The function of SLC44A4 (solute carrier family 44 member 4, Ensembl gene identifier ENSG00000204385) is as follows. Choline transporter that plays a role in the choline- acetylcholine system and is required to the efferent innervation of hair cells in the olivocochlear bundle for the maintenance of physiological function of outer hair cells and the protection of hair cells from acoustic injury (By similarity) (PubMed:23651124, PubMed:28013291). Also described as a thiamine pyrophosphate transporter in colon, may mediate the absorption of microbiota- generated thiamine pyrophosphate and contribute to host thiamine (vitamin B1) homeostasis (PubMed:24379411, PubMed:26741288). {ECO:0000250|UniProtKB:Q7T2B0, ECO:0000269|PubMed:23651124, ECO:0000269|PubMed:24379411, ECO:0000269|PubMed:26741288, ECO:0000269|PubMed:28013291}. [Isoform 3]: Also has thiamine pyrophosphate transporter activity. .