Schmidt M, Du Sart D, Kalitsis P, Fraser N, Leversha M, Voullaire L, Foster D, Davies J, Hills L, Petrovic V
Murdoch Institute, Royal Children's Hospital, Parkville, Melbourne, Australia.
Am J Med Genet. 1991 Feb-Mar;38(2-3):411-5. doi: 10.1002/ajmg.1320380252.
Over 30% of female carriers of the fragile X [fra(X)] syndrome are clinically affected. A nonrandom X chromosome inactivation in these cases could be a plausible explanation. A review of previous studies addressing this question showed inconclusive results; thus, we analysed the X inactivation pattern in fibroblasts of 4 unrelated, mentally retarded fra(X) carriers with a high expression of the fragile site Xq27.3. Using Southern analysis with a highly polymorphic probe M27 beta that recognizes methylation differences between the active and inactive X chromosome we found a 50/50 inactivation pattern in 2 cases and skewed patterns in the other 2. As biased patterns were also observed in control females we conclude that at present no evidence exists for a nonrandom X chromosome inactivation in the fra(X) syndrome in females.
