Childhood asthma: aspects of global environment, genetics and management

The prevalence of asthma in children dramatically increased over the past two decades. In Taiwan, the prevalence of childhood asthma has risen to around 10% in the 1990s, in contrast to a prevalence of about 1% in the 1970s. Currently, Australia and New Zealand have the highest prevalence in the world (> 15%). African and Asian countries have a low prevalence of about 5 to 10%. In general, countries in coastal, temperate and subtropical zones have the highest mite-sensitive asthma prevalence. Countries in the subarctic or in semiarid areas have a lower prevalence. Indoor allergens such as house dust mites, cockroaches and fungi usually cause perennial asthma; outdoor allergens such as grass and tree pollens as well as outdoor fungi induce seasonal asthma. A gene on chromosome 11q13 is significantly linked to maternal inheritance of asthma, and possibly involves polymorphisms in the beta subunit of the high affinity IgE receptor. Cytokine genes in chromosome 5q31-33 are known to regulate IgE production resulting in various severities of allergic diseases. Recent studies suggest that pollutants such as diesel exhaust, O3, NO2, and SO2, together with allergens and susceptible genes are likely to promote IgE production and allergic reactions. As a result, asthma is apparently not a single gene disorder, but a disease determined by the interaction between gene and environment. In practice, immunopharmacological interventions to block IgE-mediated early bronchospasm and late inflammatory reactions are the major regimens for asthma treatments. This makes possible a step-wise self-management based on portable monitoring of airway resistance using the peak expiratory flow rate (PEFR). Early avoidance of allergen exposure in utero as well as early anti-inflammatory therapy in infancy have decreased the prevalence of allergic diseases. A combination of both strategies may bring much more benefit in the prevention of childhood asthma. As progress in therapeutic gene vaccines as well as genetic immunoregulation continues, we expect early environmental avoidance and genetic vaccines may prevent childhood asthma in the near future.