Novel mutations in the Wiskott-Aldrich syndrome protein gene and their effects on transcriptional, translational, and clinical phenotypes

Wiskott-Aldrich syndrome (WAS) is an X-linked recessive immunodeficiency ch aracterized by thrombocytopenia, eczema, and recurrent infections, and caus ed by mutations in the WAS protein (WASP) gene. WASP contains several funct ional domains through which it interacts with proteins involved in intracel lular signaling and regulation of the actin cytoskeleton. In this report, 1 7 WASP gene mutations were identified, 12 of which are novel. DNA of affect ed males and obligate carriers was PCR amplified and analyzed by SSCA, hete roduplex analysis, and direct sequencing. The effects of the mutations at t he mRNA and protein level were ascertained by RT-PCR and Western blot analy ses. All missense mutations were located in exons 1-4. Most of the nonsense , frameshift and splice site mutations were found in exons 6-11. Mutations that alter splice sites led to the synthesis of several types of mRNAs, a f raction of which represented the normally spliced product. The presence of normally spliced transcripts was correlated with a milder phenotype. When o ne such case was studied by western blotting reduced amounts of normal-size WASP were present. In other cases as well, a correlation was found between the amount of normal or mutant WASP present and the phenotypes of the affe cted individuals. No protein was detected in two individuals with severe WA S. Reduced levels of a normal-size WASP with a missense mutation were seen in two individuals with XLT. It is concluded that mutation analysis at the DNA level is not sufficient for predicting clinical course. Studies at the transcript and protein level are needed for a better assessment. Hum Mutat 14:54-66, 1999. (C) 1999 Wiley-Liss, Inc.