Handbook of Genetic Counseling/Autism-1

Autisim

What is autism?

 * Disorder of brain function that appears early in life -- before the age of 3
 * Autism belongs to a family of related brain conditions affecting behavior early in life, which are often referred to as pervasive developmental disorder
 * Cause of autism is unknown

Traits associated with autism

 * social detachment, e.g., failure to smile at parents and an unawareness of events around them
 * abnormal language development, such as repeating phrases in a mechanical voice
 * unusual repetitive movements, e.g., rocking and flicking fingers
 * mental retardation (usually in more severe cases)
 * Traits vary in severity and persist into adulthood
 * Some individuals with autism have amazing skills (e.g. Rainman)

Incidence

 * Savant syndrome is quite rare (only about 200 cases ever recorded)
 * childhood autism is more common, affecting about one in 700 children
 * Boys are affected four times more often than girls

Can autism "run in families"?

 * If a child has autism, each of the parent's later children has a 3% to 9% chance of having autism.
 * This is 100 to 200 times greater than in the general population.
 * Believed to be multifactorial inheritance
 * Genetic component supported by twin studies


 * The second study used the same twins, but changed the definition of autism
 * new definition was looser -- people with milder behavioral problems were counted as autistic

Genes involved in autism

 * no gene found yet
 * Several candidate regions on chromosomes have been identified through linkage studies

Differential Diagnosis
(known genetic conditions that may share some symptoms of autism)
 * Fragile X syndrome (the FMR1 gene on the X chromosome).
 * Tuberous sclerosis (the TSC1 gene on chromosome 9).
 * Duplications of part of the long arm of chromosome 15.
 * Untreated phenylketonuria (the PAH gene on chromosome 12)

Environmental factors

 * UNKNOWN
 * Autism was thought to result from certain events before or shortly after birth
 * Infection of the brain with herpes virus and infection of the pregnant mother with rubella virus
 * Problems with brain structure are associated with autism, including hydrocephalus and, very rarely, a brain tumor
 * 1993 British study was reviewed by both the Medical Research Council in Great Britain and the Centers for Disease Control in the United States
 * The Centers for Disease Control concluded that: "to date there is no conclusive evidence that any vaccine can cause autism"

Web sites resources

 * The autism page at the National Institute for Neurological Disorders and Stroke:
 * The MedlinePlus web site for autism:
 * The February 2000 issue of Scientific American has an article entitled "The Early Origins of Autism" (full text not on-line).
 * More about autism from the National Immunization Program at the Centers for Disease Control:
 * Diagnosis, assessment and interventions for Autistic Spectrum Disorders: