Ornithine transcarbamylase (OTC; EC 2.1.3.3) deficiency (OTCD; OMIM#311250) is an X-linked (Xp21.1)1 rare disease with a prevalence of 1 in 40,000–80,0002–6 caused by an inborn error of metabolism of the urea cycle. Here, OTC is linked to hyperinsulinemic hypoglycemia, familial, 4.