Genetic implications of Rett syndrome.

Cytogenetic analysis in 14 girls with the Rett syndrome revealed a deletion on the short arm of the X chromosome (del(X) (pter;p22] in one, and a fragile site on chromosome Xp22 in six of the girls. Two hypotheses concerning the genetic background to the Rett syndrome are suggested; an X-linked dominant mutation theory and a two-step mutation theory.