These data, together with data from previous reports, suggest that for much of the known photosynthetic eukaryotic diversity, plastid DNA mutations occur less frequently than those in mitochondrial DNA.
However, these mutations occur less frequently than missense mutations, which can have either minimal or catastrophic effects on protein folding and function [ 14].
In contrast, missense mutations occur less frequently in MSI cancers, but tend to be oncogenic, as is the case of mutations affecting KRAS, BRAF and PI3KCA in MSI CRC (16).
EGFR mutations occur less frequently among Caucasians (10 15%) compared to East Asians (30 60%) (Lynch et al, 2004; Paez et al, 2004) in contrast to KRAS mutations for which the situation is opposite – Caucasians vs East Asians, 25 50% vs 5 15%, respectively (Mao et al, 2010; Roberts et al, 2010).
We confirmed these findings in the validation series, with TGFBR2 and MSH3 microsatellite mutations occurring less frequently in MSI-H rectal and sigmoid carcinomas than in MSI-H colon carcinomas elsewhere (P = 0.00005 and P = 0.0000005, respectively, when considering all MSI-carcinomas of both series).
From South Africa, Van Rie et al [ 37] reported similar results, whereas Barnard and colleagues [ 23] reported that this mutation occurred less frequently (37.6%; p = 0.01).
A combination of a truncating mutation in APC and an activating mutation in K-ras occurred less often than the sole occurrences of mutations in both genes.
Our previous analyses demonstrated that within the 186 adenocarcinomas tested, BRAF and K-RAS mutations occurred together less frequently than expected by chance (χ2 test, p = 0.009).
The most frequently observed katG mutation was katG S315T1 (in 38 of 43 strains, 88.4%), whereas katG S315T2 (2.3%) and unknown mutations (i.e., no hybridization to the katG WT nor to either of the mutation probes, 9.3%) occurred less frequently.
