Gap junction gamma-1 protein (GJC1), also known as gap junction alpha-7 protein (GJA7) and connexin 45 (Cx45) — is a protein that in humans is encoded by the GJC1 gene. Cx45 is a component of gap junctions, which are composed of arrays of intercellular channels that provide a route for the diffusion of low molecular weight materials from cell to cell. Alternatively spliced transcript variants encoding the same isoform have been described. GJs consist of 3 major connexin (Cx) isoforms—Cx43, Cx40, and Cx45—each of which are characterized by chamber-specific regional distribution and permeation properties. Cx45 is strongly expressed in the early embryonic myocardium and is required for cardiac development (1). Homozygous Cx45-deficient mice are embryonic lethal; however, in the adult heart, Cx45 is expressed mainly at the SA and AV nodes and is not essential for survival of adult mice. Disease-causing mutations in GJ gamma-1 protein (GJC1), which encodes Cx45, have not yet been identified.