Allergies: Genetics... Nothing to be Sneezed at

For most, the first hints of summer mean it’s time to clean the barbeques, cry at the cost of suntan lotion and stock up the freezer with ice cream. However, for others, it means the start of itchy eyes, incessant sneezing, and scratchy throats. That’s right, its hay fever season. But why isn’t everyone affected? The answer may lie in genetics.

Hay fever is just one of several in a family of allergic conditions. Other members include asthma, eczema, and food allergies, and with 50% of children in the UK suffering from at least one of those conditions, allergies are the most common chronic disease in Europe.

Allergies themselves are caused when the body mistakes a harmless substance for a harmful one, triggering an immune response, with symptoms ranging from mild to life threatening. What is interesting, though, is that it appears that allergies can be passed through families. Indeed, when one parent experiences allergies, there is a 50% chance that their child will have allergies too, rising to 75% when both parents experience allergies. This is compared to a 20% chance when neither parent has allergies.  This has led scientists to believe that genetics may play a role.

However, to understand the role of genetics, we must first understand the mechanism behind an immune response driving an allergic reaction. I’ll use the analogy of a night club security team to help me explain. Normally, when a harmful foreign molecule enters the body, it is met by the body’s bouncers, called an antigen presenting cell. This bouncer decides that the molecule is harmful, restrains it, takes its specific ID and gives the ID to its manager: an immune cell, called a T-cell. The T-cell gets his head of security, another immune cell called a B-cell, who takes the ID of the harmful molecule and creates a protein, called an antibody, which will continuously scan the body (the nightclub) for that specific foreign molecule, in case it manages to sneak back in to cause harm. If the foreign molecule enters the body again, the antibodies recruit two special bouncers called a mast cell and a basal cell, which releases anti-inflammatory chemicals to fight against the foreign molecule, causing mucus secretion (runny nose), dilation of blood vessels (red eyes) and stimulate sensory nerves (feeling itchy), and generally causes the symptoms associated with an allergic reaction.

Now that we understand what happens when a harmful foreign substance enters the body, (like venom or bacteria) we can begin to understand why the body sometimes reacts to a harmless foreign molecule (like pollen, animal fur and some foods) by mistake. As with everything in the body, the immune system is created and controlled by genetics. It is genes which help the bouncer successfully decide whether a foreign molecule is harmful, and it is genes which make the antibodies to scan the body for the foreign molecule. Changes to the gene sequence, called mutations, happen naturally and randomly, with every human developing 50-90 non-harmful mutations over their lifetime. If one of these mutations occur in any of the genes which impact the immune response, this can put someone at a higher risk of developing allergies. Over the years, there have been over 1,000 published studies identifying many different genes associated with the development and severity of an allergic reaction. This means that allergies are a polygenic condition, where the cumulative effect of several genes cause the development and severity of the allergy.

However, genetics is not solely to blame for the development of allergies, because there is still a 20% chance of developing allergies even if no one in your family suffers from them. Therefore, like many things, the person’s environment also plays a role in allergy development. Air pollution, a ‘too-hygienic’ childhood, and several other environmental factors have also been linked to allergies.

Therefore, overall, there does appear to be a genetic cause in the development of allergies, but, like many things, environmental factors also play a role in the development and severity. It is, however, vital to continue to research the genetic components of allergies, which could become vital key in predicting allergy onset, as well as create a more personalised therapy technique to treat allergic reactions.

 

References

https://www.news-medical.net/health/Allergies-and-Genetics.aspx

https://www.youtube.com/watch?v=dU_4fAcKzEU

https://www.youtube.com/watch?v=llZFx8n-WCQ

https://www.jacionline.org/article/S0091-6749%2809%2901742-4/fulltext

https://www.allergyuk.org/information-and-advice/statistics

https://en.wikipedia.org/wiki/Mutation#Mutation_rates

 

Disclaimer

The information in this blog is for information and entertainment purposes only. I am not a medical professional, so I have never and will never give medical advice in this blog. You should always speak to a healthcare professional about your unique health needs. My opinions are entirely my own and do not reflect the organisations or people I work for. I only discuss published literature in this blog which are referenced with links.


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