The Rett syndrome: genetics and the future.

Genetic and nongenetic explanations of female-limited disease, such as the Rett syndrome, are reviewed, with emphasis on the possibility of a disturbance of late-replicating X-chromosome heterochromatinization. A possible disturbance of X-chromosome late-replication, as demonstrated by BUdR terminal pulse-labelling is described for a specific Rett syndrome patient.