Phenotypic heterogeneity of sitosterolemia

Area of Science:

• Genetics
• Metabolic Disorders
• Cardiovascular Science

Background:

• Sitosterolemia is a rare autosomal recessive disorder affecting lipoprotein metabolism.
• It is characterized by xanthomas and elevated plasma plant sterol levels, primarily sitosterol.
• Mutations in the ABCG5 or ABCG8 genes, encoding intestinal sterol transporters, are the known cause.

Purpose of the Study:

• To report novel nonsense mutations in ABCG5 and ABCG8 genes in Canadian subjects with sitosterolemia.
• To describe the clinical spectrum of vascular involvement associated with these mutations.
• To evaluate the efficacy of different lipid-lowering therapies.

Main Methods:

• Genetic sequencing to identify mutations in ABCG5 and ABCG8.
• Clinical evaluation of five Canadian subjects with sitosterolemia.
• Assessment of plasma sterol and LDL-cholesterol levels before and after treatment.

Main Results:

• Five subjects with sitosterolemia were identified, including four related Caucasians with ABCG8 S107X and one Japanese-Canadian with ABCG5 exon 3 I/D mutation.
• Two subjects, a 5-year-old and a 75-year-old, presented with symptomatic coronary atherosclerosis, illustrating a wide spectrum of vascular disease.
• Ezetimibe and bile acid sequestrants showed the greatest reduction in plasma sitosterol and LDL-cholesterol, while statins had a less pronounced effect.

Conclusions:

• Nonsense mutations in ABCG5 or ABCG8 can lead to a broad range of clinical phenotypes in sitosterolemia.
• The study expands the known genetic and clinical variability of this rare disorder.
• Targeted lipid-lowering therapies demonstrate variable efficacy in managing hypersterolemia and associated cardiovascular risks.