Abstract
The ability to identify the inactivated X chromosome with routine G- or Q-banding would have broad clinical and research applicability. We recently reported that the inactivated X frequently bends or folds in region Xql3Xq21 (Flejter et al, Am J Hum Genet 36:218, 1984). The fold occurs in about 88% of prometaphase, 50% of early metaphase, 30% of midmetaphase, and 10% of late metaphase inactive X's. In prometaphase, the site of folding includes Xq11.2 and Xq13.3, infrequently extending to Xq21.1. An omega-shaped loop is frequently formed between sub-bands Xq11.2 and Xq13.3. It is paradoxical that the inactive X is the only chromosome identifiable in interphase, yet in metaphase it cannot be distinguished from its active homolog. The specific inactivation-associated fold at region Xq1 resolves that paradox and is a useful marker of the inactive X. 1. The KOP translocation, t(X; 14)(q13; q32), has nearly all of Xq translocated to 14q (Allerdice et al, Am J Med Genet 2:223, 1978). Cell line GM0074 has one normal 14, one Xq-, two der (14) chromosomes, and a Y. One der(14) folded in 10/18 cells scored, confirming translocation of the inactivation center adjacent to 14q distal. 2. Metaphase cells from other primates had a specific fold in the same region as in the human X: at Xq13-Xq21 in 2 gorillas, 1 chimp, 2 pygmy chimps, 1 orang, 1 baboon, 1 rhesus and 1 stump-tail monkey. This is further evidence for evolutionary conservation of the X chromosome. One chimpanzee exhibited the fold at Xq24; we suspect a pericentric inv in this individual. We have not seen a frequent fold in the X of a bat (Tadarida brasiliensis), Chinese hamster (Cricetulus griseus), or rat kangaroo (Potorous tridactylis). 3. Regarding the relationship of X inactivation and intelligence in fra(X)(q28) carriers, we observe that in cells of normal carriers the fold was mostly on the fragile X-positive chromosome, whereas in cells of an affected carrier the fold was mostly on the fragile X-negative chromosome. This is evidence that inactivation of the fragile X chromosome is positively correlated with intelligence in carriers.
Article PDF
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Van Dyke, D., Flejter, W., Worsham, M. et al. 868 A PRACTICAL METAPHASE MARKER OF THE INACTIVE X CHROMOSOME. Pediatr Res 19, 255 (1985). https://doi.org/10.1203/00006450-198504000-00898
Issue Date:
DOI: https://doi.org/10.1203/00006450-198504000-00898