The many genes of autism

Drs. Norbert Herzog & David Niesel

Drs. Norbert Herzog & David Niesel

Medical Discovery News

In the past decade, autism has garnered a lot of media attention. Lately much of the focus has been on finding the cause. Much is still a mystery, despite confirming that vaccines and parenting are not responsible. Now a new study of twins has given us another clue, revealing that the influence of genetics on the development of autism may be between 56 and 95 percent.

According to the Centers for Disease Control, one in 68 children have autism, a neurodegenerative disorder that exists on a spectrum, meaning its symptoms and their severity varies tremendously. A hallmark feature of autism is impaired social interaction, noticeable even in babies. Those with autism find it difficult to interpret what others are thinking or feeling because they miss the social clues most take for granted. Other symptoms can include repetitive movements such as spinning or rocking, speech delays and self-destructive behaviors. Children with autism can also have a variety of other conditions including epilepsy, Tourette’s syndrome, learning disabilities and attention deficit disorder.

The cause of autism is probably rooted in genetics and environment. Comparing sets of twins is a well-established way of clarifying the extent of both these influences. Scientists in London studied over 6,400 pairs of twins in England and Wales between 1994 and 1996, all raised by their parents in the same environments. The data they collected revealed that the chance of identical twins having autism was 77 to 99 percent, whereas the chance of nonidentical twins having autism was 22 to 65 percent. This suggests that additive genetic factors contribute to 56-95 percent of autism cases. This is far higher than previous estimates, which assumed environmental influences were more of a factor.

While no one gene has been attributed to autism, the majority of the genes that are associated seem to be linked to one specific symptom. For example, the gene EN2 is often studied for its role in autism because it is critical to midbrain and cerebellum development. Reelin, a protein found mainly in the brain, also plays an important role in autism development. In adults, reelin is important to learning and memory and is critical to inducing and maintaining long-term neuronal connections. Autistic individuals consistently show elevated levels of serotonin, otherwise known as the feel-good hormone. This has led researchers to examine the role of genes involved in serotonin regulation as potential causes of autism. Another hormone system called arginine-vasopressin affects social behavior, so one of the genes that regulates it is a candidate for autism as well. These are just a few of the many genes being studied.

As more people become aware of autism and more children are diagnosed, the pressure is building to further understand this disorder. Discovering the causes might translate to better diagnostics and treatment for autism.

Professors Norbert Herzog and David Niesel are biomedical scientists at the University of Texas Medical Branch. Learn more at medicaldiscoverynews.com.

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