Thyroid Hormone Status in Sitosterolemia Is Modified by Ezetimibe

Objectives To assess the association between biomarkers of thyroid status and 5α-stanols in patients with sitosterolemia treated with ezetimibe (EZE). Study design Eight patients with sitosterolemia (16-56 years of age) were studied during 14 weeks off EZE therapy and 14 weeks on EZE (10 mg/day). Serum thyroid biomarkers (free triiodothyronine [FT3], free thyroxine [FT4], FT3/FT4 ratio, thyroid-stimulating hormone), 5α-stanols (sitostanol and cholestanol), and cholestanol precursors (total cholesterol and its synthesis marker lathosterol, and 7α-hydroxy-4-cholesten-3-one cholestenol) were measured at baseline and during the 14 weeks off EZE and on EZE. Results EZE increased FT3/FT4 (10% ± 4%; P =.02). EZE reduced plasma and red blood cells sitostanol (−38% ± 6% and −20% ± 4%; all P <.05) and cholestanol (−18% ± 6% and −13% ± 3%; all P <.05). The change in plasma cholestanol level on EZE inversely correlated with the change in FT3/FT4 (r = −0.86; P =.01). EZE lowered total cholesterol (P <.0001) and did not affect 7α-hydroxy-4-cholesten-3-one cholestanol. EZE increased (P <.0001) lathosterol initially, but the level was not sustained, resulting in similar levels at week 14 off EZE and on EZE. Conclusion In patients with STSL, 5α-stanols levels might be associated with thyroid function. EZE reduces circulating 5α-stanols while increasing FT3/FT4, implying increased conversion of T4 to T3, thus possibly improving thyroid hormone status. Trial registration ClinicalTrials.gov NCT01584206.