Practical and theoretical considerations concerning the genetics of the Rett syndrome.

The Rett syndrome is exclusively found in girls. Considerable interest has been focused on a possible genetic background. The evidence for such an etiology is not conclusive and the findings in support of such a hypothesis are given. The few twin data and family data together with the chromosomal investigation indicate an X-linked inheritance. The recurrence risk in a family with one Rett girl is about 0.3%. Prenatal diagnosis is not recommended for the time being, as the only diagnosis, possible is prenatal sexing and most girls are healthy as the recurrence risk is low.