Nonradioactive characterization of low-level heteroplasmic mitochondrial DNA mutations by SSCP-PCR enrichment.

Mitochondrial DNA (mtDNA) mutations have been implicated in an increasing number of human diseases. Many of these mutations are heteroplasmic and are only present at low levels in readily accessible human tissue such as blood. The technique of single-stranded conformational polymorphism (SSCP) allows the detection of mtDNA variants from peripheral blood, but characterization of these variants by automated sequencing is hampered by the low level of heteroplasmy. We have therefore developed a technique for the enrichment of mtDNA mutations that allows reliable sequence data to be obtained even if the variant mtDNA represents only 1% of the total mtDNA. The procedure involves the excision, purification and subsequent PCR amplification of selected DNA fragments from SSCP gels. The techniques can be applied to other heterogeneous mutations such as mosaic mutations in skin biopsies or somatic oncogene mutations in tumor tissue.