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Asthmatics often suffer from depression and anxiety disorders. Why that is the case has now been investigated in twins. Now they also know the role genes are playing here.

As if it wouldn’t be enough that once in a while the bronchia narrow until breathing air becomes difficult, for instance when the bar is crowded at night with smokers or one has to rush for the bus. Sometimes panic accompanies asthma or the dark shadow of melancholia. There are hints that asthmatics suffer more often from depression and anxiety disorders than otherwise healthy people.

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Swedish scientists wanted to know whether asthma can be responsible for a psychiatric disorder, and what role genes may play here. Sandra Tendner and her colleagues (1) from the Karolinska Institute Stockholm evaluated for this the data from more than 25,000 monozygotic and dizygotic twins. And indeed, asthmatic twins suffered more often from depression and anxiety disorders. However, the next generation was not affected by the disorder of the air passage. Genes seem to not be responsible for it, and neither other familial factors. But maybe it is the disease itself that makes patients responsive.

For some time now, scientists noted an association between Asthma and psychiatric disorders such as depression and anxiety. But how this may occur remains a puzzle. Twin studies are ideal to find out the role genes may play. Since the gene pool of monozygotic twin pairs is identical to (nearly) 100%, while the agreement is only 50% in dizygotic twins.

The twins in the study were between 20 and 47 years old and were part of the Swedish Twin Registry. Some years ago a major part of them had provided health information in telephone interviews and online surveys. Patients and prescription registries provided further information. In poly-generational registries, the scientists found that the twins were parents of nearly 33,000 children. With their help, they wanted to investigate whether asthma maybe not only increases the risk of those affected by depression and anxiety disorders but also that of their off-springs.

Two issues draw their attention during the evaluation: of the 1,465 twins with a diagnosis of asthma, 25% also suffered from a severe depression and around 7% from an anxiety disorder. In contrast, of those 23,220 twins without asthma, only 15.5% had a depression and 3,6% an anxiety disorder.

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Genes seem to play a minor role here. Since when they compared to their twin pairs they noted a similar pattern, irrespective of whether twins were monozygotic or dizygotic. This was found to be also in agreement with the fact that children of depressive or anxious mothers were affected in only 6.7% of cases.

Other family factors could also be excluded to be responsible for these results. Scientists currently think that asthma itself makes people susceptible to develop depression and anxiety, e.g. via the immune system and the brain-body stress axis. Other factors that may play a role may be other diseases, whether and how frequently someone smokes, or the treatment of asthma. In fact, certain asthma medications may occasionally induce depressive episodes as adverse events. Altogether, the scientists noted, the number of asthma-affected twins was rather small and requires the results to be confirmed by further studies.

This is part 3 of a series covering twin health provided by Paul Enck from the Tübingen University Hospital and science writer Nicole Simon.

References:

Tedner SG, Lundholm C, Olsson H, Almqvist C. Depression or anxiety in adult twins is associated with asthma diagnosis but not with offspring asthma. Clin Exp Allergy 2016;46:803-12.

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