Published online: October 25, 2017
The impact of early life exposure to cat and dog on the risk of childhood asthma has been studied extensively. However, previous results have pointed in different directions; some describe the exposure as a risk factor, others find it protective for disease. This suggests that the genetic makeup of the child may be pivotal for these environmental exposures to exert their effects. Genetic variation at the chromosome 17q21 locus is the strongest known genetic risk factor for childhood asthma and the high-risk genotype determines an early-onset asthma phenotype with recurrent asthmatic episodes and acute severe exacerbations.
In a study recently published in The Journal of Allergy and Clinical Immunology (JACI), Stokholm and colleagues studied gene-environment interactions between cat and dog exposure from birth and 17q21 genotype of the child in relation to the risk of developing asthma during the first 12 years of life. This study was performed in 377 children from the Copenhagen Prospective Studies on Asthma in Childhood2000 (COPSAC2000), who were born to asthmatic mothers. The study examined both the effect of exposure to either a cat or a dog from birth and the effect of each type of pet. The levels of cat and dog allergens in the children’s homes were also studied, as were the number of episodes with pneumonia and bronchiolitis from birth to age 3 years. The results on asthma development were replicated in 604 children from the unselected COPSAC2010 cohort during the first 5 years of life.
The researchers report a gene-environment interaction between cat exposure from birth and 17q21 genotype. Cat exposure attenuated the risk of asthma development during the first 12 years of life in children with the high-risk genotype, but had no effect in children with the low-risk genotype. Increasing levels of cat allergens collected in the children’s homes were associated with increased protection from asthma in these high-risk children. The researchers found no such effects of exposure to dog. The high-risk asthma 17q21 genotype was also associated with a higher risk of pneumonia and bronchiolitis, and this risk was likewise decreased in children exposed to cat. Replication studies showed similar results on asthma risk.
The observed gene-environment interaction suggests a role of early life exposure to cats for attenuating the risk of childhood asthma, pneumonia and bronchiolitis in genetically susceptible individuals. In this study, there were no effects of exposure to dog from birth on asthma risk. This gene-environment interaction add to the growing literature on exposures to animals at birth and asthma risk and may guide future preventive measures in children with the high-risk 17q21 genotype.
The Journal of Allergy and Clinical Immunology (JACI) is an official scientific journal of the AAAAI, and is the most-cited journal in the field of allergy and clinical immunology.