The Indian (IN 023) blood group system: an update

This update of the Indian (IN 023) blood group system (Xu Q. The Indian blood group system. Immunohematology 2011; 27:89-93) focuses on the discovery and clinical significance of new antigens, antibodies, and genetics since that review. The system now comprises six antigens, of which the more recently identified antigens are high-prevalence antigens (HPAs) IN:005 (INRA) and IN:006 (INSL); rare individuals lacking these antigens are found among the people from the Indian subcontinent. The Indian (IN) antigens are located on CD44, a single-pass transmembrane glycoprotein encoded by the <i>CD44</i> gene on chromosome 11 at position p13. The absence of these HPAs is associated with homozygous missense mutations in CD44: 255C>G in exon 3, c.449G>A in exon 5 (for IN:-5, p.Arg150His), and c.276C>A in exon 3 (for IN:-6, p.His92GIn).