WAS and Wiskott-Aldrich syndrome: Affecting between 1 in 50,000 and 1 in 250,000 live births,[6] almost always boys only, WAS is caused by mutations in the WAS gene (ID: 7454) that impair or eliminate expression of the WAS protein (WASp).[7] Over 400 pathogenic WAS variants spanning the gene sequence have been described[3] and there is a genotype-phenotype correlation; the severity of the clinical phenotype can be predicted by the type of gene mutation and the latter’s impact on WASp expression levels.[8] Mutations result in the absence of WASp cause the classic WAS phenotype.