Mutations in PIK3R1, referred to as APDS2, have also been identified in a number of immunodeficiency patients, with the most frequent mutation resulting in a splice variant that removes exon 11 (resulting in a p85α with region 434–475 deleted, located at the N-terminus of the iSH2 domain) (88–92). Here, PIK3R1 is linked to Immunodeficiency.