Autosomal dominant Stargardt-like macular dystrophy - Founder effect and reassessment of genetic heterogeneity

Objectives: To characterize a disease-associated haplotype in 7 families wi th autosomal dominant Stargardt-like macular dystrophy and to determine whe ther these families share a common ancestor. Methods: Twenty-five polymorphic DNA markers spanning known dominant Starga rdt-like gene loci were used to determine the haplotype associated with dis ease. In addition, an extensive genealogical investigation searching for a common ancestor shared by all of the 7 families was performed. Results: We clinically evaluated 171 patients and genotyped 145 samples. Th e same DNA haplotype on chromosome 6q16 was shared by all evaluated affecte d members within the 7 families. In addition, we were able to genealogicall y join all of the families into one larger family consisting of 31 branches and 2314 individuals. Twenty-seven branches have known living descendants, with 7 branches having affected family members. In addition, we refined th e critical region for the gene to approximately 1000 kilobases (kb) and eli minated part or all of 9 candidate disease-causing genes. Conclusions: Our study indicates that most reported cases of autosomal domi nant Stargardt-like macular dystrophy in North America are part of a single larger family associated with a gene locus on chromosome 6q16. Furthermore , the DNA haplotype associated with disease is useful in excluding individu als with phenotypically similar retinal conditions. Clinical Relevance: The disease-associated haplotype allows for more accura te genetic counseling to be given to individuals with a Stargardt-like phen otype inherited in an autosomal dominant pattern.