Receptor for retinol uptake STRA6 (also known as "stimulated by retinoic acid gene 6 protein") is a multitransmembrane domain protein, which acts as a retinol transporter for the complex retinol-retinol binding protein (RBP/RBP4). It acts by removing retinol (vitamin A) from RBP/RBP4 and transports it across the plasma membrane, where it can be metabolized. This mechanism does not depend on endocytosis []. Vitamin A and its derivatives are essential for vision and many other biological processes. In humans, defects in STRA6 are the cause of microphthalmia syndromic type 9 (MCOPS9); also called Matthew-Wood syndrome or Spear syndrome. Microphthalmia is a clinically heterogeneous disorder of eye formation, ranging from small size of a single eye to complete bilateral absence of ocular tissues (anophthalmia). In many cases, microphthalmia/anophthalmia occurs in association with syndromes that include non-ocular abnormalities. MCOPS9 is a rare clinical entity including as main characteristics anophthalmia or severe microphthalmia, and pulmonary hypoplasia or aplasia [, , ].In addition to serving as a retinol transporter, STRA6 is a ligand-activated cell surface signaling receptor that activates JAK/STAT signaling upon binding to the retinol-RBP complex [].
