CHI3L1 and obesity due to melanocortin 4 receptor deficiency: CHI3L1 has been found in increased quantities in the serum and lungs in patients with asthma.159–161 Moreover, a promoter SNP (−131C → G) in CHI3L1 is associated with elevated serum CHI3L1 levels, asthma, bronchial hyper responsiveness, and measures of pulmonary function.162 Interestingly, CHI3L1 is induced by a high fat diet and contributes to the genesis of obesity and asthma.74 Mechanistically, CHI3L1 promotes bronchial smooth muscle cell proliferation and migration through a PAR-2–dependent mechanism.33