Ankyrin repeat-rich membrane-spanning protein (ARMS), also designated kinase D-interacting substance 220 or Kidins220, is a highly conserved protein containing multiple domains, including four putative transmembrane domains and several ankyrin repeats. ARMS is expressed in regions rich in neurotrophin (Trk) and ephrin (Eph) receptors, such as the brain and neuroendocrine cells (where it concentrates at the tip of neurites) and in plastic areas of the adult brain. It is also detected in peripheral blood immature dendritic cells and PC12 cells. ARMS functions as a substrate for protein kinase D and is a downstream target for both Trk and Eph receptors. It is a highly conserved protein, which suggests it has an evolutionary conserved role. The gene encoding for the protein maps to chromosome 2p24.