Allergies Genetics

Strong evidence suggests a link between allergies and genetics. The evidence for genetic allergies lies in family histories of allergies and asthma as well as clinical studies of genetic allergy in twins. The situation, however, is neither clear nor obvious: most studies suggest we inherit an inclination toward getting allergies, rather than specific allergies themselves.

The Allergic Response

An allergy occurs when the body’s immune system mistakes a harmless substance for a threat. This substance becomes the allergy trigger, or allergen. Upon exposure to the allergen, white blood cell action is activated by IgE antibodies, resulting in the release of histamine and a rapid inflammatory response.

An allergy attack can be mild, such as the runny nose and itchiness caused by hay fever (an allergy to pollen). More severe allergies can cause asthma, or in the worst scenarios life-threatening anaphylaxis.

Allergy Symptoms

Allergy symptoms vary depending on the part of the body affected. Some allergic reactions only affect one area of the body. The most dangerous type of allergic reaction, anaphylaxis, affects the entire body.

Symptoms may affect any combination of the following body parts:

  • Eyes: bloodshot eyes, itchiness, swelling, watery eyes.
  • Face: headache, swelling of the eyelids, face, tongue, lips or throat.
  • Gastrointestinal Tract: abdominal pain, diarrhea (with or without blood), nausea, vomiting.
  • Nose: runny nose, sinus inflammation, sneezing, or stuffy nose.
  • Respiratory System: chest tightness/pain, cough, shortness of breath or wheezing.
  • Skin Reactions: blisters, crusting, eruptions, hives, rashes, redness, swelling or weeping.

Families and Genetic Allergies

The evidence for genetic allergies is based primarily on family histories. Children seem to be more likely to develop allergies if one or both parents have allergies or asthma. However family histories do not seem to indicate what form allergies take. A parent may have an allergy to peanuts, while the child develops an allergy to dust mites.

In other words, while we appear to inherit a tendency to develop allergies, people don’t necessarily inherit the same allergies as their parents.

Genetic Allergy Research and Twins

If a specific genetic allergy existed, one would expect to see evidence in studies of identical twins, who share the same genetic codes. If, for instance, a peanut allergy was a true genetic allergy, if one twin developed the allergy the other should as well.

Studies do suggest that in at least some cases this is true. A large scale study of 3,600 pairs of identical and fraternal twins in the Netherlands found that 50 to 80 percent of the time identical twins shared the same allergies, while fraternal twins only shared allergies in 25 to 40 percent of cases.

While twins may share allergies, they do not necessarily share the same symptoms. A pair of identical twins may be allergic to peanuts, but while the allergy causes respiratory symptoms in one, it may cause the other twin to break out in hives. Even if genetic allergies exist, it seems how allergies are expressed is influenced by environment and exposure.

Eczema and Genetic Allergies

Research at the Oregon Health and Science University has found a genetic link between atopic dermatitis and food allergies that lends credibility to the concept of the genetic allergy. The study discovered a mutation in the filaggrin gene lead to “breaches ” in the skin’s outer layer, the epidermis. These breaches allow allergens and irritants to enter the skin, resulting in the release of IgE antibodies.

A link between food allergies and atopic dermatitis, or eczema, has been known for some time. However, it was thought that food allergies cause the eczema. The Oregon research suggests that the source of the eczema is what causes the food allergy.

As genetic allergy research continues, similar discoveries will shed more light on genetic allergies and their complex relationship with the environment and allergens.

Resources

Borish, L. (n.d.). Genetics of allergy and asthma. Retrieved March 23, 2009, from the PubMed Web site: http://www.ncbi.nlm.nih.gov/pubmed/10353570.

HealthDay News (2008, February 4). AAD: Genetic defect in skin barrier linked to eczema. Retrieved March 23, 2009, from the Modern Medicine Web site: http://www.modernmedicine.com/modernmedicine/Allergy