Mental retardation in association with a balanced X-autosome translocation and random inactivation of the X chromosomes.

A women whose karyotype shows an apparently balanced reciprocal translocation, 46,X,t(Xq +; 10q-) is described. She is profoundly mentally retarded and shows minor physical abnormalities with normal sexual development. There is a random pattern of late replication of the normal X and X involved in the translocation, whereas in most balanced X-autosome translocations there is preferential inactivation of the normal X.