US researchers have identified a gene that seems to play a significant role in the development of asthma. Reporting in the New England Journal of Medicine, Carole Ober and her colleagues at the University of Chicago found that people can either be protected from asthma or find their risk of developing it increased, depending on which version of the CHI3L1 gene they inherit.

'This is exciting because it connects asthma susceptibility to a whole new pathway at the protein and the genetic levels. There is a good deal more we need to find out about this connection, but now we know where to look', said Ober.

The breakthrough sprang from the group's work with the Hutterites, a Christian farming community from South Dakota in the US. Their genetic isolation has limited their genetic variation - making important pathological changes within their genome easier to distinguish. They also have a high prevalence of asthma.

A number of studies have shown the biomarker YKL-40 - the protein product of CHI3L1 - to be raised in people with asthma. Ober went on to prove that this trend extends to Hutterites and additionally that it was passed down through families in the same manner as asthma - highlighting a genetic basis for the increase.

Further investigation of the gene by her team threw up two different versions: 131C and 131G. They showed that people who have two copies of 131C had twice the chances of developing asthma than those who had none, while two copies of 131G halved the risk of the disease. The findings were confirmed in more genetically diverse populations in the US and Germany.

Researchers tempered excitement generated by the discoveries, with a warning that the gene only accounted for a small proportion of asthma cases. 'Relative to other asthma genes, this one has the biggest effect we have seen', Ober said. 'It won't account for all cases of asthma, some people will have asthma caused by a different gene, but if you have the CC version you are twice as likely to have asthma as those who don't have it'.