Scientists are learning more about the biology behind conditions that affect the brain, including autism spectrum disorder, schizophrenia and Alzheimer’s disease.
Genes, brain chemicals and the way nerve cells connect can all influence how the brain develops and works, but many pieces of the puzzle are still poorly understood.
One protein that has received relatively little attention is called indoleamine 2,3-dioxygenase 2, or IDO2. It is involved in the body’s processing of tryptophan, an amino acid that people obtain from foods containing protein.
Tryptophan can be broken down through a series of chemical reactions known as the tryptophan–kynurenine pathway. Chemicals produced along this pathway can affect the brain, immune system and nerve-cell activity, and earlier research has linked changes in the pathway with several brain and psychiatric conditions.
To investigate IDO2, Associate Professor Yasuko Yamamoto and colleagues at Fujita Health University in Japan studied mice that had been genetically changed so they could not produce the protein. The researchers compared these animals with ordinary mice to see how losing IDO2 affected behavior and the brain.
The study was published in The FEBS Journal. The mice without IDO2 showed several unusual behaviors, including more repetitive grooming, less exploration and greater difficulty adjusting when their surroundings changed.
They also behaved differently during tests involving other mice. The researchers described some of these changes as autism-like behaviors, but mouse behavior cannot reproduce the full experience of autism in people and does not mean that IDO2 loss has been shown to cause human autism.
The team then examined what was happening inside the animals’ brains. Removing IDO2 changed chemicals in the tryptophan pathway and was associated with changes in dopamine in brain regions including the striatum and amygdala.
Dopamine is a chemical messenger that helps brain cells communicate. It is involved in motivation, learning, movement and responses to rewards, so changes in dopamine activity can influence behavior in many different ways.
Another important finding involved brain-derived neurotrophic factor, usually shortened to BDNF. This protein supports the growth and survival of nerve cells and helps the brain strengthen or change connections as it learns.
Mice without IDO2 had lower BDNF levels and differences in tiny structures called dendritic spines. These structures sit on nerve cells and help them receive messages from other cells, making them important for communication within brain networks.
The researchers also found changes in microglia, immune-related cells that live in the brain. Microglia normally help maintain brain tissue and respond to injury, but their shape and activity can change depending on what is happening around them.
In the modified mice, more microglia appeared in a highly active form rather than their usual monitoring form. The researchers believe these changes, together with altered BDNF and brain chemistry, could help explain the animals’ unusual behavior.
Importantly, the team performed experiments that restored IDO2 activity. After IDO2 was restored, some of the behavioral differences improved, giving the researchers stronger evidence that the protein itself was involved rather than simply being an unrelated genetic change.
The scientists also searched human genetic information from 309 people with autism and identified an IDO2 mutation in one 16-year-old girl. One case is far too little evidence to show that IDO2 is a common cause of autism, but it gives researchers a reason to investigate the gene in much larger groups.
Autism is a complex developmental condition with many genetic and biological influences, and there is unlikely to be one single cause or treatment. This study therefore represents an early clue rather than a new therapy, and findings from genetically modified mice must be confirmed through much more human research.
Still, understanding IDO2 may reveal more about how tryptophan processing, dopamine, BDNF and immune-related brain cells interact. Future studies could determine whether this pathway contributes to autism or other brain conditions and whether it can eventually provide useful targets for treatment.
If you care about autism, please read studies about a new cause of autism, and cats may help decrease anxiety for kids with autism.
For more information about health, please see recent studies about vitamin D that may hold the clue to more autism, and results showing strange eating habits may signal autism.
Copyright © 2026 Knowridge Science Report. All rights reserved.
