Early contact with pet dogs protects genetically susceptible children from eczema

Having a dog at home could help to prevent eczema in children who are genetically prone to the condition, a study suggests.

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.

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.

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.

The study also pointed to a similar effect among young children with older siblings, but further studies are needed to confirm the link. Scientists suggest that exposure to a variety of bacteria at an early age, through contact with dogs and other children, could be behind the protective effect.

Populations used in the study were limited to those from a white European background. Research involving a more diverse group of people is needed to better understand interactions between genetic and environmental factors linked to eczema in other ancestral groups, the team say.

The study is published in the journal Allergy: https://onlinelibrary.wiley.com/doi/10.1111/all.16605 [URL will become active after embargo lifts]. The international research team included scientists from the UK, Germany, Denmark, Netherlands, Norway, Spain, United States, Ireland, France, Sweden, Australia, Italy and Kuwait.

The most difficult questions I'm asked by parents in clinic are about why their child has eczema, and how they can help. We know that genetic make-up affects a child's risk of developing eczema and previous studies have shown that owning a pet dog may be protective, but this is the first study to show how this may occur at a molecular level. More work is needed, but our findings mean we have a chance to intervene in the rise of allergic disease, to protect future generations."

Professor Sara Brown, University of Edinburgh's Institute of Genetics and Cancer

Dr. Marie Standl, from Helmholtz Munich, said "This study sheds light on why some children develop eczema in response to environmental exposures while others don't. Not every preventive measure works for everyone – and that's precisely why gene–environment studies are crucial. They help us move toward more personalized, effective prevention strategies."