Protective role of IL-18 -137G/C polymorphism in a North Indian population with asthma: a pilot study.
BACKGROUND
IL-18, a pleiotropic, pro-inflammatory cytokine that plays a major role in innate as well as acquired immunity, has been implicated in asthma etiology and this is the first study investigating the role of IL-18 -137G/C (rs 187238) promoter polymorphism in asthma pathogenesis in a North Indian population.


METHODS
A pilot study was conducted with a total of 824 subjects, out of which 410 were asthma patients including 323 patients suffering from allergic rhinitis and 414 healthy controls from regions of North India. Tetra-Primer Amplification Refractory Mutation System Polymerase Chain Reaction (Tetra-Primer ARMS PCR) was used for genotyping the IL-18 -137G/C polymorphism.


RESULTS
While the homozygous wild (GG) genotype was equally prevalent in asthma patients as well as control subjects (70.0%), the homozygous mutant (CC) genotype was more prevalent among the controls (8.0%) than in asthma patients (3.4%), which yielded a significant protection or decreased risk towards asthma. Statistical analysis revealed Odds Ratio (OR)=0.43 (95% CI=0.21-0.85), Chi2 (χ2)=6.93 and p-value=0.008 (p<0.005). Moreover, a few asthma phenotypic traits also revealed significant protective associations with the polymorphism.


CONCLUSIONS
The IL-18 -137G/C polymorphism confers a significant protection from asthma in the studied North Indian population. This is the first study to report the protective association of the polymorphism with the disease.