New insights into risk factors of asthma

The prevalences of bronchial asthma in the Asia-Pacific region range from 0 to 24% and appear to be increasing in some countries. The increased prevalence of asthma may be related to the urbanization of these countries or areas. Risk factors relating to the development of asthma are multiple and complex. These include: Predisposing or genetic factors: (atopy and bronchial hyperresponsiveness; BHR) that increase an individuals susceptibility. Longitudinal studies in children have shown that BHR precedes asthma in some individuals. A gene governing BHR is located near a major locus that regulates serum IgE levels on chromosome 5 q. An additional gene that determines the specificity of the immune response located in the human leukocyte antigen complex (HLA) may govern the specificity of the immune response to common aeroallengens in some individuals. Causal Factors: inhaled allergens are the most important causal factors of asthma, which include indoor allergens (domestic mites, animal, cockroach and fungus allergens), domestic mites being the most common potential allergen, and outdoor allergens (pollens from trees, grasses and weeds). Owing to the geographic location and different sensitivity to allergen between races, allergens vary from area to area. Certain drugs, food and food additives are also the cause of asthma attack. Contributing factors: smoking is an important trigger and a serious problem in most Asian-Pacific countries. Air pollution in particular sulfur dioxide (SO2), nitrogen dioxide (NO2) and respirating particles are common contributing factors. Very low concentration of SO2 (0.5 ppm) can cause bronhospasm in asthmatics. A combination of low concentration of SO2 and NO2 often encountered in heavy traffic further enhances the airway responsiveness to inhaled allergen. In addition, respiratory virus infection is closely associated to the development of asthma in childhood.