Alpha-1-fetoprotein (AFP) is formed mainly in embryonic tissues, where it serves as a transport protein. After birth, very little AFP is formed. Elevated serum or blood levels in children and adults indicate tumors, among other things.
What is alpha-1 fetoprotein?
Alpha-1 fetoprotein is a protein that is produced in the entodermal tissue during embryogenesis. The entodermal tissue develops from the yolk sac and is the starting point for the development of various tissues and organs such as the digestive tract, liver, pancreas, thymus, thyroid, respiratory organs, urinary bladder, or urethra. Alpha-1-fetoprotein is produced from the fourth week of pregnancy mainly in the yolk sac and in smaller amounts also by the growing liver of the fetus. Its concentration reaches its highest levels in the twelfth to sixteenth weeks of gestation. Shortly after birth, synthesis of AFP comes to an almost complete halt. In adults and children, higher concentrations are signs of pathological processes in the body. Thus, alpha-1-fetoprotein serves as a tumor marker. Blood and serum concentrations in pregnant women are measured to diagnose neural tube defects in the fetus or, for example, to detect Down syndrome. The protein consists of 591 amino acids. In most cases, only one chain is present. Dimeric or trimeric protein chains rarely occur in alpha-1 fetoprotein.
Function, action, and roles
The alpha-1 fetoprotein possesses great importance for the growing embryo. Therefore, it is also produced in greater concentrations in embryonic tissues (especially in the yolk sac). It serves as a transport protein during embryogenesis. Thus, it enables the transport of the trace elements nickel and copper in the fetal blood. It is also responsible for the transport of bilirubin and fatty acids in the fetal blood. For this reason, elevated levels can also be measured in serum, blood plasma or amniotic fluid in pregnant women. The yolk sac of the embryo is the actual metabolic organ until the liver is formed. It requires alpha-1 fetoprotein to make the developing embryo increasingly independent of the maternal bloodstream. After birth, this protein is no longer necessary and is synthesized only in very small quantities in the digestive tract. However, the production of alpha-1 fetoprotein increases during tumor growth.
Formation, occurrence, properties, and optimal levels
In nonpregnant women as well as men and children, the normal concentration of alpha-1 fetoprotein in blood plasma and serum is less than seven nanograms per milliliter. However, there is a gray area up to 20 nanograms per milliliter. It should be mentioned in this regard, however, that no clear limits have been set in Germany. However, if the concentration of AFP exceeds 40 nanograms per liter, possible cancer growth should also be considered. In pregnant women, concentrations of AFP are elevated in blood plasma, serum and, of course, amniotic fluid. Serum AFP concentrations are always determined in pregnant women as part of prenatal screening tests. Here, the concentrations are given as so-called MoM values. MoM means “multiple of the central value”. During pregnancy, AFP concentrations increase exceptionally and change constantly depending on the stage of pregnancy. At the same time, the AFP concentration in serum should not exceed the value of 2.5 MoM, because increased values may indicate a neural tube defect of the fetus. The normal value in pregnant women is 05, to 2.0 MoM. Lower levels of alpha-1-fetoprotein, in turn, may indicate trisomies such as Down syndrome.
Diseases and disorders
Abnormal levels of alpha-1-fetoprotein in blood plasma or serum indicate pathologic processes in both pregnant and nonpregnant women, as well as children and men. If the levels are elevated in pregnant women, it may be a neural tube defect in the growing child. The neural tube defect is characterized by incomplete closure of the neural tube. The open neural tube allows larger amounts of alpha-1 fetoprotein to enter the blood plasma or amniotic fluid of the pregnant woman. If the concentration is above 2.5 MoM, these malformations should be considered and further ultrasound examinations should be performed.Thus, such congenital neural tube defects as anencephaly (missing brain) or spina bifida (open back) can be detected, as well as abdominal wall defects. If the concentration of AFP is below 0.5 MoM, trisomy 21 (Down syndrome) or other trisomies may also be present. However, abnormal AFP levels in pregnant women only provide an indication of possible defects. Imaging procedures such as ultrasound examinations in particular must confirm the diagnosis. Elevated levels also occur in multiple pregnancies or in a misdated pregnancy. However, targeted ultrasound examinations can already be performed in the borderline range of 2.0 to 2.5 MoM. Higher limits may be present in the amniotic fluid. For example, 2.5 MoM is indicated here between the 13th and 15th week of pregnancy. However, the limit value in the amniotic fluid rises to as much as 4.0 MoM by the 24th week of pregnancy. In non-pregnant women, children and men, only elevated AFP concentrations have any medical significance. If levels are above 40 nanograms per milliliter, there may be evidence of a tumor. Therefore, AFP serves as a tumor marker for such cancers as liver cancer, lung cancer, cancer of the digestive tract, testicular cancer, or ovarian cancer. In this context, the elevated alpha-1-fetoprotein levels again only provide indications but no proof of a tumor. Other examination methods must be used to confirm the diagnosis. The concentrations of AFP in serum or blood plasma can also be elevated in chronic hepatitis, liver cirrhosis or Louis Bar syndrome. Louis-Bar syndrome is a genetic neurodegenerative disorder.
