The EU probably has the most detailed, carefully drafted and thought-out GM regulations in the world. All Member States can give their opinion during the GM approval process, and the precautionary principle underlies it.
New biotech crops on the market come stacked with multiple artificial genes*. In such cases, even if the 'parent' single-trait crops have already been accepted, the EU quite rightly considers the crop to be a new GM organism needing its own regulatory approval.
How the EU system works in practice, however, is less impressive.
Despite concerns raised by France, Germany, Austria and Belgium that GM maize, 'MON89034', could cause adverse health effects, the European Food Safety Authority (EFSA) gave it a favourable opinion, and the European Commission approved it in 2011. Since then, nine stacked maize varieties bred using MON89034 have been approved.
MON89034 itself contains two 'Bt' insecticide-producing DNA constructs: one is an entirely synthetic gene combining two previously-used Bt toxins and, therefore, has no natural counterpart; the second is a less commonly deployed Bt gene.
Doubts about the safety of MON89034 have arisen from the results of industry feeding studies. These found two out of twenty female rats fed a high dose of GM chow (33% of the total diet) developed signs of chronic progressive kidney disease, including cell proliferation (which can be a pre-cursor to cancer), inflammation and water retention. Both rats had bladder stones likely linked to the kidney tissue abnormalities observed. One of the affected rats died after two weeks on the GM diet.
Concerns have also been raised that the entirely synthetic gene product in MON89034 had a degree of similarity to a major allergen in kiwi fruit, and that the same two females with bladder stones had a low thyroid/parathyroid weight. Further testing of the crop was requested, and refused.
Doubts now extend to the safety of the stacked strains derived from MON89034.
Protein profiling (proteomics) has shown protein changes in gene-stacked crops which don't exist in the single-trait parents, and which indicate GM-induced disturbances in the energy and detoxification biochemistries. While the total Bt toxin load per plant is, of course, much greater in the multi-trait offspring than in any of the parent plants, it's been found that individual transgene expression is reduced by as much as 41% once they've been stacked with others (see Note).
What all this adds up to is stressed plants which may lack resilience in the field, may generate unhealthy by-products, and are certainly not the sum of all the Bt 'parts' which went into their manufacture 
How was the EFSA able to ignore all these safety concerns and approve stacked GM crops without requiring lengthy feeding trials?
- The kidney disease link to MON89034 was dismissed using historical data for the strain of rats used. Apparently, bladder stones have been observed in 0.49% of control rats, and astonishingly this became a reason to dismiss as 'chance' the finding of bladder stones in 10% of test rats. COMMENT Another way to view this is that these rats have a low natural susceptibility to kidney disease which became magnified by a factor of twenty under the influence of the GM diet.
- The allergenicity and thyroid/parathyroid link to MON89034 seem to have been dismissed as implausible. COMMENT Implausibility seems to be a catch-all excuse to throw out inconvenient data.
- Possible interactions between stacked genes and their products were dismissed by applying the unscientific extrapolation of the perceived safety of single-trait parent crops to equal safety when the traits are all packed together in one plant.
- Extended feeding tests seem to have been avoided by inventing a rule that, before these are required, potential hazards have to be identified during previous studies. COMMENT This assumes the previous studies (which will have been carried out by those wanting to profit from the GMO) have been adequate and comprehensive.
It's clear from the scientific literature (Kuiper et al.) that the top brass in the EFSA are not in favour of long-term feeding tests using whole GM foods. The tactics described above seem to be a way of avoiding these tests which are most likely to indicate harm without actually saying so, and without appearing to break their own rules.
On the other hand, maybe the EFSA is just trying not to displease the biotech industry?
None of these science-avoidance tactics are justifiable when your health and the future safety of your food is at stake.
 Bt TOXINS DON'T ACT IN A VACUUM - February 2016
*In 2014, stacked GM cotton reached almost 80% of US cotton plantings, while stacked GM maize made up 76% of the planted maize area there.
Note. This reduction in Bt production may be a result of a number of unpredicted effects. For example, the energy burden (bio-burden) on the plant of being forced to produce so much foreign protein, and/or the presence of duplicated artificial DNA sequences in different added constructs which could be silencing each other.
- Scientists warn of dangers of multi-toxin Bt crops, GM Watch 7.12 15
- Sarah Zanon Agapito-Tenfen, et al., 2014, Effect of stacking insecticidal cry and herbicide tolerance epsps transgenes on transgenic maize proteome, BMC Plant Biology 14
- Harry A. Kuiper, et al., 2013, New EU legislation for risk assessment of GM food no scientific justification for mandatory animal feeding trials, Plant Biotechnology Journal
- Angelika Hilbeck and Mathias Otto, 2015, Specificity and combinatorial Effects of Bacillus thuringiensis Cry Toxins in the Context of GMO Environmental Risk Assessment, Frontiers in environmental Science
- Considerations on the applicability of OECD TG 453 to whole food/feed testing, EFSA Journal, 2013 11(7)
- GM maize approved in the EU caused kidney disease and bladder stones in rats, GM Watch, 14.02.18
- Stacking traits in a GMO is found to cause unexpected synergistic effects, GM Watch 17.12.14
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