FOOD ALLERGY: ALL IN THE GENES?

If atopy is inherited, then the genetic information that is passed on from parent to child must in some way be faulty. Studies of atopic families have led to some understanding of the genetic mechanisms involved, and they help to explain some puzzling features of the problem.

Current research suggests that atopy is not due to a simple defect affecting just one gene: many different genes are probably involved, each one producing a small effect that adds to the total. This explains why the severity of atopic disease varies from one person to another – the more ‘allergic’ genes a person has, the worse are their symptoms.

It is also possible for parents with no obvious atopic symptoms to produce an atopic child. Both are probably carrying genes that can contribute to atopy, but have not produced any effect in the parents themselves. These ‘silent’ genes may by masked by other, more beneficial genes in the parents. Or each parent may lack certain crucial ‘bad’ genes, that are needed for atopy to develop. Whichever is the case, the ‘silent’ genes can become more vociferous if their circumstances change. When all the parental genes are reshuffled to produce eggs and sperm, and then combined with genes from the other parent, a different genetic setting is produced. In this setting, the formerly ‘silent’ genes may have a much stronger effect, producing symptoms in the child.

Genes are not the whole story, however. The fact is that identical twins -who are genetically exactly the same – can differ in terms of allergy. One maybe afflicted and not the other, suggesting that something they have been exposed to in their environment (such as a viral infection) is also important. What seems likely is that the tendency to allergy is inherited and that environmental factors, especially early in life, may push the individual over into an allergic reaction. It is interesting that babies born in the spring are more likely to develop hay-fever later in life. Certainly, in the case of food, early exposure to potential allergens is risky for the children of atopic parents.

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