In particular, Villa et al. have demonstrated that hypomorphic mutations, and especially missense mutations in exons 2 and 3 of the gene affecting interaction of WASP with WIP and stability of the WASP protein, cause isolated X-linked thrombocytopenia (XLT) (109), which may even be intermittent (110). The gene discussed is WAS; the disease is thrombocytopenia 1.