CHI3L1 and Crouzon syndrome-acanthosis nigricans syndrome: We believe both mechanisms are involved since numerous studies have shown that YKL-40 is related to metabolic syndrome and its components (hypertension, hyperlipidemia, cardiovascular and cerebrovascular diseases), various cancers, obstructive sleep apnea syndrome, chronic allograft nephropathy, and Alzheimer disease [15,24–27].