Are food allergies genetic? How to test for the most common food allergies?

A food allergy is a medical condition in which exposure to certain foods can trigger a harmful immune response. This allergic reaction occurs because the immune system attacks certain food proteins which are naturally harmless. In the US, an allergic reaction to food sends someone to the emergency room every 3 minutes. Efforts to establish a national awareness initiative regarding food allergies began decades ago by worried parents and family members who were concerned about the lack of advancement in food allergy research. Food Allergy Awareness month was established in 1998 and is celebrated every May, to raise awareness and inform, as well as provide support to the almost 250 million people affected by food allergies worldwide.

Food allergy vs food intolerance

Physical reactions to certain foods are common, but most are caused by a food intolerance rather than a food allergy [1]. Both food intolerance and food allergy can cause the same signs and symptoms.

However, a food allergy affects the immune system. Even small amounts of certain foods can trigger a range of symptoms, which can be severe or life-threatening. In contrast, food intolerance often affects only the digestive system and causes less serious symptoms.

Causes of food intolerance include:

• Absence of an enzyme needed to fully digest food, e.g., lactose intolerance
• Irritable bowel syndrome. This chronic condition can cause cramping, constipation, and diarrhea.
• Sensitivity to food additives, e.g., sulfites used to preserve dried fruit, canned goods, and wine can trigger asthma attacks 

What are the most common food allergies?

The most common types of food allergies are immunological responses to proteins found in cow-based milk, eggs, fish, shellfish, peanuts, tree nuts, soy, and wheat [2]. Although some food allergies, like those to cow-based milk, may be outgrown, those to foods such as nuts and shellfish are lifelong, and people affected should take the necessary precautions to avoid life-threatening reactions.

What are the symptoms of food allergies?

Because there is no cure, food allergies can only be managed by avoiding “trigger” foods and by quickly identifying and treating reactionary symptoms. Reactionary symptoms caused by a food allergy include [2]:

• Abdominal pain, diarrhea, nausea, or vomiting
• Hives, itching (rash), or eczema
• Shortness of breath
• Swelling of the face or other areas of the body
• Tingling in the mouth

The duration of the symptoms varies depending on the type of allergy and can range from a few minutes after exposure to a few hours or even a few days later. In severe cases, a food allergy can cause anaphylaxis. 

What are the causes and risk factors of food allergies?

In people with a food allergy, the immune system mistakenly identifies a specific food as harmful. When exposed to certain foods, the immune system triggers cells to release an antibody known as immunoglobulin E (IgE) to neutralize the allergy-causing food or food substance (the allergen) [3].

When consuming the food the next time, IgE antibodies sense it and signal the immune system to release a chemical called histamine, as well as other chemicals, into the bloodstream. These chemicals cause allergy symptoms. However, what causes the immune system to mistakenly perceive harmless proteins as a threat remains unclear.

Food allergy risk factors include:

• Family history. You’re at increased risk of food allergies if asthma, eczema, hives, or allergies such as hay fever are common in your family.
• Other allergies. If you’re already allergic to one food, you may be at increased risk of becoming allergic to another. Similarly, if you have other types of allergic reactions, such as hay fever or eczema, your risk of having a food allergy is greater.
• Age. Food allergies are more common in children, especially toddlers and infants. As children grow older, their digestive systems mature and their bodies are less likely to absorb food or food components that trigger allergies.
  Fortunately, children typically outgrow allergies to milk, soy, wheat, and eggs. Severe allergies and allergies to nuts and shellfish are more likely to be lifelong.

• Asthma. Asthma and food allergies commonly occur together. When they do, both food allergy and asthma symptoms are more likely to be severe.

Why is the prevalence of increased prevalence

According to the Centers for Disease Control and Prevention (CDC), the prevalence of food allergies has risen by 50% from 1997 to 2011. Notably, the prevalence of food allergies appears to be rising among children under the age of 18. There is no single explanation as to why the rates of food allergies are rising, but a few theories point to environmental factors related to Western lifestyles, pollution, dietary changes, and less exposure to microbes which alter the response of our immune systems. Additionally, as society becomes more aware of food allergies and better at diagnosing them, more numbers are reported.

What are the implications of food allergies?

Individuals with a food allergy and their families suffer a financial strain, as well as a heavy psycho-social burden. The annual cost of caring for children with a food allergy in the USA is estimated to 25$ billion. Some of the social and psychological challenges faced by these individuals include limited activities outside the home, social isolation, depression, panic attacks, and anxiety. The inadequacy of available treatment options is another factor causing anxiety to individuals and their caregivers.

How to diagnose a food allergy? Skin prick, patch test, and blood test

For someone to be diagnosed with a food allergy, an allergist is required to perform a specialized test. The test method used in each case varies. The most common test method used for food allergies is with a skin prick. This is used for allergens that have an immediate response. During the skin prick test, the doctor will place a series of drops containing potential allergens on the individual’s skin surface and pricks the skin. If there is an allergic reaction, the skin may start swelling and cause redness.

For allergens with a delayed response, a patch test can be used. During a patch test, the doctor will place tiny cups containing small amounts of pure food on the individual’s back and leave them for 48 hours. In cases where skin tests do not work, are considered unsafe, or are not available for a suspected allergen, a blood test is required. The doctor will check the patient’s blood sample for antibodies produced by our immune system against various potential allergens.

Genetics of food allergies

Studies suggest that there may be a genetic predisposition to the development of food allergies. There is compelling evidence that implicates environmental factors in the pathogenesis of these allergies, and one’s chances of having a particular type of allergy are increased if one’s parents are also affected by the same allergy.

Can food allergies be inherited?

A study by Sicherer et al. [4] showed that there was a concordance rate of nearly 65% in identical twins with a peanut allergy, which was higher than the less than 10% seen among dizygotic pairs. These results were in line with the findings of heritability among other allergic diseases such as allergic rhinitis, atopic dermatitis, and asthma.

Another study by Tsai et al. [5], found that most of the children in their investigation had some type of food allergy. They were able to identify genes possibly linked to peanut allergy suggesting that particular genomic regions harboring these genes on a particular chromosome pose a significant risk for the allergy. This was observed in approximately one-fifth of the population in their study.

In a genome-wide association study by Marenholz et al. [6], the largest of its kind in the world involving food allergies, researchers investigated about 1,500 children from the United States and Germany, who have food allergies. Over 5 million genetic variations were studied in the participants compared to controls. A food challenge test was done to establish a true food allergy to the reported food to rule out possible intolerance. This study was able to identify five loci that increase genetic susceptibility to food allergies. Of these five loci, four were strongly correlated with those associated with other types of allergies.

Conclusion

Living with a food allergy or having a family member with a food allergy causes an effect on the overall quality of life. Food allergies may have a genetic component, but allergy susceptibility appears to be influenced by genetic predisposition and environmental factors. It is important to remember that allergies within families may also reflect shared environmental conditions that contribute to the development of food allergies. There is still much to be done in terms of research establishing the link between genetics and food allergies, but contemporary data illustrates that greater clarity is on the horizon. This, in turn, will help with the optimization of management, and possibly even the prevention of food allergies. 

References

[1] Mayo Clinic. Food allergy vs. food intolerance: What’s the difference? Retrieved 28 November 2022 from https://www.mayoclinic.org/diseases-conditions/food-allergy/expert-answers/food-allergy/faq-20058538

[2] Healthline. The 8 Most Common Food Allergies. Retrieved 28 November 2022 from https://www.healthline.com/nutrition/common-food-allergies

[3] Mayo Clinic. Food allergy. Retrieved 28 November 2022 from https://www.mayoclinic.org/diseases-conditions/food-allergy/symptoms-causes/syc-20355095

[4] Sicherer SH et al. Genetics of peanut allergy: a twin study. J Allergy Clin Immunol. 2000 Jul;106(1 Pt 1):53-6. doi: 10.1067/mai.2000.108105. PMID: 10887305. https://www.jacionline.org/article/S0091-6749(00)71311-X/fulltext

[5] Tsai HJ et al. Familial aggregation of food allergy and sensitization to food allergens: a family-based study. Clin Exp Allergy. 2009 Jan;39(1):101-9. doi: 10.1111/j.1365-2222.2008.03111.x. Epub 2008 Oct 30. PMID: 19016802; PMCID: PMC2729087. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2729087/

[6] Marenholz I et al. Genome-wide association study identifies the SERPINB gene cluster as a susceptibility locus for food allergy. Nat Commun. 2017 Oct 20;8(1):1056. doi: 10.1038/s41467-017-01220-0. PMID: 29051540; PMCID: PMC5648765. https://www.nature.com/articles/s41467-017-01220-0