Degrades chitin, chitotriose and chitobiose. May participate in the defense against nematodes and other pathogens. Isoform 3 has no enzymatic activity. Random endo-hydrolysis of N-acetyl-beta-D-glucosaminide (1->4)-beta-linkages in chitin and chitodextrins. Monomer. A small proportion is lysosomal. Detected in spleen. Secreted by cultured macrophages. A 24 bp duplication in exon 10 leads to the activation of an alternative splice site and the production of an inactive protein resulting in chitotriosidase deficiency [MIM:614122]. About 6% of the population are deficient for CHIT1 activity, while 35% are carriers and show reduced enzyme levels. People with CHIT1 deficiency appear perfectly healthy. Very high plasma levels of CHIT1 are found in patients with Gaucher disease type 1 (GD I). Can be used as diagnostic aid and to evaluate the success of treatment that brings levels back to normal. Duplication of 24 bp in exon 10 leads to the use of a cryptic splice site. The normal splice site is still present but not used. Belongs to the glycosyl hydrolase 18 family. Chitinase class II subfamily. Extended N-terminus.