If an endogenous ligand is found, the orphan receptor is "adopted" or "de-orphanized".
Another example of an orphan receptor site is the PCP binding site in the NMDA receptor,[10] a type of ligand-gated ion channel.
GPCR orphan receptors are usually given the name "GPR" followed by a number, for example GPR1.
In the GPCR family, nearly 100 receptor-like genes remain orphans.
However, with modern molecular biology techniques such as reverse pharmacology, screening of cDNA libraries, and whole genome sequencing, receptors have been identified based on sequence similarity to known receptors, without knowing what their ligands are.