Mitochondrial DNA Copy Number Variation in Asthma Risk, Severity, and Exacerbations.

Background: Asthma pathophysiology is associated with mitochondrial dysfunction. Mitochondrial DNA copy number (mtDNA-CN) has been used as a proxy of mitochondrial function, with lower levels indicating mitochondrial dysfunction in population studies of cardiovascular diseases and cancers.

Objectives: We investigate whether lower levels of mtDNA-CN are associated with asthma diagnosis, severity, and exacerbations.

Methods: MtDNA-CN is evaluated in blood from two cohorts: UK Biobank (UKB) (asthmatics n = 39,147; non-asthmatics n = 302,302) and Severe Asthma Research Program (SARP) (n = 1283 asthmatics, non-severe n = 703).

Results: Asthmatics have lower mtDNA-CN compared to non-asthmatics in UKB (beta, -0.006 [95% CI, -0.008 to -0.003], P = 6.23×10^-6). Lower mtDNA-CN is associated with asthma prevalence, but not severity in UKB or SARP. mtDNA-CN declines with age but is lower in asthma than in non-asthmatics at all ages. In one-year longitudinal study in SARP, mtDNA-CN is associated with risk of exacerbation; those with highest mtDNA-CN have the lowest risk of exacerbation [OR 0.333 [95% CI, 0.173 to 0.542], P = 0.001]. Biomarkers of inflammation and oxidative stress are higher in asthma than non-asthmatics, but the lower mtDNA-CN in asthma are independent of general inflammation or oxidative stress. Mendelian Randomization (MR) studies suggest a potential causal relationship between asthma-associated genetic variants and mtDNA-CN.

Conclusion: MtDNA-CN are lower in asthmatics than in non-asthmatics and are associated with exacerbations. Low mtDNA-CN in asthma are not mediated through inflammation but are associated with the genetic predisposition to asthma.