A study published in Scientific Reports, and publicized by the Global Down Syndrome Foundation, is changing the perception of Down syndrome as a brain disorder and categorizing it as immune system dysfunction instead.

According to Joaquin Espinosa, executive director at the Crnic Institute for Down Syndrome who also worked on the study, intellectual disability related to Down syndrome may be the result of a hyperactive immune system.

The study looked at the blood protein levels of people with and without Down syndrome and found that those with Down syndrome have higher protein levels. The extra chromosome that leads to Down syndrome, a third copy of chromosome 21, encodes for certain proteins that are part of immune system regulators.

One such immune system regulator is interferons. Interferons interfere with viral infections in the body and stimulate the entire immune system to fight off an infection. Interferons are typically only activated in the presence of an infection, but in people with Down syndrome, they are activated constantly. This can predispose them to autoimmune disorders, according to the Global Down Syndrome Foundation.

Another type of immune cell is the microglia. They defend the brain and central nervous system against infections. In people without Down syndrome, these cells are only activated when there is an infection. In people with Down syndrome, they are constantly active, which can have poisonous effects on the brain, leading to cognitive deficits. Microglia are also hyperactivated in people with Alzheimer’s, which is also common among people with Down syndrome.

Hyperactivity of the immune system can be found in multiple parts of the body of someone with Down syndrome. Because of this hyperactivity, people with Down syndrome are more likely to develop autoimmune disorders, which is when the body attacks healthy cells instead of invaders such as viruses. Common autoimmune disorders among those with Down syndrome include type 1 diabetes, rheumatoid arthritis and alopecia areata. Around 30 percent of those with Down syndrome develop one or more autoimmune conditions, according to Espinosa.

This hyperactivity of the immune system could also explain why people with Down syndrome are less likely to develop cancers with solid tumors but are more likely to develop leukemia, a cancer of the white blood cells, which are a part of the immune system.

Fortunately, there are drugs approved by the Food and Drug Administration that can treat overactive parts of the immune system, Espinosa said. The downside is that these drugs lower the immune system response which could lead to more viral infections.

Espinosa plans to expand his research to study how these drugs that are already used to treat autoimmune disorders can potentially treat the risks, such as autoimmune disorders and leukemia, and symptoms associated with Down syndrome. This research may help people with Down syndrome improve cognitively through drugs that already exist.

“I do not discount the possibility that there is a process of lowering this hyperactivation,” Espinosa said. “We may be able to improve cognitive function, of course, that would depend on when this intervention would be made.”

Early childhood intervention using drugs designed to treat autoimmune disorders may help improve cognitive performance in people with Down syndrome. Espinosa added that it could help adults with Down syndrome as well.

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