Background
Inherited methylmalonic acidemia is characterized by mitochondrial dysfunction, oxidative stress, and damage of mitochondria-rich organs in children. It is unclear whether methylmalonic acid (MMA) is related to poor prognosis in adults. The study aims to investigate the associations of MMA with all-cause and cause-specific mortality in the general population.
Methods
Overall, 23,437 adults from the US National Health and Nutrition Examination Survey (NHANES) were enrolled. NHANES 1999–2004 and 2011–2014 were separately used as primary and validation subsets (median follow-up 13.5 and 2.8 years, respectively). Circulating MMA was measured with gas chromatography/mass spectrophotometry. Hazard ratios (HR) were estimated using weighted Cox regression models.
Results
During 163,632 person-years of follow-up in NHANES 1999–2004, 3019 deaths occurred. Compared with participants with MMA <120 nmol/L, those with MMA≥250 nmol/L had increased all-cause and cardiovascular mortality in the multivariable-adjusted model [HR(95%CI), 1.62 (1.43–1.84) and 1.66 (1.22–2.27), respectively]. The association was especially significant among participants with normal cobalamin. MMA remained an independent predictor of all-cause mortality occurring whether within 5-year, 5–10 years, or beyond 10-year of follow-up (each p for trend≤0.007). That association was repeatable in NHANES 2011–2014. Moreover, baseline MMA improved reclassification for 10-year mortality in patients with cardiovascular disease (net reclassification index 0.239, integrated discrimination improvement 0.022), overmatched established cardiovascular biomarkers C-reactive protein or homocysteine.
Conclusions
Circulating level of mitochondrial-derived MMA is strongly associated with elevated all-cause and cardiovascular mortality. Our results support MMA as a surrogate biomarker of mitochondrial dysfunction to predict poor prognosis in adults. The biological mechanisms under cardiovascular disease warrant further investigation.
