Recently, liver diseases caused by urea cycle disorders (only ARG1 deletion, ASS deletion, and citrulline deletion) have been modeled with hiPSC-Heps, while in vitro modeling of ornithine transcarbamylase deficiency (OCTD), which is the most common cause of urea cycle disorders, has rarely been reported [112,113,114]. The gene discussed is ARG1; the disease is urea cycle disorder.