In normal liver, two isoforms (OTC‐t1 and OTC_t2) have been described, suggesting a role for post‐transcriptional control.33 In rat‐derived hepatomas, treatment with azacitidine induced OTC gene activation, suggesting epigenetic regulation may play a role.34 Studies of rare patients with congenital ASS and OTC deficiencies may shed further insight into the function and control of these enzymes.35 The gene discussed is OTC; the disease is hepatocellular carcinoma.