Detection of ultrarare somatic mutation in the human TP53 gene by bidirectional pyrophosphorolyslis-activated polymerization allele specific amplification

The detection of ultrarare mutation in the presence of excess amounts of normal genomic DNA is highly advantageous in a number of circumstances, including: 1) identification of minimal residual disease for improved cancer chemotherapy; 2) measurement of mutation load to assess environmental mutagen exposure or endogenous DNA repair; and 3) prenatal diagnosis of paternally, derived mutations within fetal cells in the maternal circulation. Bidirectional pyrophosphorolysis activated polymerization allele,specific amplification (Bi-PAP-A) utilizes two opposing 3'-terminal blocked oligonucleotides (P*s) with 1 nucleotide overlap at their 3' termini. The selectivity of Bi-PAP-A derives from the serial coupling of pyrophosphorolysis and DNA polymerization. A total of 13 Bi-PAP-A assays were developed and validated for the human p53 gene (TP53). The sensitivity and specificity of each assay were determined with mutated and wild-type DNA templates, respectively. Bi-PAP-A has a sensitivity of one molecule for most assays and a selectivity (sensitivity: specificity) greater than 1:10(7)-1:10(9) for four of all six mutation types. Four assays with high selectivity were used to detect rare somatic mutations in blood white cells. The silent g.13147C > G (p.R156) mutation was present at an estimated frequency of 1.1 x 10(-7). The g.14523A > T (p.E285V), g.14487G > C (p.R273P), and g.14060G > C (p.G245R) mutations were undetectable with frequencies less than 2.0 x 10(-8). We conclude that Bi-PAP-A is a general and rapid method for detecting ultrarare mutations.