Clinical diversity and chromosomal localization of X-linked cone dystrophy (COD1)

X-linked progressive cone dystrophy (COD1) causes progressive deterioration of visual acuity, deepening of central scotomas, macular changes, and bull's-eye lesions. The cone electroretinography (ERG) is variably abnormal in affected males, and the rod ERG may also be abnormal. The clinical picture of heterozygous females ranges from asymptomatic to a widespread spectrum of cone-mediated dysfunction. A prior linkage study demonstrated linkage between the COD1 locus and the marker locus DXS84, assigned to Xp21.1, with no recombination. In the present study, we have clinically characterized a large four-generation family with COD1 and have performed a linkage analysis using seven polymorphic markers on the short arm of the X chromosome. No recombination was observed between the disease and the marker loci DXS7 and MAOA, suggesting that the location of COD1 is in the region Xp11.3, distal to DXS84 and proximal to ARAF1.