Peanut allergy is a serious and relatively common food hypersensitivity for which there is currently no cure. Could genetic engineering provide a solution by producing hypoallergenic nuts?
What is peanut allergy?
Current estimates suggest up to 1.8% of school-entry age children are allergic to peanuts (Peanut Allergy UK). The severity of the condition can vary from mild stomach pains or a rash to anaphylactic reactions. Severe attacks can be life-threatening, and can be initiated by contact with a very small amount of the offending food.
An allergic reaction occurs when the body is stimulated to mount an immune response to a specific molecule known as an allergen. Most immune responses are effective in killing sources of infection, thus protecting our body from disease. However, in allergies the immune response is triggered by an otherwise harmless protein. Allergic reactions are referred to as hypersensitivity reactions, and may themselves cause damage to the body.
There is currently no cure for peanut allergy; management of the condition involves avoidance of foods containing allergens, and precautionary steps such as carrying an Epipen for rapid administration of adrenaline should an anaphylactic reaction occur.
What are the allergens involved?
So far, eight peanut allergens have been officially recognised as capable of inducing a hypersensitivity reaction in peanut allergy sufferers. They are named Ara h 1 through to Ara h 8. Ara h 1 and Ara h 2 are the most highly allergenic, and antibodies to these two allergens are found in a large proportion of sufferers (Burks et al, 1995). Most of these allergens are seed storage proteins, the function of which is believed to be the provision of a source of nitrogen for the developing plant ( European Bioinformatics Institute database). Seed storage proteins do not appear to be expressed anywhere else in the plant other than in the seed.
One possible reason why allergens may cause an immune response is their resistance to digestive enzymes and thermal breakdown. Many studies have been conducted to demonstrate this, including an experiment by Maleki et al (2000) in which Ara h 1 was subject to treatment with gastrointestinal enzymes. This produced large proteolytic fragments capable of evoking an immune response.
Possible genetic modification
The genes coding for allergens in the peanut plant could be rendered non-functional by genetic engineering techniques. In a study by Herman et al (2003), a technique involving introducing antisense RNA copies of an allergen gene into soybean plants was used. The RNA completely blocked the expression of the allergen in the altered plants, meaning the seeds produced would not cause an immune response in allergy sufferers. More importantly, the transgenic plants showed no obvious differences in growth, development, reproduction and seed maturation.
Research is currently underway using a different technique known as post-transcriptional gene silencing (PTGS) to alter peanut plants with a view to suppressing expression of the allergen Ara h 2. In this technique a new truncated copy of the Ara h 2 gene is introduced, and expression of this should lead to the degradation of the truncated and the endogenous mRNA coding for Ara h 2, resulting in no allergen being produced in the plant. Results from these studies are not yet available.
Could genetic modification be the answer?
Engineering transgenic peanut plants which produce hypoallergenic peanuts may well be possible. However, with such a large number of allergens implicated in the condition it seems unlikely this will provide a complete solution to the problem ( Burks, 2008). Altering the genome of the peanut plant to remove or neutralise sufficient allergens is likely to result in so many changes that the new transgenic plant may not be viable, and in any case will be so far removed from the original as to be no longer a peanut. However, it is possible that smaller changes might result in less allergenic nuts which may reduce the level of sensitivity of sufferers in the future.
Sources
MP de Leon, JM Rolland, RE O’Hehir “The Peanut Allergy Epidemic: Allergen Molecular Characterisation and Prospects for Specific Therapy” Expert Reviews in Molecular Medicine 9 (2007)
H Dodo, K Konan, O Viquez “A genetic Engineering Strategy to Eliminate Peanut Allergy” Current Allergy and Asthma Reports 5:27-73 (2005)
EM Herman, RM Helm, R Jung, AJ Kinney “Genetic Modification Removes and Immunodominant Allergen from Soybean” Plant Physiology 132:36-43 (2003)
AW Burks “Peanut Allergy” Lancet 371:1538-1546 (2008)
AW Burks, G Cockrell, JS Stanley, RM Helm, GA Bannon “Recombinant Peanut Allergen Ara h 1 Expression and IgE Binding in Patients with Peanut Hypersensitivity” Journal of Clinical Investigation 96:1715-1721 (1995)
SJ Maleki, RA Kopper, DS Shin “Structure of the Major Peanut Allergen Ara h 1 May Protect IgE-Binding Epitopes from Degradation” The Journal of Immunology 164:5844-5849 (2000)
Peanut Allergy UK website
“IPR006044 11-S seed storage protein, plant” European Bioinformatics Institute
Read on:
The Development of Hypoallergenic Foods for Soybean Allergy
Veronica Mitchell - Veronica studied veterinary medicine at Cambridge University before becoming a secondary school science teacher. She enjoys writing about ...
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