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Wiskott-Aldrich syndrome (WAS) is a fully penetrant X-linked recessive disorder characterized by thrombocytopenia with small platelets, eczema, and defects of both T-cell and B-cell immunity. Obligate carriers of this disorder show no signs of the gene defect because in the cell lineages primarily affected by the disorder they demonstrate preferential use of the normal, nonmutant X as the active X. This can be explained by the selective disadvantage in proliferation and/or survival experienced by the cells with the mutant X as the active X. We have recently evaluated an 8-year-old girl with a disorder phenotypically identical to WAS. Cytogenetic studies did not show any structural abnormalities of the X chromosome and X chromosome inactivation analysis showed that both of her X chromosomes could function as the active X. These findings suggest that there is an autosomal recessive disorder that is very similar to classic WAS.

Wiskott-Aldrich syndrome (WAS) is a fully penetrant X-linked recessive disorder characterized by immunodeficiency, thrombocytopenia, and severe eczema. WAS is a life-threatening disease, with a poor quality of life and high mortality rate in childhood. The gene responsible for the disease has been localized to the proximal short arm of the X- chromosome and recently isolated through positional cloning and named WAS protein (WASP). We have characterized 17 WAS families. We have developed a rapid, nonradioactive screening protocol for identifying WASP gene alterations in genomic DNA. Our method allows simultaneous evaluation of single strand confirmation polymorphism and heteroduplex formation. We have identified 15 novel mutations that involve single basepair changes, or small insertions or deletions, all of which result in premature stop cordon, frame shift with secondary premature stop codon, or splice site defect. These studies document the considerable heterogeneity of the location of mutations in the WASP gene causing full-blown WAS and show the efficiency and rapidity of a screening approach for mutation identification in WAS that will be useful for carrier detection and prenatal diagnosis.

Diagnosis of X-linked adrenoleukodystrophy is based upon demonstration of high levels of very long chain fatty acids. More recently, in addition to biochemical analysis, closely linked DNA probe St14 has been used for prenatal diagnosis in informative families. Identification of heterozygotes is particularly important, both in order to specifically address only carrier females to prenatal diagnosis, and because appropriate dietary therapy is now available to treat those heterozygotes presenting with neurological symptoms. We report two pedigrees in which carrier detection was performed by a combination of biochemical and molecular genetic analysis. Such approach should allow extremely high accuracy in carrier detection.