These conditions include Ras Homolog gene family member H (RhoH) deficiency (97), T lymphocyte-specific protein tyrosine kinase (LCK) deficiency (98, 99), Serine/threonine kinase 4 (STK4) deficiency (100, 101), and IL-2-inducible T cell kinase (ITK) deficiency (102–106). The gene discussed is ITK; the disease is hyperinsulinemic hypoglycemia, familial, 4.