alpha fetoprotein(redirected from a fetoprotein)
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a protein normally produced during the 12th-15th weeks of gestation, decreasing thereafter, but appearing in the blood in certain tumors, such as embryonal carcinomas of the testis and ovary, hepatoma, and less often in patients with carcinomas of the pancreas, stomach, colon, or lung. When present, a useful marker in following the course of a tumor.
alpha fetoproteinA protein encoded by the AFP gene on chromosome 4q25 that is produced by the yolk sac and liver during embryonic development and thought to play the same role as serum albumin in adults. It bind copper, nickel, fatty acids and bilirubin and occurs naturally as a monomer, homodimer and homotrimer. Alpha fetoprotein is typically measured in two contexts: during pregnancy, either in amniotic fluid or serum as a screen for neural tube defects or other developmental defects (see table); and in adults suspected of hepatocellular carcinoma or germ cell tumours—i.e., testicular, ovarian, and far less commonly, of the stomach and pancreas (for the latter two of which AFP has no practical diagnostic utility).
AFP elevation in pregnancy
• Cardiovascular—Fallot’s tetralogy.
• CNS defects—Anencephaly, spina bifida, other open neural tube defects, hydrocephaly, cyclopia, microcephaly, sacrococcygeal teratoma.
• GI defects—Oesophageal and duodenal atresia with impaired foetal swallowing, omphalocele due to transudation, gastroschisis, pseudo-obstruction and short bowel.
• Hematology—Fetomaternal haemorrhage, hydrops fetalis.
• Immunodeficiency syndromes—SCID and/or ADA deficiency, combined T- and B-cell defects, ataxia-telangiectasia.
• Miscellaneous—Cystic hygroma, Turner syndrome, foetal demise, twin gestation, congenital nephrotic syndrome.
AFP is also increased in infants at high risk of foetal death up to 4–5 months after screening, regardless of the presence of neural tube defects or multiple gestations.