Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Research adds to evidence that autism is a brain 'connectivity' disorder

11.01.2010
Tuberous sclerosis, commonly associated with autism, is linked to defects in axon guidance

Studying a rare disorder known as tuberous sclerosis complex (TSC), researchers at Children's Hospital Boston add to a growing body of evidence suggesting that autism spectrum disorders, which affect 25 to 50 percent of TSC patients, result from a miswiring of connections in the developing brain, leading to improper information flow.

The finding may also help explain why many people with TSC have seizures and intellectual disabilities. Findings were published online in Nature Neuroscience on January 10.

TSC causes benign tumors throughout the body, including the brain. But patients with TSC may have autism, epilepsy or intellectual disabilities even in the absence of these growths. Now, researchers led by Mustafa Sahin, MD, PhD, of Children's Department of Neurology, provide evidence that mutations in one of the TSC's causative genes, known as TSC2, prevent growing nerve fibers (axons) from finding their proper destinations in the developing brain.

Studying a well-characterized axon route – between the eye's retina and the visual area of the brain – Sahin and colleagues showed that when mouse neurons were deficient in TSC2, their axons failed to land in the right places. Further investigation showed that the axons' tips, known as "growth cones," did not respond to navigation cues from a group of molecules called ephrins. "Normally ephrins cause growth cones to collapse in neurons, but in tuberous sclerosis the axons don't heed these repulsive cues, so keep growing," says Sahin, the study's senior investigator.

Additional experiments indicated that the loss of responsiveness to ephrin signals resulted from activation of a molecular pathway called mTOR, whose activity increased when neurons were deficient in TSC2. Axon tracing in the mice showed that many axons originating in the retina were not mapping to the expected part of the brain.

Although the study looked only at retinal connections to the brain, the researchers believe their findings may have general relevance for the organization of the developing brain. Scientists speculate that in autism, wiring may be abnormal in the areas of the brain involved in social cognition.

"People have started to look at autism as a developmental disconnection syndrome – there are either too many connections or too few connections between different parts of the brain," says Sahin. "In the mouse models, we're seeing an exuberance of connections, consistent with the idea that autism may involve a sensory overload, and/or a lack of filtering of information."

Sahin hopes that the brain's miswiring can be corrected by drugs targeting the molecular pathways that cause it. The mTOR pathway is emerging as central to various kinds of axon abnormalities, and drugs inhibiting mTOR has already been approved by the FDA. For example, one mTOR inhibitor, rapamycin, is currently used mainly to prevent organ rejection in transplant patients, and Sahin plans to launch a clinical trial of a rapamycin-like drug in approximately 50 patients with TSC later this year, to see if the drug improves neurocognition, autism and seizures.

In 2008, Sahin and colleagues published related research in Genes & Development showing that when TSC1 and TSC2 are inactivated, brain cells grow more than one axon – an abnormal configuration that exacerbates abnormal brain connectivity. The mTOR pathway was, again, shown to be involved, and when it was inhibited with rapamycin, neurons grew normally, sprouting just one axon.

Supporting the mouse data, a study by Sahin and his colleague Simon Warfield, PhD, in the Computational Radiology Laboratory at Children's, examined the brains of 10 patients with TSC, 7 of whom also had autism or developmental delay, and 6 unaffected controls. Using an advanced kind of MRI imaging called diffusion tensor imaging, they documented disorganized and structurally abnormal tracts of axons in the TSC group, particularly in the visual and social cognition areas of the brain (see image). The axons also were poorly myelinated – their fatty coating, which helps axons conduct electrical signals, was compromised. (In other studies, done in collaboration with David Kwiatkowski at Brigham and Women's Hospital, giving rapamycin normalized myelination in mice.)

Sahin has also been studying additional genes previously found to be deleted or duplicated in patients with autism, and finding that deletion of some of them causes neurons to produce multiple axons – an abnormality that, again, appears to be reversed with rapamycin.

"Many of the genes implicated in autism may possibly converge on a few common pathways controlling the wiring of nerve cells," says Sahin. "Rare genetic disorders like TSC are providing us with vital clues about brain mechanisms leading to autism spectrum disorders. Understanding the neurobiology of these disorders is likely to lead to new treatment options not only for TSC patients, but also for patients with other neurodevelopmental diseases caused by defective myelination and connectivity, such as autism, epilepsy and intellectual disability."

The current study, titled "Tsc2-Rheb signaling regulates EphA-mediated axon guidance," was funded by grants from the National Institutes of Health, the John Merck Scholars Fund, Tuberous Sclerosis Alliance, the Manton Foundation, the Children's Hospital Boston Translational Research Program, and the Children's Hospital Boston Mental Retardation and Developmental Disabilities Research Center.

Duyu Nie was first author on the paper. Coauthors were Duyu Nie, Alessia Di Nardo, Juliette M Han, Hasani Baharanyi, Ioannis Kramvis, and ThanhThao Huynh, all of the F.M. Kirby Neurobiology Center and Department of Neurology, Children's Hospital Boston; Sandra Dabora of Brigham and Women's Hospital; Simone Codeluppi and Elena B Pasquale of the Burnham Institute for Medical Research, and University of California San Diego; and Pier Paolo Pandolfi of Beth Israel Deaconess Cancer Center.

Children's Hospital Boston is home to the world's largest research enterprise based at a pediatric medical center, where its discoveries have benefited both children and adults since 1869. More than 500 scientists, including eight members of the National Academy of Sciences, 13 members of the Institute of Medicine and 12 members of the Howard Hughes Medical Institute comprise Children's research community. Founded as a 20-bed hospital for children, Children's Hospital Boston today is a 396-bed comprehensive center for pediatric and adolescent health care grounded in the values of excellence in patient care and sensitivity to the complex needs and diversity of children and families. Children's also is the primary pediatric teaching affiliate of Harvard Medical School.

James Newton | EurekAlert!
Further information:
http://www.childrenshospital.org/newsroom

More articles from Health and Medicine:

nachricht A promising target for kidney fibrosis
21.04.2017 | Brigham and Women's Hospital

nachricht Stem cell transplants: activating signal paths may protect from graft-versus-host disease
20.04.2017 | Technische Universität München

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

Molecular libraries for organic light-emitting diodes

24.04.2017 | Life Sciences

Research sheds new light on forces that threaten sensitive coastlines

24.04.2017 | Earth Sciences

Making lightweight construction suitable for series production

24.04.2017 | Machine Engineering

VideoLinks
B2B-VideoLinks
More VideoLinks >>>