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MUTATIONS

Hypoxanthine phosphoribosyltransferase: HPRT gene

  • A membrane-situated salvage enzyme which transfers purines such as hypoxanthine back into the intracellular nucleic acid precursor pool.
  • A non-essential enzyme (in lymphocytes); so mutations are not lethal and can accumulate in the lymphocyte pool.
  • The HPRT gene lies on the X chromosome, so only one functional copy is present in each cell, and a single mutational event can make a cell hprt--.
  • Cells (usually lymphocytes) are incubated at fairly low density in cell culture medium. Mutant cells are selected by incubating with the toxic purine analogue 6-thioguanine which kills wild-type cells. Survivors form clones which are counted.
http://meddev.uio.no/elaring/lcms13/ernaeringslaere/nutr-cancer-biology/illustrations/hprt.JPG

There is apparently an inverse correlation between HPRT mutant frequency and plasma vitamin C. But smokers tend to have higher MFs and lower vitamin C. This is a nice example of smoking as a confounding factor.