GCH1 and obstructive sleep apnea syndrome: Interestingly, as shown in Table 3, for the first time we found a significant difference between the severe and mild-to-moderate OSA patients in terms of the genotype of rs841 (GCH1), where GA genotype was more frequently observed in the mild-to-moderate OSA patients (Crude OR = 0.3, 95% CI = 0.12–0.78; P = 0.01, after adjusting for age, gender, BMI, OR = 0.21, 95% CI = 0.07–0.62; P = 0.005).