Thus, the unusual phenotypic features and mental retardation associated with the presence of a r(X) cannot be explained solely on the basis of presence or absence of XIST.
The expression patterns of XIST and the 3 X-linked genes androgen receptor (AR), fragile X mental retardation (FMR1 ) and Glypican 3 (GPC3 ) were studied by reverse transcriptase-polymerase chain reaction.
One of the cases with severe MR and a complete FXD pattern neither lacked the XIST gene nor had uniparental X isodisomy, and we discuss the mechanism of the failure of XCI in this case.
Small ring (X) chromosomes lacking the XIST gene at Xq13.2 have been associated with a severe phenotype that includes mental retardation, facial dysmorphism and congenital abnormalities.