G-TwYST study A combined chronic toxicity and carcinogenicity study in rats fed GM maize NK603 : main statistical report

Abstract

The purpose of oral toxicity study A in the EU project G-TwYST was to assess the effects of genetically modified (GM) maize NK 603, grown both with and without the use of RoundUp, when fed to rats for a period of up to two years at incorporation rates of 11% and 33% in the feed. The effects were assessed relative to the responses for male and female rats fed the near-isogenic non-GM maize, and the differences were compared, using classical and new statistical methods. The experimental design was a complete randomized block design with cage as the experimental unit. Five types of feed were administrated to cages with 2 rats in each cage. Experimental units, i.e. cages, were organized in blocks of 5 cages, and the feeding groups were randomized within blocks. Treatment identity was blinded for everyone involved in the experiments and for the statistical analysts until after decisions were made about outliers in the data. The four feeding groups with GM maize were each compared to the feeding group with non-GM maize for 36 variables at 3 months, 40 variables at 6 months, 44 variables at 12 months and 37 variables at 24 months, and for males and females separately. The variables were body weight, growth rate, feed intake, haematology, clinical chemistry and organ weights. Only data for animals that survived the experiment were statistically analysed. In total, 1256 comparisons on quantitative variables were made. In addition, the times of death were analysed using survival analysis, and an analysis of mortality at 24 months. Using classical statistical tests at the 5% false positive level (= 0.05), among the 1256 comparisons of GM groups to the non-GM group on quantitative variables, 80 (6.4%) significant differences were found using the parametric t-test, and 72 (5.7%) significant differences using the non-parametric Wilcoxon test. Using the tests at the 1% false positive level (= 0.01), there were 13 (1.0%) significant differences using the t-test (lowest P-value 0.002), and also 13 (1.0%) significant differences using the Wilcoxon test (lowest P=value 0.005). The number of significant test results is therefore equal or slightly higher than the expected false positive rate of the tests, and it was relatively high in the 12 months data (11% for the t-tests, and 9% for the Wilcoxon tests). The patterns of significant results are open for toxicological interpretation. Statistical tests were also performed based on the factorial structure of the feeding groups using analysis of variance. Using statistical tests at the 5% false positive level (= 0.05), 13 (4%) significant effects were found among 314 comparisons of the average of the four GM groups with the non-GM group, which therefore does not exceed the expected number of false positives given the nominal test level. More significant effects were found within the set of four GM groups. In 32 (10%) of the 314 cases there was a significant interaction effect, i.e. the differences between the GM groups with and without RoundUp were dependent on the GM inclusion rate 11%...

G-TwYST study A combined chronic toxicity and carcinogenicity study in rats fed GM maize NK603 : statistical report, 3 months data

“…The results of G-TwYST study A, except for the histopathological results which are reported separately, are given in five reports: four specific reports about the statistical analysis for data measured after 3, 6, 12 and 24 months, and a main report summarising all study results (Goedhart & van der Voet 2018). This report is about the results after 6 months.…”

“…More details are provided in several appendices to this report. For a description of the statistical methods, and for a summary and discussion of results for all months, the reader is referred to the main study A report (Goedhart & van der Voet 2018).…”

Statistical analysis of differential white blood cell counts for G-TwYST studies A and C

“…Statistical analysis of the G-TwYST studies was reported in Study A: Goedhart & van der Voet (2018a, 2018b2018c, 2018d Study B: Goedhart & van der Voet (2017) Study C: Goedhart & van der Voet (2018f) Note that for Study A there are separate reports for data acquired after 3, 6, 12 and 24 months as well as a main report. Study B and C were 3 months studies only.…”

G-TwYST study A combined chronic toxicity and carcinogenicity study in rats fed GM maize NK603 : statistical report, 24 months data

“…The results of G-TwYST study A, except for the histopathological results which are reported separately, are given in five reports: four specific reports about the statistical analysis for data measured after 3, 6, 12 and 24 months, and a main report summarising all study results (Goedhart & van der Voet 2018). This report is about the results after 24 months.…”