Clinical features of a Stargardt-like dominant progressive macular dystrophy with genetic linkage to chromosome 6q.

BACKGROUND AND OBJECTIVE

We identified a large family affected with a macular dystrophy whose main clinical features are similar to those of Stargardt's disease. Unlike true Stargardt's disease, the disorder in this family is inherited in an autosomal dominant fashion. We sought to identify the chromosomal location of the disease-causing gene and to clinically define the phenotype in a number of affected family members.

METHODS

Thirty-two family members underwent clinical examination. A total of 23 affected family members were identified, and these patients were genotyped at candidate loci with short tandem repeat polymorphisms. The LINKAGE computer program was used for linkage calculations.

RESULTS

Affected patients had normal vision in early childhood but began to experience difficulty with central vision between 5 and 23 years of age. Fundus examination early in the disease course revealed flecks in the macula. Central atrophy developed later, with visual acuity decreasing to 20/200 or worse in all patients older than 31 years. Fluorescein angiography revealed no evidence of choroidal silence. Electroretinograms were near normal in younger affected individuals and were most notable for prolonged implicit times in a 73-year-old patient. Chromosome linkage analysis revealed the disease-causing gene to be located near the centromere on the long arm of chromosome 6. The maximum lod score was 5.5 (theta = 0) with marker D6S280. Multipoint analysis resulted in a peak lod score of 6.2 in the interval between markers D6S313 and D6S252 and excluded the interval containing the North Carolina macular dystrophy gene.

CONCLUSIONS

This autosomal dominant macular dystrophy is clinically similar to Stargardt's disease, with the exception of its pattern of inheritance. The clearly progressive nature of the disease distinguishes it from North Carolina macular dystrophy, whose causative gene is also located on the long arm of chromosome 6. Identification of the gene involved in this disease may provide clues to the pathogenesis of age-related macular degeneration.