Interestingly, we have also found that plasma Smad4 levels in OSA patients are related to the nocturnal recording time with oxyhaemoglobin saturation below 90% (CT90) (r = 0.290, p = 0.038, Figure 2D), a clinical parameter of hypoxaemia severity in OSA patients. This evidence concerns the gene SMAD4 and obstructive sleep apnea syndrome.