Letter: Pusztai's results

Sir: The attempt by Professor Rhodes and Dr Finn (letters, 3 March) to clarify the Pusztai affair was misleading.

They imply that lectins are not really toxic (making Dr Pusztai's results appear significant) by saying they exist naturally on mammalian cells. This is true, but it is also irrelevant.

Those used in Dr Pusztai's work were plant lectins and these are all toxic to something. Their purpose is to make animals eating them feel ill and stop. Like other proteins, lectins are inactivated by cooking. Dr Pusztai fed GNA lectin raw to rats and an effect on digesta retention was observed in one experiment. Should anyone be too surprised? In any case Dr Pusztai was unable to replicate this effect a second time.

In all other instances the GNA lectin could not be shown to have any significant effect at all, even when added directly to feed at 100 times the concentration expressed in the GM tubers. So why the fuss? It is because the addition of another lectin (Con A) to feed resulted in rats with impaired immune systems.

The amount added was 5,000 times the concentration expressed by the potatoes themselves. If you feed a known poison to rats at 5,000 times its normal level it is not surprising if they end up ill. The Rowett Institute concluded that "the results were far too variable to reach statistical significance and too inconsistent to draw any meaningful conclusions". Following Dr Pusztai's public inferences to the contrary, suspension was perhaps inevitable.

Professor Rhodes and Dr Finn conclude by saying that Dr Pusztai was certainly not trying to imply that GM foods are unsafe, but simply carrying out impartial research. This too is misleading. Dr Pusztai has actually said, "We are assured this (GM food) is safe but if you asked me I wouldn't eat it."

This is not the voice of impartiality. As a postgraduate biological science student there are certain regulations I would like to see introduced in the production of GM foods. However, if in my work I had produced such unfounded conclusions and statements as those made by Dr Pusztai, my supervisor would have doubtless hit the roof.

MARK MADDOX BSc MSc GIBioL

Nuneaton, Warwickshire