Is Genetics One of the Causes of Asthma?

Your Family Impacts Asthma Risk

Asthma Genetics
Genetics of Asthma. Science Photo Library/Getty Images

Question: Is Genetics One of the Causes of Asthma?

Answer: Yes and no (don't you love it when a doctor gives you a straight unambiguous answer!!).

Studies show that more than half of childhood asthma cases are related to inheritance (meaning that often a parent or family member had or has asthma, too). Scientists have identified a number of different genes that appear to play a role in the pathophysiology of asthma or interact with specific triggers.

Unlike many current diseases identification of the genes has not led to clinical trials, specific therapies or understanding what patients might respond to certain therapies as has been demonstrated in some cancers. Currently it does not appear that identification of any single gene will lead to such a therapy, but there is some hope that targeting clusters of genes may be a promising approach. Nearly half of all asthma is felt to be caused by environmental factors.

A whole host of other risk factors increase asthma risk, too. Genetics certainly explains some, but not all cases of asthma. More than than likely whether or not you develop asthma depends on a combination of risk factors related to:

Genetics is thought to possibly explain some of the differences seen in groups impacted by asthma. While asthma tends to impact the children of those with higher levels of education and income, inner city, African Americans appear to be at increased risk.

Some hypothesize this could be due a genetic susceptibility as well as exposure to particular environmental exposures such as cockroach allergens.

Family History & Asthma

Genetics can be very complicated and difficult to understand. However, you can think of this very simply by asking a single question: Does a family history of asthma increase my risk of developing asthma?

Let's take a look....

Having one parent with asthma increases a child's risk of developing asthma three-fold, while both parents having asthma increases a child's risk by six times. Similarly, a family history of asthma among adults in the family also has been shown to increase risk of developing asthma.

There Are a Number of Other Potential Asthma Causes

Asthma occurs in may different settings, but the reasons for the differences that are seen are not well understood. While asthma impacts one in 7 children, adults also get asthma. The asthma impacting children is primarily allergic, which is often different than the asthma that impacts adults. Some patients appear to be prone to more severe disease or more risk of sudden deterioration of their asthma. Finally, asthma that occurs as a result of industrial causes (baker's responding to inhaled flour or painters responding to inhaled paint additives.

Rural Lifestyle Protective of Asthma

On the other hand we know that certain factors can also protect against asthma.

Studies consistently show that growing up in a rural area appears to be protective of asthma. Living on a farm and interacting with farm animals and drinking unpasteurized milk is associated with lower risk of asthma. This is not just tru in the United States; growing up on a farm in Africa appears to be similarly protective. If you grow up in the city, having pets and more siblings appears similarly protective of developing asthma. All of these observations tend to support the Hygiene Hypothesis that states that exposure to microbes in early childhood decreases your risk of asthma.

Do I Need Genetic Testing?

Probably not. The Human Genome Project led to many advances in science with the sequencing of the human genome. Linkage analysis is a type of test that looks to see if there are similar gene abnormalities in patients with a certain disease. A number of these studies have been preformed in asthma and identified 10 regions that may have a potential impact in asthma. Most appear to have some role in the development or response of tissue in the respiratory epithelium. Other genes have been identified by comparing the genes of patients with asthma to patients without asthma. Similarly, studies looking at different races has also identified a number of different genes that may be implicated in asthma. Finally, a number of studies have looked at gene environment interactions. For example, the presence of certain genetic variants coupled with exposure to environmental tobacco smoke has been shown to increase asthma risk compared to patients not exposed to environmental tobacco smoke.

So, genetics play a significant role in the development of asthma, but is not the only risk factor you need to consider. You can talk with your doctor if you are considering having a child and want to try to prevent allergic disease in a young child. There are a number of different steps that you can take.

Sources:

Bracken MB, Belanger K, Cookson WO et. al. Genetic and Perinatal Risk Factors for Asthma Onset and Severity: A Review and Theoretical Analysis Epidemiol Rev 2002 24: 176-189.

Duffy DL, Martin NG, Battistutta D, Hopper JL, Mathews JD. Genetics of asthma and hay fever in Australian twins. Am Rev Respir Dis 1990;142:1351-8.

Litonjua AA, Carey VJ, HA Burge, Weiss ST, Gold DJ. Parental History and the Risk for Childhood Asthma Does Mother Confer More Risk than Father? Am. J. Respir. Crit. Care Med., Volume 158, Number 1, July 1998, 176-181

Bottema RW, Reijmerink NE, Kerkhof M, Koppelman GH, Stelma FF, Gerritsen J, Thijs C, Brunekreef B, van Schayck CP, Postma DS. Interleukin 13, CD14, pet and tobacco smoke influence atopy in three Dutch cohorts: the allergenic study. Eur Respir J. 2008;32(3):593.

Hu F, Persky V, Flay B, Richardson J. (1997) An epidemiological study of asthma prevalence and related factors among youg adults. J Asthma, 34, 67-76.

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