Background
IgE-mediated food allergy affects up to 8% of infants and children in
industrialized countries and often starts early in infancy (1).
Especially infants with eczema are at high risk for developing food
allergies and it is the current understanding that sensitization occurs
via the cutaneous route due to an impaired skin barrier function (2, 3).
Accordingly, a high peanut consumption in the household has been shown
to be a possible risk factor for developing peanut allergy in infancy
(4). Moreover, we demonstrated that food proteins, such as peanut and
hen’s egg can be found not only in the eating area, but also in bed dust
and increase with consumption, further supporting the hypothesis of
cutaneous sensitization (5, 6). Therefore, German S3-guidelines on
allergy prevention recommend that peanut allergy should first be ruled
out in infants with moderate to severe atopic dermatitis, before
introducing peanut into the infant´s diet for preventive purposes (7).
What about other food allergens such as tree nuts? It has been shown
that infants with eczema are at risk for multiple food sensitizations
(8). During the last decades, nutrition across Western countries has
changed substantially as for example vegan and plant-based diets have
become a growing trend (9). Tree nuts, such as cashews, hazelnuts and
walnuts are a nutritional mainstay of plant-based diets (10). Moreover,
plant-based alternatives for milk and milk-products often contain tree
nuts and such products are gaining in popularity among consumers (11).
These changes in dietary habits may lead to a wider spread of tree nut
allergens in households, increasing the risk for cutaneous exposure in
infants. Moreover, tree nuts are very potent allergens, as evidenced by
having caused up to 21% of all fatal anaphylaxis cases among children
between 1992 and 2018 in the United Kingdom (12). Among tree nuts,
hazelnut, cashew and walnut are the most common triggers inducing
anaphylaxis in children in Europe (13). Regarding the clinical
reactivity, sensitization to 2S albumins of peanut and tree nuts have
been shown to be associated with severe allergic reactions (14). Ana o
3, the 2S albumin of cashew, discriminates between allergic and tolerant
children better than cashew-specific IgE and probability curves for Ana
o 3-specific IgE have been calculated, a 95% probability could be
estimated at 2.0 kU/l (15). Similarly, the 2S albumin of hazelnut, Cor a
14, estimates the probability for a positive clinical reaction, with a
90% probability for hazelnut allergy at 47.8 kU/l (16). Concerning
walnut, the 2S albumin Jug r 1 has been shown most accurate for
estimating the risk for clinical relevant walnut allergy (17). There are
hints, that individuals with peanut allergy have a higher likelihood of
being allergic to tree nuts compared to the general population (18, 19).
Therefore, the question comes up what to recommend in a peanut-allergic
child: To eat, to screen, or to avoid as it has been recently discussed
in this journal (20)? To date, there are scarce data on the
sensitization patterns to tree nuts in very young infants and children
with peanut sensitization. Therefore, the aim of this study was to
investigate, how often peanut-sensitized infants and toddlers are
sensitized to cashew, hazelnut and walnut and their seed storage
proteins, which might be associated with a high risk for clinical
reactivity. We hope to add some important information to this
discussion.