The function of ABCG4 (ATP binding cassette subfamily G member 4, Ensembl gene identifier ENSG00000172350) is as follows. ATP-dependent transporter of the ATP-binding cassette (ABC) family that may be involved in the cellular efflux of sterols, in particular cholesterol and desmosterol (a cholesterol precursor), to high-density lipoprotein (HDL) (PubMed:15240127, PubMed:33141061). May play an important role in the removal of amyloid-beta peptides from brain, in a process that can be antagonized by desmosterol. However it is unclear whether ABCG4 can directly transport amyloid-beta peptides or whether peptide export may be facilitated due to changes in the membrane lipid environment (By similarity). Induces apoptosis in various cells (PubMed:27228027). {ECO:0000250|UniProtKB:Q91WA9, ECO:0000269|PubMed:15240127, ECO:0000269|PubMed:27228027, ECO:0000269|PubMed:33141061}.