A PCR-BASED NONRADIOACTIVE X-CHROMOSOME INACTIVATION ASSAY FOR GENETIC-COUNSELING IN X-LINKED PRIMARY IMMUNODEFICIENCIES

The Wiskott-Aldrich syndrome (WAS), X-linked severe combined immunodef iciency (SCIDX1), and X-linked agammaglobulinemia (XLA) are severe con genital immunodeficiencies with X-linked inheritance. Although rare, t hey are all associated with severe infections from early in life, and high morbidity and mortality. Female carriers of these diseases can be identified by a non-random pattern of X-chromosomal inactivation in c ell lineages targeted by each gene defect. For patients with WAS, SCID X1 or XLA, the demonstration of non random X-Chromosome inactivation i n their mothers can be used to confirm clinical diagnosis. Furthermore , analysis of X-Chromosome inactivation in at risk females allows prec onceptional carrier detection, thus representing an important aid in g enetic counseling. For each disease we established a PCR-based, non ra dioactive assay at the human androgen receptor (HUMARA) locus, that al lows analysis of X-Chromosome inactivation in the affected cell types and in tissue specific controls to exclude the issue of skewed X-chrom osomal inactivation. In our study, 50 females with a known family hist ory of XLA [19], WAS [18], and SCIDX1 [13],were examined. A carrier st atus was established in 19 females (7 XLA, 6 WAS, 6 SCIDX1) and exclud ed in 29( 11 XLA, 11 WAS, 7 SCIDX1). Only in 2 cases (4%) the assay wa s not informative.