Consistent with a common etiology, Volna et al. found that increased levels of MMP-9 were positively correlated with hypoxemic severity indexes due to OSA (i.e., oxygen desaturation index (ODI) and sleep time spent at oxygen saturation below 90% (SpO2 < 90%)) in men suspected of OSA [55]. Here, MMP9 is linked to obstructive sleep apnea syndrome.