Association of alpha globin gene copy number with exhaled nitric oxide in a cross-sectional study of healthy Black adults.

Introduction: The genetic determinants of fractional exhalation of nitric oxide (FeNO), a marker of lung inflammation, are understudied in Black individuals. Alpha globin () restricts nitric oxide signalling in arterial endothelial cells via interactions with nitric oxide synthase; however, its role in regulating the release of NO from respiratory epithelium is less well understood. We hypothesised that an gene deletion, common among Black individuals, would be associated with higher FeNO.

Methods: Healthy Black adults were enrolled at four study sites in North Carolina from 2005 to 2008. FeNO was measured in triplicate using a nitric oxide analyzer. The -3.7 kb gene deletion was genotyped using droplet digital PCR on genomic DNA. The association of FeNO with copy number was evaluated using multivariable linear regression employing a linear effect of copy number and adjusting for age, sex and serum immunoglobulin-E levels. Post-hoc analysis employing a recessive mode of inheritance was performed.

Results: 895 individuals were in enrolled in the study and 720 consented for future genetic research; 643 had complete data and were included in this analysis. Median (25th, 75th) FeNO was 20 (13, 31) ppb. genotypes were: 30 (4.7%) -a/-a, 197 (30.6%) -a/aa, 405 (63%) aa/aa and 8 (1.2%) aa/aaa. Subjects were 35% male with median age 20 (19, 22) years. Multivariable linear regression analysis revealed no association between FeNO and copy number (β=-0.005 (95% CI -0.042 to 0.033), p=0.81). In the post-hoc sensitivity analysis, homozygosity for the HBA gene deletion was associated with higher FeNO (β=0.107 (95% CI 0.003 to 0.212); p=0.045).

Conclusion: We found no association between copy number and FeNO using a prespecified additive genetic model. However, a post hoc recessive genetic model found FeNO to be higher among subjects homozygous for the deletion.