How likely are twins to develop type 1 diabetes?

Posted on 02 August 2018

Female twins lying down with their legs up, wearing matching outfits.

Twins of people diagnosed with type 1 diabetes are much more likely to develop the condition within three years than other siblings, according to the results of a recent study.

This was true of both identical and non-identical twins who were already known to be at high risk of developing type 1 diabetes.

Researchers analysed 288 identical twins and 630 non-identical twins, amongst 48,000 siblings of people living with type 1 diabetes.

These results come from the long-term TrialNet programme, which JDRF helps to fund. TrialNet is an international network of researchers dedicated to preventing type 1 diabetes.

Why did they do this research?

Family members of people living with type 1 diabetes have a roughly 1 in 20 chance of developing the condition, compared with a 1 in 300 chance in the general population. Previous work suggests that twins in particular are very likely to develop type 1 diabetes if the other twin has the condition, although estimated rates have varied.

As part of their work, TrialNet offers risk screening for close family members of people diagnosed with type 1 diabetes.

The body forms immune proteins known as autoantibodies before type 1 diabetes develops. Having more than one type of autoantibody indicates that the person is quite likely to develop type 1 diabetes.

One aim of this particular study was to investigate the risk of developing type 1 diabetes in twins and siblings who have one or more autoantibody/ies.

What did they do?

TrialNet researchers collect blood samples from participants at the initial screening and then once or twice a year to check for the presence of high-risk immune proteins that precede type 1 diabetes.

In this analysis, the team looked at whether siblings of people with type 1 diabetes had autoantibodies in the initial screening and how many types. The researchers then checked how many of the participants developed type 1 diabetes within three years.

What did they find?

If they had multiple autoantibodies at the initial screening, identical twins had a 69% chance, non-identical twins a 72% chance and other siblings a 47% chance of developing type 1 diabetes within three years.

The risk of developing type 1 diabetes was generally lower in those who only had one type of autoantibody initially, with a 69% risk for identical twins, 13% for non-identical twins and 12% for other siblings.

What does this mean for type 1?

These results reinforce previous findings that twins are at greater risk of developing type 1 diabetes than other siblings.

The average age for initial screening was 11 however, and so these results may not be applicable to twins diagnosed at all ages.

In their paper, the researchers suggest that the difference in risk for twins versus other siblings might be due to differences in what they’re exposed to. Twins share the same environment in the womb and almost exactly the same environment shortly after birth. Other siblings however experience the womb and external environment at different times from each other, and so are exposed to different things, which might alter the risk of developing type 1 diabetes.

What’s the next step?

The researchers note in their paper that this study covered a relatively brief period of three years, and that it would be useful to continue following this group of participants to see how the risk of developing type 1 diabetes changes over longer periods of time.

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