Food allergy series: Atopy, risk factors and frequency
- Food allergy generally refers to IgE mediated reactions in literature
- Other reactions can cause severe food reactions via different mechanisms
- Food allergy reacts to specific allergen following skin or mucosal contact (mouth, GI tract)
- Sensitization is when your body makes IgE to something.
- Allergy is when your body makes IgE to something and that thing makes you sick.
- Atopy is the tendency of a person to develop allergic diseases like asthma.
- The term “allergic march” describes progressive accumulation of atopic conditions starting in the first year of life.
- Allergic march usually begins with atopic dermatitis and progresses to allergic rhinitis, asthma, and food allergy.
- Severe eczema developed in the first six months of life is associated with increased risk of peanut, milk and egg allergies.
- Most food allergies are due to egg, cow’s milk, wheat, soy, shellfish, peanuts and tree nuts.
- 4% of children with food allergies have multiple food allergies.
- Children with multiple food allergies are most likely to have severe reactions.
- Adolescents ages 14-17 are more likely to have severe reactions.
- Peanut, cashews, walnuts and shellfish allergies are most likely to be severe.
- Largest studies on food allergy use patient reported information which is not the most reliable.
- Many people eliminate foods from their diets based upon suspicion of allergy. This is usually unnecessary.
- 89% of patients with atopic dermatitis were shown to have no reactions to suspect foods on oral challenge.
- 4% of US households had children with multiple food allergies.
- 3% of US households had children with history of severe allergic reaction.
- In Canadian households, 8% of people have food allergies.
- In Australia, 3% of children are allergic to peanuts and 8.9% are allergic to raw eggs.
- Risk factors for food allergies include:
- Atopy
- Low vitamin D
- Reduced consumption of omega-3 polyunsaturated fatty acids
- Reduced consumption of antioxidants
- Increased use of antacids
- Obesity
- Increased hygiene
- Delaying exposure to common allergens
- Family history of food allergies
- Specific HLA profiles
- Male children are more likely to develop food allergies.
- Black children are most likely to develop food allergies, followed by Asian children, then White children.
- Children of immigrants in the US are at higher risk than children of American born parents.
- People living in households earning more than $50,000/yr are more likely to be diagnosed with food allergies.
- Childhood allergies to milk, egg, wheat and soy are more likely to resolve.
- Childhood allergies to peanut, tree nut, fish and shellfish are more likely to persist.
MTHFR, folate metabolism and methylation
- MTHFR stands for methylenetetrahydrofolate reductase.
- MTHFR is an enzyme involved in folate metabolism.
- If there is not enough MTHFR, your body cannot break down enough folate.
- Some folate broken down by your body is used to methylate DNA.
- DNA methylation is one of the ways your body regulates which genes are turned on and off.
- A single nucleotide polymorphism (SNP) is a mutation in DNA sequence at one place.
- SNPs are very common.
- There are multiple known SNPs that can occur in the MTHFR gene.
- The two SNPs of interest in the MTHFR gene are called C677T and A1298C.
- C677T mutation is found in 10% of North Americans, most commonly Hispanics and those of Mediterranean descent.
- Having two copies of the C677T (called “being homozygous”) can cause mild MTHFR deficiency and result in too much homocysteine.
- Increased homocysteine has been studied in connection to many conditions but the results are inconclusive.
- A1298C mutation is not known to elevate homocysteine.
- A1298C mutation may cause deficiency of BH4, which is important in neurotransmission and formation of nitric oxide.
- There is no strong support in peer reviewed literature for the association of C677T or A1298C with disease. Many studies contradict each other.
- There is no known link between MTHFR mutations and mast cell disease.
- DNA methylation is one of the ways your body controls which genes are turned on and off.
- Methylation is important in cancer.
- Methylation of tumor suppressor genes causes them to be turned off, resulting in cancers.
Mast cells, heparin and bradykinin: the effects of mast cells on the kinin-kallikrein system
- The kinin-kallikrein system is a group of hormones that affect inflammation, blood pressure, coagulation and pain perception.
- It also affects the cardiovascular system, including cardiac failure.
- This system produces bradykinin.
- Bradykinin has many functions, including GI contraction, bronchoconstriction, induction of cell proliferation, collagen synthesis and release of many molecules.
- Bradykinin causes blood vessels to dilate, decreasing blood pressure.
- Bradykinin affects sodium excretion from the kidneys, further decreasing blood pressure.
- Bradykinin opposes the action of angiotensin II, which increases blood pressure.
- Mast cells release bradykinin and molecules to make it.
- Mast cells also release heparin, which can initiate bradykinin formation.
- Too much bradykinin causes angioedema.
- Mast cell degranulation occurs with physical trauma in part due to formation of bradykinin.
- Bradykinin induces release of histamine, serotonin and other molecules.
- Monophasic anaphylaxis is one episode of anaphylaxis symptoms.
- Biphasic anaphylaxis is a second episode of anaphylaxis symptoms after resolution of symptoms.
- Late onset anaphylaxis occurs several hours after exposure to trigger.
- Protracted anaphylaxis is a long episode of anaphylaxis symptoms despite treatment.
- Higher doses of corticosteroids may decrease incidence of second phase.
- Studies on frequency of biphasic anaphylaxis differ on rate of incidence, but most report around 20% of patients have biphasic anaphylaxis.
- Second phase can occur over a day after the first.
- Biphasic patients had longer lasting initial anaphylaxis reactions.
- Biphasic patients statistically receive less epinephrine for the initial reaction, which may result in the second reaction.
- Delay in administration of epinephrine, inadequate dosing of epinephrine and need for large doses of epinephrine make biphasic anaphylaxis more likely.
- Previous cardiovascular history, older age and use of beta blockers are risk factors for biphasic reactions.
- Oral ingestion of trigger makes biphasic reactions more likely.
- Not clear if mastocytosis patients are more likely to experience biphasic reactions.
- Throat symptoms are common in MCAS.
- MCAS reactions can cause inability to swallow or breathe due to angioedema.
- Breathing difficulty requires epinephrine.
- Low level difficulty of breathing (feeling like you can’t get a deep breath) is the most common MCAS respiratory symptom.
- Chest x-ray and pulmonary function testing are usually normal in MCAS patients.
- Prostaglandin D2 is a potent bronchoconstrictor.
- Allergic asthma is not uncommon in MCAS.
- Inhalation can cause anaphylaxis.
- There have been cases of patients who can ingest a food but react to inhalation, such as Baker’s asthma.
- Fragrance is one of the top five allergens in North American and European countries.
- Fragrance allergy can cause skin, eye and respiratory problems.
- Perfume can cause asthma and other respiratory problems through an unclear mechanism.
- A significant portion of the population reacts adversely to scented products, even when worn by others.
- 5% of general population found scented products on others to be irritating.
- 19% had symptoms from exposure to air fresheners.
- 9% had symptoms from exposure to scented laundry products.
- Essential oils can cause allergic reactions regardless of the purity.
- Some essential oils have been tied to severe allergic reactions, such as clove oil.
- Oils of citrus fruits liberate histamine and cause mast cell symptoms.
- In mast cell patients, scents can cause severe full body reactions that are potentially life threatening or fatal.
- MCAS patients may experience many types of pain.
- Bone pain, osteopenia and osteoporosis are common in MCAS.
- Joints and soft tissues are often painful.
- Mast cells are involved in chronic lower back pain and complex regional pain syndrome.
- Serotonin can amplify pain signals in chronic pain.
- Increased serotonin and mast cell counts are found in some patients with chronic abdominal pain.
- 95% of body serotonin is found in the peritoneal cavity.
- Tricyclic antidepressants inhibit serotonin release and are sometimes used for abdominal pain.