Hepatocyte transplantation is an evolving, on-demand treatment for patients suffering from monogenic metabolic diseases, such as deficiency in alpha-1 antitrypsin (A1AT), ornithine transcarbamylase (OTC), or carbamoyl phosphate synthase 1 (CPS-1), or Crigler-Najjar syndrome1. This evidence concerns the gene SERPINA1 and metabolic disease.