SH2D1A and hyperinsulinemic hypoglycemia, familial, 4: In 2006, Rigaud et al. demonstrated that mutations in the gene that encodes the X-linked inhibitor-of-apoptosis XIAP (also termed BIRC4) resulted in another X-linked lymphoproliferative syndrome, XLP2, distinct from SAP deficiency XLP (XLP1) [11].