Pathogenic variants in BTK lead to X-linked agammaglobulinemia (XLA) or Bruton’s disease (6), a prototypic PAD related to severe impairment in B-cell ontogeny and maturation due to the crucial role of Btk in pre-B/B-cell receptor (BCR) signaling. Here, BTK is linked to Bruton-type agammaglobulinemia.