Genetic Risk: Current evidence suggests that as many as 12 or more genes on different chromosomes may be involved in autism, to different degrees. These genetic differences likely account for the wide variability in autism. Some genes may place a person at greater risk for autism, called susceptibility genes, and may run in families. Other genes may cause specific symptoms or determine how severe those symptoms are. Or, genes with physical errors called mutations can happen spontaneously and add to the symptoms of autism because the genes or gene products aren’t working properly. It is generally thought these mutations account for a minority of autism cases.
Runs in Families: Among some brothers or sisters of a child with autism there is only a moderate risk of also having autism, for example 2%. While this is much higher than the likelihood of a child having autism if there are no siblings with ASD, it is still fairly low. On the other hand, in some types of autism the likelihood of recurrence in the same family is much higher, e.g. 10-15% depending on the type of autism. Consult your pediatrician’s clinical geneticist for accurate information in your family’s case.
DIsabilities Associated with Autism: Other risk factors for autism. Children with Tuberous Sclerosis or Fragile X syndrome are also more likely to have autism. Families with other biological relatives with autism spectrum disorders, such as parents, grandparents, aunts or uncles and first cousins are at higher risk for having a child with autism. Cornelia de Lange Syndrome and Prader Willi Syndrome are also associated with autism risk.
Infection and Drug Risks: A variety of physical risk factors are associated with autism. Maternal pregnancy during which measles, mumps, rubella, influenza,
chicken pox, herpes or pneumonia were contracted increases autism risk. Infections an infant experiences after birth can increase the risk, such as meningitis, have been implicated in ASD. Of specific infections known to affect the developing brain, rubella has been most commonly reported to be associated with ASD. There is an association of fetal alcohol syndrome with autism risk and a larger association of maternal use of some anti-epileptic drugs and autism risk.
Epilepsy and Autism: Other problems commonly associated with autism: About 1/3 of individuals with autism develop some form of epilepsy by adulthood. These seizures can nearly always be controlled with anti-epileptic medication.
Summary: The bulk of evidence suggests most forms of autism result from genetic susceptibility genes combined with other genes which control specific autism symptoms. Some genetic risk runs in families which has to be determined on a case by case basis. Just because you have one child with autism does not automatically mean there is very high risk other children will have autism, though it is clearly higher than chance. There is very strong evidence a variety of maternal infections and early post-natal children’s infections (e.g. Rubella) can increase the risk of autism. There is some evidence very low birthweight babies born prematurely also have increased autism risk.