Eczema, asthma, egg allergy among early-life risk factors for tree nut allergy
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Preschool children with egg allergy, eczema or asthma appeared at increased risk for tree nut symptoms and storage protein sensitization in early adulthood, according to study results published in Clinical & Experimental Allergy.
Also, sensitization to tree nut storage protein during childhood appeared to more strongly correlate with tree nut allergy symptoms than sensitization to tree nut extract, results showed.
“This study increases the understanding of tree nut allergy in a general population, followed from infancy up to adulthood,” Jessica Bager, MD, of the department of women’s and children’s health at Karolinska Institutet in Sweden, and Anna Asarnoj, MD, PhD, pediatric allergologist at Karolinska Institutet, told Healio. “There is a reported increase in prevalence of tree nut allergy in the past decades, which makes it more important to really understand how common it is, who has a higher risk for developing it and how this allergy is clinically manifested.
“Despite its clinical relevance, tree nut allergy is an understudied area,” they added. “More studies on the development of tree nut allergy over time are needed, especially those that also include oral food challenges with tree nuts.”
Thus, the researchers sought to determine the prevalence of tree nut allergy at age 24 years in relation to sensitization at extract and molecular allergen levels, symptoms and early-life factors in a population-based birth cohort comprised of 2,215 participants from the BAMSE study, a Swedish birth cohort of those born between 1994 and 1996 in Stockholm.
Participants completed questionnaires with data on tree nut ingestion and symptoms at age 12, 16 and 24 years, and they underwent IgE sensitization at age 24 years to hazelnut, walnut, pecan, cashew, pistachio, Brazil nut and almond extracts and allergen molecules (Cor a 1, 9, 14 [hazelnut]; Ana o 3 [cashew]; Jug r 1 [walnut]).
Overall, 217 participants (9.8%) reported clinical symptoms to tree nuts at age 24 years or avoided tree nuts at that age with symptoms reported at age 12 or 16 years. Also, 470 participants (21.2%) were sensitized to any tree nut — with hazelnut (20.6%) and almond (7.6%) being the most common — and 175 participants (7.9%) reported both symptoms and sensitization to any tree nut.
Researchers reported a 14.6% rate of tree nut sensitization among the 1,996 participants who reported no tree nut allergy symptoms, meaning the majority of those with tree nut sensitization were asymptomatic.
“We were surprised that the majority of the tree nut-sensitized individuals in our cohort did not report any symptoms at all,” Bager and Asarnoj said. “We had expected most of the sensitized individuals to at least report mild oral allergy syndrome symptoms, related to cross-reactions to birch pollen.”
Overall, 3.5% of participants had sensitization to any of the tested tree nut storage proteins.
Ninety-seven percent of participants sensitized to hazelnut extract also were sensitized to birch pollen extract. Of those sensitized to Cor a 1, all but one were also sensitized to birch pollen extract, whereas only 9% were sensitized to Cor a 14 and 14% to Cor a 9.
In adjusted analyses, early-life factors associated with tree nut symptoms plus tree nut storage protein allergen molecule sensitization included eczema at 1 to 2 years (OR = 2.53; 95% CI, 1.21-5.32), egg allergy at 4 years (OR = 8.5; 95% CI, 2.15-33.6) and asthma at 4 years (OR = 5.59; 95% CI, 2.35-13.3).
A comparison of allergic phenotype factors among individuals with storage protein (n = 79) vs. tree nut extract-only (n = 400) sensitization showed more severe signs of extensive allergic disease — including greater prevalence of severe asthma, adrenaline autoinjector use and elevated exhaled nitric oxide — among the storage protein-sensitized group.
The researchers noted that their inability to verify tree nut symptoms with food challenges served as a limitation to this analysis.
“Because our study reveals that most extract‐based tree nut‐sensitized individuals do not have tree nut allergy, our conclusion is that extract-based IgE testing for tree nuts without a specific clinical suspicion should not be performed,” Bager and Asarnoj told Healio. “Also, we confirmed that testing for specific allergen molecules is a more reliable method to find clinically relevant allergy, rather than extract based IgE-testing.”
For more information:
Anna Asarnoj, MD, PhD, can be reached at anna.asarnoj@ki.se.
Jessica Bager, MD, can be reached at jessica.bager@stud.ki.se.