In fact, plasma MMP9 levels are elevated in patients with obstructive sleep apnea (Franczak et al., 2019a; Mashaqi et al., 2021), and urinary MMP2 activity has been shown to increase in accordance with obstructive sleep apnea severity (Franczak et al., 2019b). Here, MMP9 is linked to obstructive sleep apnea syndrome.