Most UCD patients (n = 54; 68.4%) also received arginine + citrulline at least once during follow-up, with the highest use of the combination in patients with OTC deficiency (38/57; 66.7%) or CPS1 deficiency (13/15; 86.7%). This evidence concerns the gene CPS1 and hyperinsulinemic hypoglycemia, familial, 4.