Alpha-fetoprotein (AFP) is a member of the albuminoid gene superfamily, which includes albumin, vitamin D-binding protein (Gc), and alpha-albumin. AFP is a glycoprotein composed of 591 amino acids and a carbohydrate moiety. It is a major plasma protein produced by the yolk sac and the liver during fetal development and is considered the fetal counterpart of serum albumin.
AFP has the ability to bind to copper, nickel, fatty acids, and bilirubin. It exists in monomeric, dimeric, and trimeric forms. As one of the several embryo-specific proteins, AFP is a dominant serum protein in early human embryonic life, as early as one month, when albumin and transferrin are present in relatively small quantities. AFP is first synthesized by the yolk sac and liver between 1-2 months of human development and is then primarily produced by the liver. A small amount of AFP is also produced by the gastrointestinal tract of the human conceptus.
It has been established that AFP may reappear in elevated amounts in adult serum in association with normal restorative processes and malignant growth. Alpha-fetoprotein (AFP) serves as a specific marker for hepatocellular carcinoma (HCC), teratocarcinomas, and neural tube defects (NTDs).