Placental alkaline phosphatase

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RefSeq (mRNA)



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Alkaline phosphatase, placental type also known as placental alkaline phosphatase (PLAP) is an allosteric enzyme that in humans is encoded by the ALPP gene.[1][2][3]


There are at least four distinct but related alkaline phosphatases: intestinal (ALPI), placental (this enzyme), placental-like (ALPPL2), and liver/bone/kidney (ALPL) (tissue-nonspecific). The first three are located together on chromosome 2, whereas the tissue-nonspecific form is located on chromosome 1. The coding sequence for this form of alkaline phosphatase is unique in that the 3' untranslated region contains multiple copies of an Alu family repeat. In addition, this gene is polymorphic and three common alleles (type 1, type 2, and type 3) for this form of alkaline phosphatase have been well-characterized.[3]


Alkaline phosphatase, placental type is a membrane-bound glycosylated dimeric enzyme, also referred to as the heat-stable form, that is expressed primarily in the placenta, although it is closely related to the intestinal form of the enzyme as well as to the placental-like form.[3]

Clinical significance

PLAP is a tumor marker, especially in seminoma[4][5][6] and ovarian cancer.[7] PLAP is reliable only in non-smokers, as smoking interferes with measurement of PLAP,[8] since serum concentrations of PLAP are increased up to 10-fold in smokers and its measurement is therefore of little value in this group.[9]


  1. Kam W, Clauser E, Kim YS, Kan YW, Rutter WJ (Feb 1986). "Cloning, sequencing, and chromosomal localization of human term placental alkaline phosphatase cDNA". Proc Natl Acad Sci U S A. 82 (24): 8715–9. doi:10.1073/pnas.82.24.8715. PMC 391507. PMID 3001717.
  2. Henthorn PS, Knoll BJ, Raducha M, Rothblum KN, Slaughter C, Weiss M, Lafferty MA, Fischer T, Harris H (Sep 1986). "Products of two common alleles at the locus for human placental alkaline phosphatase differ by seven amino acids". Proc Natl Acad Sci U S A. 83 (15): 5597–601. doi:10.1073/pnas.83.15.5597. PMC 386335. PMID 3461452.
  3. 3.0 3.1 3.2 "Entrez Gene: ALPP alkaline phosphatase, placental (Regan isozyme)".
  4. "European Group on Tumor Markers. A European Based Expert Group on Tumor Markers. Germ cell cancer". Archived from the original on 2012-04-26.
  5. W. Albrecht; et al. (2004). "Testicular tumor markers: Corner-stones in the management of malignant germ cell tumors" (PDF). J Lab Med. 28 (2): 109–115. doi:10.1515/labmed.2004.018. Archived from the original (PDF) on 2011-01-24.
  6. Sturgeon C (August 2002). "Practice guidelines for tumor marker use in the clinic". Clin. Chem. 48 (8): 1151–9. PMID 12142367.
  7. Fishman WH (December 1987). "Clinical and biological significance of an isozyme tumor marker--PLAP". Clin. Biochem. 20 (6): 387–92. doi:10.1016/0009-9120(87)90003-8. PMID 3325192.
  8. Schmoll HJ, Souchon R, Krege S, et al. (September 2004). "European consensus on diagnosis and treatment of germ cell cancer: a report of the European Germ Cell Cancer Consensus Group (EGCCCG)". Annals of Oncology. 15 (9): 1377–99. doi:10.1093/annonc/mdh301. PMID 15319245.
  9. "Tumor Markers in Testicular Cancers" (PDF). Archived from the original (PDF) on 2010-11-12.

Further reading