TCF7L2 and fatty liver disease: Mutations in PNPLA3, MBOAT7, TM2SF6, PTPRD, FNDC5, IL-1B, PPARGC1A, UCP2, and NNMT directly induce steatosis in the liver, while polymorphisms in TCF7L2, SAMM50, IL-6, and AGTR1 genes indirectly promote liver steatosis by increasing lipolysis in adipose tissue and skeletal muscle, resulting in a higher supply of FFAs to the liver.