gms | German Medical Science

Myopia affects more than 20% of all individuals in the Caucasian population and is associated with increased risk of visual loss. The etiology of myopia is complex. Experiments have emphasized the importance of visual input in emmetropisation but it is also evident that the development of human myopia is influenced by genetic factors. Autosomal dominant transmission with weak penetrance is assumed by several authors. Two discrete loci have been identified for dominantly inherited simple high myopia. Five loci have so far been identified to be probably involved in these process. An X-linked recessive form (MYP1) and four autosomal forms (MYP2/18p11, MYP3/12q21, MYP4/ 7q36 and MYP5/17q21).

In total eight families were available for moleculargenetic analysis. Blood samples were collected from 97 consenting participants. A prerequisite for the inclusion in the study as myopic a refractive error of > -3dpt was necessary. Linkage analysis was performed in one great 30 person family with 15 myopic individuals using the markers D12S1706, D12S327 on chromosomes 12 and the markers D18S63 and D18S481 on chromsome 18.

Linkage analysis was initiated in the largest family with 15 myopic individuals using markers spanning the target regions on chromosomes 18p and 12q. While the latter locus could be excluded, the phenotype segregated in 12 of 15 affected individuals with an identical haplotype on chromosome 18p. This haplotype was also found in 5 of 8 dependant unaffected individuals.

Acceptance of linkage to chromosome 18p in this family is conditional on the occurrence of phenocopies and reduced penetrance in this pedigree. Haplotyping of the other families with the known loci and a whole genome scan to search for susceptibility loci in families with nonsyndromic myopia are underway.