Do Allergies Run In Families?
| Can You Inherit An Allergy?
"My mother had asthma as a child, and so did her brother. In fact he died from it. My father has never had any allergies but his sister had bad hay fever all her life. Out of the 5 of us, only my brother George is completely allergy-free. I have eczema and so does my brother. My daughter has developed asthma and has an allergy to dust mite which makes her nose run all the time. Do allergies run in the family?"
What Jayne is describing here is a good example of an atopic family - one where classical allergies of one kind or another affect many family members. The members of such a family are called atopic's. This means, an underlying tendency for allergy is coded in your DNA - it is heredity.
Not all atopic's develop allergies - with luck you might escape - but more often than not, it leads to allergies than can settle on the skin (atopic eczema), the nose (perennial allergic rhinitis or hay fever), the air passage (asthma) or the mouth/digestive tract (food allergy). These diseases, which recur down the generations in atopic families like Jaynes, are known as the classical allergic diseases.
Studies estimate that if one parent is atopic, the risk of you becoming atopic is between 20 and 58 percent. If both are atopic the risk ranges between 50 and 80 percent. Luck plays a big part!
Atopic tendency is coded in our DNA - the genes are passed down from parent to child. But there are multiple of genes involved (which is why classical allergic diseases are multi-gene inheritances). For example, there are other genes that make asthma more likely to occur, and if these are also in place, it increases the likelihood of a child developing the disease even more. There are probably other genes that make atopic eczema more likely too.
Genes alone are not enough, however. Environment (diet, air pollution, dust mite, pollen and even medicines) also play a part in promoting allergic reactions. In other words DNA and the external world interact to produce allergic diseases. What exposure a person has in the months and years after birth seem to be particularly important. All this helps to explain why allergies are on the increase, even though genetically speaking we are not so different from our grandparents or great grandparents.
Can You Inherit A Food Sensitivity?
Doctors are divided on this question, it seems there isn't enough evidence to say yet. Lactase deficiency (leading to problems digesting milk products) seems to have the most evidence to provide a heredity link. Yet, it can't be a coincidence that food intolerances and chemical intolerances often affect several members of a family. However some doctors argue that these are 'learned illness behavior' among family members. Inheritance does however seem to play a more definite role in celiac disease and dermatitis herpetiformis (Duhring's disease, a chronic blistering of the skin).
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