Sitosterolemia With Two Heterozygous Variants Including a Novel Mutation c.1800T>A in the ABCG5 Gene: A Case Report of a Rare Condition in a Young Saudi Girl

Sitosterolemia is a rare autosomal recessively inherited lipid disorder characterized by an accumulation and deposition of phytosterols in various tissues with decreased biliary excretion leading to various complications. We report a case of a three-year-old Saudi girl who exhibited xanthomas and elevated cholesterol levels. Initially, she was misdiagnosed with familial hypercholesterolemia, but subsequent testing of the low-density lipoprotein receptor gene by next-generation sequencing ruled out this condition. Two heterozygous variants were identified in the ABCG5 gene through a whole exome sequencing study. These variants, namely c.1336C>T and c.1800T>A, have been characterized as pathogenic and likely pathogenic, respectively, with the latter being a novel mutation associated with sitosterolemia. The patient responded positively to treatment with ezetimibe, resulting in controlled cholesterol levels and decreased xanthoma size.