Mutations in the ABCA1 gene (ATP-binding cassette transporter 1) have been reported in Tangier disease (TD). TD is an autosomal recessive disorder characterized by an absence of plasma HDL, cholesterol ester depositing in the reticulo-endothelial system and deviations in cellular lipid trafficking. ABCA1 mediates the apo-A1 associated export of cholesterol and phospholipids from the cell. It is expressed on the plasma membrane and the Golgi complex, and is regulated by cholesterol flux. Regulation of the cholesterol flux between HDL and macrophages is competitive between ABCA1 and SR-BI.