COPD is a major medical problem and leads to a significant morbidity and mortality among the adult population. Several factors have been suggested as risk factors for COPD, including environmental and genetic, supporting the notion that the etiology of COPD is multifactorial and/or multigenic. One of the important risk factors is cigarette smoking, where a significant number of smokers develop COPD. 1 American Thoracic Society statement Standards for the diagnosis and care of patients with chronic obstructive pulmonary disease: definitions, epidemiology, pathophysiology, diagnosis, and staging. Am J Respir Crit Care Med. 1995; 152: S78-S83 Crossref Google Scholar ,2 Burrows B Knudson RJ Cline MG et al. Quantitative relationships between cigarette smoking and ventilatory function. Am Rev Respir Dis. 1977; 115: 195-205 PubMed Google Scholar ,3 Bascom R Differential susceptibility to tobacco smoke: possible mechanisms. Pharmacogenetics. 1991; 1: 102-106 Crossref PubMed Scopus (67) Google Scholar Although inherited deficiency of α1-antitrypsin is one of the documented risk factors, this accounts for < 1% of the COPD cases. 1 American Thoracic Society statement Standards for the diagnosis and care of patients with chronic obstructive pulmonary disease: definitions, epidemiology, pathophysiology, diagnosis, and staging. Am J Respir Crit Care Med. 1995; 152: S78-S83 Crossref Google Scholar ,4 Brantly ML Paul LD Miller BH et al. Clinical features and history of the destructive lung disease associates with α1-antitrypsin deficiency of adults with pulmonary symptoms. Am Rev Respir Dis. 1988; 138: 327-336 Crossref PubMed Scopus (266) Google Scholar Other genetic polymorphisms have been associated with increased susceptibility to developing COPD. 5 Smith CAD Harrison DJ Association between polymorphism in gene for microsomal epoxide hydrolase and susceptibility to emphysema. Lancet. 1997; 350: 630-633 Abstract Full Text Full Text PDF PubMed Scopus (391) Google Scholar ,6 Horne SL Cockcroft DW Dosman JA Possible protective effect against chronic obstructive lung disease by the GC2 allele. Hum Hered. 1990; 40: 173-176 Crossref PubMed Scopus (71) Google Scholar In addition, the expression of the disease itself is complex, ie, some COPD patients may develop predominately airway disease and others parenchymal disease.