Does 24bp Duplication of Human CHIT1 Gene (Chitotriosidase1) Predispose to Filarial Chyluria? A Case-Control Study.

Abstract

Chyluria which is endemic in many parts of the world is mainly caused by Wuchereria bancrofti. CHIT1 (chitotriosidase) is produced by macrophages and plays an important role in the defense against chitin containing pathogen such as filarial parasite. Variation in the coding region with 24 bp duplication allele results in reduced CHIT1 activity that enhance the survival of parasite which may play a role in the occurrence of disease. To examine the role of 24bp duplication of CHIT1 gene in patients of filarial chyluria (FC). A case-control study was carried out where 155 confirmed FC patients and equal number of age-, sex- and residence-matched controls without any symptoms or signs of lymphatic filariasis, confirmed by negative immunochromatographic card test (ICT) and IgG/IgM combo rapid antibody test, from a hospital-based population were enrolled. Filarial aetiology was confirmed on the basis of DEC-provocative test (Giemsa staining), ICT and IgG/IgM- antifiarial antibody test. The patients positive by either of these tests were enrolled as FC cases. 24bp duplication in CHIT1 gene in FC was detected by the product size 99bp of amplified gene using polymerase chain reaction. The mean ages of patients and controls were 38.25±12.09 and 35.45±12.53 years, respectively while male: female ratio was 2.4:1. The mean duration of illness in chyluria patients was 62.81±60.83 months and mean number of episodes was 2.54±1.11. Homozygous wild type, heterozygous and homozygous mutant frequencies were 10.3%, 81.3% and 8.4% in FC patients and 18.7%, 75.5%, and 5.8% in controls, respectively. The 24bp duplication in CHIT1 gene showed a significant association in Heterozygous (HT) genotype with Odd Ratio (OR) of 1.95, 95% Confidence Interval (CI) (1.01-3.77); p=0.04. However, the homozygous mutant genotype (TT) was found to be non-significant with OR of 2.61, 95% CI (0.91-7.45); p=0.07. The combination of both HT+TT was also found to be significant with OR of 2.00, 95% CI (1.03-3.85); p=0.03. In this study from Northern India, CHIT1 gene polymorphism showed an influence as a possible risk factor for susceptibility to FC. Further studies need to be done on a larger number of FC patients in different regions of the country.