In addition, homozygous mutations in the PIK3R1 gene resulting in the absence of p85α have been defined as a cause of agammaglobulinemia [3,4]. Besides this, autosomal dominant loss-of-function mutations in the PIK3R1 gene encoding the p85α, p55α and p50α regulatory subunits cause activated PI3-kinase-δ syndrome type 2 (APDS2) [5]. Here, PIK3R1 is linked to agammaglobulinemia.