Interpatient variability in rates of asthma progression: can genetics provide an answer?

A Drosophila asthma model - what the fly tells us about inflammatory diseases of the lung

Asthma and COPD are the most relevant inflammatory diseases of the airways. In western countries they show a steeply increasing prevalence, making them to a severe burden for health systems around the world. Although these diseases are typically complex ones, they have an important genetic component. Genome-wide association studies have provided us with a relatively small but comprehensive list of asthma susceptibility genes that will be extended and presumably completed in the near future. To identify the role of these genes in the physiology and pathophysiology of the lung, genetically tractable model organisms are indispensable and murine models were the only ones that have been extensively used. An urgent demand for complementary models is present that provide specific advantages lacking in murine models, especially regarding speed and flexibility. Among the model organisms available, only the fruit fly Drosophila melanogaster shares a comparable organ composition and at least a lung equivalent. It has to be acknowledged that the fruit fly Drosophila has almost completely been ignored as a model organism for lung diseases, simply because it is devoid of lungs. Nevertheless, its airway system shows striking similarities with the one of mammals regarding its physiology and reaction towards pathogens, which holds the potential to function as a versatile model in asthma-related diseases.

Using genetics to predict the natural history of asthma?

Clinical practice reminds us that there is considerable variability in the course of asthma over time. Treatment of patients with asthma would be considerably improved if one could accurately predict the likely course of disease over the life course. Recently, with the advent of the era of genome-wide association studies, there has been a monumental shift in our understanding of the genetic factors that underlie inherited susceptibility to asthma. Genes have been identified that modulate many aspects of the natural history of asthma, such as susceptibility to atopy, altered lung development, and susceptibility to more severe disease. Heritability studies have even suggested a role for genetic factors in remission of asthma. However, although the discovery of novel genetic factors underlying disease susceptibility has undoubtedly improved our understanding of disease pathogenesis, whether these advances have improved the ability to predict the natural history in individual patients is questionable, and the application of genetic testing to clinical practice remains some way off.

Asthma: clinical expression and molecular mechanisms

Asthma is a complex disorder that displays heterogeneity and variability in its clinical expression both acutely and chronically. This heterogeneity is influenced by multiple factors including age, sex, socioeconomic status, race and/or ethnicity, and gene by environment interactions. Presently, no precise physiologic, immunologic, or histologic characteristics can be used to definitively make a diagnosis of asthma, and therefore the diagnosis is often made on a clinical basis related to symptom patterns (airways obstruction and hyperresponsiveness) and responses to therapy (partial or complete reversibility) over time. Although current treatment modalities are capable of producing control of symptoms and improvements in pulmonary function in the majority of patients, acute and often severe exacerbations still occur and contribute significantly to both the morbidity and mortality of asthma in all age groups. This review will highlight some of the important clinical features of asthma and emphasize recent advances in both pathophysiology and treatment.

Acquired somatic mutations in the microsatellite DNA, in children with bronchial asthma

OBJECTIVES

High incidence of genetic alterations at the microsatellite (MS) DNA level has been reported in asthmatic adults.

WORKING HYPOTHESIS

The aim of this study was to investigate whether microsatellite instability (MSI) and loss of heterozygosity (LOH) were detectable phenomena in children with asthma.

METHODOLOGY

DNA was extracted from sputum and blood cells of 27 children (10.8 +/- 2.5 years) with mild to moderate asthma, and from 8 healthy, never-smoked young adults. Fourteen polymorphic MS markers, namely D5S207, D5S820, D5S637, D6S344, D6S2223, D6S263, SGC35231, D11S1253, D11S1337, D11S97, USAT24G1, D13S273, D14S258, and D14S292, located on chromosomes (chr) 5q, 6p, 11q, 13q, and 14q were used to assess MSI and LOH.

RESULTS

None of the healthy subjects exhibited any genetic alteration. Five out of 27 children (18.5%) exhibited MSI or LOH in sputum cells versus blood samples from which 3 in the marker USAT24G1 (chr 13q14.1), 1 in the marker D14S258 (chr 14q23-q24.3), and 1 in the marker D5S637 (chr 5q12-q13). Compared to a previous study, with asthmatic adults, whereas MSI and/or LOH was exhibited in approximately 60% of the cases, the current study reported <20% of genetic alterations, at the MS DNA, in asthmatic children.

CONCLUSIONS

Our results showed that genetic instability in the MS DNA, is present in asthmatic children, but to less extent than in adult asthmatics from previous studies. These findings may support the hypothesis that somatic mutations may be early acquired in the natural course of asthma and could represent another contributor to the molecular pathogenesis of the disease. However, further studies are needed to clarify this hypothesis.

Advances in pediatric asthma in 2008: where do we go now?

This year's summary focuses on recent advances in pediatric asthma as reported in Journal publications in 2008. New National Asthma Education and Prevention Program asthma guidelines were released in 2007 with a special emphasis on asthma control. Attention was redirected to methods that could reduce impairment, specifically symptom control, and minimize risk, including exacerbations. Journal theme issues in 2008 focused on several relevant asthma topics including asthma exacerbations, exercise-induced bronchospasm, asthma and obesity, and occupational asthma. This review highlights Journal articles and related articles that reinforce principles of the guidelines and also direct us to new information that will advance asthma care for children. A major step forward will be finding ways to implement the asthma guidelines.

Allergy, asthma, and inflammation: which inflammatory cell type is more important?

: A recent review in Allergy, Asthma, and Clinical Immunology suggested that eosinophils play a minor role, if any, in the inflammatory spectrum of asthma and allergic inflammation. The article that dealt with mast cells suggested that the presence of these important cells within the smooth muscle layer in asthmatic airways renders this cell type primal in asthma and an obvious and important target for therapy. This article proposes that in a complex inflammatory milieu characterizing the complex syndromes we call asthma, no single cell phenotype is responsible for the condition and thus should be a sole target for therapeutic strategies. Our reductionist approach to research in asthma and related conditions has provided us with convincing evidence for multiple roles that immune, inflammatory, and structural cell types can play in complex diseases. The next stage in understanding and ameliorating these complex conditions is to move away from the simplistic notion of one cell type being more important than another. Instead, what is needed is to acquire knowledge of intricate and exquisite biological systems that regulate such conditions in both health and disease involving various cell types, mediators, pharmacologically active products, their multifaceted capacities, and their socio-biological networking.