Asthma in the genes
A question that puzzled scientists through the ages. But thanks to new advances in the study of genetics we are on the brink of a discovery that will revolutionise the diagnosis and treatment of asthma.
Like it or not, we generally have our parents to thank for our physical features, how we develop, and how we respond to our environment. Not only that but many diseases and allergies, including asthma, also run in families. The chances of developing asthma however are not solely due to our genetic make–up. We are in the hands of both nature and nurture because environmental factors – such as our home environment, the food we eat and our lifestyle – also plays a part in the development of asthma.
This 'balance' of genetic and environmental factors is most clearly shown in studies involving identical twins. If asthma was solely a genetic condition, identical twins (who have the same genes) would have the same chances of developing asthma. But studies have shown that in at least 20 per cent of cases only one identical twin will develop the condition. Similarly, if asthma was solely governed by environmental factors, identical twins would have the same chances of developing asthma. But studies have shown that in at least 20 per cent of cases only one identical twin will develop the condition. Similarly, if asthma was solely governed by environmental factors, identical twins would have the same chances of developing asthma as non-identical twins – but studies have shown that the chances of developing asthma are more than twice as high if twins are identical. These research findings imply that rather than inheriting asthma itself, we inherit a 'tendency' to develop asthma. And this inherited 'tendency' will only come to fruition if we are also exposed to the environmental stimuli that trigger asthma.
Genetic studies have also revealed that asthma is a complex condition. We know that genes play a part in predisposing someone to developing asthma, and we also know that there isn't a single 'asthma gene'. Instead, the combined effects of several genes add up to produce a susceptibility to asthma. Whilst some genes increase the susceptibility to developing asthma, others lower the chances of developing the condition.
Back to Asthma basics
So how do we develop asthma? Traits are inherited because genes are passed from parent to child at conception. Scientists now believe that every person has about 30,000 genes which are made up of a chemical called DNA (or deoxyribonucleic acid).DNA carries all the biological information that makes individuals unique. DNA carries information in the same way that the human alphabet conveys limitless amounts of information. Just as we form a language from sentences, pieces of DNA (letters) connect together to form a gene (sentence) that describes how proteins should be made to develop the cells of a living organism.
Genes are found linked together in each cell on extremely long, twisted strands of DNA, called chromosomes. Every cell in our body contains 23 pairs of chromosomes. One set of chromosomes is inherited from the mother and one from the father.
Abnormalities in our genes can make us more susceptible to diseases. Some diseases are caused by a single gene abnormality. For example, people with Cystic fibrosis have a defect in one particular gene on chromosome 7. Babies with Down's syndrome have an extra chromosome. Asthma has a more complex genetic basis. Researchers working on behalf of the National Asthma Campaign have been trying to identify the different genes that predispose people to developing asthma. They have achieved a great deal over the last few years in their quest to unravel the asthma puzzle.
Researchers with particular interests in the future of genetic research worked alongside Hospital practitioners and discovered one of the genes on chromosome 11 that produces IgE antibodies, making some people susceptible to allergies.
After years of research this is an extremely exciting time for us. We may have finally pinpointed why some people are more susceptible to allergic asthma and these findings really laid the foundations for much of their consequent work.
Other National Asthma Campaign-funded projects have made similar exciting discoveries about asthma genes. We now know that certain genes on chromosomes 3, 5 and 6 are also involved with the development of asthma and allergy.
By identifying more 'asthma genes' scientists hope to aid the development of targeted asthma treatments. Researchers are also looking at ways to switch on and off the asthma genes that prevent or encourage the disease, and investigating why some people respond better to asthma medication.
The Human Genome Project
The Human Genome Project (HGP) was launched in October 1990, by the US Department of Energy and the National Institutes of Health. This international project is set to be completed in 2003. Initial results from the HGP and other privately funded projects hit the headlines earlier this year. They indicated that scientists will soon be able to discover all the genes that determine every physical characteristic of the human body and to identify and record the common DNA sequences that distinguish one person from another. A number of National Asthma Campaign researchers have been assisting with the Human Genome Project by specifically investigating regions of the human genome that influence asthma and allergies.The Human Genome Project has been hailed by scientists as one of the most important breakthroughs of all time. It will really provide us with a wealth of information about the causes of diseases. Identifying all the genes that make up the human body, and how these genes work, will revolutionise biology and medicine. Knowledge about the effects of DNA variations among individuals could lead to new ways to diagnose, treat and prevent diseases.
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