Sibling data reveal genetic clusters across 22 autoimmune diseases

Autoimmune diseases arise when the immune system mistakenly attacks the body’s own tissues. Researchers have long known that these diseases tend to run in families, but the genetic relationships between different autoimmune diseases have remained unclear.

In the current study, researchers analyzed data from Swedish national registers. The material included more than 6.3 million individuals born between 1932 and 1983, including nearly 3.84 million sibling pairs. In total, 22 autoimmune diseases were studied from 1969 to 2013.

The researchers found that more than 707,000 individuals, or 11.2% of the study population, had at least one autoimmune disease. Around 1.3% had more than one such diagnosis.

The study is published in the Journal of Clinical Investigation.

No common genetic basis

By studying how diseases occurred among siblings, researchers were able to estimate the extent to which different diseases share genetic risk. The results revealed an extensive network of genetic connections between autoimmune diseases. At the same time, the study found no evidence that all autoimmune diseases share a strong common genetic basis.

Instead, distinct groups of related diseases emerged. Connective tissue diseases, endocrine autoimmune diseases and autoimmune gastrointestinal diseases each formed separate genetic clusters. Diseases affecting the nervous system, by contrast, showed weaker genetic links to one another.

“Previous knowledge of how autoimmune diseases are related has mainly been based on studies of individual disease pairs or smaller groups of the most common conditions. This study provides a much broader picture and shows, from a wider perspective, how different diseases share genetic risk,” says Jakob Skov, associate professor at the Department of Medicine, Solna, Karolinska Institutet.

Some of the strongest genetic associations were observed between psoriasis and psoriatic arthritis, autoimmune hepatitis and primary biliary cholangitis, and systemic lupus erythematosus and Sjögren’s syndrome. Multiple sclerosis stood out for having relatively weak genetic associations with most of the other autoimmune diseases included in the study.

“This knowledge may help increase awareness of the risk of related autoimmune diseases among patients and their family members,” Skov continues.

The researchers note that the study is based on a very large population data set, making it possible to investigate both common and rare diseases. One limitation is that the sibling model used cannot fully distinguish genetic factors from certain shared environmental factors.

The study was conducted by researchers from Karolinska Institutet, Uppsala University, the University of Gothenburg, Örebro University, Region Värmland and several international collaborators.

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