The CTL2 blood group system consists of two high-prevalence antigens, VER and RIF, carried on the Choline like transporter 2 (CTL2) protein, also known as SLC44A2 (solute carrier family 44 member 2). This multi-pass protein consists of 706 amino acids (isoform 1), with predicted 10 transmembrane domains and 5 extracellular loops. The protein is encoded by SLC44A2, 42,103 bases, chromosome 19p13.2 (chr19:10,602,455-10,644,557) (GRCh38/hg38). The rare VER– null phenotype is associated with hearing impairment in the upper frequency range.