GSTT1 and GSTM1 gene copy number analysis in paraffin-embedded tissue using quantitative real-time PCR.

GSTT1 and GSTM1 genes possess an inherited deletion associated with a lack of enzyme activity. The heterozygous condition of this deletion is difficult to determine in low-quality DNA with existing PCR protocols. We designed and validated a multiplex real-time PCR assay by adapting the DeltaDeltaCt relative quantification method for the analysis of GSTT1 and GSTM1 markers to accurately differentiate the three genotypes ( *1/1, *1/0, and *0/0) in degraded DNA from formalin-fixed paraffin-embedded tissue. Gene copy number values obtained provide for unambiguous homozygous and heterozygous differentiation. The efficacy shown by the PCR assay endorses its usefulness for complete genotyping of glutathione S-transferases in archival tissues.