ABCA9 is a member of the superfamily of ATP-binding cassette (ABC) transporters and contains two transmembrane domains and two nucleotide binding folds. ABC proteins transport various molecules across extra- and intracellular membranes. ABC genes are divided into seven distinct subfamilies (ABC1, MDR/TAP, MRP, ALD, OABP, GCN20, and White). ABCA9 is a member of the ABC1 subfamily and is clustered with four other ABC1 family members on chromosome 17q24. Transcriptional expression of the ABCA9 gene is induced during monocyte differentiation into macrophages and is suppressed by cholesterol import. ABCA9 May play a role in monocyte differentiation and lipid homeostasis.