Genetic analysis of multiple sclerosis in Shetland.

In a family study of all patients with multiple sclerosis in Shetland the number of inbred patients, although high for Britain and higher than in Orkney, is not higher than the number among controls, and the inbreeding coefficients suggest that there is no recessive involvement of rare genes in the aetiology. The kinship coefficients show close interweaving of ancestries of patients and controls and eliminate from the aetiology any involvement of recently introduced single genes dominant or codominant in effect. Family histories show that single locus inheritance is unlikely. Any genetic involvement is likely to be polygenic, but on a multifactorial hypothesis the estimates of heritability are very low. The findings suggest that the genetic contribution to the aetiology of the disease in Shetland is slight.