SH2D1A and autoimmune lymphoproliferative syndrome: ALPS and DALD display a similar clinical picture and share an inherited defect of Fas function and the modifying effect exerted by variants of OPN, PRF1, and SH2D1A. However, DN T cell expansion is only present in ALPS, which may mark immunopathological differences because a direct role has been ascribed to these cells in ALPS development.