Bornholm eye disease (BED) consists of X-linked high myopia, high cylinder,optic nerve hypoplasia, reduced electroretinographic flicker with abnormalphotopic responses, and deuteranopia. The disease maps to chromosome Xq28and is the first designated high-grade myopia locus (MYP1). We studied a second family from Minnesota with a similar X-linkedphenotype, also of Danish descent. All affected males had protanopia insteadof deuteranopia.
X chromosome genotyping, fine-point mapping, and haplotype analysisof the DNA from 22 Minnesota family individuals (8 affected males and 5 carrierfemales) and 6 members of the original family with BED were performed. Haplotypecomparisons and mutation screening of the red-green cone pigment gene arraywere performed on DNA from both kindreds.
Significant maximum logarithm of odds scores of 3.38 and 3.11 at thetas;= 0.0 were obtained with polymorphic microsatellite markers DXS8106 and DXYS154, respectively, in theMinnesota family. Haplotype analysis defined an interval of 34.4 cM at chromosomeXq27.3-Xq28. Affected males had a red-green pigment hybrid gene consistentwith protanopia. We genotyped Xq27-28 polymorphic markers of the family withBED, and narrowed the critical interval to 6.8 cM. The haplotypes of the affectedindividuals were different from those of the Minnesota pedigree. Bornholmeye disease–affected individuals showed the presence of a green-redhybrid gene consistent with deuteranopia.
Because of the close geographic origin of the 2 families, we expectedaffected individuals to have the same haplotype in the vicinity of the samemutation. Mapping studies, however, suggested independent mutations of thesame gene. The red-green and green-red hybrid genes are common X-linked colorvision defects, and thus are unrelated to the high myopia and other eye abnormalitiesin these 2 families.
X-linked high myopia with possible cone dysfunction has been mappedto chromosome Xq28 with intervals of 34.4 and 6.8 centimorgan for 2 familiesof Danish origin.