The 2588G→C Mutation in the ABCR Gene Is a Mild Frequent Founder Mutation in the Western European Population and Allows the Classification of ABCR Mutations in Patients with Stargardt Disease

In 40 western European patients with Stargardt disease (STGD), we found 19 novel mutations in the retina-specific ATP-binding cassette transporter ( ABCR) gene, illustrating STGD's high allelic heterogeneity. One mutation, 2588G→C, identified in 15 (37.5%) patients, shows linkage disequilibrium with a rare polymorphism (2828G→A) in exon 19, suggesting a founder effect. The guanine at position 2588 is part of the 3′ splice site of exon 17. Analysis of the lymphoblastoid cell mRNA of two STGD patients with the 2588G→C mutation shows that the resulting mutant ABCR proteins either lack Gly863 or contain the missense mutation Gly863Ala. We hypothesize that the 2588G→C alteration is a mild mutation that causes STGD only in combination with a severe ABCR mutation. This is supported in that the accompanying ABCR mutations in at least five of eight STGD patients are null (severe) and that a combination of two mild mutations has not been observed among 68 STGD patients. The 2588G→C mutation is present in 1 of every 35 western Europeans, a rate higher than that of the most frequent severe autosomal recessive mutation, the cystic fibrosis conductance regulator gene mutation ΔPhe508. Given an STGD incidence of 1/10,000, homozygosity for the 2588G→C mutation or compound heterozygosity for this and other mild ABCR mutations probably does not result in an STGD phenotype.