People develop asthma because of an interaction between the genes they inherit and the environment in which they live. Researchers are studying families in different ethnic and geographic communities to identify which genes are related to asthma. So far multiple genes appear to be involved. Genetic studies have also revealed differences in the way patients respond to medications. Understanding the genetics of asthma should provide clues to preventing the disease and help physicians select the most effective treatments for individual patients.
There has been an ongoing debate on whether asthma is caused predominantly by a genetic factor or the environment in which one lives. Several studies have been conducted, and although research shows support in the area of genetics, research does not support it as the one and only cause of asthma.
In Arizona a study took place involving 344 families. The researchers conducted the study to see if asthma was passed on to the children from their parents. In families with parents not having asthma, the percentage of children with asthma was 6%. One parent with asthma the percentage was 20. When both had asthma the number of children with asthma was 60%. This shows a significant connection between genetics and asthma. When studying other conditions and genetics twins are better candidates for conducting research. Identical twins have the same genetic makeup; however, fraternal twins do not. In 1995 two researchers Sarafino and Goldfedder did research to support the theory that both genetics and the environment were significant in the cause of asthma.
Three hundred twenty-five pairs of twins were studied out of eighty-four pairs of twins at least one twin had asthma. These sets of twins became the focus of the study. The eighty-four consisted of 39 identical twins and 55 fraternal twins. Of the 39 pairs of identical twins, 23 pairs both had asthma (59%), of the fraternal twins only 13 out of 55 (24%) both had asthma.
The experiment proved an interrelationship between the environment and asthma. Solely based on genetics all the identical twins both would have asthma. If asthma were only caused by the environment, identical and non-identical twins would have the same chances of developing asthma. The research found instead that we inherit the tendency to develop asthma. Asthma occurs when exposed also to environmental triggers of asthma.
When asthma runs in families the genetic factor is a stronger contributor to asthma when it does not run in families genetic factors are not as dominant. The environmental factor then becomes the domineering factor. For certain we know that there is not one particular gene that causes asthma. Instead we know that several genes interact with one another, this making people more susceptible to asthma. People can have genes that predispose them to asthma, and yet they never acquire any of its symptoms.
Genetic research can be very complicated because of the 3 following factors: interactions between genetic predisposition, environment and gene interactions. Progress is being made in this area. Some of the researchers have made claims to have found certain genes to be on of the causes of asthma.
Researchers from the University of Southampton conducted a study called Respiratory Cell and Molecular Biology. In this study they found a connection between a specific gene and asthma. This gene is called ADAM33. It is located on the 20th chromosome; it is expressed in the lung and muscle cells. The ADAM gene according to researchers relates to asthma when it causes the airways to over respond and constricts the airway passage.
Another experiment conducted by Zou, Young et.al; found several other genes on specific chromosomes that affect a person's susceptibility to asthma. The experiment was called Microarray profile of differentially expressed genes in a monkey model of allergic asthma. The monkey had allergies and induced asthmatic attacks. They were given treatments that challenged their breathing. The monkeys were given an antigen or interleukin-4. These treatments induced asthmatic attacks. Their lung tissue was then collected after 4, 18, and 24 hour intervals and the tissue was analyzed. The samples were compared to monkeys that were not given the treatment who were normal.
This experiment allowed them to use a new technique that is used for analysis. They were able to view cDNA on microarrays. cDNA is special because it only contains introns (which is protein coding information) this lead to identifying the gene. Microarray technology helps gain insight into global gene-expression profiles in asthma. The profiles lead to identifying asthma-associated genes. Microarrays are a gene chip technology. The cDNA are in sequence and seen on high density glass slides. Then the sequenced genes are hybrized to cDNA probes which come from RNA-contains both exonsandintrons which coded and non coded information.
The two sets of cDNA probes can be labeled with two different fluorescent dyes. This gives a clearer view of the genes. Microarrays can detect the thousands of levels of gene differential expressions simultaneously.
During an asthma attack different genes are expressed in airway constriction. In the experiment with the monkeys, the scientist caused any genes that were related to asthma to be expressed. The genes appeared different than the controlled monkey group.
From the study gene expression provided a large scale profile. Microarrays with real-time PCR (Polymerase Chain Reaction) which is a quantity of DNA that is amplified by repeated sessions of replication and separation; proved to be a powerful tool for identifying and validating different types of genes which are expressed in a disease model.