Table II.

Overview of GH18 family members encoded in the human genome, their molecular function and disease implications

HGNC symbol	Species	Molecular functions	Disease involvement	Key references
CHIT1	All mammals	Endochitinolytic activity, hydrolysis of GlcNAc containing glycosides, e.g. LacDiNAc	Asthma, fungal infection, H. pylori infection, Gauchers disease and sarcoidosis	Hollak et al. (1994), van Eijk et al. (2005), Gavala et al. (2013), Lee et al. (2012),Cozzarini et al. (2009)
CHIA	All mammals	Endochitinolytic activity, stimulate PI3K and AKT signaling	Asthma and nematode infection	Boot et al. (2001), Zhu et al. (2004), Hartl et al. (2009), Nance et al. (2012)
CHI3L1	All mammals	Glycoside and protein binding, mediate IL-13 signaling, stimulate MAPK signaling	Asthma, fibrosis, cancer, intestinal inflammation and bacterial infection	Houston et al. (2003), He et al. (2013), Lee et al. (2009), Tang et al. (2013), Francescone et al. (2014), Tran et al. (2014), Dela Cruz et al. (2012), Shao et al. (2009)
OVGP1	All mammals	Protein binding	Suggested as a marker of ovarian cancer	Kadam et al. (2006)
Chil2	Absent in rodents	Glycoside binding, stimulate MAPK signaling	Arthritis	Areshkov et al. (2011), Steck et al. (2002), Miyatake et al. (2013)
CTBS	All mammals	Exochitinolytic activity, lysosomal glycoprotein turnover	None	Aronson et al. (1989), Persichetti et al. (2012)
CHID1	All mammals	Glycoside binding, stimulate MAPK signaling	Arthritis	Kzhyshkowska et al. (2006), Xiao et al. (2014)

Orthologs of the genes encoding the two active endochitinases, CHIA and CHIT1, the non-hydrolytical CHI3L1, OVGP1 and CHID1, as well as the exoacting CTBS, are found in all mammals. The CLP-encoding Chil2 is absent in rodents, which in exchange feature four rodent-specific CLP-encoding genes (Chil3, Chil4, Chil5 and Chil6).