We compared the mRNA expressions of three rate-limiting enzymes, RALDH1, RALDH2 and RALDH3, between liver cancers and normal liver tissues, and found that the mRNA expressions of RALDH1 and RALDH2 were slightly but significantly increased in HCC compared with that in normal liver (S1A–S1D Fig). The gene discussed is ALDH1A1; the disease is liver cancer.