Background: Previously, an association has been reported between an increased risk of asthma and a polymorphism in the Clara cell secretory protein (CC16) gene [namely, an adenine to guanine substitution in the CC16 gene at position 38 (A38G) downstream from the transcription initiation site within the noncoding region of exon 1]. Homozygous individuals for the polymorphic sequence (AA genotype) were reported to have a significant (6.9 fold) increased risk of developing asthma. This finding has not been confirmed independently.
Objective: To validate the association of CC16 A38G polymorphism to asthma in a separate well-characterized population through a case-control study.
Methods: We conducted an association study using a sample of 217 unrelated Northern European Caucasians. Individuals were clinically characterized by a validated respiratory questionnaire, spirometry and bronchial reactivity measurement, and genotyped for the A38G polymorphism using PCR and restriction digestion. Association analysis was performed using the nonparametric Chi-squared tests.
Results: In the unselected population, 43.3% participants were homozygous for the CC16*G allele and 45.4% were heterozygous (AG). We observed no significant difference in the distribution of positive bronchial reactivity to methacholine (at FEV1 PC20 of </= 8 mg/mL) across the three genotypes. Homozygous individuals for the CC16*A allele did not demonstrate an increased risk of asthma when compared to heterozygous or GG homozygotes. In addition, no significant difference was observed in the distribution of the CC16*A or *G alleles in the asthmatics vs. non-asthmatics.
Conclusion: CC16 polymorphism A38G does not influence the predisposition to asthma in this sample.