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Clues to cause of autism may be tied to synapses

Children with autism spectrum disorders often are hypersensitive to sensory stimulation such as caused by noise or crowds. A new study, published in the journal Neuron, on Aug. 21 suggests one reason for this and a possible root cause for autism. The study is titled Loss of mTOR-Dependent Macroautophagy Causes Autistic-like Synaptic Pruning Deficits.

Kayleigh Norton, Applied Behavior Analysis therapist, reviews numbers with six-year-old Carl.
Kayleigh Norton, Applied Behavior Analysis therapist, reviews numbers with six-year-old Carl.
photo by Airman 1st Class Dennis Sloan U.S. Air Force/pubic domain

As an infant develops, their brain grows explosively. Millions of neurons, nerves, appear. The neurons pass their electrical signals to each other through synapses. Normally, the number of synapses is stabilized and controlled by a "pruning" process.

The study authors looked at the brain tissue of 20 deceased children between the ages of two and 20. About half were autistic. The New York Times, in an article dated Aug. 21, reported that the brains of autistic children seemed to have more synapses as they got older than their contemporaries. Both groups began with similar numbers but as they aged, the authors found "biomarkers and proteins in the brains with autism that reflected malfunctions in the system of clearing out old and degraded cells, a process called autophagy." That suggests that "pruning", is not taking place at the same rate as in non-autistic children.

While not conclusive, this study adds weight to the theory that overconnectivity in the brain is one primary cause of autism. It may also contribute to the far higher rates of epilepsy in autistic patients.

The Times article reports that studies in mice suggest that there may be a medical answer for the "pruning" issue. At this time, however, the medication studied has far too many side effects for use in children. In addition, treatment only seems to work in those mice with impaired pruning. It has no effect on those with a broken pruning ability.