Twinning In Twins: A Diagnosis Seldom Comes Alone 

Double and triple sickness – some chronic conditions often occur together. Scientists have now investigated whether genetic material lies behind this; among other things, they looked at twins. 

They are among the most powerful diseases. One in five people in Europe suffer from chronic pain, one in 15 will suffer from severe depression this year, and more than half of all deaths in the EU are due to cardiovascular disease. Taken on its own, therefore, each of these diseases causes a great deal of suffering. But as it turns out, these diseases in particular often occur together.

So far, scientists can only answer in part why this is the case. It is known that age, gender, and social environment can increase the likelihood of suffering from one or more chronic diseases. But what about other factors? Scientists from the University of Dundee, the University of Oxford, and King’s College London have now discovered that genes are also involved.

For their study (1), the researchers worked with two large cohorts: The Generation Scotland with its more than 24,000 participants, and also with almost 3,000 female twins of the TwinsUK cohort. In the Scottish cohort, the scientists first looked at how often chronic pain, depression, and heart complaints occur individually or together in the subjects. They then compared the data with the results of siblings. They tried to calculate factors that could influence the result. These included age, gender, education, or the fact that someone smokes a lot.

The researchers found that anyone from Generation Scotland who suffered from one of the three diseases also had a higher risk for one or both other diseases. People with depression in the study were more than twice as susceptible to chronic pain as people without depression. For people with angina, the risk even quadrupled. And those suffering from depression and heart problems were nine times more likely to suffer from chronic pain.

In addition, the siblings of patients with one of the diseases were more likely to suffer from one of the other two diseases than unrelated persons. For example, if your own brother or sister had heart problems or depression, your risk of chronic pain increased. The result remained significant even then when the researchers adjusted the results with regard to the age of the subjects and their social environment. This speaks for a strong influence of genes.

Using the TwinUK data, the scientists now also examined the role of the genetic material in twins. The researchers compared identical and fraternal siblings. This is because the genome of identical twins is almost 100 percent the same, compared to as that of non-identical twins. In fact, the researchers’ data confirmed that genes contribute to the co-occurrence of chronic pain and heart diseases in twins. However, the comparison of the twins also shows that environmental influences must also be responsible for this — probably those that are shared by the twins, such as family environment, for example — as well as factors and experiences that only have an influence on one of the twins.

For Blair Smith, Professor of Population Sciences at Dundee’s School of Medicine, the results shake the existing picture of chronic diseases. They show for the first time that genes are not only important for determining the risk of chronic diseases, but also for the simultaneous occurrence of other impairments, as he points out in a press release from his university. Their results would indicate that these and perhaps other chronic diseases share biological causes.

Further investigations would now have to try to find the genes responsible for this.

This is part 21 of a series covering twin health provided by Paul Enck from the Tübingen University Hospital and science writer Nicole Simon. Further studies in twin research can be found at TwinHealth website. Translation was done with the assistance of DeepL translator.

Reference:

1. van Hecke, Hocking LJ, Torrance N, Campbell A, Padmanabhan S, Porteous DJ, McIntosh AM, Burri AV, Tanaka H, Williams FM, Smith BH. Chronic pain, depression and cardiovascular disease linked through a shared genetic predisposition: Analysis of a family-based cohort and twin study. PLoS One. 2017 Feb 22;12(2):e0170653.