Stimulated by retinoic acid gene 6 protein homolog (STRA6) is a 74 kDa broadly expressed transmembrane protein that does not belong to any particular family of proteins. Human STRA6 is 667 amino acids (aa) in length. It contains nine transmembrane regions and one potential N-linked glycosylation site in the first extracellular domain. In addition, there are three splicing variants producing four isoforms. There is no signal sequence. Human STRA6 is 80% identical to bovine STRA6 and 74% identical to mouse and rat STRA6. STRA6 may act as a high-affinity cell-surface receptor for the complex retinol-retinol binding protein (RBP/RBP4). Defects in STRA6 are the cause of Spear syndrome and Matthew-Wood syndrome.