Clinical Study: XIST Gene and Pattern of X-Inactivation in Children with Ring-X Turner Syndrome

Objectives: To evaluate the presence of XIST on ring X and to correlate the pattern of ring X replication to the IQ level. Subjects: Fifteen cases with TS who had 45,X/46,X,r(X). They were subjected to I.Q. estimation, FISH using WCP for X, locus specific identifier for XIST, differential replication pattern with BrdU for r(X). Results: By FISH, it was noted that these rings were derived entirely from the X chromosome. XIST was not deleted in all cases, a very small percentage of mosaic cell line was found in three cases who had deleted XIST and also two of them had double r(X). Ten cases had small rings, 5 had large rings. MR was found in 90% of cases with small r(X) while the large r(X) had normal mentality. A significant correlation was found between the presence of small ring X and lower IQ level. The correlations between the IQ level and age at presentation, percentage of r(X) and presence of active r(X) were not reaching a significant level. Conclusion: FISH is useful in identification of hidden cell line. The mentality in TS is affected by the presence of small r(X) and the presence of functioning XIST gene on the r(X).