A risk factor is something that increases your likelihood of getting a disease or condition.

You can develop autism with or without the risk factors listed below. However, the more risk factors you have, the greater your chance of developing autism. There is no known way to change your child's risk for autism.

Genetics is believed to play a role in the risk of autism. This is because the condition is more common in:

  • Families
  • Identical twins

Recent studies have linked deletions in a section of chromosome 16. This chromosome abnormality may account for a small percentage of autism cases.

Caucasian males are more likely to be affected by autism than females. But, when girls are affected, they may have more profound symptoms.

Older parents, such as a woman over age 35, may have a higher risk of having a child with autism.

Autism occurs more frequently in children with rare genetic disorders or other medical conditions, including:

  • Tuberous sclerosis—A rare, multi-system genetic disease. It causes benign tumors to grow in the brain and on other vital organs. The organs include the kidneys, heart, eyes, and skin. It commonly affects the central nervous system. This results in a combination of symptoms. These include seizures, developmental delay, behavioral problems, skin abnormalities, and kidney disease.
  • Fragile X syndrome —A hereditary disorder of the X chromosome. It is the most common cause of inherited intellectual disability.
  • Neurofibromatosis —A genetic disorder of the nervous system. It causes tumors to grow on the nerves in any part of the body. Neurofibromatosis can also produce other abnormalities. These include changes in the skin and deformed bones.
  • Phenylketonuria (PKU)—A genetic disorder of the enzyme that breaks down phenylalanine. Phenylalanine is an amino acid found in certain foods. Without a proper diet, PKU can lead to intellectual disability.
  • Problems during pregnancy or delivery, including rubella —Rubella is a mild, highly contagious illness that is caused by a virus. The symptoms are a rash, swollen glands, and joint pain. If a pregnant woman has rubella, it can cause birth defects in her baby. Other possible risk factors include breech delivery and birth at less than 35 weeks gestation.
  • Epilepsy —This term refers to any disorder characterized by recurrent seizures. A seizure can have many symptoms. You may lose consciousness, stare into space, have abnormal jerking of the muscles, or experience abnormalities of sensation or emotion.
  • Tourette’s syndrome
  • Newborn encephalopathy—This is a syndrome of disturbed brain function. It results in breathing difficulties, problems with reflexes, seizures, and other symptoms.
  • Moebius syndrome, cytomegalovirus, herpes encephalitis—These are sometimes listed as associated conditions.
  • Birth defects—Birth defects may also make a child more likely to develop autism.
  • Fetal alcohol syndrome—Caused when a mother drinks alcohol during pregnancy. It can cause birth and developmental defects in the child.
  • Angelman syndrome—A genetic disorder that affects the nervous syndrome and causes delayed development, intellectual disability, speech problems, and problems with movement and balance.
  • Rett syndrome—A problem with the development of the nervous syndrome. It is most common in girls.
  • Smith-Lemli-Opitz—A metabolic disorder caused by a gene mutation. People with the disorder cannot make enough cholesterol.
  • West syndrome—Causes a specific type of seizure seen in an epilepsy syndrome of infancy and childhood.

There has been much attention around a link between vaccines and autism. This is partly because of a vaccine preservative called thimerosol. But, studies have not found an association between vaccines and the development of autism.