Localization of loci for hypoxanthine phosphoribosyltransferase and glucose-6-phosphate dehydrogenase and biochemical evidence of nonrandom X chromosome expression from studies of a human X-autosome translocation.

Abstract

A unique and complex karyotypic rearrangement involving chromosomes X, 3, 7 and 21 is reported. Blood cells and fibroblasts from the proband do not express the maternal allele for glucose-6-phosphate dehydrogenase (G6PD), providing biochemical evidence for nonrandom expression of X-linked genes in balanced X-autosome translocations. The break point on the X chromosome, at the junction of Xq27-Xq28, separates the loci for hypoxanthine phosphoribosyltransferase (HPRT) and G6PD. Studies of mouse-human hybrids derived from the proband''s cells indicate that G6PD, at q28, is clearly distal to all other X loci now assigned. From these and previous studies, HPRT can be localized to that segment between Xq26 and Xq27. The inactive X phenotype in hybrid cells is apparently stable.