Published: Feb. 25, 2011
Updated: Feb. 25, 2011
Parents frequently ask me about what causes autism. I explain that little is known about the causes, but geneticists are beginning to understand some of the reasons kids develop autism.
Dr. Yong-hiu Jiang, who specializes in pediatric medical genetics, answers frequently asked questions parents often have about the link between genetics and autism.
-- Dennis Clements MD, PhD, MPH
Autism is the name given to a group of developmental brain disorders that are characterized by poor social interaction and communication and by restricted or repetitive behavior. These signs appear before a child is three years old.
For many children with autism, we do not know the cause. However, for some children, autism is caused by a change in their genetic information (DNA).
Genetic changes causing autism can occur in a single gene or can involve missing or extra pieces of chromosomes that include many genes (microdeletions and microduplications).
Some people with autism have other symptoms, such as specific physical differences or learning problems, which are part of a genetic syndrome.
Examples of genetic syndromes that include autism as a symptom include:
In rare cases, autism can also be part of clinical presentation of a metabolic disorder (a genetic condition in which the body cannot break down or make a specific substance).
Findings from twin and family studies led scientists to believe that genetic differences are an important cause of autism. However, non-genetic factors may also have a role.
Unless a known genetic change has been found in a child, doctors cannot be sure exactly how autism is inherited in the family. It may be caused by inheriting a combination of multiple genes from both parents or by a new genetic change that is only present in the child’s DNA.
Although we still have a lot more to learn, scientists have already learned a great deal by studying the genetics of autism over the last decade. This knowledge is helping doctors to find the cause of autism in some children.
A diagnosis of a change in a specific gene or a microdeletion or duplication can help to tailor medical, developmental, or school interventions and to answer the questions many parents have about the chances that other children in the family could also have autism.
Therefore, pediatricians now routinely recommend a clinical genetics evaluation after a child is diagnosed with autism.
During the clinic visit, a clinical genetics doctor or genetic counselor will ask questions about your child's medical and developmental history and collect a detailed family history.
If your child has had previous medical evaluations or blood tests, it is helpful to bring those records with you. The doctor will also perform a detailed physical examination.
At the end the visit, the doctor will discuss whether your child may have a known genetic syndrome and whether any genetic tests might be helpful in finding the cause of your child's condition. If you have any questions about the evaluation, testing, or your child’s health, you can ask the doctor or genetic counselor during the visit.
Clinical genetics doctors usually decide which types of genetic tests to order after evaluating your child.
The samples needed are usually blood and urine. Other more specific tests may also be ordered at the end of visit.
The following blood tests are often requested:
The following urine tests are often requested:
Chromosome microarray (CMA) is a new method of analyzing chromosomes for a large number of genetic disorders. With a single test, CMA analyzes all chromosomes simultaneously for extra or missing pieces of genetic material.
CMA has much higher sensitivity for finding these types of chromosome differences than the older chromosome test called a karyotype. However, it is not able to find all genetic changes in a person's DNA.
Since CMA was developed, many large research studies have shown that it finds chromosome differences thought to cause autism in about 5 to 10 percent of children with the condition.
CMA also can detect many other common genetic disorders that cause intellectual disabilities.
In most cases, knowing the genetic cause for autism in a child will not lead to a cure. However, knowing the genetic change may help you better understand your child's condition and know what to expect in the future.
Your child's physician may be able to recommend specific preventive care measures and guide routine health monitoring for your child.
Research on autism genetics is moving at a fast pace. Due to the development of cutting edge techniques, human genetics researchers are now able to analyze the entire genetic blueprint (genome) of a person.
This technology can be used to find out more about genetic causes of autism.
Neuroscientists are looking for differences in how the brain develops and works in people with autism. Such research studies are ongoing at Duke and other research institutes nationwide. If you are interested in participating in these studies, please contact Dr. Yong-hui Jiang, MD, PhD.
-- Yong-hui Jiang, MD, PhD, is a pediatric medical geneticist at Duke Children's Hospital.
-- Dennis Clements, MD, PhD, MPH, is the chief of primary care pediatrics at Duke Children's Hospital.