FRAGILE-X SYNDROME - SEARCH FOR PHENOTYPIC MANIFESTATIONS AT LOCI FOR HYPOXANTHINE PHOSPHORIBOSYLTRANSFERASE AND GLUCOSE-6-PHOSPHATE-DEHYDROGENASE

Abstract

Individuals with the form of X-linked mental retardation associated with the presence of a cytologically variant X chromosome having a secondary constriction or fragile site at Xq 27-28 (Fra X) were studied. The hypothesis that deletions or modifications at neighboring loci occur as a consequence of events at the fragile site was tested. Skin fibroblasts and peripheral blood lymphocytes from affected males were analyzed with respect respect to the expression of 2 X-linked enzymes: glucose-6-phosphate dehydrogenase (G6PD) and hypoxanthine phosphoribosyltransferase (HPRT); loci for these enzymes are known to be located in the region of the fragile site. Although the number of cells resistant to thioguanine (HPRT-deficient) obtained from some cultures from 1 Fra X male and blood cells of another was greater than expected, the frequency of these cells was not increased in cultures from other Fra X males. Evidently, the G6PD activity and electrophoretic mobility in Fra X males is similar to that in normal cells, thus, providing no evidence for the loss of the long-arm telomere in the fragile X syndrome.