The Lutheran blood group system consists of 29 antigens carried on a single pass type 1 membrane glycoprotein (aka CD239, basal cell adhesion molecule, B-CAM, Lutheran glycoprotein) with five disulfide-bonded, extracellular, immunoglobulin superfamily (IgSF) domains, which has adhesion properties and may mediate intracellular signalling. There are two glycoprotein isoforms, products of alternative splicing of BCAM; the longer isoform, consists of 628 amino acids (NM_005581.4 transcript 1), whilst the shorter isoform, consists of 588 amino acids (NM_001013257.2 transcript 2).