the gpr56 is grouped in the b family of gpcrs. this gpcr group have long n termini characterized by an extracellular “cysteine box” and hydrophilic, potentially mucin-rich. the cysteine box contains four conserved cysteines and two tryptophans arranged in a specific fashion (c-x2-w-x6-16-w-x4-c-x10-22-c-x-c) just before the first transmembrane domain and serves as a cleavage site in some members of this group of g protein–coupled receptors. although, the molecular and cellular mechanisms of how gpr56 regulates brain development remain largely unknown. these types of receptors play an essential role in biological processes including embryonic development, central nervous system (cns), immune system, and tumorigenesis.