Background: The T-cell immunoglobulin domain and mucin domain (TIM) gene family and the gene for IL-2-inducible T-cell kinase (ITK), located in chromosome 5 q 33 and potentially involved in the T-cell proliferation and differentiation, are good candidate genes for allergic diseases.
Objective: We assessed the role of polymorphisms in the TIM family genes and ITK in atopy, eczema, and asthma.
Methods: Twenty-one polymorphisms in the TIM-ITK gene cluster were genotyped in 564 children enrolled in the Tucson Children's Respiratory Study. Skin prick tests to common allergens were performed at age 6.1 years (n=508), age 10.8 years (n=539), and age 16.6 years (n=424). Asthma and eczema were assessed by questionnaire at these 3 points. Averaged relative risks were estimated.
Results: One 15-bp insertion/deletion in exon 4 of TIM 1 was significantly related to atopy and eczema (relative risk associated with carrying at least 1 rare allele=1.24 [1.07--1.45], P=.005; and 1.43 [1.01--2.01], P=.004, respectively). The 3 tested single nucleotide polymorphisms (SNPs) in TIM 3 were significantly related to atopy and eczema. One of them, at position +4259 calculated from the translation start site, predicts a putative change in the amino acid sequence of the protein, and was the most strongly related to atopy (relative risk=1.28 [1.12--1.47]; P=.0003). SNPs in the 5' genomic region in ITK, which show moderate linkage disequilibrium with those in TIM 3, had an independent effect on atopy. None of the polymorphisms studied was related to asthma.
Conclusion: Our findings support a potential role for SNPs in TIM 1, TIM 3, and ITK, independent of each other, in allergic diseases.