ABCG5 is a sterol transporter that functions as an obligate heterodimer with ABCG8, forming an ATP-binding cassette (ABC) transporter complex 1. This heterodimer mediates ATP- and Mg2+-dependent transport of dietary plant sterols and cholesterol across cell membranes 1, playing an essential role in selective sterol excretion from hepatocytes into bile and regulation of intestinal cholesterol absorption 234. The ABCG5/G8 complex maintains sterol homeostasis by pumping sterols out of hepatic and intestinal cells 5, and can be upregulated by LXRα signaling to promote cholesterol excretion 6. Loss-of-function mutations in ABCG5 cause sitosterolemia (phytosterolemia), an autosomal recessive lipid storage disorder characterized by intestinal hyperabsorption and reduced hepatic secretion of plant sterols and cholesterol 78. Patients develop elevated LDL cholesterol, tendon xanthomas, and premature atherosclerosis, potentially mimicking familial hypercholesterolemia 8. However, sitosterolemia responds dramatically to dietary modification and ezetimibe, unlike homozygous FH, making accurate diagnosis clinically important 89. Dietary therapy alone reduces cholesterol levels by approximately 50%, with ezetimibe providing additional 18-20% reduction 9.