Purpose of Review
This review provides an overview of the chitinase and chitinase-like proteins, chitotriosidase (CHIT1), YKL-40, and acid mammalian chitinase (AMCase), and to summarize the genetic studies of asthma and immune mediated diseases with polymorphisms in the genes encoding these proteins: CHIT1, CHI3L1, and CHIA, respectively.
Polymorphisms in the CHIT1, CHIA, and CHI3L1 genes influence chitotriosidase enzyme activity, AMCase activity, and YKL-40 levels, respectively. Regulatory SNPs in CHI3L1 were also associated with asthma, atopy, and immune-mediated diseases, and nonsynonymous SNPs in CHIA were associated with asthma. No CHIT1 polymorphisms, including a common nonfunctional 24-bp duplication allele, have been associated with asthma.
These genes represent novel asthma susceptibility genes. Variation in CHI3L1 and CHIA have been associated with asthma risk. Polymorphisms in CHIT1 have not yet been associated with asthma, but few studies have been reported. Given that chitotriosidase is the major chitinase in the airways and a common nonfunctional allele is present in many populations, additional studies of this gene are also warranted. Lastly, studies of all three genes need to be conducted in populations of diverse ancestries.