Adult Brain Requires MeCP2 for Proper Functioning

A paper published online today in Science provides evidence that the Methyl-CpG-Binding Protein 2 (MeCP2) is required throughout life to maintain healthy brain function. The findings are reported from the Baylor College of Medicine lab of Huda Zoghbi, HHMI investigator and Director of the Jan and Dan Duncan Neurological Research Institute.

Mutations in MeCP2 cause the autism spectrum disorder Rett Syndrome, and have been seen in some cases of classic autism, childhood schizophrenia and milder neuropsychiatric conditions such as anxiety and learning disabilities.

Rett Syndrome strikes little girls almost exclusively, with first symptoms usually appearing before the age of 18 months. These children lose speech, motor control and functional hand use, and many suffer from seizures, orthopedic and severe digestive problems, breathing and other autonomic impairments. Most live into adulthood, and require total, round-the-clock care.

Using sophisticated genetic engineering tools, Christopher McGraw, an MD/PhD student in the Zoghbi lab, inhibited production of the Mecp2 protein in mature adult mice at 9 weeks of age. He characterized the mice and found that by 19 weeks the animals began displaying symptoms reminiscent of the classic Rett Syndrome mice which are missing Mecp2 protein from conception: impaired gait and locomotion, hind-limb clasping, motor abnormalities, impaired learning and memory. Lethality in both sets of mice took place approximately 13 weeks after removing MeCP2.

Rett Syndrome has been considered a neurodevelopmental disorder, due to the onset of symptoms in early childhood. The appearance of these symptoms after removal of Mecp2 in adult mice suggests that there may be no discrete time period during which MeCP2 is critical for normal development, and argues against categorizing the disorder as neurodevelopmental.

Joshua Sanes, the Director of the Center for Brain Science at Harvard and Professor in Harvard’s Department of Molecular and Cellular Biology, commented on the broader impact of Zoghbi’s findings. “This work not only sheds new light on the pathogenesis of Rett Syndrome, but also raises fascinating questions about a central dogma in neuroscience - that genes affecting the brain act differently during the “critical period” than they do in adulthood. In at least some instances, Zoghbi’s result tells us, this may not be the case.” Sanes was not involved in this work.

The findings are also valuable from a clinical perspective, since they suggest that certain potential treatments for the disorder, such as small molecule drugs, may need to be maintained throughout the lifetime of individuals afflicted with Rett Syndrome.

“Given the parallels between autism and Rett Syndrome with regard to age of onset of symptoms and clinical features, these findings raise the possibility that several autism spectrum disorders might indeed result from failure of maintaining neuronal function rather than alterations of key developmental programs,” says Zoghbi.

Monica Coenraads, Executive Director of the Rett Syndrome Research Trust which helped fund this work, and mother of a teenaged daughter with Rett Syndrome, says “Although Rett is a relatively rare disorder, it provides opportunity for broader neurological insights. Huda Zoghbi’s new work challenges some central tenets in neuroscience. It is gratifying to see that Rett research is teaching us important lessons about the brain.”