COEXISTENCE OF MACULAR CORNEAL-DYSTROPHY TYPE-I AND TYPE-II IN A SINGLE SIBSHIP

Background-Macular corneal dystrophy (MCD) is an inherited autosomal r ecessive disorder that has been subdivided into two primary immunophen otypes, MCD types I and II. The MCD type I gene has been localised pre viously to chromosome 16q22 and suggestive evidence provided that MCD type II gene is also linked to this region. Here an unusual family is reported where both MCD types I and II are found in a single sibship. Methods-Immunoreactivity to an anti-keratan sulphate monoclonal antibo dy (5-D-4) was evaluated in patients' serum and in corneal tissue obta ined at keratoplasty. Chromosomal haplotypes were constructed using mi crosatellite repeat markers spanning the region of the MCD type I locu s. Results-Immunological studies demonstrated that two of the affected siblings have MCD type II while one has MCD type I. Haplotype analysi s suggests that all three affected sibs inherited one identical parent al haplotype. However, the two MCD types differ in their alternative c hromosome with both MCD type II children sharing an identical haplotyp e, different from their MCD type I sibling.Conclusion-The findings in this study support the hypothesis that the genes for MCD types I and I I co-localise to the same region of chromosome 16 and are likely to be due to allelic manifestations of the same abnormal gene.