Abstract
A whole X chromosome study of families in which Rett syndrome had been diagnosed in more than one member indicated that the region between Xq27 and Xqter was the most likely region to harbour a gene which may be involved in the aetiology of the disease. Further, more detailed studies of Xq28 detected weak linkage and a higher than expected sharing of maternally inherited alleles. It is suggested that there may be more than one gene involved in the aetiology of this syndrome, particularly as the very rare families in which more than one girl is affected often show variable clinical symptoms.