Unlike other reported cases of DIAPH1 deficiency, this child did not have seizures nor respiratory infections and had only one major infection with Candida. These results indicate that signs of immune dysregulation, such as inflammatory bowel disease, may be the most prominent symptom in infants with DIAPH1 deficiency. The gene discussed is DIAPH1; the disease is hyperinsulinemic hypoglycemia, familial, 4.