Asthma is the most common chronic diseases in children in the UK, Europe and America, with more than a million young people in Britain currently receiving regular treatment. Nursery attendance in early life was thought to protect against the later development of asthma by increasing exposure to microbes which may help the immune system mature faster.

Now, by testing 1,000 children in two population-based birth cohorts from the United Kingdom and the United States, researchers from UHSM & the USA have demonstrated that this protective effect of early-life day care attendance against asthma appears dependent on a specific gene.

In a newly-published report, researchers found that nursery was protective, but only among 80% of children carrying a particular variant in the TLR2 gene. However, among the remaining 20% children (with a different variant of the same gene), nursery attendance actually tended to have the opposite effect – i.e. it increased the risk of asthma.

The research team studied 727 children in Manchester and 263 in Tucson, Arizona. The children were divided into two groups. The first included children who regularly attended nursery during the first two years of their life. The second were children who were looked after at home.

A series of tests were undertaken, including detailed questionnaires on wheezing symptoms, skin pricks to test for common allergies and lung function tests to measure airway reactivity. All the children were tested for the variants in TLR2 receptor gene.

Professor Adnan Custovic, of the University of Manchester and MAHSC (Manchester Academic Health Science Centre) who co-led the study, explains: "When we looked at all children, early-life day-care attendance appeared to protect against subsequent asthma. However this concealed the fact that, whilst in some children day care was strongly protective, in a subgroup of children it actually increased the risk of disease. Whether nursery was beneficial or detrimental depends, it would seem, on the genetic make-up of the child. The apparent protective effect which we observed when we analysed all children resulted from the fact that children with one genetic variant (in whom day care was associated with less asthma) outnumbered children with the other genetic variant (in whom nursery was associated with more asthma) by a factor of 4 to 1."

The results suggest that among asthmatic patients, only those with particular genetic susceptibility might benefit from a specific intervention (or drug), whereas the same intervention (or drug) among patients with a different susceptibility might cause harm. It will be critically important to develop tests which will accurately identify individual patients who may benefit from any specific intervention or drug (and those who will get worse).