David Schubert replies

It is indeed a fortunate facet of science that the quantitative aspect of authorship does not dictate the validity of the conclusions! The impetus for my commentary was my repeated laboratory observation that the slightest genetic modification of a cell leads to completely unpredicted phenotypes. A careful reading of the plant literature supported my conclusions from animal cells. The commentary int-ended to raise this concern in the context of generating further impetus for labeling and stringent testing of GM food. I had no a priori commitment to a particular technology, no pre-existing political ideology, and I did not deliberately ignore any pertinent published material. I do believe, however, that both replies suffer from these problems. They make claims about technology and safety-testing requirements that do not exist, use my statements out of context, and are rather adroit at the use of tenses to skirt questions regarding testing.

The issue of traditional breeding versus genetic modification has been extensively discussed. I have, however, always wondered how it can be claimed that they are the same when genes from completely different species (sometimes kingdoms!) are expressed in genetically modified (GM) food products. Although the biological world works by variation and selection, this is generally accomplished in the context of a normal complement of endogenous genes that, though perhaps different, are allelic. This is quite distinct from GM plants where many copies of a gene are introduced and integrate randomly1. It is my experience and that of others that the response to (trans)genes is completely unpredictable, not specific and predictable as argued. Genetic modification is also distinct from breeding two strains that have been safely consumed for extended periods of time. Parrot and colleagues cite multiple gene deletion in varieties of maize to illustrate their argument that “unintentional consequences” are much more likely to occur in breeding than in biotechnology. However, maize is unique because its genome comprises 80% retrotransposons. It has evolved to deal with redundancy; most other species have not. The fact that plants are capable of producing toxins is a very good argument for testing.

I stated that the illness caused by Shawa Denko KK (Tokyo, Japan) GM tryptophan “was highly correlated with contaminants,” not that it definitively caused the disease. I used this as an argument for labeling GM material. There is certainly no good evidence in reviewed journals that it was the purification procedure that caused the problems or that only people who used this brand took larger amounts and therefore became ill. The company has destroyed the bacteria and has paid large out of court settlements.

The most important issue to me is rigorous safety testing. The statements made in the replies that address this issue are completely misleading. Although it is true that in Europe laws are being formulated that require stringent testing of GM foods, in the United States, the FDA has no mandatory safety approval regulation for GM foods and no specific testing requirements2. There are no all-inclusive mandatory food-safety testing requirements in the United States. The cited testing protocols are only suggestions for producers. There is, however, an effort by a consumer advocacy group, the Center for Science in the Public Interest3, to require GM food products to obtain FDA safety approval. With respect to testing technology, Parrot and colleagues claim that “the protein produced in the new host is subjected to extensive biochemical characterization to confirm that the protein produced is the one and only one intended.” However, there is no technique that can assay all cellular proteins. The best to date is 2,528 out of the rice genome of 50,000 genes (a mere 5%)4!

I am very pleased that both letters support rigorous testing of GM food and hopefully all involved will back efforts to hasten mandatory rules through the FDA.

See Divergent perspectives on GM food by Parrott et al. and the Divergent perspectives on GM food - Letter 2 by A. Avery.