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 gene clusters designated alpha, beta and gamma, all of which contain multiple tandemly arranged genes. The protocadherein gamma cluster consists of three subfamilies (A, B and C). As a member of the gamma subfamily A, PCDHGA12 (Protocadherin gamma A12), also known as Cadherin-21 and Fibroblast cadherin-3, is a 932 amino acid protein that is one of 22 proteins encoded by the protocadherin gamma cluster. Typical of gamma protocadherins, PCDHGA12 contains six cadherin motifs and is a type I transmembrane receptor expressed in the central nervous system. Ubiquitously expressed with lowest levels in spleen, PCDHGA12 is thought to be involved in cell signaling. There are three isoforms of PCDHGA12 that are produced as a result of alternative splicing events.