A relationship between the serum leptin level and the presence of OSA was confirmed (WMD=3.90 ng/ml, 95%CI=3.04-4.75, P<0.0001; Figure 2), and we chose the random-effects model owing to the high level of heterogeneity (I2 = 93.8%; Table 3). This evidence concerns the gene LEP and obstructive sleep apnea syndrome.