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WASHINGTON -- Among the younger siblings of children who consumed peanut allergens as part of the LEAP trial, there was a trend toward peanut sensitization, though this effect was reduced if peanut was introduced early, results from an "unintentional" randomized trial showed.

Of the younger siblings, 20% of those who had a sibling who was a peanut avoider in LEAP had peanut sensitization compared with 30.4% of those who had a sibling who was a peanut consumer (P=0.055), reported Gideon Lack, MD, of King's College London, during the American Academy of Allergy, Asthma & Immunology annual meeting.

Notably, for the younger siblings of peanut consumers, those who had peanut introduced in the first year of life had a significantly lower rate of sensitization than those who did not introduce peanut (18.3% vs 44.4%, P=0.002).

Furthermore, peanut allergy rates were significantly higher in the siblings of peanut consumers who did not eat peanut products compared with those who did (17.9% vs 3.7%, P=0.01).

"In this prospective randomized study, we saw a concerning increase in sensitization and allergy in the younger siblings of consumers compared to the younger siblings of avoiders," Lack said. "The effect of sensitization and allergy is accentuated and more apparent in the younger siblings that did not consume peanuts in the first year of life. These findings support the dual allergen exposure hypothesis -- cutaneous exposure in the absence of oral consumption leads to sensitization."

The (Learning Early About Peanut) originally focused on infants with severe eczema, egg allergy, or both, who were randomly assigned to either avoid or consume peanut products until they were 5 years old. The study showed that introducing peanuts to patients at an early age "significantly decreased the frequency of the development of peanut allergy among children at high risk for this allergy and modulated immune responses to peanuts."

However, Lack explained, in some LEAP participant families, there were instances of peanut allergy being reported among the younger siblings of the participants, creating what the researchers described as "an unintentional randomized trial."

"Some initially interesting, and then, concerning anecdotes came [from] the parents of the LEAP participants during the course of the study," he said, noting that parents reported an allergic reaction to peanuts among 13 younger siblings of peanut consumers. "Is it coincidence? Is it ascertainment bias, is it a real effect?"

"So, it is possible that by exposing the younger siblings of the LEAP participants to high levels of peanuts and much lower levels in the younger siblings of avoiders, we might have been inducing sensitization and allergy," he added.

There were a total of 298 younger siblings of LEAP participants included in this analysis -- 144 were the younger siblings of LEAP avoiders, while 154 were the younger siblings of LEAP consumers. Mean age was 10.5, with ages ranging from 7.2 to 15.5.

Peanut sensitization was defined as an allergen-specific immunoglobulin E (Sp-IgE) of ≥0.35 kU/L, Sp-IgE to the individual peanut component Arachis hypogaea 2 ≥0.1 kU/L, or a skin prick test to peanut ≥3 mm.

No differences were observed for hen's egg sensitization, an allergen included in the initial LEAP study.

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