Allergies are caused when a person's immune system overreacts to a harmless foreign protein (allergen) that is breathed in, touched, eaten, or injected. The immune system attacks the "invader" by generating large amounts of an antibody called immunoglobin E (IgE). The IgE molecules attach themselves to mast cells in tissues, which in turn release powerful inflammatory chemicals, including histamines. This inflammatory response, called an allergic reaction, produces symptoms such as itching, sneezing, runny nose, and watery eyes. In severe cases, it may also result in rashes, hives, breathing difficulties, asthma attacks, and even a life-threatening condition known as anaphylaxis.
In the U.S., allergies affect nearly 1 in 5 adults and 1 in 4 children. The social and economic costs of allergies are monumental. It is estimated that allergies cost American society over $8 billion annually in lost productivity and direct costs such as medications and office visits. Hay fever alone is the fifth leading chronic disease in adults, resulting in close to four million lost or missed work days each year. There is currently no cure for allergies, although they can usually be managed with prevention and treatment.
Environmental factors have long been known to play a role in determining if an individual will develop allergies. Childhood avoidance of certain allergens has been shown to substantially decrease the risks of a person developing allergies later on.
Breastfeeding (especially in the first six months of an infant's life) has also been shown to guard children against allergies. There is also evidence that, when it comes to allergies, the environment can help protect a person at a genetic level (epigenetics).
There is an undeniable correlation between cleaner environments and a rise in autoimmune diseases and allergies. A 2010 Australian study published in the journal Allergy found that children who were in utero while their mothers spent time in a farm setting were less likely to develop allergies than those who were born and raised in urban environments. Children who spent time on farms were also protected, according to researchers. The benefits are believed to be due to both the mother and child's exposure to certain strains of bacteria. Studies are ongoing.
Scientists have known for some time that there is a genetic component to allergies. For instance, if one parent has an allergy of any type, there is a 1 in 3 chance that his or her child will have an allergy, but not necessarily the same kind. If both parents have allergies, the number jumps to 7 in 10.
In 1997, researchers found a possible suspect. The study, which was published in the New England Journal of Medicine, found a mutation located in "the tail end" of the interleukin-4 receptor that appeared to make people more susceptible to allergies. Much more in fact.
“We have found that if you have this mutation, you are 10 times more likely to be allergic,” said Talal A. Chatila, M.D., an associate professor of pediatrics and the senior author of the study. “This is one of the strongest associations so far between any one particular gene and allergies.
A 2008 German study built upon the earlier findings. Using research from the Human Genome Project (HGP), scientists from the Helmholtz Zentrum München, in collaboration with researchers from the Department of Dermatology and Allergy and the Center for Allergy and Environment (ZAUM) of the Technical University of Munich, discovered a "major gene for allergic diseases." The gene, FCER1A, encodes the alpha chain "of high affinity IgE receptor," according to the study.
"Most people with allergies are atopic," explained lead researcher Stephan Weidinger, "meaning they have a genetic tendency to develop allergies. To detect the genetic factors we examined the genomes of more than 10,000 adults and children from the whole of Germany."
These findings are already helping to guide research into the development of new drugs, which could help provide relief for millions of allergy sufferers worldwide.
Currently, physicians can treat certain allergies by giving patients repeated low-dose shots of an allergen, which leads to a tolerance of those substances. The procedure, known as de-sensitization, doesn't work for everyone, however.
For instance, those with severe food allergies may be put at risk of deadly anaphylactic shock by the treatment itself.
New research, based on the earlier gene studies, may help. Investigators working with genetically engineered proteins have found that they can interfere with the types of allergic reactions that cause hay fever, asthma, and certain food allergies—at least in mice.
Researchers are hopeful that they'll work in human beings as well. According to Andrew Saxon who is leading the studies at the University of California, Los Angeles, the new treatment may eventually help to "defuse the allergy bomb" and allow even the most sensitive patients to receive the shots.