Having read our correspondence with Rosie about corn allergy/intolerance Dr Michael Radcliffe (Consultant in Allergy Medicine and Clinical Research Fellow in Allergy Royal Free NHS Trust and University of Southampton) sent us the following email.

Dear Michelle,

I have been so intrigued by Rosie's blog that I thought I would write.

Rosie, more than most, needs to be properly assessed at a regional NHS allergy centre. Provocative challenge testing appears advisable to determine if purified corn derivates, such as glucose syrup and maltodextrin, are well tolerated. If this can be shown, how much easier her life would become.

Corn Allergy

You are right that true (IgE-mediated) corn (=maize) allergy is very rare. Symptoms are immediate and conventional (skin prick or specific IgE blood tests) are almost always positive. The internet may give the false impression that corn allergy is common in the US, but almost certainly it is corn intolerance that is mostly being described. A consortium of allergy physicians across Italy, Germany and Switzerland studied true allergy to corn, but managed to find only 23 cases between them. When challenged blind half reacted to 2.5 grams or less of green (unrefined) corn, whilst just two patients reacted to 100 micrograms or less. Reactions were mild in all but five cases; like Rosie these five appeared to be at risk of corn anaphylaxis. The main corn allergen was found to be a protein, one of a class known as Lipid Transfer Proteins (LTPs). LTPs are vital to plant metabolism being responsible for conveying phospholipids from their site of biosynthesis to cell and mitochondrial membranes that are unable to form them. LTPs are also important to allergy physicians being responsible for cases of allergy and even anaphylaxis due to Rosacea fruits (typically peach) and tree nuts (typically hazelnut).

Corn Intolerance

By contrast I believe corn intolerance to be quite common. Symptoms are never immediate and obvious, and this is why sufferers have never considered corn intolerance to be their problem. Diagnosis is not straightforward, I have never found conventional allergy tests nor any other objective test to be helpful. Sufferers normally present with medically unexplained symptoms and significant quality of life impairment. Diagnosis can be quite challenging; supervised exclusion and challenge starting with a few foods type of exclusion diet is the only validated method. To diagnose corn intolerance, the exclusion diet needs to be followed exactly (e.g. toothpastes contain corn derivatives) and the most severely afflicted sufferers are obviously the better motivated to comply precisely and this limits the application.

If a major reduction of symptoms does not occur after 2-3 weeks on the exclusion diet, it is abandoned. If major improvement does occur, each food is then reintroduced in turn at one or two day intervals; typical symptoms recurring within a few hours indicating a positive test. Those with corn intolerance are amongst those with the most troublesome and diverse symptoms. Unrelenting headaches and migraine, fatigue and mood disturbances, joint and muscle pains and upper respiratory symptoms are common. Quite a few will react also to other foods, often milk, often wheat and the other gluten-containing grains, and in a few cases all the grains need to be excluded to establish full remission of symptoms. I have found corn intolerance to be rather common amongst the hundreds of patients I have placed on exclusion diets during the last thirty years. All are usually delighted to find the explanation for their symptoms and a way, even if tedious, of gaining relief.

Reactions to Corn Derivatives

On a more encouraging note, it is possible that Rosie might find that she does not react to highly purified derivatives of corn. Whilst unrefined forms of corn such as corn-on-the-cob, popcorn and corn flour will contain sufficient protein to cause allergy, corn oil is unlikely to contain the allergenic protein in sufficient quantity. Whilst glucose syrup, invert sugar syrup, fructose syrup, dextrose, dextrin, maltodextrin and xantham gum may be troublesome to those with corn intolerance (for which we do not understand the mechanism), there is a chance that these would not cause symptoms for those with true corn allergy depending on that individual's corn allergy threshold and the degree of purification. Hydrolyzed plant or vegetable protein and textured vegetable protein products may cause problems for those with corn intolerance, but whilst they normally contain corn protein, the hydrolysis process denatures this protein making it much less likely to cause allergy.

I hope this helps – keep up the good work!

Dr Michael Radcliffe
Consultant in Allergy Medicine and Clinical Research Fellow in Allergy
Royal Free NHS Trust and University of Southampton
Private Allergy Clinic at Sarum Road Hospital, Winchester

First published in June 2011

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