Autism spectrum disorder has no single known cause. Given the complexity of the disorder, and the fact that symptoms and severity vary, there are probably many causes. Both genetics and environment may play a role.
Genetics. Several different genes appear to be involved in autism spectrum disorder. For some children, autism spectrum disorder can be associated with a genetic disorder, such as Rett syndrome or fragile X syndrome. For other children, genetic changes (mutations) may increase the risk of autism spectrum disorder. Still other genes may affect brain development or the way that brain cells communicate, or they may determine the severity of symptoms. Some genetic mutations seem to be inherited, while others occur spontaneously.
Environmental factors. Researchers are currently exploring whether factors such as viral infections, medications or complications during pregnancy, or air pollutants play a role in triggering autism spectrum disorder.
No link between vaccines and autism spectrum disorder
One of the greatest controversies in autism spectrum disorder centers on whether a link exists between the disorder and childhood vaccines. Despite extensive research, no reliable study has shown a link between autism spectrum disorder and any vaccines. In fact, the original study that ignited the debate years ago has been retracted due to poor design and questionable research methods.
Avoiding childhood vaccinations can place your child and others in danger of catching and spreading serious diseases, including whooping cough (pertussis), measles or mumps.

Diagnosis of Autism: What We Do Know
Autistic children benefit from early diagnosis, preferably in the first two years of life. Early diagnosis allows behavioral therapy or other treatments to begin early when it seems to be most effective. If you are concerned about your child, talk to your doctor about a referral to see a specialist who can help determine if follow-up is needed. Signs of autism may include symptoms such as:
• no babbling or pointing by age 1
• no single words by 16 months or two-word phrases by age 2
• no response to name
• loss of language or social skills
• poor eye contact
• excessive lining up of toys or objects
• no smiling or social responsiveness

A final diagnosis should be made by a team of qualified professionals including a neurologist, psychologist, psychiatrist, and speech pathologist. The outlook for children with autism is improving as we learn more, and many children can improve significantly within a few years of treatment.

Risk factors
The number of children diagnosed with autism spectrum disorder is rising. It’s not clear whether this is due to better detection and reporting or a real increase in the number of cases, or both.
Autism spectrum disorder affects children of all races and nationalities, but certain factors increase a child’s risk. These may include:
• Your child’s sex. Boys are about four times more likely to develop autism spectrum disorder than girls are.
• Family history. Families who have one child with autism spectrum disorder have an increased risk of having another child with the disorder. It’s also not uncommon for parents or relatives of a child with autism spectrum disorder to have minor problems with social or communication skills themselves or to engage in certain behaviors typical of the disorder.
• Other disorders. Children with certain medical conditions have a higher than normal risk of autism spectrum disorder or autism-like symptoms. Examples include fragile X syndrome, an inherited disorder that causes intellectual problems; tuberous sclerosis, a condition in which benign tumors develop in the brain; and Rett syndrome, a genetic condition occurring almost exclusively in girls, which causes slowing of head growth, intellectual disability and loss of purposeful hand use.
• Extremely preterm babies. Babies born before 26 weeks of gestation may have a greater risk of autism spectrum disorder.
• Parents’ ages. There may be a connection between children born to older parents and autism spectrum disorder, but more research is necessary to establish this link.

Problems with social interactions, communication and behavior can lead to:
• Problems in school and with successful learning
• Employment problems
• Inability to live independently
• Social isolation
• Stress within the family
• Victimization and being bullied

There’s no way to prevent autism spectrum disorder, but there are treatment options. Early diagnosis and intervention is most helpful and can improve behavior, skills and language development. However, intervention is helpful at any age. Though children usually don’t outgrow autism spectrum disorder symptoms, they may learn to function well.