PNPO and hepatocellular carcinoma: Initially, PNPO deficiency itself was hypothesized to be a potential risk factor for liver disease and consequent HCC.9As was pointed out in a recent review, 30% of published patients with PNPO deficiency show liver involvement.15However, two of our patients had ALDH7A1 deficiency—who also received high-dose PLP—developed either severe hepatatoxicity or HCC, pointing instead to PLP exposure as the likely common denominator.