LEP and obstructive sleep apnea syndrome: Consistent with two recent systematic reviews and a meta-analysis [25, 39] on leptin and LEPR gene polymorphisms in OSA, no polymorphisms (Gln233Arg, Lys656Asn, Lys109Arg, 19A/G, Pro1019Arg, or 2548G/A) were found to be associated with OSA risk.