In recent years, scientists have learned a lot more about mental health conditions such as autism, schizophrenia, and Alzheimer’s disease.
Researchers now know that changes in genes and problems with certain brain chemicals may play a role in these conditions.
Even so, the brain is extremely complex, and many important parts of it are still not fully understood. One of the mysteries involves a little‑known protein called indoleamine 2,3‑dioxygenase 2, or IDO2.
Proteins are tiny working parts inside our cells that help the body function properly. In the brain, proteins control how nerve cells grow, communicate, and stay healthy. IDO2 is involved in a chemical process called the tryptophan–kynurenine pathway. This pathway breaks down tryptophan, a natural substance found in foods like eggs, cheese, fish, and nuts.
When tryptophan is processed in the body, it produces several chemicals that can affect mood, thinking, and behavior. Scientists have already linked this pathway to depression, anxiety, and other psychiatric conditions, which made them curious about the role of IDO2.
To learn more, Associate Professor Yasuko Yamamoto and her team at Fujita Health University in Japan carried out an experiment using mice.
Animal studies are often used in early research because mice share many biological similarities with humans. The researchers compared normal mice with special mice that were genetically modified so they did not have the IDO2 gene. These were called IDO2 knock‑out mice.
The scientists wanted to see whether removing this protein would change how the mice behaved or how their brains worked. What they found was surprising. The mice without IDO2 showed behaviors that were similar to some traits seen in people with autism.
They had difficulty adjusting to new places, spent a long time repeating the same grooming actions, and showed less curiosity about their environment. When placed with other mice, they also had trouble learning social behaviors.
To understand why this happened, the researchers examined the mice’s brain chemistry. They discovered that without IDO2, the tryptophan pathway worked differently.
This change affected dopamine, an important brain chemical that helps control motivation, pleasure, movement, and learning. Abnormal dopamine levels are known to be linked to several mental health conditions.
The team also found lower levels of a substance called brain‑derived neurotrophic factor, or BDNF. This molecule helps brain cells grow, stay healthy, and form strong connections with each other. It is especially important for learning and memory.
When BDNF levels were reduced, the mice’s brain cells showed fewer mature connections. Under a microscope, the researchers could see that the communication points between neurons looked less developed.
Another important finding involved microglia, special immune cells in the brain that protect and maintain nerve cells. Normally, microglia quietly monitor the brain and clean up unnecessary connections.
In the IDO2 knock‑out mice, however, these cells shifted into a more active state that breaks down damaged cells. This change may have disrupted normal brain development and communication.
In an exciting part of the study, the researchers restored the IDO2 gene in the modified mice. After this, many of the unusual behaviors became closer to normal. This result suggests that IDO2 may play an important role in brain function and behavior.
To explore whether this discovery might also matter for humans, the team examined brain samples from more than 300 people with autism. They found one teenager with a change in the IDO2 gene. Although this was only one case, it hints that the protein could be relevant to people as well.
This research offers a new direction for understanding autism and possibly other mental health conditions. Scientists hope that learning more about IDO2 could one day lead to better treatments that target the underlying biology rather than just the symptoms.
While much more research is needed, the findings show how even a small and little‑known protein can have a big impact on the brain.
Researchers are also exploring other ways to support people with autism and related conditions, including therapies, lifestyle changes, and supportive environments.
Every new discovery helps build a clearer picture of how the brain works and how it can be protected. Studies like this bring hope that future treatments will be more effective and personalized, helping people live healthier and more independent lives.
If you care about Alzheimer’s, please read studies about the likely cause of Alzheimer’s disease, and new non-drug treatment that could help prevent Alzheimer’s.
For more health information, please see recent studies about diet that may help prevent Alzheimer’s, and results showing some dementia cases could be prevented by changing these 12 things.
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