Autism and Genes : Part 4

by National Institute of Health

(Page 4 of 4)

Another study found that increased head size in ASD patients was associated with a different mutation in the HOXA1 gene. About 20 percent of persons with autism have large head size. It is one of the most consistently reported physical features of persons with autism. Now researchers want to know whether the mutation affects head size in persons with autism only, or if it affects head size in general, regardless of ASD status.

Several other genes have come forward as potential candidates, including:

The Reelin (RELN) gene on chromosome 7 - This gene plays a crucial role in the development of connections between cells of the nervous system. Researchers think that abnormal brain connectivity plays a role in autism, which makes Reelin a good candidate. In addition, persons with autism and their parents and siblings have lower levels of certain types of the Reelin protein, which may mean that gene is not functioning normally.

The HOXD1 gene - This homeobox gene is critical to the formation of certain brain structures. This gene is involved in Duane syndrome, a disorder that causes eyemovement problems and sometimes occurs with autism. In one study of persons with autism, nearly 94 percent of participants had mutations in the same regions of HOXD1, which could mean that the region contributes to ASDs.

Gamma-amino-butyric acid (GABA) pathway genes - GABA compounds are neurotransmitters, which means they help parts of the nervous system communicate with each other. GABA receptor genes are involved in early development of parts of the nervous system and help with communication between these parts throughout life. A problem in the GABA pathway can cause some of the symptoms of ASDs. For instance, epilepsy may result, in part, from low levels of GABA compounds. Many persons with autism also have epilepsy and also show low levels of GABA. Current research focuses on genes that, when their structure or function is incorrect, cause autism-like problems in mice.

Serotonin transporter gene on chromosome 17 - The serotonin transporter allows nerve cells to collect serotonin so that they can communicate. Serotonin is a neurotransmitter involved in depression, alcoholism/problem drinking, OCD, and other disorders. Research shows that persons with autism have higherthan- normal levels of serotonin - ranging between 25 percent and 50 percent higher than persons without autism. This higher serotonin level may result from problems with the serotonin transporter that arise from errors in the gene.

Body chemicals that may play a role in autism

The body makes many chemicals that help it function correctly. When these chemicals are missing or incorrect, the body may have problems functioning properly, which may result in symptoms of autism or other disorders. Researchers are now trying to uncover how body chemicals might be involved in autism, so they can learn how the genes that make these chemicals might also play a role. Researchers are also studying whether medications might regulate or control these chemicals to create normal chemical levels. Normalizing the chemicals in a person with ASDs might reduce symptoms.

As mentioned earlier, GABA may play a role in autism and definitely plays a role in epilepsy. Levels of different types of GABA compounds are abnormally low in persons with autism. Researchers believe that these low levels may contribute to autism. In studies of mice, disrupting the GABA pathway causes seizures, extreme reactions to touch and sound, and stereotyped actions - symptoms also common in autism. Research now focuses on whether medications used to treat these problems can also reduce some of the symptoms of autism.

Another brain chemical mentioned earlier - serotonin - is also out-of-balance in many persons with autism. High serotonin levels may explain why persons with autism have problems showing emotion and handling sensory information, such as sounds, touch, and smells. Researchers now focus on whether medications that regulate serotonin levels may improve behavior in persons with autism. They also examine the genes that make and regulate serotonin and its pathway components to see if they can find any changes or patterns.

What does the future hold for studies of genes and autism?

Scientists in the CPEA Network and their colleagues who study the genetic mechanisms of autism hope that these studies will reveal the main cause or causes of autism. Doctors could then test for the gene or genes to detect autism early in life so that intervention can begin when it is most effective. Or, researchers could develop drugs that change or regulate the gene or genes to help normalize body chemicals and body functions.

Researchers share their information and their methods to see if other researchers can replicate their findings. Having several scientists get the same results "confirms" that discovery. Once confirmed, a discovery becomes the stepping stone to other discoveries. To date, however, not all genetic studies have gotten the same results. Therefore, additional work is still important.

Scientists also look beyond genes to find factors that may play a role in autism, including things in the environment. Environmental features can affect how genes function, which may contribute to the symptoms of ASDs. By understanding genetic and environmental causes of autism, scientists may better understand how to treat it and maybe even how to prevent it. Doctors and scientists continue to study genes, the environment, and gene-environment interactions until they solve the mysteries of autism.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.