CHI3L1 and obstructive sleep apnea syndrome: Overall, no significant differences in CHI3L1 levels (3.87 ± 0.05 vs. 3.79 ± 0.05, p = 0.08) and CHIT1 activity (3.17 ± 0.09 vs. 3.20 ± 0.09, p = 0.08) were found among OSA patients before and after PAP treatment.