Purpose: Myopia, or nearsightedness, is a visual disorder of high and growing prevalence in the United States and in other countries. Pathologic high myopia, or myopia of </=-6.00 D, predisposes individuals to retinal detachment, macular degeneration, cataracts, and glaucoma. Autosomal dominant (AD) nonsyndromic high-grade myopia has been mapped to loci on 18p11.31, 12q21-q23, 17q21-q23, and 7q36. This is the report of significant linkage to a novel locus on the long arm of chromosome 2 in a large, multigenerational family with AD high-grade myopia.
Methods: The family contains 31 participating members (14 affected). The average spherical refractive error for affected individuals was -14.46 D (range, -7.25 to -27.00). Before a genome screening was undertaken, linkage to intragenic or flanking markers for the myopic genetic syndromes of Stickler syndrome types I, II, and III; Marfan syndrome; and juvenile glaucoma were ruled out. In addition, no linkage was found to the known AD high-grade myopia loci listed above. A full genome screen of the family was performed with 382 microsatellite markers with an average intermarker distance of 10 cM. SimWalk2 software was used for multipoint linkage analysis based on an AD model with a penetrance of 90% and a disease allele frequency of 0.01.
Results: Fine-point mapping with an additional nine custom-made and five commercial markers yielded a maximum two-point lod score of 5.67 at marker D2S2348. Results of multipoint analysis indicate that the 1-unit support intervals for this new locus spans approximately 9.1 cM from (238.7 to 247.8 cM) on the chromosome 2 genetic map at q37.1.
Conclusions: A novel locus for AD high-grade myopia has been determined, providing further evidence of genetic heterogeneity for this disorder.