Acute respiratory tract infections and mannose-binding lectin insufficiency during early childhood

Context Hospital-based studies have found that increased susceptibility to certain infections is associated with low serum levels of mannose-binding l ectin (MBL) due to MBL variant alleles, However, the contribution of MBL in sufficiency to incidence of common childhood infections at a population lev el is unknown, Objective To investigate the effect of MBL insufficiency on risk for acute respiratory tract infection (ARI) in unselected children younger than 2 yea rs. Design and Setting Population-based, prospective, cohort study conducted in Sisimiut, Greenland, Participants Two hundred fifty-two children younger than 2 years who were f ollowed up weekly between August 1996 and August 1998 for morbidity surveil lance. Main Outcome Measure Risk of ARI, based on medical history and clinical exa mination, compared by MBL genotype, determined from blood samples based on presence of structural and promoter alleles. Results A 2.08-fold (95% confidence interval [CI], 1.41-3.06) increased rel ative risk (RR) of ARI was found in MBL-insufficient children (n = 13) comp ared with MBL sufficient children (n = 239; P < .001), The risk association was largely restricted to children aged 6 to 17 months (RR, 2.92; 95% CI, 1.78-4.79) while less effect (RR, 1.47; 95% CI, 0.45-4.82) and no effect (R R, 1.00; 95% CI, 0.42-2.37) was shown among children aged 0 to 5 months and 18 to 23 months, respectively, Conclusion These data suggest that genetic factors such as MBL insufficienc y play an important role in host defense, particularly during the vulnerabl e period of childhood from age 6 through 17 months, when the adaptive immun e system is immature.