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In a first consideration, the G-TwYST consortium intended to perform rat feeding trials with GM maize NK 603 and MON810 based on OECD Test Guidelines and according to EFSA recommendations. In autumn 2014, EFSA published an explanatory statement regarding the applicability of the Guidance of the EFSA Scientific Committee on conducting repeated-dose 90-day oral toxicity study in rodents on whole food/feed for GMO risk assessment and proposed to consider an increased inclusion rate for maize (e.g. up to 50%) rather than a standard inclusion rate of 33%. In addition, the G-TwYST Advisory Board and several stakeholders criticized the suggested chronic toxicity feeding trial with MON810, which only included one instead of typically two dosage groups because of animal housing capacity limitations and financial constraints. Moreover, several stakeholders criticized that potential toxic effects such as immunotoxicity and endocrine disruption were not taken into consideration.


Major changes

By taking into account all the above-mentioned considerations, the G-TwYST consortium took the following decisions:

  1. to perform the original 90-day feeding trial with GM maize NK603 at an inclusion rate of 11 and 33%;
  2. not to perform the 2-year feeding trial with the GM maize MON810*;
  3. to perform a further 90-day feeding trial with GM maize NK603 at an inclusion rate of 50%;
  4. to perform the original combined chronic toxicity/carcinogenicity feeding trial with GM maize NK603 at an inclusion rate of 11 and 33%;
  5. to analyze potential immunotoxic and endocrine effects in the 90-day feeding trial with GM maize NK603 at an inclusion rate of 11 and 33%.


Written comments

Seven stakeholders representing industry, civil society, science and competent authorities filed more than 100 written comments to the G-TwYST draft study plan. Comments and responses were split in 8 categories:

  1. General comments
  2. Cultivation
  3. Feed production and plant analysis
  4. Feed quality
  5. Design of the feeding trials
  6. Data collection
  7. Statistical analysis
  8. Other issues

The full report (PDF) is available here.


Final study plans


Final study plans with track changes


Draft study plans

The draft study plans consist of 6 documents:


  1. The G-TwYST 90-day subchronic toxicity study in rats fed GM maize NK 603;
  2. The G-TwYST 90-day NK603 Feeding Trial Study Plan - Supplementary Information: Maize and diet production as well as maize and diet analyses;
  3. The G-TwYST combined chronic toxicity and carcinogenicity study in rats fed GM maize NK603;
  4. The G-TwYST combined chronic toxicity/carcinogenicity NK603 Feeding Trial Study Plan - Supplementary Information: Maize and diet production as well as maize and diet analyses;
  5. The G-TwYST 2-year carcinogenicity study of rats with GM maize MON810;
  6. The G-TwYST  2-Year MON810 Feeding Trial Study Plan - Supplementary Information: Maize and diet production as well as maize and diet analyses.



*In the frame of G-TwYST it was originally planned to perform a 2-year carcinogenicity feeding trial with the GM maize MON810 at an inclusion rate of 33% on top of the 2-year study with maize NK603. Due to financial and animal housing constraints, it was not possible to include a further experimental group with an inclusion rate of e.g. 11% for the maize MON810 study. Hence, it would not have been possible to analyse a dose-effect relationship with this trial data.
Moreover, in the stakeholder consultation it was strongly recommended to include a 50% maize NK603 diet in the 90-day study with maize NK603, pushing the maize content of the diet to the limit of what is considered acceptable in terms of nutritional balance.

Given the constraints in time, lab space (the number of animals we can house at the same time) and funding we are not able to follow all recommendations, i.e. both including a 50% diet in the 90-day study and largely increasing the number of animals in a maize MON810 combined 2-year study, so we chose to focus on an approach that will ensure most robust outcomes in terms of science and statistics. The best way to achieve that is dropping the 2-year maize MON810 study and include an additional 90-day study with maize NK603 (study plan 2) with a 50% diet.


It should be mentioned that in the frame of GRACE 90-day feeding trials as well as a 1-year chronic toxicity feeding trial have been performed with maize MON810.

Latest news

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G-TwYST Interim Report available

15 February 2017


The G-TwSYT team completed a publicly available Interim report with information about the progress that has been made in the first 1.5 years of the project. The report can be downloaded here.

Value and pitfalls of stakeholderconsultation

17 January 2017


In 2013 the Dutch Commission on Genetic Modification (COGEM) published a topic report on alarming studies on the safety of GMOs. COGEM pointed out that while repetition of ‘alarming studies’ is sometimes the only way to reject or confirm the results, stakeholder participation during investigation may increase its social robustness.

In a letter sent to the Secretary of State of Infrastucture and Environment on January 11, 2017 COGEM adds some reflections on the value and possible pitfalls of stakeholder participation based on experiences in and results of the GRACE project.

The COGEM letter states that the involvement of stakeholders in this project has been meticulous and transparent and has finally contributed to the validity of the results also from a broader social perspective. However, COGEM also noticed that some stakeholders were too fixated on their own arguments and vision, that reflection and interaction became difficult. According to COGEM this situation significantly hampered the achievement of broadly supported conclusions. On the basis of this experience COGEM also proposed some guidelines for improving such processes.


Read the full letter >

Scientific quality criteria (2)

28 November 2016


So far, we have received comments on the proposed scientific quality criteria from the Federal Office of Consumer Protection and Food Safety, Germany (BVL) on October 5th, 2016. The comments can be downloaded here.


The G-TwYST research team responded to the BVL comments on November 28th, 2016. The response can be downloaded here.