['Atopy or atopic syndrome is an allergic hypersensitivity subject to hereditary influences. Aberrant expression of chitinase 3-like 1 (CHI3L1), also known as YKL-40 or HC gp-39, is involved in the pathogenesis of inflammatory and allergic diseases.', 'The genetic contribution of CHI3L1 gene to atopic susceptibility was investigated using an integrated population genetic and molecular analysis.', 'Genetic variations in CHI3L1 were identified and genotyped in 295 unrelated patients with atopy and 180 control subjects. Serum YKL-40 and IgE levels were analyzed according to genotype. The effects of a promoter polymorphism (g.-247C/T) on promoter activity were examined in reporter and protein binding assays.', 'In the case-control association analysis, the g.-247C/T polymorphism at the promoter region (rs10399805; P = 0.0062) and the IVS7+82C/T polymorphism at intron 7 (rs2275353; P = 0.0056) of CHI3L1 showed a significant association with atopy. Subjects with the g.-247T risk allele had significantly higher serum YKL-40 (P < 0.0001) and IgE (P = 0.012) levels. An in vitro promoter assay using THP-1 human monocyte cells revealed that the C to T conversion at g.-247 induced a more than twofold increase of reporter gene expression. Moreover, the g.-247T allele showed an increased affinity for CCAAT enhancer-binding protein, a well known transcriptional activator, by electrophoretic mobility shift assay. Accordingly, subjects with the g.-247TT genotype showed a 2.5-fold increase in CHI3L1 mRNA expression in peripheral blood cells compared with those with the g.-247CC genotype.'] Is genetic variation in the promoter region of chitinase 3-like 1 associated with atopy?