A novel model of human brain development and degeneration proposed by scientists at the University of California, Los Angeles, implicates chinks in the fatty armor that coats the brain's internal wiring in such childhood developmental disorders as autism and attention-deficit/hyperactivity disorder.
From a review of scanned and autopsied brain tissue, the investigators said they unraveled the role of the insulation, called myelin, in these conditions.
Laden with more cholesterol than any other brain component, the sheet of fat encases the spindly nerve-cell extensions called axons, permitting them to carry messages to their neighbors in the safety and security of their shield.
The thicker and heavier the cells' coat, the faster and more effective their communication, said team leader Dr. George Bartzokis, professor of neurology at the David Geffen School of Medicine and director of the UCLA Memory Disorders and Alzheimer's Disease Clinic and the Clinical Core of the UCLA Alzheimer's Disease Research Center.
The pioneering neuroscientist said he discovered that myelin production continues unabated throughout the first four decades of life before peaking and plummeting at age 45.
His latest research portrays the protective shield as the neural system's Achilles' heel, vulnerable to a host of environmental assaults.
"Myelination, a process uniquely elaborated in humans, arguably is the most important and most vulnerable process of brain development as we mature and age," Bartzokis said in an interview. "The effect of all toxins should be examined in this context. At present, this is rarely done."
Without adequate insulation, cells won't connect properly, he said. He came to that conclusion after conducting a series of experiments that showed a breakdown in the sheath can expose the naked wiring beneath and open the gates to an array of neurological and behavioral problems.
Bartzokis's hypothesis holds that humans "myelinate" different circuits at various points in life, which could explain the sizeable differences between brain diseases of the young and old.
An early disruption of the process, for instance, may throw for a loop the development of the basic circuits that govern language and social communication, two key impairments in autism, Bartzokis said.
A glitch during the early school years could hamper the ability to process information efficiently and effectively, leading to deficits in attention that characterize ADHD, he said.
Later in life, the result of a malfunction could be Alzheimer's disease, Bartzokis conjectured.
To Bartzokis, the human brain is akin to the high-speed Internet.
"The speed, quality and bandwidth of the connections determine the brain's ability to process information, and all these depend in large part on the insulation that coats the brain's connecting wires," he said.
The findings may explain why developmental disorders leave no calling card in the brain, scientists said.
"There's no dead anything on autopsy," Bartzokis said. "Those brain connections just never developed normally."
The good news about myelination comes in feminine packages: Bartzokis's studies show female brains make better myelin, which could explain why boys are at much greater risk for autism, ADHD and other similarly routed problems.
On a similar front, U.S. and French investigators conducting mouse experiments found the males had 20 percent to 40 percent more of the cells that form myelin in the brain and spinal cord than did the females.
The females produced up to twice as many of the cells, but twice as many of them died, making for a much higher turnover rate in this group, the investigators reported in the Journal of Neuroscience.
The discovery of the unexpectedly large gender gap may help clear up some of the mystery of how male-female differences are generated in the brain, which in turn may provide critical clues into why disorders such as autism, ADHD, depression and multiple sclerosis are so uneven-handed in their distribution between the sexes, the authors said.
(Note: In this multi-part installment, based on dozens of reports, conferences and interviews, Ped Med is keeping an eye on autism, taking a backward glance at its history and surrounding controversies, facing facts revealed by research and looking forward to treatment enhancements and expansions. Wasowicz is the author of the new book, "Suffer the Child: How the Healthcare System Is Failing Our Future," published by Capital Books.)
Next: Autism as extreme maleness
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