Sitosterolemia is a rare disease with severe clinical manifestations

Sitosterolemia is a rare autosomal recessive dyslipidemia caused by a defect in sterol transporters, leading to excess absorption and insufficient excretion of plant sterols and cholesterol. The clinical picture ranges from xanthomatosis to early atherosclerosis and hematological disorders, often mimicking familial hypercholesterolemia. Three clinical observations are presented, illustrating the diagnostic difficulties and the effectiveness of pathogenetic therapy. Case 1 : a 15-year-old female patient with severe hypercholesterolemia and negative results of testing for the classic genes of familial hypercholesterolemia; whole-genome sequencing revealed two variants in ABCG8 ( c.1269G>T , p.Glu423Asp ; c.322+456C>T ). A diet low in phytosterols and ezetimibe ensured the achievement of target values of low-density lipoprotein cholesterol. Case 2: a 21-year-old patient with early generalized xanthomatosis and extremely high phytosterol levels; a nonsense variant of ABCG8 c.1083G>A , p.Trp361Ter was detected. Administration of ezetimibe in combination with a bile acid sequestrant resulted in a significant decrease in cholesterol. Case 3: a boy aged 2 years 7 months with multiple xanthomas; compound heterozygosity of ABCG8 ( c.1715T>C , p.Leu572Pro ; c.883G>A, p.Gly295Arg ) was detected. Ezetimibe resulted in a significant decrease in low-density lipoprotein cholesterol and regression of xanthomas. These observations confirm the need for quantitative determination of phytosterols and extended genetic search in “atypical familial hypercholesterolemia” . Strict dietary restrictions and ezetimibe remain the basis of treatment; the effectiveness of statins is limited. Early recognition improves prognosis and reduces the risk of cardiovascular complications.