Within the group of PID patients (group II), all the patients diagnosed with SCID, XLA, Hyper IgM syndrome (HIGM) or Ataxia-telangiectasia (A-T) (n = 21) had detectable levels of serum IgA at birth, although all of them are IgA-deficient today (n = 10) or at the time of hematopoietic stem cell transplantation (n = 11). This evidence concerns the gene CD79A and Ataxia-telangiectasia.