FCHO1 (FCH domain only 1) is an 889 amino acid protein that contains one FCH domain and exists as multiple alternatively spliced isoforms. The gene encoding FCHO1 maps to human chromosome 19, which consists of over 63 million bases, houses approximately 1,400 genes and is recognized for having the greatest gene density of the human chromosomes. It is the genetic home for a number of immunoglobulin (Ig) superfamily members, including the killer cell and leukocyte Ig-like receptors, a number of ICAMs, the CEACAM and PSG family, and Fc receptors (FcRs). Key genes for eye color and hair color also map to chromosome 19.