A computer-oriented linkage analysis scheme

Linkage studies of Best's macular dystrophy

Genetic linkage studies are presented for nine kindreds with Best's vitelliform macular dystrophy (BVMD). This condition is an autosomal dominant macular dystrophy with reduced penetrance and highly variable expressivity. Asymptomatic carriers were identified with electro-oculography, fundus photographs and fluorescein angiography. Blood and saliva specimens were obtained from informative family members and genotyped for 26 polymorphic genetic traits. No firm evidence was found for linkage between BVMD and 18 informative markers; the highest positive lod score was z = 0.57 for GPT1 at a recombination fraction of theta = 0.30. An atypical form of vitelliform macular dystrophy (VMD-1) is linked to GPT1 (theta less than 0.05) and is provisionally assigned to chromosome 16pter-p11. Our data are not sufficient to rule out loose linkage for GPT1 and BVMD. Thus we were not able to determine whether BVMD and VMD-1 are allelic mutations or separate genetic disorders. Additional linkage and gene mapping studies of these loci and BVMD (as well as other atypical forms of macular dystrophy) would be useful to further delineate these disorders.

The development of human linkage analysis

The principles of linkage detection and measurement are traced from the first discovery of linkage to its present-day use in human genetics. Some indications are given of their success and of the present problems and challenges facing them.

A linkage study of HLA and inherited adenocarcinoma of the colon

A kindred with the familial cancer syndrome is reported in which every confirmed affected member of the pedigree had at least one primary carcinoma of the colon. The average age at which cancer appeared was 38 years, and multiple primary neoplasm occurred in 23% of the cancer patients. Transmission of the cancer trait is consistent with an autosomal dominant mode of inheritance. Colonoscopy eliminated the presence of any unsuspected cancers in family members at risk. HLA typing was done, and by direct typing or inference, data were available on 66 living and deceased individuals. There were four informative matings in the kindred, the offspring of which showed only three crossovers of a possible 17. The lod score totaled 1.06 at a recombination fraction of 0.20. The need for cooperative efforts of many investigators in HLA linkage studies is emphasized, along with the potential value of such an approach.