Receptor tyrosine kinase-like orphan receptor 1 (ROR1), also known as neurotrophic tyrosine kinase, it is a member of the ROR family within receptor tyrosine kinases (RTK) superfamily. Human ROR1 is a type I transmembrane protein with 937 amino acids (aa) in length. It contains a 29 aa signal sequence, a 377 aa extracellular domain (ECD), a 21 aa transmembrane segment, and a 510 aa cytoplasmic region. ROR1 expressed strongly in human heart, lung and kidney, but weakly in the CNS. At developmental stage, it expressed at high levels during early embryonic development. ROR1 has been shown to have very low kinase activity in vitro and is unlikely to function as a tyrosine kinase in vivo. It may act as a receptor for wnt ligand WNT5A which may result in the inhibition of WNT3A-mediated signaling.