Clinical Information

Allergies to tree nuts are relatively prevalent and can result in severe reactions. The main culprits in tree nut allergies include walnut, almond, pistachio, cashew, pecan, hazelnut, macadamia, Brazil nut, and pine nuts. Tree nut allergy often appears in young children and estimates of prevalence range from 0.1% to greater than 5% of the population, dependent on geographical region.

In the case of nut-induced allergic reactions, as with many other foods, symptoms usually present within minutes of ingestion. Over 80% of reactions to tree nuts involve allergy related respiratory symptoms. Tree nut allergies are one of the most dangerous types of allergic reaction with 20% to 40% of cases of related anaphylaxis and 70% to 90% of fatalities attributable to nut exposure, including peanut exposure.

Hazelnut allergy can occur upon ingestion as a systemic food allergy that can be associated with severe reactions or as oral allergy syndrome, often associated with pollen allergy (pollen-food allergy syndrome). It is the most common tree nut allergy in Europe. Sensitization to birch pollen is strongly associated with hazelnut sensitization with 84% of those with birch pollen allergy being sensitized to hazelnuts.

Components of hazelnut allergy can be used to stratify risk of severe systemic reactions. Hazelnut allergy can be severe or can be pollen related and less severe. The component protein Cor a 1 is heat and digestion labile and is often cross-reactive with birch pollen sensitivity due to cross-reactivity between homologous allergens of hazelnut and birch pollens (PR-10 proteins Cor a 1 and Bet v 1). Sensitization to Cor a 1 component protein is mainly associated with local reactions posing a lower risk of severe systemic reaction. Pollen-related hazelnut allergy is often observed in adults, with symptoms limited to the oropharyngeal cavity. However, systemic symptoms and even anaphylaxis have been infrequently reported with sensitivity to Cor a 1.

Cor a 8 is a heat and digestion stabile nonspecific lipid transfer protein that exhibits sensitization in 8% to 17% of hazelnut allergy cases in the United States, with high prevalence in areas that lack birch trees. Cor a 8 sensitization can be associated with clinically silent hazelnut tolerant individuals, oral allergy syndrome or in some cases severe allergy. Peach allergy may be associated with sensitivity for Cor a 8.

Cor a 9 and 14 are heat and digestion stable protein component that are associated with higher risks or severe, systemic reaction. Cor a 9 and Cor a 14 sensitization serve as excellent diagnostic markers for identifying direct hazelnut allergy and for prediction of potentially severe symptoms. Sensitization to Cor a 9 (a legume like globulin) was observed in 10% of hazelnut allergic individuals and has been established to be associated with severe systemic reactions. Other studies have put the sensitization rate or Cor a 9 to be as much as 35%. Cor a 9 may show crossreactivity to11S globulin protein components of walnut (Jug r 4), peanut (Ara h 3), Brazil nut (Ber e 2), soybean (Gly m 6), cashew (Ana o 2), almond (Pru du 6) and pistachio (Pis v 2).  Sensitization to Cor a 14 (a 2S albumin allergen) has been observed in 6% of allergic individuals and is associated with moderate and severe systemic reactions. Cor a 14 is highly heat and digestion resistant and serves as an excellent prediction for clinical allergy. Cor a 14 sensitization has been reported in 15% of individuals with severe symptoms, 5.6% of individuals with moderate symptoms, and 4% of those with localized symptoms. Its cross reactivity is limited to walnut (Jug r 1) and pecan (Car i 1) protein components. Cor a 14-sIgE determination was a better predictor of oral food challenge sensitivity than other hazelnut component allergens (Cor a 1, Cor a 8 and Cor a 9).