A chromosome survey of a hospital for the mentally subnormal.

A cytogenetic survey of 756 resident, but otherwise unselected, mentally retarded patients in a Scottish hospital is reported. The karyotypes of all patients were examined using orcein-stained cells, and those found to be abnormal, other than those with standard trisomy 21, were further investigated using a banding technique. A total of 103 patients were found to have an abnormal chromosome complement, of whom 91 had Down's syndrome (including six with translocations), six had some other autosomal abnormality, and six had an abnormality of the sex chromosome complement, including two with an XXYY complement. Details of the clinical and cytogenetic features are presented.