Concerning the prognosis of patients with XLP with HLH, fatal outcomes, such as neurologic involvement, were more frequently observed in patients with SAP deficiency than in those with XIAP deficiency; 2 of 13 (15.4%) SAP-deficient patients developed HLH with CNS symptoms and died soon after diagnosis, while in XIAP-deficient patients, all three patients with HLH lacked CNS symptoms and remain alive. Here, XIAP is linked to hyperinsulinemic hypoglycemia, familial, 4.