X-inactivation pattern in an Ullrich-Turner syndrome patient with a small ring X and normal intelligence

In a description of 8 girls who had Ullrich-Turner syndrome (UTS) with a small r(X), mental retardation, and other unusual findings, it was hypothesized that the distinctive phenotype was associated with the loss of the X inactivation center from the r(X) and lack of genetic inactivation of the ring [Van Dyke et al., 1992]. Here, we present a 17-year-old young woman with 45,X/46,X,r(X)(?p11q13) mosaicism, Ullrich-Turner syndrome, and normal intelligence. In situ hybridization with the X-centromere DNA probe DXZ1 (Oncor, Inc., Gaithersburg, MD) was performed on previously G-banded slides, and the probe hybridized to the centromere regions of the normal X and the ring. The r(X) appears to be inactivated since a buccal smear demonstrated 5% Barr bodies. Furthermore, DAPI stain and FISH analysis with the X-centromere DNA probe DXZ1 was employed to distinguish the inactive X from the active X, and verified the presence of a sex chromatin mass in fibroblasts. These observations are consistent with the active-ring-X-and-mental-retardation hypothesis since the ring in this patient, although very small, appears to be normally inactivated and she has normal intelligence.