Q:

9/9/2013  
I recently saw a 17 month-old boy with confirmed allergy to flaxseed by Immunocap RAST. There is no evidence of milk allergy. He has not been exposed to any other seed. Would you recommend he be tested to other seeds?

A:

Thank you for your inquiry.

Flaxseed contains at least five or six different allergens, and the major one may be a dimer consisting of a pair of 28 kDa monomers that are held together by disulfide bonds. It has been suggested that the allergen is malate dehydrogenase (MDH-1) (see Reference Numbers 1 and 2 below). Although anaphylaxis to linseed was first described in the 1930’s, there have only been a handful of reports since then (see Reference Numbers 3 and 4). This may explain why there is a dearth of information regarding the potential cross-reactivity between flaxseed and other allergens, including other seeds. To my knowledge, and according to a search of the literature, there has only been one article investigating this potential cross-reactivity (the abstract of this article is copied for you below).

Based upon this single article, there is rather limited cross-reactivity, and if one did check for such cross-reactivity, it would probably be sufficient, according to the present state of our knowledge, to look at only those allergens which were found to be cross-reactive in this article.

Nonetheless, as you know, the simple presence of specific IgE against a potentially cross-reacting antigen would not necessarily mean that your patient would react clinically to this allergen. Thus, interpretation of these results must be guarded. Nonetheless, a negative test for specific IgE would give some reassurance that your patient could ingest that food without difficulty.

Thank you again for your inquiry and we hope this response is helpful to you.

References:
1. Lezaun A, Fraj J, Colas C, Duce F, Dominguez MA, Cuevas M, Eiras P. Anaphylaxis from linseed. Allergy 1998; 53(1):105-6.
2. Leon F, Rodriguez M, Cuevas M. The major allergen of linseed. Allergy 2002; 57(10):968.
3. Alonso L, Marcos ML, Blanco JG, Navarro JA, Juste S, del Mar Garces M, Perez R, Carretero PJ. Anaphylaxis caused by linseed (flaxseed) intake. J Allergy Clin Immunol 1996; 98(2):469-70.
4. Leon F, Rodriguez M, Cuevas M. Anaphylaxis to Linum. Allergol Immunopathol (Madr) 2003; 31(1):47-9.

Abstract:
Eur Ann Allergy Clin Immunol. 2010 Jun;42(3):103-11.
Prospective study of sensitization and food allergy to flaxseed in 1317 subjects.
Fremont S, Moneret-Vautrin DA, Franck P, Morisset M, Croizier A, Codreanu F, Kanny G.
Source
Laboratoire de Biochimie et Biologie Moléculaire, Hôpital Central, Nancy.
Abstract
Background: Foods containing flaxseed proteins rich inpolyunsaturatedfatty acids are new on the market.
Objectives: In a population of patients attending the allergology department, we evaluated the frequency of sensitization to flaxseed, characterized allergens and looked for modifications related to industrial processing.
Methods: Natural, heated and extruded flaxseeds were tested using prick-in-prick tests (PIP using the fresh seed), SDS PAGE, immunoblots, immunoblot inhibition and Fourier Transform Infrared (FTIR) spectroscopy.
Results: PIP tests to natural flaxseed were positive in 5.8% of the 1317 patients. 73 of 77 PIP-positive patients were atopic. There was cross-reactivity with five seeds. peanut, soybean, rapeseed, lupine and wheat, and with rape pollen. Immunoblot inhibition by bromelain confirmed the presence of specific IgE to cross-reactive carbohydrate determinants (CCD). 0.15% of this population presented with food allergy to flaxseed and positive PIP to heated and extruded flaxseed. Two sera showed that clinically relevant allergens in industrial products had MW between 25 and 38 kDa. Sensitization to processed flaxseed characterized only the allergic subjects. FTIR spectroscopy showed major modifications in 3 and alpha structures following industrial processing.
Conclusion: Positive prick tests to natural flaxseed were mainly due to cross-reactions. Flaxseed allergy is rare and could be detected by PIP to heated extruded flaxseed. Increasing consumption calls for monitoring of clinical risk.

Sincerely,
Phil Lieberman, M.D.

AAAAI - American Academy of Allergy Asthma & Immunology