Asthma
Introduction
Asthma is a chronic lung disease characterized by recurrent episodes of breathing problems and symptoms such as breathlessness, wheezing, chest tightness, and coughing. These episodes are also known as exacerbations or attacks.
Many factors can trigger an asthma attack, including allergens, infections, exercise, abrupt changes in the weather, or exposure to airway irritants, such as tobacco smoke.
Upon exposure to such a factor, the immune system overreacts as if it was fighting off a harmful parasite. An immunoglobulin E (IgE) antibody molecule, central to the allergic reaction, is produced and may cause mast cells to rapidly releases its characteristic granules and various hormonal mediators into the airways tissues. The air passages then become inflamed, causing temporary constriction of the airways and the production of excess mucus leading to coughing, wheezing, and difficulty breathing -- an asthma attack
Prevalence, onset
Over 30 million people in Europe now have asthma, a number greater than the population of the Netherlands and Belgium combined. Throughout Europe, the prevalence of asthma is generally higher in urban areas compared with suburban and rural areas.
The prevalence of allergic asthma has increased decades earlier in western Europe with respect to eastern Europe. This is probably attributable to changes in lifestyle that had already occurred rather than to air pollution. The recent increase in asthma prevalence has been particularly marked in the former East Germany, which now has prevalence rates similar to those in former West Germany. Similar increases are expected to occur in the former socialist countries of the Baltic region in coming years, as these communities increasingly adopt Western lifestyles.
Although allergic diseases can arise at any age, they generally begin in childhood. The most frequent presentation is dermatitis in infants. The development of this "atopic" condition is associated with an allergic constitution due to heredity or genetics, or to the environment, for instance indoor and outdoor pollution. The disease often progresses from atopic dermatitis to allergic rhinitis and then to asthma. This evolution is known as "allergy march". However, there are cases where asthma can start without a warning. This usually happens in young children.
Allergic and asthmatic symptoms are associated with indoor and outdoor air quality. In 1999-2004, asthma prevalence in children across the European study centres varied from less than 5% to over 20%. Children with asthma have long been recognized as particularly sensitive to outdoor air pollution. Many common air pollutants, such as ozone, sulfur dioxide, and particulate matter are respiratory irritants and can exacerbate asthma. Air pollution also might act synergistically with other environmental factors to worsen asthma. For example exposure to ozone may enhance a person's responsiveness to inhaled allergens. Whether long term exposure to these pollutants can actually contribute to the development of asthma is not known.
There are also other agents that can initiate the sensitisation process in people. These are certain antibiotics, viruses and airborne agents such as diesel particles. They can act by different mechanisms. For example viruses may reduce epithelial defences whereas diesel particles cause T-cell activation. This period may last many decades- some people may start to exhibit asthma only later in their lives. Interestingly, males get asthma earlier in life than women. Women however "catch up" when they are in their 50s. There are no satisfactory explanation for the male/female differences.
Genetics
Specific genes may not be exactly equal in different individuals, which may result in slight to severe differences in functionality. There is no single "asthma gene". Many genes interact and slight differences from the 'norm' may cause susceptibility to asthma. So far only a few genes have been identified as being correlated to asthma. Still, individuals may have one or more genes to predispose him/her to asthma without ever suffering from its symptoms. The genes may never be expressed because of lack of environmental stimuli. Because of the many interactions between genetic predisposition, environment and gene interactions, genetic research is very complicated.
In Arizona, researchers revealed a strong correlation between asthma and genetics when examining 344 families. Among families with neither parent having asthma only 6% of the children developed asthma, while in families with both parents having asthma 60% of the children had asthma.
Twins are excellent candidates for genetic research. In 1995 Sarafino and Goldfedder conducted research to prove that both genetics as well as the environment play a role in the contraction of asthma: among identical twins asthma occurred for 59% in both individuals. Among only 24% of the non-identical twins both individuals had asthma.
On the remote South Atlantic island Tristan da Cunha , 50% of the population are asthmatic due to heredity transmission of a mutation in the gene CC16. The islands have a population of 275 people. The high incidence of asthma is largely caused by the inevitable marriages among distantly related couples, for example marriages between second degree cousins, that comes with having such a small gene pool.
New technologies have brought possibilities to screen differences in individual genes among large groups of people. Researchers from the Molecular Epidemiology group at the GSF National Research Centre for Environment and Health in Neuherberg, near Munich, have been involved in such a large-scale study. The team examined over 300,000 genetic markers in thousands of asthmatic children and compared this data with those of healthy controls. They identified a gene, named ORMDL3, which may contribute to the risk of childhood asthma if its activity is different when compared to healthy people. The gene therefore is now a promising object of research: it could help to improve the prevention and diagnosis of asthma, and possibly to develop a new therapy.
Treatment, cure
At present there is no cure for asthma. However, asthma is treatable: medications, asthma management and education are improving all the time. Reducing exposure to environmental allergens and pollutants will reduce the frequency and severity of attacks for children with asthma, reduce their need for medicine, and improve their lung function.
There are two main types of drugs used for treating Asthma, and these are most commonly taken using an aerosol inhaler. Preventers reduce the sensitivity of the cells in the lungs to house dust mites and other allergens. Most of these drugs contain steroids. Relievers are taken for immediate action to up the airways and are steroid free, possibly a better choice for children.
Other currently available asthma treatments include: Leukotriene modifiers, Mast cell stabilizers, Antimuscarinics or anticholinergics, which have a mixed reliever and preventer effect. Antihistamines are often used to treat allergic symptoms that may underlie the chronic inflammation.
Following the discovery of specific genes that may be involved in certain asthma patients, novel drugs have been developed to modify their activity. An immunoglobulin E monoclonal antibody to a gene called ADAM 33, possibly responsible for the muscle-development in the airway, was developed by Stephane Holgate in Southampton. Other researchers focus on other genes or on specific cell types that show abnormal activities in asthma patients.
Prevention
Children who grow up in a farming environment show lower levels of atopic sensitization, hay fever, and asthma than children of the same age not living in such an environment. Some of the initial observations were made in the USA in the late 1980s. This was later termed the "hygiene hypothesis".
A number of investigations provided good evidence that this is due to an early-life contact with cowsheds, farm animals, and/or consumption of products like raw milk. Also, it had been indicated that microorganisms might have an important effect on the development of allergies, and thus the question arose of which farm microbial organisms, their products, or both might induce or influence allergy-protective mechanisms.
Recent research results indicate that Acinetobacter lwoffii and Lactococcus lactis strains, two types of bacteria that were isolated from farm cowsheds possess strong allergy-protective properties. In the film "Out of breath - understanding asthma" it is shown how these conclusions were reached and how the research was conducted.
