ROR1 and ROR2 are orphan receptor tyrosine kinases that are most closely related to MuSK and the Trk family of neurotrophin receptors. They are characterized by the presence of extracellular frizzled-like cysteine-rich domains and membrane-proximal kringle domains, both of which are assumed to mediate protein-protein interactions. The ROR family RTKs are evolutionarily conserved among Caenorhabditis elegans, Drosophila, mice, and humans. Although the functions of ROR kinases are unknown, similarities between ROR and MuSK and Trk kinases have led to speculation that ROR kinases regulate synaptic development. It was shown that CAM-1, a C. elegans ortholog of the ROR family RTKs, plays several important roles in regulating cellular migration, polarity of asymmetric cell divisions, and axonal outgrowth of neurons during nematode development. mROR1 and mROR2 may play differential roles during the development of the nervous system.