SH2D1A and X-linked lymphoproliferative syndrome: XLP-1 is a rare immune disorder associated with various immune defects in boys, including impaired cytotoxic T lymphocyte (CTL) function, hypo-/dysgammaglobulienemia, and loss of natural killer T (NKT) cells (Panchal et al., 2018), with congruent phenotypes recapitulated in Sap-deficient mice (Czar et al., 2001).