Association of common haplotypes of surfactant protein A1 and A2 (SFTPA1 and SFTPA2) genes with severity of lung disease in cystic fibrosis

Most individual cystic fibrosis transmembrane conductance regulator (CFTR) mutations appear not to correlate directly with severity of lung damage in cystic fibrosis (CF). Components of innate immunity, namely, mannose-binding lectin (MBL2), and surfactant protein A1 and A2 genes (SFTPA1 and SFTPA2), were shown to be critical in pulmonary host defenses. A pilot association study was conducted to identify genetic modifiers of lung disease in adult patients with CF. The structural and promoter (-221 x/y) variants of MBL2, variants at codons 19, 50, 62, and 219 of SFTPA1, and at codons 9, 91, and 223 for SFTPA2, were studied in 135 adults with CF and compared to their forced expired volume in 1 sec (FEV₁), diffusion of CO (DLCO), and other pulmonary scores. Predicted FEV₁ was significantly lower in adults with the SFTPA1 6A³ allele and SFTPA2 1A¹ allele (P=0.01 and 0.009, respectively). The extended haplotype 6A³/1A¹, which includes SFTPA1 and SFTPA2, was associated with lower pulmonary function, using FEV₁ (P=0.005) and poor pulmonary scores which were determined by American Medical Association, American Thoracic Society, and modified Shwachman-Kulczycki scores. Lower FEV₁ and DLCO values were associated with MBL2 coding variants in those who had the ΔF508 CFTR mutation (P=0.03 and 0.004, respectively). These results support the current hypothesis that variants in pulmonary host defense molecules are potentially genetic modifiers of pulmonary disease in CF Further work in larger populations is required to provide important new insights into the pathogenesis of CF.