Macular degeneration associated with aberrant expansion of trinucleotide repeat of the SCA7 gene in 2 Japanese families

Abstract

Objective: To evaluate the macular function of Japanese patients with a trinucleotide repeat expansion in the spinocerebellar ataxia type 7 (SCAT) gene. Methods: Ophthalmic findings in patients whose DNA analysis revealed expanded alleles of the trinucleotide repeat in the SCA7 gene were evaluated. Results: Trinucleotide repeat was expanded from 40 to 48 in affected patients (control subjects, 12 repeats). Affected patients were characterized by different degrees of visual acuity decrease (0.09-0.9), a tritan axis color vision, a coarse granular appearance of the macular region on scanning laser ophthalmoscopy, depression of multifocal electroretinograms, and macular degeneration. However, pigmentary changes were not observed in the retina. The trinucleotide repeat was longer and the onset of macular dysfunction was earlier in the younger generation. One patient in a family manifested decreased visual acuity 10 years preceding other neurologic signs. Conclusions and Clinical Relevance: Patients with SCA7 mutations showed macular dysfunction or degeneration with expansion of CAG repeat in the SCA7 gene. However, the lesions were less pigmented than those previously reported. Patients also showed ophthalmologic anticipation, which has not been reported for the ocular changes in other patients who have trinucleotide repeat expansion of the responsible genes.