CYP7A1 and familial hypercholesterolemia: CYP7A1 is the initial and rate‐limiting enzyme in the bile acid biosynthesis process,[18] and the lack of CYP7A1 impeded the clearance of serum cholesterol, resulting in progressive hypercholesterolemia in Tsc1Dmp1 mice, which was observed as early as 3 months of age.