Environmental risk factors at heart of JIA

JIA

By Clare Pain

1 Apr 2015

Only-children have nearly double the risk of JIA, finds a study from the Murdoch Childrens Research Institute that adds weight to the hygiene hypothesis behind the disease.

ARC Future Fellow, Dr Justine Ellis (PhD) of the Institute said a similar finding was apparent in a study published in 1999, but the MCRI research has been the first to look at younger siblings and to find that exposure seemed to be particularly important.

“When we looked at younger siblings we saw a strong association and also a lot of consistency between the control group comparisons, which wasn’t present for older sibling analyses,” says Ellis who published the work with Dr Jane Munro, a paediatric rheumatologist at the Royal Children’s Hospital in Melbourne.

“We also looked at exposure to siblings in terms of cumulative years and there was a very strong association of risk [reduction] with younger siblings. Three or more years of exposure to younger siblings by school entry age was associated with a two-fold decrease in risk of JIA”

“We concluded that younger siblings appeared to be more important than older siblings and we think that potentially that could be because the early life infant and child infections that the younger child is bringing into the household are important in priming the immune system,” she says.

“Of course, we need to really understand what the sibling exposure is actually standing as a proxy for – we suspect it is infections – but we don’t yet know that.”

Part of the CLARITY study investigating childhood arthritis risk factors, the case-controlled study reported in Arthritis and Rheumatology compared 302 Victorian cases of JIA with 676 hospital controls, and 341 community-based controls.

“Jane and I began CLARITY because it was obvious to us that there was very little research going on around the world to understand what causes juvenile arthritis. We decided we would focus on the genetic and environmental factors and the interactions between them.

“This sibling study is really getting at the heart of the environmental factors – and nobody was really looking at environmental factors – so it was an important study to do.”

 

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