| The genomes of any two individuals will differ. This genomic difference can be attributed mainly to polymorphisms such as single nucleotide polymorphisms (SNPs) and point mutations. While certain SNPs have the potential to be used as predictors of disease states, point mutations have been linked to numerous diseases (e.g. cancer). Therefore the need to detect these genomic polymorphisms is of high importance to the biomedical field. The research presented here focused on developing electrospray ionization (ESI) quadrupole mass spectrometry (MS) and ESI-quadrupole time-of-flight (Q-TOF) MS for the detection of SNPs and point mutations in the tumor suppressor gene p53 and the oncogene K-ras following polymerase chain amplification from human cells. It was determined that appropriate sample preparation (e.g. ethanol precipitation, sample heating) and instrumental configuration to limit DNA adducts, were both vital for successful ESI-quadrupole MS analysis of intact PCR products. ESI-quadrupole MS was able to detect two p53 SNPs, a guanine (G) to cytosine (C) tranversion (40.0 Da shift) and a C to thymine (T) transition (15.0 Da shift). In a second study, focused on examining the limitations of resolution for ESI-quadrupole and ESI-Q-TOF MS, SNPs and point mutations in heterozygous p53 and K-ras genotypes resulting in lower mass differences (e.g. adenine (A) to T transversion, 9.0 Da shift) were characterized. The higher resolution of ESI-Q-TOF MS proved essential for the detection of A to T shifts in heterozygous PCR products. While MS analysis allowed for the discrimination of the K-ras mutations, only tandem mass spectrometry (MS/MS) allowed for the differentiation of isomeric K-ras mutants (e.g GGT and TGT). ESI-Q-TOF MS/MS was able to discriminate the isomeric K-ras mutants on account of the relative abundance of their sequence specific fragment ions. To help automate MS/MS discrimination, SpecDiff, a tool for differentiating isomeric pairs by identifying peaks that differ in relative abundance between spectra was created. The usefulness of SpecDiff was demsonstrated, as it was able to rapidly detect discriminating fragment ions. Thus, it is suggested that the combination of MS and MS/MS can be an essential tool for the rapid detection of cancer causing mutations in patient samples. |
