PIK3CA and immune system disorder: Oncogenic mutations in PIK3CG are widely distributed, which is distinct from the oncogenic hotspot mutations seen in the helical and kinase domain of PIK3CA. There has been limited analysis of the functional consequences of oncogenic PIK3CG mutants, with the R1021 residue in the regulatory motif of the kinase domain being unique, as mutations of this residue exist in both immunodeficiencies and tumours.