Mental Retardation in A Girl with Turner's Syndrome with An Active Ring X Chromosome Missing XIST

Abstract

We report a three-year-old girl with mental retardation (MR) (developmental quotient, ~30) and syndactyly of the right 3rd and 4th fingers, together with common features of Turner's syndrome. Chromosomal analysis for peripheral lymphocytes showed a 45, X[97]/46, X, r(X)[3] karyotype, and fluorescence in situ hybridization analysis revealed loss of XIST from the ring X chromosome. The results suggest that MR of this girl is attributable to active disomy of the ring X chromosome missing XIST. Although the r (X) chromosomes are rarely present in rapidly dividing lymphocytes in the present type of case, they would be preserved in a fairly large fraction of the central nervous cells which stop mitosis in early fetal life.