Protocadherins are a large family of cadherin-like cell adhesion proteins that are involved in the establishment and maintenance of neuronal connections in the brain. There are three protocadherin (PCDH) gene clusters, designated alpha, beta and gamma, all of which contain multiple tandemly arranged genes. PCDHGA9 (Protocadherin gamma-A9) is a 932 amino acid that is one of 22 proteins encoded by the protocadherin gamma cluster. The protocadherein gamma cluster consists of three subfamilies (A, B and C) and PCDHGA9 is a member of the gamma subfamily A. PCDHGA9 is a type I transmembrane receptor containing six cadherin motifs and is expressed in the central nervous system where it localizes to synapses. Members of the gamma cluster of protocadherins are essential for neuronal survival. There are two isoforms of PCDHGA9 that are produced as a result of alternative splicing events.