A variation in the CHI3L1 gene increases susceptibility to asthma, bronchial hyper-responsiveness and decline in lung function, a study claims.

Researchers studied a genetically isolated population, the Hutterites of South Dakota, finding that the gene variant caused increased blood levels of asthma biomarker YKL-40.

A slightly different version of the genetic variation was found to lower YKL-40 levels and give protection against asthma.

The study which focused on the Hutterites, a US religious community descended from around 90 people, collected clinical data on asthma from more than 700 people between 1996 and 1997.

Blood samples from the participants were stored and YKL-40 levels were measured in recent analysis. This found that mean YKL-40 was increased in Hutterites with asthma or hyper-responsive airways.

Researchers also found that elevated YKL-40 levels were transferred from generation to generation implying that genetic differences were responsible.

Variations in the CHI3L1 gene were analysed with one slight genetic difference identified between people with asthma and those without in the promoter part of the gene.

The variation changes one DNA base pair at the 131C/G location in the CHI3L1 gene. Those with asthma were more likely to have a cytosine (C), rather than guanine (G) at this location.

People who inherited two copies of a C at -131 had higher YKL-40 levels and an asthma prevalence of 0.20, while those with CG had intermediate YKL-40 levels and an asthma prevalence of 0.12, the report noted. People with GG had the lowest YKL-40 levels and a prevalence of 0.08, less than half that of the CC allele.

"This evolutionarily ancient pathway involving the innate immune system plays a surprisingly important role in asthma pathogenesis and a single genetic variant in the CHI3L1 gene may account for most of this risk," lead author Carol Ober said.

Researchers believe the discovery could have a significant impact on drug development.

"For some people, if you block YKL-40 you might dramatically reduce the severity of the disease. Knowing the genotype at SNP -131C might identify those who [are] most likely to benefit from such a treatment," she added.

The findings are reported in the New England Journal of Medicine.

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