Genetic disorders on the island of St Helena.

The island of St Helena lies in the South Atlantic ocean and is isolated by distance from any land mass and by lack of a harbour or airfield. In these circumstances there could be an unusual pattern of inherited disease, and for this reason we have attempted to document the presence and frequency of genetic conditions in the population, which numbers approximately 5 500. Genetic disorders identified included autosomal dominant genu valgum, hereditary angioneurotic oedema, Christmas disease and pseudo-achondroplasia. The presence of the autosomal recessive form of retinitis pigmentosa provides a possible explanation for the occurrence of that condition in the islanders of Tristan da Cunha, since they have ancestral links with the St Helena community. The recognition of these genetic disorders in this isolated population has practical implications in terms of clinical management and the provision of medical services.