Understanding Peanut Allergy: Diagnosis, Cross-Reactivity, and Treatment Challenges

1. Peanut Allergy • 10% of children are sensitized but only 1-2% have symptoms • Usually life-long • Symptoms range from local reactions to anaphylaxis • Very small quantities can give symptoms

2. Doctor's challenges • Is it a genuine peanut allergy or are the symptoms caused by cross reactivity? • Is there a risk for systemic reactions? • Is strict avoidance necessary? • Is emergency medication needed? Genuine or due to cross reactivity?

3. Common clinical practice Patient At 6 years Anamnesis SPT to birch At 16 years Anamnesis SPT to peanut sIgE to peanut Diagnosis Advice Caroline, 16 years Rhinitis and conjunctivitis +4 Local reactions to peanuts +4 26 kUA/l Peanut allergy Avoid peanuts Emma, 16 years Rhinitis and conjunctivitis +4 Local reactions to peanuts +4 28 kUA/l Peanut allergy Avoid peanuts

4. Using components in clinical practice Patient Anamnesis Component testing Ara h 1 Ara h 2 Ara h 3 Ara h 8 Ara h 9 Diagnosis Advice Caroline, 16 years Local reaction to peanuts Pollen and peanut allergies kUA/l < 0.1 < 0.1 < 0.1 33 < 0.1 Pollen-associated peanut allergy Suitable for re-introduction Emergency medication unnecessary Emma, 16 years Local reaction to peanuts Pollen and peanut allergies kUA/l 2.1 12.3 3.3 10.3 < 0.1 Genuine peanut allergy Strict peanut avoidance Emergency medication necessary Improved diagnoses and altered advice

5. Peanut components

6. Peanut components

7. Peanut components Ara h 2 Ara h 1 Ara h 8 Ara h 9 Ara h 3 Latin name: Ara h = Arachis hypogaea

8. Peanut components

9. Peanut components

10. Peanut components Ara h 2 Ara h 1 Ara h 8 Ara h 3 Ara h 9 CCD Ara h 5 Latin name: Ara h = Arachis hypogaea

11. Risk assessment of peanut components

12. Risk assessment of peanut components

13. Ara h 1, Ara h 2, Ara h 3 • Peanut-specific markers • Storage proteins – proteins expressed in legumes, seeds and nuts • Present in high amounts • Stable and heat resistant proteins that may cause systemic reactions

14. Ara h 9 • A cross-reactivity marker, associated with allergy to peach and peach-related fruits • A Lipid Transfer Protein (LTP). • LTPs are present in plant foods (e.g. nuts and fruits), weed and tree pollen • Present in low amounts • Stable and heat resistant protein that may cause systemic reactions

15. Cross reactivity - peach and peanut Sensitization to Peanut Ara h 9 likely induced via sensitization to peach

16. Ara h 8 • Associated with allergy to birch and birch-related tree pollen • A PR-10 protein, homologous to the birch component Bet v 1 • Labile protein - mainly causing local symptoms • Present in low amounts

17. Cross reactivity - birch and peanut Sensitization to peanut Ara h 8 is likely induced via sensitization to birch

18. Ara h 5 • A profilin protein • Profilins are • highly cross-reactive • expressed in tree-, grass- and weed pollen, in plant-derived foods and latex • labile proteins, seldom associated with clinical symptoms • present in very low amounts

19. Sensitization frequencies and clinical reactions show geographical differences

20. Sensitization frequencies and clinical reactions show geographical differences

21. In conclusion

22. In conclusion

23. What does Molecular Allergology add? • Assess the risk for systemic reactions • Differentiate between genuine peanut allergy and pollen-related peanut allergy • Ensure relevant dietary advice and avoid unnecessary elimination

24. Extra slides

25. From the literature

26. Peanut allergens in Arachis hypogaea Arachis hypogaea = peanut