Alpha-1-fetoprotein is a protein produced in endodermal tissue during embryogenesis . The endodermal 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 system, urinary bladder or urethra .

From the fourth week of pregnancy, alpha-1-fetoprotein is mainly produced in the yolk sac and, to a lesser extent, in the developing fetal liver. Its concentration reaches its highest values ​​in the twelfth to sixteenth week of pregnancy. Shortly after birth, the synthesis of AFP comes to an almost complete standstill. In adults and children, higher concentrations are signs of pathological processes in the body. Thus, the alpha-1-fetoprotein serves as a tumor marker.

The measurement of blood and serum concentrations in pregnant women is carried out to diagnose neural tube defects in the fetus or to detect Down syndrome. The protein consists of 591 amino acids. Usually there is only one chain. Dimeric or trimeric protein chains are rare in alpha-1-fetoprotein.

Function, effect & tasks

The alpha-1-fetoprotein is of great importance for the growing embryo. It is therefore also formed in larger concentrations in the embryonic tissue (especially in the yolk sac). It serves as a transport protein during embryogenesis. 

It enables the transport of the trace elements nickel and copper in the fetal blood . Besides, it is also responsible for the transport of bilirubin and fatty acids in the blood of the fetus. This is why elevated levels in the serum, blood plasma or amniotic fluid can also be measured in pregnant women . The yolk sac of the embryo is the actual metabolic organ until the liver develops. 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 only synthesized in very small amounts in the digestive tract. However, alpha-1-fetoprotein production increases as tumors grow.

Formation, Occurrence, Properties & Optimal Values

In non-pregnant women, 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. However, it should be mentioned that no clear limit values ​​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, the concentrations of AFP in the blood plasma, serum and of course in the amniotic fluid are increased. The serum AFP concentration is 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 median”. During pregnancy , the AFP concentrations exceptionally increase and change constantly depending on the phase of pregnancy.

The AFP concentration in the serum should not exceed the value of 2.5 MoM, since increased values ​​may indicate a neural tube defect in the foetus. The normal value for pregnant women is 0.5 to 2.0 MoM. In turn, lower levels of alpha-1-fetoprotein may indicate trisomies such as Down syndrome .

Diseases & Disorders

Deviating values ​​of alpha-1-fetoprotein in the blood plasma or serum indicate pathological processes in both pregnant and non-pregnant women, 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. Larger amounts of alpha-1-fetoprotein enter the blood plasma or amniotic fluid of the pregnant woman through the patent neural tube. If the concentration is above 2.5 MoM, these abnormalities should be considered and further ultrasound examinations should be performed. In this way, such congenital neural tube defects as anencephaly (missing brain) or spina bifida (open spine) as well as abdominal wall defects can be detected. If the concentration of AFP is below 0.5 MoM, trisomy 21 (Down syndrome) or other trisomies can also be present.

However, deviating AFP values ​​of pregnant women only give an indication of possible defects. In particular, imaging procedures such as ultrasound examinations must confirm the diagnosis. Elevated values ​​also occur in multiple pregnancies or in the case of an incorrectly dated pregnancy. However, targeted ultrasound examinations can already be carried out in the borderline range of 2.0 to 2.5 MoM. Higher limit values ​​may be present in the amniotic fluid. For example, 2.5 MoM are given here between the 13th and 15th week of pregnancy. However, the limit value in the amniotic fluid even increases to 4.0 MoM by the 24th week of pregnancy.

In non-pregnant women, children and men, only elevated AFP concentrations are of medical significance. If the values ​​​​are over 40 nanograms per milliliter, there may be an indication 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 . The increased alpha-1-fetoprotein values ​​only provide indications but no proof of a tumor. Other examination methods must confirm the diagnosis.

The concentrations of AFP in the serum or blood plasma can also be increased in chronic hepatitis , in liver cirrhosis or in Louis-Bar syndrome . Louis-Bar syndrome is a genetic neurodegenerative disease.