degeneration. The disorder has been shown to be caused by the expansion of CAG repeats in the first coding exon of the SCA7 gene. The aim of this study was to investigate ophthalmic and genetic features of two patients in a Japanese SCA7 family.
In a 25–year–old female proband, best–corrected visual acuity (BCVA), funduscopy, Goldmann kinetic perimetry, full–field electroretinography and optical coherence tomography were performed. Blood samples were obtained from the proband and her affected mother. To determine the number of CAG repeats of the SCA7 gene, PCR amplification was performed using primers, one of which was FAM–labeled, followed by analysis with a DNA analyzer (ABI 3700) and the GeneScan software.
BCVA was 0.1 in both eyes. The proband had atrophic macular degeneration and central scotomas with I–2e targets. The full–field electroretinograms showed normal rod b–waves and normal mixed rod–plus–cone responses, but significantly reduced cone and 30–Hz flicker responses. Genetic analysis revealed that the number of CAG repeats was 43 to 57 with a peak with 47 or 48 repeats, in addition to wild–type alleles with 10 CAG repeats in both the patients.
The ocular manifestation of the proband indicated progressive cone dystrophy with impaired central visual function. Anticipation and germline instability are seen within SCA7 families particularly when transmitted by a male. There was no difference in the peak of CAG repeats between the proband and her mother, suggesting meiotic stability during maternal transmission. The variation of the CAG repeat number may indicate somatic mosaicism due to mitotic instability. Support: Ministry of Education, Culture, Sports, Science and Technology Japan (TH) (#16791073)
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