Cyclin M2, also known as CNNM2 or ACDP2 (ancient conserved domain-containing protein 2), is an 875 amino acid multi-pass membrane protein that contains two CBS domains and belongs to the ACDP family. Expressed in a variety of tissues with highest expression in placenta, brain and kidney, cyclin M2 functions as a divalent metal cation transporter that mediates the transport of several different metal cations, including Mg2+, Co2+ and Fe2+. Cyclin M2 exists as multiple alternatively spliced isoforms and, contrary to its name, exhibits no cyclin-like function in vivo. The gene encoding cyclin M2 maps to human chromosome 10, which houses over 1,200 genes and comprises nearly 4.5% of the human genome. Defects in some of the genes that map to chromosome 10 are associated with Charcot-Marie Tooth disease, Jackson-Weiss syndrome, Usher syndrome, nonsyndromatic deafness, Wolman’s syndrome, Cowden syndrome, multiple endocrine neoplasia type 2 and porphyria.