If treatment of colesevelam, fish oil in conjunction with ezetimibe, will lead to further reduction in plasma plant sterol levels in sitosterolemia patients. We hypothesize that treatments with fish oil, colesevelam and ezetimibe will maximize decrease in plasma concentrations of sitosterol and other plant sterols in sitosterolemia patients.

Ezitimibe significantly lowers plant sterol levels in the blood of patients with sitosterolemia. However, plant sterol levels remain substantially elevated compared to those in healthy individuals. Thus, combination therapy needs to be considered. Agents that provide cardiovascular benefits such as colesevelam, a second-generation bile acid sequestrant, and fish oil are potential candidates to help further reduce sterol levels, but have yet to be evaluated in sitosterolemia patients.

The purpose of this study is to dtermine the effects of colesevelam, fish oil and combination therapy (fish oil + colesevelam) on plant sterols, cholesterol and cardiovascular risk factors in sitosterolemia patients treated with ezetimibe. The results of this study will enhance knowledge on the pathogenesis of sitosterolemia and the mechanisim of actions of colesevelam and fish oil as adjunct therapies to ezitimibe in patients with the disease.

Inclusion Criteria:

1. Confirmed diagnosis of homozygous sitosterolemia as established by genotyping and/or clinical parameters
2. Receiving ezetimibe treatment
3. Over 8 years of age (no maximum)
4. Concomitant illnesses or conditions

Exclusion Criteria:

1. Pregnancy
2. Intellectual disability
3. Bowel or biliary obstruction
4. Known hypersensitivity to colesevelam or any ingredients of colesevelam