X-inactivation in girls with Rett syndrome.

Cytogenetic studies have been carried out on a series of nine girls with Rett syndrome, six of their mothers and nine normal female controls. No abnormality of the X-chromosome has been observed in any subject. X-inactivation studies using various methods of detecting the timing of individual band replication were performed. The overall pattern seen was essentially the same in all subjects, but in the patients with Rett syndrome there may be an alteration in the timing of the X-inactivation process in the region Xp11.3 or 4→Xp21