50 new genes for eye colour discovered

11th March 2021

Women looking into camera

The genetics of human eye colour is much more complex than previously thought, according to a new study published today.

An international team of researchers led by King’s College London and Erasmus University Medical Center Rotterdam have identified 50 new, previously unknown genes for eye colour in the largest genetic study of its kind to date. The study, published in Science Advances, involved the genetic analysis of almost 195,000 people across Europe and Asia.

These findings will help to improve our understanding of eye diseases such as pigmentary glaucoma and ocular albinism, where eye pigment levels play a role.

In addition, the team found that eye colour in Asians with different shades of brown is genetically similar to eye colour in Europeans ranging from dark brown to light blue.

This study builds on previous research in which scientists had identified a dozen genes linked to eye colour, believing there to be many more. Historically, scientists thought that variation in eye colour was controlled by one or two genes only, with brown eyes dominant over blue eyes.

Co-senior author Dr Pirro Hysi, King’s College London, said:

 “These findings are exciting because they bring us to a step closer to predicting with a high degree of confidence the colour of the eyes based on DNA information alone. In certain circumstances, that could allow parents to predict the eye colour of their future children, based on the parents’ genetics. But these findings will also be important and tremendously improve our understanding of many diseases that we know are associated with specific pigmentation levels.”

Co-senior author Dr Manfred Kayser, Erasmus University Medical Center Rotterdam, said:

“Amongst other relevancies, this study delivers the genetic knowledge needed to improve eye colour prediction from DNA as already applied in anthropological and forensic studies, but with limited accuracy for the non-brown and non-blue eye colours.”

27 years of seeing double

17th September 2019 – by Paz Garcia

Every four years since 2000, identical twins Tracey and Julia make a trip to St Thomas’ Hospital in London. But they don’t go for treatment – they go to meet researchers who are working to make new treatments possible for others.

Tracey and Julia are two out of more than 14,000 twins who take part in TwinsUK, a study which follows twins throughout adulthood to understand how various health conditions develop and the genetics behind them.

They signed up to TwinsUK after a former colleague mentioned it to them, as Julia explained:

“My sister Tracey convinced me to sign up to TwinsUK. One of Tracey’s work colleagues mentioned the study to her as she’d signed up with her twin. After reading an article in Woman’s Own magazine, we both joined TwinsUK 6 months after the initial launch.”

Julia and Tracey

Studying twins

How can we tell whether a particular condition is due to genetics and/or our environment and lifestyle? The answer of course is twins.

Professor Tim Spector is the Director of TwinsUK. What started as an arthritis study with a few hundred twins in 1992 turned into what we now know as TwinsUK – a long-term study of 14,000 twins.

Professor Spector explained the reasoning behind studying twins:

“Twins are the perfect experiment. Identical twins have identical genes. Non-identical twins, or “fraternal” twins, only share half their genes with each other. We can make comparisons to work out to what extent nature or nurture cause different conditions and diseases.”

When both twins in a pair have the same condition, researchers say they are ‘concordant’. If only one twin in a pair has the condition and the other doesn’t, they are ‘discordant’. Researchers can then design studies which take advantage of twins’ unique set-up.

For example, if more identical twin pairs are concordant for a particular condition than non-identical twins, then that condition is likely influenced to a greater extent by genes than by the environment.

Conversely, if identical twin pairs are discordant for a particular condition, then researchers can investigate whether other aspects such as their environment or lifestyle may have a stronger influence on the development of the condition.

That’s not all twins can do. TwinsUK is uniquely placed to identify the molecular systems underpinning health and development of disease. The sheer volume of data TwinsUK collects means that their twins are amongst the most studied in the world. TwinsUK holds hundreds of thousands of pieces of information. Genetics, age, weight, blood pressure, bone density, gut bacteria, blood cell counts – you name it, they have it. As if that wasn’t enough, TwinsUK now wants to ramp up data collection and explore personal, social and ambient environmental influences in more detail. This includes studying the impact of things such as physical lifestyle, pollution, pesticides and inequality.

The researchers are not trying to answer one big question with all this data. They’re working in a wide range of areas such as ageing, type 2 diabetes, back pain and sensory impairment, to answer lots of different questions about health and how conditions develop throughout the life course of an adult. All of the work brings us closer to understanding how the human body works – in sickness and in health.

Sharing is caring

TwinsUK doesn’t carry out their work alone. Considering the enormous amount of data collected, it wouldn’t be possible, and there are lots of other researchers and specialists who want to take a closer look at the data as part of their own research.

Dr Claire Steves, Deputy Clinical Director for TwinsUK explained:

“It’s important that we share our data with other health researchers so that we can make the best use of it. It’s only fair to the twins – after all, it would be unethical not to get the most value out of the samples and health measures they so generously provide.”

To this end, the TwinsUK Resource Executive Committee has approved more than 800 data sharing requests, covering 150,000 samples shared with 100 collaborators. This means that even years after it was collected, the twins’ data and samples continue to be used to advance health research for everyone.

That’s not where the sharing ends either. TwinsUK has contributed to more than 850 scientific publications as well, ensuring that the results of health research carried out using the twins’ data and samples are made available to other researchers around the world.

Looking ahead, TwinsUK has ambitions to work more closely with other cohort studies, particularly other twin studies. This will encourage more cross-cohort work, and researchers will be able to learn from each other – which can only be a good thing for health research.

The twin experience

Sharing data and publishing the results of research however are the end products of a research process that starts with the twins. Central to TwinsUK are the twin visits, where pairs of twins come into St Thomas’ Hospital for a full day of mental and physical health checks and tests. In addition, twins may be offered the chance to take part in specific studies that TwinsUK is carrying out at that time.

“The visits up to St Thomas’ have been interesting and revealing. It’s great that you have the opportunity to help with research, from taking vitamin supplements, which helped with research into eye problems, to having MRI scans to check the brain,” mused Tracey.

Some of the tests may be unusual, but that doesn’t deter Julia:

“The studies and tests are also very safe. The fact that any procedures and studies are carefully and intricately explained makes me feel relaxed about what’s going to happen. It’s always interesting and sometimes fascinating or even surprising to hear the results of the studies.”

Tracey added:

“Finding out we were tone-deaf was surprising, but answered a few questions as to why music always sounded perfect!”

The twins do receive some health test results, but most take part to help with research, like Julia:

“Personally, I feel honoured to be a part of TwinsUK and if the studies my twin and I take part in can help make a difference to other people’s health then that has got to be a good thing.”

Looking ahead

The TwinsUK team has no intention of slowing down. TwinsUK wants to remain at the cutting edge of scientific cohort studies, and so the team are looking to expand: their connections, their data collection, and most importantly, their registry.

Whereas up until now TwinsUK has only studied adults, they recently received permission to recruit and study twins all the way from birth. This adds another dimension to the research programme, and will help researchers understand how diseases develop throughout the whole life course of a person.

Dr Deborah Hart, Executive Director:

“We’re really excited to be opening up TwinsUK to more people. Like Tracey’s work colleague, if you’re a twin and know some twins who would be interested, do point them towards us.”

And for anyone thinking about signing up, Tracey has a few words of encouragement:

“The staff and twins that you meet have been amazing. I can honestly say it’s been lovely taking in part with the research, and I’ve made lovely friends and memories along the way.”

TwinsUK is currently recruiting same-sex identical and non-identical twins over the age of 18. We will soon begin to recruit under 18s. Find out more on twinsuk.ac.uk/twinzone or call the team on 020 7188 5555.

Read the paper here – TwinsUK: The UK Adult Twin Registry Update

TwinsUK is funded by the Wellcome Trust, Medical Research Council, European Union, the National Institute for Health Research (NIHR)-funded BioResource, Clinical Research Facility and Biomedical Research Centre based at Guy’s and St Thomas’ NHS Foundation Trust in partnership with King’s College London.

Do different types of cells in fat matter in health research?

28th May 2019 – by Paz Garcia

Cartoon of doctor measuring person's waist

The variability of cell types found in fat are partly under genetic control and need to be taken into account in health research, according to new TwinsUK research.

Fat is made up of a variety of different types of cells, including ones that store fat and others that form the immune system.

Researchers from the Department of Twin Research and Genetic Epidemiology investigated the mixture of cells that make up fat in samples from over 1,000 donors.

The work was published in the American Journal of Human Genetics.

Why did they do this research?

While we may not usually think of it in such terms, fat is actually the largest organ in the body that releases hormones.

We know that fat plays a role in the development of various health conditions such as heart disease and type 2 diabetes. Many researchers have therefore focused on studying fat.

Researchers however have largely not considered the proportions of the different types of cells in fat in their analyses.

The TwinsUK team therefore decided to investigate the different types of cells present in fat.

What did they do?

The researchers analysed fat samples collected from 766 twins from TwinsUK and 326 donors from another study.

The team used computational methods to estimate the relative proportions of four different types of cells in each fat sample.

They also looked at whether the proportions of cells were genetically inherited and linked with traits of obesity.

What did they find?

There is a lot of variation between people in the proportions of different cells they have in their fat.

The team found that proportions of cell types in fat is genetically inherited and is linked to body fat distribution.

What does this mean?

Researchers studying the links between fat and health conditions will need to take into account the variety of different cells present in fat. Dr Craig Glastonbury, first author on the study, explained:

“Our results indicate that it is critical to account for cell-type composition on a range of standard analyses.”

In addition, the findings could help us understand why some people are at greater risk of certain conditions. Dr Kerrin Small, who worked on the study, explained:

“The results suggest that some people are genetically predisposed to have more cells that store fat, which could lead to greater fat accumulation and greater risk of conditions like heart disease and type 2 diabetes.”

What’s next?

In their paper, the researchers say that more research will be needed to understand the relationship between genetics, cells in fat and the impact on health and disease.

Body or brain behind back pain?

22nd February 2019 – by Paz Garcia

Wooden mannequin with arm on back

Back pain may be caused through the body or through the brain, according to the results of a new genetics study.

The international team, which included researchers from King’s College London, studied the genetic information of over 500,000 people.

They found genetic links between back pain and some of its known risk factors, such as depression, sleep disturbance, obesity and smoking.

Overall, the results highlight the complexity of the genetics behind back pain.

Why did they do this research?

Back pain is very common, and many adults will experience it during their lives. About one in ten people however go on to develop chronic back pain, which can be debilitating and affect people’s quality of life and ability to work.

Previously the team had identified genes linked to chronic back pain. The researchers therefore decided to carry out a much larger study, to get a better understanding of how genes are linked to back pain.

What did the team do?

The researchers used data from two existing research programmes.

The team analysed the genetic data of 509, 070 people who indicated they were experiencing back pain, and examined the links between back pain and known medical and social risk factors.

What did they find?

The team identified two further genes linked with back pain.

The researchers also found genetic links between back pain and depression, sleep disturbance, obesity and smoking, which are known risk factors for back pain.

Based on their findings and further analysis, the researchers proposed two key routes through which back pain may start.

One route was through the vertebrae – disks – that make up the backbone. The other route was through how people perceive and process pain.

What does this mean?

These results support what we currently understand about back pain. The findings will also help researchers and healthcare professionals develop strategies to treat and prevent back pain.

Dr Maxim Freidin, who led the study, explained:

“This study continues our ongoing efforts to identify genes underlying back pain.

“One of the most striking finding is shared genetic component of back pain with many other traits such as obesity, depression and anxiety, social and demographic factors. These traits co-occur with back pain and are considered as its risk factors.

“By identifying shared genetics for back pain and these traits, we provide evidence that this co-occurrence has strong biological ground. In turn, this finding may help identify causal links between back pain and its risk factors.”

Watch the short animation below to find out more about our back pain research.

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