Previous studies have reported that several single nucleotide polymorphisms might be involved in the pathogenesis of OSA both in adult and children, such as serotonin transporter (5-HTT) [59], TNF-α [49,60], fatty acid binding protein 4 [48,61], macrophage migration inhibitory factor [47], NADPH oxidase p22 sub-unit [8,50], and angiotensin I converting enzyme (ACE) [62,63]. Here, SLC6A4 is linked to obstructive sleep apnea syndrome.