Alpha-Fetoprotein

From Embryology

Introduction

The alpha-fetoprotein (AFP) or fetal alpha globulin is thought to function in the fetus in a similar role to that of serum albumin postnatally. AFP is synthesised in both the fetal liver and the yolk sac.

The AFP test is a test that is performed during pregnancy of maternal blood or fetal amniotic fluid at 16-19 weeks of gestation. The amniotic test (Amniocentesis) is more invasive than the maternal blood test. The protein is synthesized by yolk sac and liver of the fetus and is also expressed in the adult in some liver cancers and is a member of a multigenic family encoding albumin, alpha-albumin, and vitamin D binding protein.

Low levels of AFP normally occur in the blood of a pregnant woman. Abnormal amounts of the protein may indicate genetic or developmental problems in the fetes. High levels may indicate neural tube defects (spina bifida, anencephaly), the neural tube defect allows AFP to leak through into the amniotic fluid. This test can also be used in non-pregnacy testing of clinical conditions, including liver cancer.


Diagnosis Links: Prenatal Diagnosis | pregnancy test | amniocentesis | chorionic villus sampling | ultrasound | Alpha-Fetoprotein | Pregnancy-associated plasma protein-A | Fetal Blood Sampling | Magnetic Resonance Imaging | Computed Tomography | Non-Invasive Prenatal Testing | Fetal Cells in Maternal Blood | Preimplantation Genetic Screening | Comparative Genomic Hybridization | Genome Sequencing | Neonatal Diagnosis | Category:Prenatal Diagnosis | Fetal Surgery | Classification of Diseases | Category:Neonatal Diagnosis

Some Recent Findings

Trisomy 21 newborn
  • Second Trimester Prenatal Screening for Down's Syndrome (DS) in Mainland Chinese Subjects using Double-Marker Analysis of α-fetoprotein and β-human Chorionic Gonadotropin Combined with Measurement of Nuchal Fold Thickness ( NT)[1] "Second trimester prenatal screening using double-marker analysis for AFP and β-hCG combined with measurement of NT is effective for the detection of DS in Mainland Chinese pregnancies."

Protein

  • Protein first identified in the 1950's.[2]
  • AFP Levels - normal values for males or non-pregnant females is less than 10 micrograms/millilitre.
  • Member of the albuminoid gene superfamily which includes, serum albumin, vitamin D binding protein and alpha-albumin (afamin).[3]
  • Screening has low sensitivity for fetal hydrocephalus and is rarely elevated in isolated cases.[4]
    • When fetal hydrocephalus is detected, elevated AFP levels indicate that the fetus is at significant risk to have additional malformations.
  • Serum alpha fetoprotein (AFP) has also been used as a tumor marker in the adult for liver cancer (Hepatocellular carcinoma, HCC).[5]

Female Function

  • In knockout KO Mice, essential for female fertility and for expression of normal female behaviors.[6]
    • sequestrates estrogens
    • protects the female developing brain from deleterious (defeminizing/masculinizing) effects of these hormones.[7]
    • mice suffer from anovulation

Postnatal Diagnostic Uses

  • Serum α-fetoprotein (AFP) level is used as a tumour marker for the diagnosis and detection of hepatocellular carcinoma.
    • elevated AFP level (≥ 200 ng/dL)
  • Some patients have hereditary persistence of AFP and also have persistent abnormal AFP.

Protein Sequence

Length 609 Mass (Da) 68,678

>sp|P02771|FETA_HUMAN Alpha-fetoprotein OS=Homo sapiens GN=AFP PE=1 SV=1 MKWVESIFLIFLLNFTESRTLHRNEYGIASILDSYQCTAEISLADLATIFFAQFVQEATY KEVSKMVKDALTAIEKPTGDEQSSGCLENQLPAFLEELCHEKEILEKYGHSDCCSQSEEG RHNCFLAHKKPTPASIPLFQVPEPVTSCEAYEEDRETFMNKFIYEIARRHPFLYAPTILL WAARYDKIIPSCCKAENAVECFQTKAATVTKELRESSLLNQHACAVMKNFGTRTFQAITV TKLSQKFTKVNFTEIQKLVLDVAHVHEHCCRGDVLDCLQDGEKIMSYICSQQDTLSNKIT ECCKLTTLERGQCIIHAENDEKPEGLSPNLNRFLGDRDFNQFSSGEKNIFLASFVHEYSR RHPQLAVSVILRVAKGYQELLEKCFQTENPLECQDKGEEELQKYIQESQALAKRSCGLFQ KLGEYYLQNAFLVAYTKKAPQLTSSELMAITRKMAATAATCCQLSEDKLLACGEGAADII IGHLCIRHEMTPVNPGVGQCCTSSYANRRPCFSSLVVDETYVPPAFSDDKFIFHKDLCQA QGVALQTMKQEFLINLVKQKPQITEEQLEAVIADFSGLLEKCCQGQEQEVCFAEEGQKLI SKTRAALGV

References

  1. <pubmed>21870022</pubmed>
  2. <pubmed>13351554</pubmed>
  3. <pubmed>15169963</pubmed>
  4. Maternal serum alpha-fetoprotein levels in fetal hydrocephalus: a retrospective population based study. Terrence P Szajkowski, Bernard N Chodirker, Karen M MacDonald, and Jane A Evans BMC Pregnancy Childbirth. 2006; 6: 23. Published online 2006 July 7. doi: 10.1186/1471-2393-6-23. PMCID: PMC1526755
  5. <pubmed>15169963</pubmed>
  6. <pubmed>19690639</pubmed>
  7. <pubmed>16388309</pubmed>

Reviews

Search PubMed

Search PubMed: Alpha-Fetoprotein



Prenatal Diagnosis Terms

  • blastomere biopsy - An ART preimplantation genetic diagnosis technique carried out at cleavage stage (day 3), excluding poor quality embryos, detects chromosomal abnormalities of both maternal and paternal origin. May not detect cellular mosaicism in the embryo.
  • blastocyst biopsy - An ART preimplantation genetic diagnosis technique carried out at blastocyst stage (day 4-5), removes several trophoblast (trophoderm) cells, detects chromosomal abnormalities of both maternal and paternal origin and may detect cellular mosaicism.
  • cell-free fetal deoxyribonucleic acid - (cfDNA) refers to fetal DNA circulating and isolated from the plasma portion of maternal blood. Can be performed from GA 10 weeks as a first-tier test or as a second-tier test, with women with increased probability on combined first trimester screening offered cfDNA or diagnostic testing.
  • false negative rate - The proportion of pregnancies that will test negative given that the congenital anomaly is present.
  • false positive rate - The proportion of pregnancies that will test positive given that the congenital anomaly is absent.
  • free β human chorionic gonadotrophin - beta-hCG subunit of hCG used as a diagnostic marker for: early detection of pregnancy, Trisomy 21, spontaneous abortion, ectopic pregnancy, hydatidiform mole or choriocarcinoma.
  • multiples of the median - (MoM) A multiple of the median is a measure of how far an individual test result deviates from the median and is used to report the results of medical screening tests, particularly where the results of the individual tests are highly variable.
  • negative predictive value - The probability that a congenital anomaly is absent given that the prenatal screening test is negative.
  • Non-Invasive Prenatal Testing - (NIPT) could refer to ultrasound or other imaging techniques, but more frequently used to describe analysis of cell-free fetal DNA circulating in maternal blood.
  • polar body biopsy - (PB biopsy) An ART preimplantation genetic diagnosis technique that removes either the first or second polar body from the zygote. As these are generated by oocyte meiosis they detects chromosomal abnormalities only on the female genetics.
  • positive predictive value - The probability that a congenital anomaly is present given that the prenatal screening test is positive.
  • prenatal screening sensitivity - (detection rate) The probability of testing positive on a prenatal screening test if the congenital anomaly is present.
  • prenatal screening specificity - The probability of testing negative on a prenatal screening test if the congenital anomaly is absent.
  • quadruple test (maternal serum testing of a-fetoprotein Template:AFP, free B-hCG or total hCG, unconjugated estriol, and inhibin A) is a fetal chromosomal anomaly test usually carried out later in pregnancy (GA 14 to 20 weeks).
  • single nucleotide polymorphisms - (SNPs) the variation in a single DNA nucleotide that occurs at a specific position in the genome.
  • triple test - (maternal serum testing of a-fetoprotein Template:AFP, free B-hCG or total hCG, and unconjugated estriol) is a fetal chromosomal anomaly test usually carried out later in pregnancy (GA 14 to 20 weeks).


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Cite this page: Hill, M.A. (2024, March 28) Embryology Alpha-Fetoprotein. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Alpha-Fetoprotein

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G