Allergies are autoimmune conditions that can be hard to diagnose and classify, because there are different kinds of allergies, such as
Pollen Food Allergy Syndrome and
Non-IgE allergies. These different allergies may have different genes associated with them, so it is challenging to find study participants who have the same type of allergy.
The current consensus is that some people have a genetic predisposition for allergies, which means they inherit the tendency to develop allergies from their parents. Other people have allergies that are influenced by environmental factors, such as air pollution, pollen exposure, or illness.
The risk of having an allergy is 50% higher if one parent has an allergy, and 75% higher if both parents have an allergy. However, the specific type of allergy is not inherited, so a person can have a different food allergy than their sibling or parent. For example,
peanut allergy is more likely to be specifically inherited than other food allergies.
Some of the most frequently researched genes related to allergies are FLG, HLA, and IL13. These genes have different versions (not necessarily mutations) that can make a person more prone to developing allergies.
FLG is the gene that makes filaggrin, this is a protein found in the outer layers of the skin and any loss of function of this can result in an increased likelihood of allergic sensitisation through the skin.
HLA is the gene that makes human leukocyte antigens. These antigens are proteins which are found on the cell surface and detect antigens (any protein, bacteria or virus that your immune system does not recognise as part of itself and needs to make antibodies against) in those with a normal immune system. Some variants of this gene are linked to allergies to pollen, food, and Pollen Food Allergy Syndrome.
IL13 is the gene that makes interleukin 13. IL13 is a cytokine (cytokines are proteins which control the growth of blood and immune cells) which helps fight infections by causing inflammation in the mucous membranes. However, some people with different variants of this gene have abnormal responses to allergens such as food or pollen, and their immune system overreacts. This gene is associated with asthma and eosinophilic disorders.
This is not a complete list of genes that are involved in allergies, as new studies and discoveries are constantly being made. However, it is difficult to pinpoint exactly which gene variants are responsible for causing allergies, because allergies are complex and vary from person to person.
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