NOS3 and obstructive sleep apnea syndrome: Kheirandish-Gozal et al. [44] studied 36 OSAHS children (OSAHS group) and 35 children in control group, and observed a CpG site located at the proximal promoter region of endothelial nitric oxide synthase (eNOS) gene, approximating important transcriptional elements, and reported a significantly higher methylation level in OSAHS group compared with that in control group.