Allergies: they’re in our genes

Around a quarter of us will have an allergy at some point in our lives. With hayfever season on the way, we speak to one of our resident allergy experts, Professor John Holloway, on why allergies are on the increase and the influence our genes have.

Q So what exactly is an allergy?

An allergy is an immune response to a substance in the environment that is usually harmless; if you have hayfever, your immune system mistakes pollen for a harmful intruder, and ‘attacks’ it via an immune response. This immune response can cause a variety of symptoms, ranging from the runny nose and itchy red eyes we are all familiar with in hayfever to anaphylactic shock in very severe allergies.

Q Why are allergies on the increase?

Over the last five decades, there has been a steep rise in allergies in industrialised countries such as the UK, other countries across Europe and the USA. And now this is also happening in countries that are going through industrial development, such as Brazil.

We don’t know exactly why allergies are increasing, but there are a few theories. One is the ‘hygiene hypothesis’, which suggests that if our immune systems come into contact with a variety of micro-organisms early in development, that we will have fewer allergies in later life. And there is evidence for this – children who live on farms and are in contact with animals are less likely to have allergies, so there is something to say for letting your children play in the mud!

Another factor is genetics – if allergies run in your family, you are much more likely to have an allergy yourself. If both of your parents have an allergy, your risk of allergies rises by around 60 to 80 per cent. In my team, we are looking at the role of genes on allergies.

Q Can when you are born affect the allergies you may have?

Our research involves studying the epigenome, which is thought to control how the blueprint of DNA is expressed. Substances we are exposed to in our environment can affect our DNA; for example, in our previous research, we have shown that if a pregnant women smokes during pregnancy, this can cause changes to the offspring’s DNA, and these changes can persist into adulthood.

In our most recent research, we showed that specific markers on DNA link the season you are born to your risk of allergies in later life. We did this by analysing DNA samples from a large group of people born on the Isle of Wight. We found that particular changes to the DNA, known as epigenetic marks, were associated with season of birth and were still present 18 years later. By following up with the participants of the study over many years and asking them to fill in detailed questions about their health, we were able to link these birth season epigenetic marks to allergies. For example, we saw that people born in the autumn had an increased risk of eczema compared to those born in spring, and people born in autumn and winter had at increased risk of allergic diseases such as asthma.

This is an interesting finding, but we don’t yet know exactly why the time of year in which someone is born affects their risk of allergies. A couple of important factors could be the nutrients in the diet, such as vitamin D, and the amount of sunlight we are exposed to. We are hoping to do some further research to look into this. The effect we found is very small, so we aren’t recommending that people start altering pregnancy timing on the basis of these results. This study highlights the potential of the epigenome in explaining the biological mechanisms that link a range of environmental exposures in early life – not just season of birth, but potentially also diet, smoking and air pollution – to the risk of common diseases such as allergies.

Q What do you enjoy most about working at the University?

The collegiality – we have a great working environment and the ability to work with colleagues from across many different disciplines. This makes the University a great place in which to do this type of research that requires collaboration between scientists, clinicians and informaticians.

Find out more about John’s research.

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