Abstract
Structurally abnormal X chromosomes with a deletion (deletions, rings, isochromosomes) are usually late replicatiny (inactive) in female cells. An exception to this rule was found in a 19 yr old girl who had normal height and sexual development, a discordant pattern of mental deficiency, and lacked features of Turner Syndrome. In all metaphases examined from her lymphocyte and fibroblast cultures, most of the prominent band Xp21 was deleted in one of the X chromosomes. The late replicating X was identified by 3H-thymidine labelling and autoradiography in combination with Giemsa-trypsin banding, and by Brdu labelling with subsequent acridine orange staining. The normal X was late replicating in 44% of PHA stimulated lymphocytes, and in 46% of cultured skin fibroblasts.
We concluded that in this case, the Xp interstitial deletion did not interfere with random X-inactivation and that, in the tissues studied, no selection had taken place against cells with the deleted X active, although these cells should be functionally nullisomic for the deleted segment if X-inactivation was complete. However, significance of these findings for the clinical problems was assumed. Testing for x-linked genes was not informative as the patient and both parents were negative for the Xg(a) blood group and the patient had normal color vision. Somatic cell hybridization with an HPRT-deficient Chinese hamster cell line is under way in order to isolate the deleted active X.
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Francke, U. RANDOM X-INACTIVATION IN A FEMALE WITH AN INTERSTITIAL SHORT ARM DELETION OF THE X CHROMOSOME. Pediatr Res 11, 455 (1977). https://doi.org/10.1203/00006450-197704000-00512
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DOI: https://doi.org/10.1203/00006450-197704000-00512