Rett syndrome: a search for gene sources.

A series of 77 Swedish females with classical Rett syndrome were genealogically traced as far back as possible, in most cases to 1720-1750, or 7-10 generations. Details were collected concerning approximately 8,000 ancestors. Common ancestry was seen in 2 pairs of females with Rett syndrome. Thirty-nine of the 77 Rett females were traced to 9 small and separate rural areas, and 17 pairs even came from the same farm or homestead. The common origin was found equally often among descendants of the father as of the mother. In 9 cases, the father came from one and the mother from another of the 9 specific "Rett areas." These observations, combined with the finding of a raised rate of consanguineous marriages in the paternal as well as in the maternal ancestry, point to a genetic transmission. Analyses of parental ages at birth and of birth order gave normal results.