Alpha-1 fetoprotein

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Alpha-1 fetoprotein
Properties of human protein
Mass / length primary structure 591 amino acids
Secondary to quaternary structure Monomer; rarely di- / trimer
Identifier
Gene name AFP
External IDs
Occurrence
Parent taxon Mammals

Alpha-1-Fetoprotein (AFP), also Alphafoetoprotein or α 1 -Foetoprotein , is a glycoprotein in mammals that is formed during human embryonic development in the course of pregnancy by the endodermal tissue and the fetal liver , or in adults especially in tumor cells of the liver . Physiologically, the alpha-1 fetoprotein has the function of a fetal transport protein , which in particular transports copper , nickel , fatty acids and bilirubin in the fetal blood plasma .

AFP is structurally closely related to the transport proteins albumin , vitamin D-binding protein and afamin . Production begins in the four-week-old embryo, is highest in the twelfth to sixteenth week and almost completely stops after birth. In adults, plasma levels are usually less than 40 ng / ml.

Applications

Very high AFP concentrations in the maternal blood or in the amniotic fluid are an indication of occlusive defects in the unborn child. These include abdominal wall defects such as the omphalocele and gastroschisis, and neural tube defects such as the spina bifida aperta and anencephaly . In men and non-pregnant women high AFP concentrations of an active can hepatitis , liver cirrhosis and hepatocellular carcinoma (hepatocellular carcinoma, HCC) point or a nichtseminomatösen germ cell tumor. Low AFP values ​​between the 14th and 20th week of pregnancy are an indication of Down syndrome (trisomy-21) in the unborn child.

Laboratory tests

pregnancy

In the serum

The measurement of the serum AFP concentration during pregnancy can be requested as an isolated test in the laboratory. The determination of the serum AFP value can also be carried out in combination with other serum values. Then it is part of prenatal screening examinations such as the so-called triple test or the quadruple test .

Limit values

In Germany, medical guidelines for serum AFP limits published. According to them, values ​​above 2.5 MoM are indicative of a closure defect. A detailed ultrasound examination and, if the patient so wishes, an amniocentesis to examine the AFP and AChE in the amniotic fluid is then recommended as a recommendation . Serum AFP values ​​between 2.0 and 2.5 MoM are considered normal values ​​in the borderline range for which a targeted ultrasound examination can be offered.

Sources of error

Sources of error in the interpretation of the measured AFP values ​​are: misjudgment of the gestational age, non-consideration of the maternal body weight, non-consideration of the smoking status and non-consideration of the ethnic origin of the examined patient. Pregnant women of African descent in particular have significantly higher serum AFP values ​​than women of European descent. It must also be taken into account that the AFP concentrations in women with twin pregnancies are on average twice as high , that injuries to the placenta (bleeding, placenta hematomas ) can lead to an increase in AFP in the maternal serum, and that extremely high AFP values ​​in Scandinavian women on a Finnish Nephrosis (syn .: nephrotic syndrome - Finnish type).

In the amniotic fluid

In Germany, the amniotic fluid AFP value is usually measured in every amniotic fluid sample to search for neural tube defects , even if there is a different indication for amniocentesis. An increased AFP value in the amniotic fluid as well as in the serum is not considered to be evidence of the presence of a neural tube defect or other occlusive defects. Only evidence of the defect in ultrasound is considered to be conclusive . In combination with the AFP value, the acetyl cholinesterase (AChE) in the amniotic fluid is also often examined. A positive AChE value in connection with an increased AFP value is a clear indication of a neural tube defect in the fetus.

Limit values

In Germany there are no generally applicable limit values ​​for AFP in amniotic fluid. Usually, every laboratory defines this limit value itself, referring to relevant literature from publications that suggest such limit values. One of the most important publications in this context is the UK Collaborative Study on Alpha-fetoprotein in Relation to Neural-tube Defects. According to this study, the limit value for increased AFP concentrations changes gradually over the course of pregnancy. Between the 13th and 15th week the limit should be 2.5 MoM, between the 16th and 18th week it should be 3.0 MoM, between the 19th and 21st week it should be 3.5 MoM, and between the 22nd . and 24th week at 4 MoM.

Sources of error

Sources of error in the interpretation of the measured AFP values ​​are: Bloody amniotic fluid ( contamination with fetal erythrocytes ) often leads to increased AFP values, puncture after amniotic fluid replenishment leads to extremely low AFP values

Tumor markers

AFP serves as a tumor marker in the following tumors :

See also

literature

  • Klaus Dörner (Ed.): Clinical chemistry and hematology , 4th edition, Stuttgart 2001, p. 118.

Individual evidence

  1. ↑ Homologues of P02771 at OMA
  2. ↑ a b UniProt P02771
  3. ↑ INTERPRO: Alpha-fetoprotein
  4. ^ Pauer, H.-U. and Rauskolb, R. (1999) Blood tests in pregnant women to define prenatal risk for chromosomal abnormalities and neural tube defects (triple test). (Comment: Summary report on the 4th consensus meeting), medgen 11, 36-39
  5. ↑ Amniotic-fluid alpha-fetoprotein measurement in antenatal diagnosis of anencephaly and open spina bifida in early pregnancy. Second report of the UK Collaborative Study on Alpha-fetoprotein in Relation to Neural-tube Defects. Lancet. 1979 Sep 29; 2 (8144): 651-62
  6. ↑ JM Ertle, D Heider, M Wichert, B Keller, R Kueper, P Hilgard, G Gerken, JF Schlaak: A combination of α-fetoprotein and des-γ-carboxy prothrombin is superior in detection of hepatocellular carcinoma. . In: Digestion . 87, No. 2, 2013, pp. 121-31. PMID 23406785 .