Secondly, the expression of hepatic cytochrome P450 family 7 subfamily A member 1 (CYP7A1) gene, which encodes an endoplasmic reticulum membrane protein that catalyzes the conversion of cholesterol to bile acids, is positively associated with the serum level of TMAO in NAFLD patients [115]. Here, CYP7A1 is linked to metabolic dysfunction-associated steatotic liver disease.