In the subgroup analysis according to the BMI, the plasma leptin concentration for OSA patients with a BMI of <30 kg/m2 was not different compared to controls, whereas the serum leptin level in OSA patients with a BMI of <30 kg/m2 was higher than that in healthy controls, indicating that OSA might influence the leptin level. This evidence concerns the gene LEP and obstructive sleep apnea syndrome.