A second-site mutation in the initiation codon of WAS (WASP) results in expansion of subsets of lymphocytes in an Wiskott-Aldrich syndrome patient

✍ Scribed by Wei Du; Satoru Kumaki; Toru Uchiyama; Akihiro Yachie; Chung Yeng Looi; Shin Kawai; Masayoshi Minegishi; Narayanaswamy Ramesh; Raif S. Geha; Yoji Sasahara; Shigeru Tsuchiya

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 233 KB
• Volume: 27
• Category: Article
• ISSN: 1059-7794
• DOI: 10.1002/humu.20308

✦ Synopsis

Wiskott-Aldrich syndrome (WAS) is caused by mutations in the gene encoding WAS protein (WASP ). Recently, somatic mosaicism caused by reversions or second-site mutations has been reported in some inherited disorders including WAS. In this article, we describe somatic mosaicism in a 15-year-old WAS patient due to a second-hit mutation in the initiation codon. The patient originally had a single-base deletion (c.11delG; p.G4fsX40) in the WAS (WASP) gene, which resulted in a frameshift and abrogated protein expression. Subsequently, a fraction of T and natural killer (NK) cells expressed a smaller WASP, which binds to its cellular partner WASP-interacting protein (WIP). The T and NK cells were found to have an additional mutation in the initiation codon (c.1A>T; p.M1_P5del). The results strongly suggest that the smaller WASP is translated from the second ATG downstream of the original mutation, and not only T cells but also NK cells carrying the second mutation acquired a growth advantage over WASP negative counterparts. To our knowledge, this is the first report describing somatic mosaicism due to a second-site mutation in the initiation codon of any inherited disorders.