Somatic and intellectual development in a patient with 47,XX,psu dic(X)(p11.2) chromosome constitution.

An unusual form of X chromosome aneuploidy, 47,XX,psu dic(X)(p11.2), was found during an evaluation for short stature of a prepubertal girl. Unlike 45,X, 47,XXX, 48,XXXX, and 49,XXXXX females, this patient is phenotypically normal except for her short stature, which appears to be unrelated to her chromosome abnormality. X chromosome inactivation studies disclosed inactivation (late replication) of one normal X and the abnormal X chromosome in all cells examined from this patient. Therefore, she is disomic for early-replicating distal Xp loci, found in inactivated X chromosomes, and thought to remain active after lyonization. These data suggest that the presence of three or more copies of the early-replicating, active Xp loci may be responsible for the cognitive deficits and other phenotypic abnormalities seen in and other phenotypic abnormalities seen in polysomy X females.