The polymerase chain reaction and its applications in neuropathology

The polymerase chain reaction (PCR) provides a means of generating large numbers of copies of selected segments of DNA. Once amplified, the DNA can be characterized by determination of its size and sequence. For many applications, routinely-processed biopsy and autopsy material is an adequate substrate for the reaction. PCR can be used to amplify sequences of DNA that are uniquely characteristic of particular micro-organisms, allowing their rapid detection in samples of tissue or cerebrospinal fluid. The technique allows clones of cells with gene rearrangements or translocations to be detected with great sensitivity and is proving a useful way to monitor the effects of tumour therapy, particularly in patients with lymphomas and leukaemias. Further applications include the identification of gene deletions and mutations, and the assessment of cell lineage by amplification and analysis of highly polymorphic gene loci (DNA fingerprinting). Because the degree of amplification resulting from PCR is so great, even a single molecule of contaminating DNa may be detected and its significance misinterpreted. Great care, therefore, should be taken to prevent contamination of samples, particularly by the products of previous reactions, and every series of reactions should include appropriate controls.