A fragile secondary constriction on chromosome 2 in a severely mentally retarded patient.

A case is presented of an eighteen-year-old girl suffering from severe mental retardation associated with a fragile secondary constriction on the long arm of chromosome 2. The question of the relationship between the phenotypic and chromosomal abnormalities is discussed. We acknowledge the co-operation of Dr M. E. Elsarag and Dr K. M. Laurence in allowing this investigation to be made.