The human mitochondrial genome (mtDNA) is a multicopy compact circular double stranded genome, that encodes for tRNAs, rRNAs and only a small portion of mitochondrial proteins. Mitochondria have increased rates of mutations compared to nuclear DNA (nDNA); over 150 mutations in mtDNA are associated with genetic disorders. Inheritance of these is almost exclusively maternal, and is complicated due to involvement of nDNA, and the occurrence of heteroplasmy, penetrance, expressivity, phenocopies, and genocopies. Currently accounted factors are often not sufficient for explaining the type and severity of clinical symptoms observed. The main focus of molecular diagnosis has been mainly qualitative: The detection of point mutations and large indels. However; neglecting the quantitative aspects, related to mutant load, may actually debase prediction of the phenotype. Quantifying mutant load can be performed accurately, sensitively and fast using real time quantitative PCR. This technique provides apparently for a better alternative to the current gold standard: the southern blot analysis, and introduces a valuable research tool for establishing more accurate genotype/ phenotype correlations that will foster improved genetic counseling, clinical diagnosis, and patient management.

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