Autism linked to fatty nerve cell coating

New research may explain why more boys are affected by autism than girls.

There is no doubt that autism affects boys more than it does girls with most authorities putting that ratio at 4:1. Scientists have been unsure about the reasons for this uneven distribution for a long time. Now, research conducted at the University of California, Los Angeles, in the US, has uncovered a possible explanation. The research also sheds light on underlying mechanisms of autism spectrum disorders and other developmental disorders.

The researchers looked at the protective coating around the delicate axons which extend from nerve cells in the brain. This insulating jacket around the axons, known as myelin, is made predominantly from fatty substances, including cholesterol, and is essential for ensuring proper communication between cells, and therefore brain function as a whole.

After reviewing information from brain scans and autopsies, the researchers say that they can now explain the role of myelin in developmental disorders including autism and attention deficit hyperactivity disorder (ADHD). Many researchers have looked at what is going on inside the nerve cells, and at neurotransmitters, the chemical messengers in the brain, but this is the first time that myelin has been directly studied in these disorders.

The research team that carried out the myelin investigations at UCLA was led by 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.

Dr. Bartzokis was quoted as saying in an interview "The thicker and heavier the cells' coat, the faster and more effective their communication," he went on "Myelination, a process uniquely elaborated in humans, arguably is the most important and most vulnerable process of brain development as we mature and age."

This latest research suggests that the protective myelin coat on every nerve cell in the brain is the major weak spot in the neural system, and is vulnerable to a host of environmental assaults. Dr. Bartzokis commented that "The effect of all toxins should be examined in this context. At present, this is rarely done."

Dr. Bartzokis is considered a neuroscience pioneer, as this latest study demonstrates, being the first to look at the myelin sheath in this context. In previous studies he has discovered that myelin is produced continually throughout the first four decades of life before peaking and rapidly decreasing around age 45.

The researchers carried out a series of experiments that showed a thinning and breakdown in the myelin sheath can expose the nerve beneath and open the gates to an array of neurological and behavioral problems. Dr. Bartzokis says that from this it can be concluded that without adequate insulation, cells won't connect properly. This knowledge could have implications for numerous neurological and degenerative conditions, as well as for autism and ADHD.

The link to autism and ADHD comes from Dr. Bartzokis's theory that humans "myelinate" different brain circuits at various points in life, which could explain the sizeable differences between neurological disorders seen in children, adults, and the elderly.

He says that, an early disruption of the process of myelin production, for instance, may have serious consequences for the development of the basic brain circuits that govern language and social communication, two major areas of dysfunction in autism. Additionally, a problem with the protective myelin coat during the early school years could interfere with a child's ability to process information efficiently and effectively, leading to problems with attention that characterize ADHD.

Dr. Bartzokis has said that these same abnormalities of myelination in later life may result in symptoms characteristic of Alzheimer's disease and other degenerative neurological conditions.

The reason this research is a possible explanation for more boys than girls being autistic becomes apparent when you look at myelin differences between the sexes. The research carried out at UCLA found that female brains make thicker myelin than male brains, therefore providing better protection and ensuring efficient brain function. It's precisely this type of definitive difference between the sexes that scientists would look for to explain why boys are 4 times more likely to become autistic. Further research that replicates these findings would mean another mystery in the autism story would have been unraveled. Of course, it is possible that this is just one of many differences between the sexes that contribute to boys being more likely to be autistic.

The discovery of this gender difference in myelin production may result in a much greater understanding of how male-female differences are generated in the brain in a general sense too. This understanding may in turn provide insights into why disorders such as autism and ADHD, but also depression and multiple sclerosis, are so unevenly distributed between the sexes.

Dr. Bartzokis' research also opens up another avenue of investigation for researchers concerned with investigating the role of environmental toxins in autism. It's now widely accepted that autism is the result of an interaction between genetic and environmental factors. Dr. Bartzokis' assertion that the effect of all toxins should be examined in the context of his findings with regard to myelin may be an indicator of future research direction in the field of autism and environmental toxins. Differences in the level of protection afforded by myelin at different ages may be associated with different tolerances for environmental toxins. Many parents and physicians will be keen to see how this ties in with the mercury toxicity that has been associated with autistic spectrum disorders. Further research may lead to more accurate guidelines on safe levels of various chemicals in children and hopefully a corresponding reduction in the current high rate of autism cases.

The growing body of scientific research that is showing harmful effects from very low doses of chemicals that were previously thought to be safe, may also contribute to advances in this area.

Research studies such as these are opening new doorways for future autism research and shedding light on the role of environmental toxins in the conditions development.