====== Alpha-Feto protein, serum ======
{{tag>labtests}}
==== Indications ====
  * any type of movement disorder in early childhood, cerebellar ataxias, [[oculomotor apraxia]](saccadic impairment)	 	
==== Notes ====
Alpha-fetoprotein (AFP) is present in fetal serum in concentrations up to 5,000,000 μg/l. Postnatally [[https://ghr.nlm.nih.gov/gene/AFP|AFP gene]] expression is turned down with a subsequent fall of the serum concentrations to 'adult values' of about 0.5-15 μg/l from the age of 2 years onwards. Individuals with AFP deficiency and those with hereditary persistence of AFP can however be normal. During pregnancy, AFP (in maternal serum) has long been recognized as a marker for congenital anomalies of the fetus. AFP is also a biomarker for hepatocellular carcinoma and some other malignancies. 

Increased serum AFP is a biomarker for [[Ataxia Telangiectasia]], [[ataxia-oculomotor apraxia 2]] (AOA2), [[Deoxyguanosine Kinase Deficiency]](DGUOK) deficiency (hepatocerebral form of mtDNA depletion). Measurement of serum AFP is very useful in the diagnostic workup of [[autosomal recessive cerebellar ataxias]] (ARCAs).

  * **Classic Ataxia Telangiectasia**
    * Infancy/childhood
    * ↑ AFP levels 100–900 μg/l. Rarely in <1% normal values are seen[(:cite:19535770>{{pmid>long:19535770}})]
    * in Variant A-T (ATM) AFP levels are 50–500 μg/l
    * other laboratory markers include immunoglobulins, liver transaminases, chromosomal rearrangements, increased radiosensitivity
  * **Ataxia with Oculomotor Apraxia Type 1 (AOA1)**
    * AOA1 (APTX)
      *AFP 10-20 μg/l. ↑ AFP seen only in exceptional cases[(:cite:24120489>{{pmid>long:24120489}})]. 
    * AOA2 (SETX)
      * Adolescence/adulthood
      * AFP 10–100 μg/l
      * ↑ Serum Creatine kinase
    * AOA2 (PIK3R5)
      * Adolescence/adulthood
      * AFP 30–100 μg/l
      * ↑ Serum Creatine kinase
    * AOA2 (none-SETX/none-PIK3R5)
      * Adolescence/adulthood
      * ↑ Serum Creatine kinase
  * **Mitochondrial disorders ([[https://ghr.nlm.nih.gov/gene/POLG|POLG]] and [[https://www.ncbi.nlm.nih.gov/gene/425626|C10orf2]])**
    * infancy/childhood/adolescence/adulthood
    * raised serum/csf lactate

CSF AFP levels in normal infants also decline with gestational age in proportion to levels of AFP in serum[(:cite:PMID10612715>{{pmid>long:10612715}})][(:cite:15802029>{{pmid>long:15802029}})].
  * median 61 kIU/L (5th-95th centile: 2-889 kIU/L) in infants -69 to 31 days old
  * median 1.2 kIU/L (5th-95th centile: 0.1-12.5 kIU/L) in infants 32 to 110 days old