Somatic mutation in MECP2 as a non-fatal neurodevelopmental disorder in males

Rett syndrome is a cause of severe learning disability in girls and is asso ciated with a characteristic history and movement disorder. it is an X-link ed dominant condition associated with mutations of the MECP2 gene on the di stal part of the X-chromosome. If present in a male conceptus, the mutation is usually lethal. We present evidence to show that males can be affected by Rett syndrome. In the boy presented, this situation came about because c ells containing the MECP2 mutation existed alongside a normal cell line. So matic mosaicism could explain the occurrence of other X-linked dominant dis orders in males, when they would normally be lethal.