Rett syndrome, an autism spectrum disorder, causes problems with communication, coordination and movement.

AP Photo/The Idaho Statesman

A bone-marrow transplant can treat a mouse version of Rett syndrome, a severe autism spectrum disorder that affects roughly 1 in 10,00020,000 girls born worldwide (boys with the disease typically die within a few weeks of birth).

The findings, published today in Nature1, suggest that brain-dwelling immune cells called microglia are defective in Rett syndrome. The authors say their findings also raise the possibility that bone-marrow transplants or other means of boosting the brains immune cells could help to treat the disease.

If we show the immune system is playing a very important role in Rett patients and we could replace it in a safe way, we may develop some feasible therapies in the future, says Jonathan Kipnis, a neuroscientist at the University of Virginia School of Medicine in Charlottesville, who led the study.

Mutations in a single gene on the X chromosome,MECP2, cause the disease. Because they have only one X chromosome, boys born with the mutation die within weeks of birth. Girls with one faulty copy develop Rett syndrome.

Symptoms of Rett syndrome typically set in between 6 and 18 months of age. Girls with the disease have trouble putting on weight and often do not learn to speak. They repeat behaviours such as hand-washing and tend to have trouble walking. Many develop breathing problems and apnoea. Rett syndrome is classified as an autism spectrum disorder, and treatments focus on symptoms such as nutritional and gastrointestinal problems.

The MECP2 protein orchestrates the activity of many other genes, but how its alteration causes Rett syndrome is a mystery. I wish I knew, says Kipnis.

Neurons express more MECP2 than any other cell in the brain, and restoring the genes function in mouse neurons reverses some disease symptoms2.Recently, however, scientists have begun to suspect that other brain cells are also involved. Re-activating MECP2 in brain-support cells called astrocytes treats gait problems and anxiety in mice3.

Kipnis and his team focused on another class of brain cell microglia. They are the brains macrophages, a type of immune cell that sops up the detritus created by other cells. Studies have linked various immune cells to brain function, including repetitive and compulsive behaviour4, which led Kipnis to test whether replacing an immune system in mice lacking Mecp2 with cells containing the gene could improve symptoms.

More here:
Bone-marrow transplant reverses Rett syndrome in mice

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