MEDICAL MATTERS:Symptoms affect one in five children in Ireland, writes MUIRIS HOUSTON
ABOUT ONE in five schoolchildren in Ireland has asthma symptoms. This follows an increase in the respiratory disease’s prevalence in the period from 1980 to 2000. And while asthma rates seem to have stabilised in recent years, persistent cough or wheeze is still one of the most common reasons for a child to be brought for a consultation, with a worried parent asking, “Have they got asthma, doctor?”
At least they are most unlikely to be told the symptoms are due to anxiety, as was the experience of consultant paediatrician Dr Peter Greally, when, as a child, his parents brought him to see an eminent professor of paediatrics. This may be explained by the fact that, until the 1950s, asthma was seen as a psychosomatic illness; psychoanalysts regarded its symptoms as the suppressed cry of the child for its mother and initiated treatment for this “hidden depression”.
Greally, now a consultant paediatrician specialising in children’s respiratory and allergic disorders at the National Children’s Hospital in Tallaght, has recently published a book: Childhood Asthma – Your Questions Answered, which has an interesting section on potential causes of asthma.
On a possible genetic cause, Greally notes that a familial tendency to asthma was identified as far back as the 11th century. A genetic phenomenon called imprinting, where the risk of a disease being passed on is greater if the mother is affected, may account for some of the disparities in research into the genetics of asthma.
Studies in identical twins, which are often used to assess the likelihood of a genetic component in a disease, would be expected to show high rates of concordance if there was a strong genetic component to asthma. Interestingly, in twins with similarly high levels of an allergy marker called IgE, the rates of asthma in the twin pairs differ markedly, suggesting an environmental cause in those who go on to develop asthma.
A 2010 study examined the genetic make-up of some 10,000 people with asthma and 16,000 without the disease. Researchers found nine genetic regions (loci) associated with asthma, including one linked to childhood-onset asthma. But again there were no links with loci involved with IgE production.
The hygiene hypothesis of asthma development is one that has always had an inherent logic and appeal. It came about as a way of explaining the observation that allergic diseases are less common in larger families because in single-child families there is less exposure to infectious agents than in the hurly-burly of several children living under the one roof. The hypothesis has now been expanded to include exposure to viruses and bacteria in the so-called “farmyard effect”, where playing with muck seems to dampen down the allergic component of our immune system.
“Socio-economic conditions play a role in asthma and allergies, and for many years allergies were considered afflictions of the affluent. In fact, researchers have shown that there are close correlations between a country’s GDP and the prevalence of allergies and asthma,” Greally says.
“In underdeveloped countries, where asthma prevalence is generally low, and rates of natural infection are high, the antibody IgE is primarily concerned with the containment of parasites within the gut and the prevention of their dissemination throughout the body. The theory goes that in developed countries, where infection rates are low and parasitic infestation extremely rare, the IgE system has become unnecessary, and thus (allergic) diseases are by-products of this redundancy.”
But perhaps the most unusual evidence for the theory can be found following the reunification of Germany. Studies comparing the prevalence of asthma and allergy in the former East and West Germany found lower rates in the east of the country where infection and air pollution levels were high. Ten years after reunification, when socioeconomic conditions had improved in the former East Germany, asthma rates had increased to the same level as those found in West Germany.
Childhood Asthma – Your Questions Answeredby Dr Peter Greally, Liberties Press, €12.99