Allergy risks of GM foods - Dr Michael Hansen (7/9/2005)

Here's a response from Dr. Michael Hansen, a researcher with Consumers Union, to an enquiry from Luke Anderson about the recent allergy study in which Portuguese researchers gave skin prick allergy tests to at a group of adults and children to see whether they reacted differently to GM corn and soy than conventional varieties. They reported finding no differences but the research has attracted marked criticism.

Dr Hansen's response contains some fascinating and suggestive detail on the potential allergy risk of GM foods.


We don't know the rate of potential allergy risk associated with GE corn, in part because we don't know the true level of exposure to GE corn. Even though a significant percentage of the corn grown in US in GE, we don't know what the true level is in food consumed by humans. Remember that 80% of US corn is fed to animals and a huge amount of the corn products that are consumed by people are highly processed--such as in the form of corn syrup. A few years ago, a number of NGOs did testing of food and found that although GE corn and soy could be found in food items containing corn and/or soy, the percentage of the corn or soy in those products that was GE was much, much smaller (e.g. more than 10X or 20X smaller) than expected from the percentage of the US crop acreage of soy and corn was GE. This suggested that most of the GE corn and/or soy was being diverted to animal feed. So, we don't know how widespread the real exposure is. Since most Americans consume the bulk of their corn in highly processed forms, the exposure could be very low, and corn represents a small percentage of their dietary intake. This could not be said for malnourished/starving people in Africa that are sent food aid in the form of corn. Also, since the exposure to GE corn products that could contain GE protein (such as corn muffins, tortillas, etc.) could be very intermittent, it would be very difficult for someone to determine that their allergy symptoms could be linked to corn. If you eat a meal that contains GE corn and you have an allergic reaction--it could be mild, it could be more severe--it would be very difficult to determine that it was the corn that caused the reaction. First you would do a dietary recall, then exclude all those items from your diet, then bring them back one at a time to see which one is associated with the symptoms. If the next time you ate the corn and it wasn't GE corn, you would dismiss that as the source of your problem. However, I do agree that the sample size--77--is very small.

The most serious problem with the paper is that it doesn't answer the basic question of whether the inserted proteins--particularly the Cry proteins in the case of Bt crops--are allergens. The study only asks whether the process of genetic engineering increases the level of naturally-occurring proteins in corn that induce IgE-mediated food allergies, thereby increasing the severity of allergic symptoms. This kind of study is the type that Monsanto and the other companies would routinely do. But it doesn't tell you whether the protein that you've engineered the corn to produce is an allergen. The real problem is how do you test for the allergenicity of inserted proteins when those proteins have not been routinely eaten by humans. That's what led to the FAO/WHO Expert Consultation on the allergencity of GM foods, held in Rome in Jan. 2001. The report from that meeting, and the methodology that the experts developed is very, very good. A couple of conclusions from the Expert Consultation:

"2. The Consultation emphasized that all foods derived from biotechnology must be assessed for allergenic potential. . . .

5. When the expressed protein is derived from a source with no known allergenicity [as would be the case with the Cry proteins from Bt crops], the FAO/WHO 2001 decision

tree proposes that the initial investigation would also be analysis of sequence homology to known allergens from food and environmental sources. If positive matches are found with known allergens, then the protein is considered likely allergenic. . ."

Note that the authors of this new study say that the products they looked at--GE corn (Bt and herbicide-tolerant varieties) and RR soy--do not contain genes derived from sources known to trigger allergies. So, according to FAO/WHO, the first step should be to look at sequence homology (or similarity) between the inserted protein and known human allergens. But the authors didn't do that at all.

I would also point out that that a number of studies have shown that there is sequence homology (actually sequence similarity) between various transgenic proteins and known human allergens. One study, done by Dr. Steven Gendel, the head of FDA's Biotechnology Studies Branch (the research side of FDA, not the regulatory side) concluded, "although it is clear that some amino acid residues are critical for specific binding, some conservative substitutions may not affect allergenicity. Therefore, it may be prudent to treat sequence matches with a high degree of identity that occur within regions of similarity as significant even if the identity does not extend for eight or more amino acids. For example, the similarity between Cry1A(b) and vitellogenin [an egg allergen] might be sufficient to warrant additional evaluation." In addition, if you look at other characteristics of known allergens--such as molecular size, being glycoproteins, being resistant to digestion, being heat stable, etc.--some of those characteristics are shared with various Cry protein, but especially Cry9C.

A paper published by two Dutch scientists--that used the sequence homology protocol suggested by the FAO/WHO 2001 Expert Consultation, and added a couple of more conservative assumptions--found sequence homology between inserted proteins in GE products that are on the market and known human allergens. The study found that "a limited number of identical stretches shared by transgenic proteins (papaya ringspot virus coat protein, acetolactate synthase GH50, and glyphosate oxidoreductase) and allergenic proteins could be identified as (part of) potential linear epitopes" and concluded that "the positive outcomes of this approach warrant further clinical testing for potential allergenicity." See: http://www.biomedcentral.com/1472-6807/2/8 This study clearly shows that further research was needed into the potential allergenicity of GE foods. It should also be pointed out that none of the GE crops on the market have gone through the protocol/decision tree suggested by the 2001 FAO/WHO Expert


In sum, this paper dodges the main issue (it only looks at a subsidiary issue) and has such a small sample size that it's not surprizing that it didn't find anything. It should be stressed that even though it's a pretty poor study, it does call for routine postmarket testing to monitor the possibility of allergic reactions to GM foods. And that conclusion should be loudly promoted.


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