MMP9 and obstructive sleep apnea syndrome: Accordingly, an early study by Ye et al. reported that intermittent hypoxia/reoxygenation was a predictor of enhanced circulating MMP-9 in OSA patients10, while Chuang et al. found that MMP-9, but not MMP-1, -2, -3 and TIMP-1 increases during sleep in patients with OSA11.