Children with a change in their DNA that increases their chance of developing eczema were less likely to have the condition if they were exposed to a dog in early life, researchers say.
The findings provide new insights into what could cause eczema in children and how environmental factors may influence genetic risk, experts say.
The study did not look at the effect of dog exposure in the treatment of existing eczema, and experts caution that introducing a dog may make symptoms worse in some children.
Environmental effects
Eczema is an itchy skin disorder caused by a combination of genetic and environmental effects, but little is known about how the two interact.
The international study team, led by scientists from the Universities of Edinburgh and Bristol, the London School of Hygiene & Tropical Medicine and Helmholtz Munich, examined data from almost 300,000 people to investigate whether those who are prone to developing eczema might respond differently to environmental factors.
Researchers tested for interactions between the 24 most significant eczema-associated genetic variants and 18 early life environmental factors during the mother’s pregnancy and the child’s first year of life.
An initial analysis of more than 25,000 individuals suggested there may be a relationship between seven environmental factors – dog ownership, elder sibling, cat ownership, breastfeeding, smoking, antibiotic use and washing practices – and at least one established genetic variant for eczema.
Identified link
They then tried to replicate their findings in a larger group of almost 255,000 people. The strongest interaction found was between a region of DNA code that increased the risk of eczema, but in children or babies whose families owned a pet dog, that risk disappeared.
The variation in genetic code was located near a gene for interleukin-7 receptor (IL-7R) – a protein involved in immune cell function and inflammation.
Lab tests confirmed that in human skin cells with the genetic variant, molecular signals from a dog that could trigger allergy instead worked to suppress skin inflammation.
The findings suggest that the IL-7R protein may provide a potential target for future treatment or prevention of eczema, experts say.