By Allergen Bureau

Open access to current perspectives on tree nut allergy

A recent review of tree nut allergy has been published that sets out current knowledge of the nine most common tree nuts that cause allergic reactions: cashew; pistachio; walnut; pecan; Brazil nut; almond; pine nut; hazelnut; and macadamia.

The review gives an overview of what is known about each of these tree nuts as allergens and presents a table identifying the relevant protein families, the allergenic component of the protein and the protein type for each of the above tree nuts except macadamia. Of the two major types of proteins in tree nuts, metabolic and storage proteins, it is the seed storage proteins that are most commonly associated with severe anaphylactic reactions.

Botanical relationships between the different tree nuts are described, helping to explain some instances of co-allergy where people may be allergic to more than one tree nut. Although peanut is botanically related to legumes and not to tree nuts, literature reports of co-allergy between tree nuts and peanut range between 20% and 68%.

Prevalence of tree nut allergy varies by age and geographic region. From studies that used oral food challenge as an objective definition of tree nut allergy, prevalence ranged from 0.1 to 4.3 per cent of the population. Prevalence appears to have increased in children over recent decades and only an estimated 10 per cent of cases resolve with adulthood. Those who have allergies to multiple tree nuts appear least likely to experience allergy resolution.

There is currently no data on the primary or secondary prevention of tree nut allergy and management consists of strict avoidance of the causal nut(s) and prompt treatment of symptoms upon accidental exposure. Medical advice is often focused on the decision to avoid all tree nuts or only those to which a patient is clinically allergic.

The review is published with open access in the March 2018 issue of the Journal of Asthma and Allergy.