Rett syndrome and genetic drift

An X chromosome gene is assumed to be responsible for the cause of Rett syn drome (RS). However, new genealogical observations suggest involvement of a utosomal recessive gene(s) as well, at least in familial cases, To account for these and other recent observations, the theoretical model presented in 1990 by the authors of this paper is applied to the calculation of gene fr equencies. Observed frequencies of sporadic and familial cases of RS are us ed, taking into account genetic drift in inbreeded areas. Moreover, an atte mpt is made to use the proportion of RS variants in familial and sporadic c ases for the explanation of so called 'formes frustes', and as evidence for the existence of female as well as male carriers. The estimated frequency of the recessive autosome mutation, or possibly a frequent polymorphism, is 22.5%. (C) 1999 Elsevier Science B.V. All rights reserved.