Mammalian odorant receptors require accessory proteins such as RTP1 and RTP2 for functional cell surface expression. Receptor expression-enhancing protein (REEP) family members are transmembrane proteins which interact with odorant receptor proteins and may enhance the odorant receptor responses to odorants. Recently studies have shown other chemosensory receptors such as bitter taste receptors are also influenced by RTP and REEP family members. REEP3 has also been suggested as a novel candidate gene for autism and as a loci influencing the plasma levels of the liver enzyme alkaline phosphatase.