Inbreeding and genetic disease in Sottunga, Finland

Abstract

The contribution of inbreeding to the prevalence of recessive genetic diseases in the Åland Island parish of Sottunga is investigated. Genealogical data for 3,030 individuals spanning up to 15 generations were used to estimate inbreeding. This small island community shows a low average inbreeding value of .0031 for the period 1725–1975. A cohort analysis shows that inbreeding increased from 1750 to 1900, when maximum inbreeding for those born in Sottunga reached .0057. A sharp decline in inbreeding occurred thereafter. Individuals with island-born parents made the largest contributions to inbreeding in all time periods compared to those with one or two migrant parents. These trends are consistent with changing migration patterns and isolate breakdown in Åland since 1900. An analysis of pedigree development demonstrates that remote consanguinity contributed more to inbreeding through time than close consanguinity. Both the number of common ancestors and the number of paths of relationship between spouses increased dramatically through time, the latter at a much faster rate. The contribution to average inbreeding per path, however, diminished rapidly through time. This analysis indicates that inbreeding does not account for the high incidence of autosomal recessive disorders, such as tapetoretinal disease, found in the parish.