Wiskott-Aldrich Syndrome (WAS) is an X-linked recessive disease characterized by severe immunodeficiency, eczema, recurrent opportunistic and pyogenic infections, and severe thrombocytopenia with small deformed platelets. Patients with WAS have a decrease in antibody production to the carbohydrate antigens, and reduced T-lymphocyte' numbers as well as impaired functions. The membrane glycoproteins gplb in platelets and sialophorin (CD43) in T lymphocytes are structurally unstable in patients with WAS. Death may occur in the first decade of life from infection, hemorrhage or malignancy. Only males are affected. Heterozygous females are clinically normal and can be identified by pedigree analysis or non-random inactivation of the X chromosome carrying the WAS gene. Although much efforts have been expended in recent years by a number of investigators, the underlying intrinsic molecular defects of WAS have yet to be characterized. By using linkage analysis on restriction fragment length polymorphic (RFLP) markers to study families with this disorder, we have assigned the WAS gene locus to the Xpll.2-Xpll.3 region. Attempts will be made to refine the map, by increasing the number of DNA markers via jump" cosmid and x- irradiation hybrids, and yeast artificial chromosome libraries, thereby providing valuable resources for high resolution mapping over short distances of the X chromosome. Restriction endonuclease digests of genomic DNA from afflicted individuals will be analyzed on pulse field. gradient gel electrophoresis and screened with tightly linked polymorphic probes for structural anomalies. Once firm linkages are established, tightly linked DNA probes should permit accurate carrier detection and prenatal diagnosis of the disease locus. Ultimately, the work described here should lead to the identification of the defective gene and its putative transcript(s), and to a better understanding of the molecular and cellular defects in WAS individuals.