45,X 46,X, + R(X) CAN HAVE A DISTINCT PHENOTYPE DIFFERENT FROM ULLRICH-TURNER SYNDROME

We present a patient with 45,X/46,X, + r(X) mosaicism and lack of inactivation of either the normal or the ring X in the 46,X, + r(X) cells. The patient has mental retardation, syndactyly, minor facial anomalies, and a congenital heart defect. Although most patients with 45,X/46,X, + r(X) have the Ullrich-Turner syndrome, 2 previously described patients with this karyotype also had a distinct phenotype consisting of severe mental retardation, syndactyly, and abnormal face. The unusually severe phenotype in these patients was thought to be due to lack of X-inactivation of the ring X chromosome. The findings in our patient support this hypothesis.