What causes autism?
Since autism was first added to the psychiatric literature about 50 years ago, there have been numerous studies and theories about its causes. Researchers still have not reached agreement regarding its specific causes. First, it must be recognized that autism is a set of a wide variety of symptoms and may have many causes. This concept is not unusual in medicine. For instance, the set of symptoms that we perceive of as a "cold" can be caused by literally hundreds of different viruses, bacteria, and even our own immune system.
Autism is thought to be a biologically-based disorder. In the past, some researchers had suggested that autism was the result of poor attachment skills on the part of the mother. This belief has caused a great deal of unnecessary pain and guilt on the part of the parents of children with autism, when in fact, the inability of the individual with autism to interact appropriately is one of the key symptoms of this developmental disorder. Some risk factors for autism include high maternal age at the time of birth of the child, as well as maternal prenatal medication use, bleeding, or gestational diabetes. Other support of a biological theory of autism includes that several known neurological disorders are associated with autistic features. Autism is one of the symptoms of these disorders. These conditions include:
tuberous sclerosis and the fragile X syndrome (inherited disorder);
cerebral dysgenesis (abnormal development of the brain);
Rett syndrome (a mutation of a single gene); and
some of the inborn errors of metabolism (biochemical defects).
Autism, in short, seems to be the end result or "final common pathway" of numerous disorders that affect brain development. Also, brain studies have demonstrated that persons with autism tend to have a number of abnormalities in brain size. In general, however, when clinicians make the diagnosis of autism, they are excluding the known causes of autistic behaviors. However, as the knowledge of conditions that cause autism advances, fewer and fewer cases will likely be thought of as being "pure" autism and more individuals will be identified as having autism due to specific causes.
There is a strong association between autism and seizures. This association works in two ways: First, many patients with autism develop seizures. Second, patients with seizures, which are probably due to other causes, may develop autistic-like behaviors. One special and often misunderstood association between autism and seizures is the Landau-Kleffner syndrome. This syndrome is also known as acquired epileptic aphasia. Some children with epilepsy develop a sudden loss of language skills -- especially receptive language (the ability to understand). Many often also develop the symptoms of autism.
These children often, but not always, have a characteristic pattern of electrical brain activity seen on EEG (electroencephalogram) during deep sleep called electrographic status epilepticus during sleep (ESES). The usual age of onset of language loss or regression is around 4 years of age, which makes the Landau-Kleffner syndrome distinguishable from autism on these grounds, in that autism usually is first exhibited in younger children. However, in recent years, some children (very, very few) who did not exhibit overt (observable) seizures were found to have Landau-Kleffner syndrome.
The importance of these findings is that, although rare, the Landau-Kleffner syndrome can resolve spontaneously and in some cases can be treatable with prednisone, a steroid medication related to cortisone. This association between the Landau-Kleffner syndrome and autism has led many clinicians and families to search for the typical EEG pattern (ESES) in individuals with autism. This unusual EEG pattern is seen only in deep sleep, which usually requires prolonged recordings of up to 12 hours. Many, many children and adults with this disorder will display some abnormalities on their sleep EEG, but probably very few have true Landau-Kleffner syndrome that will respond to treatment.
It must also be noted that prednisone, in the very high doses used to treat Landau-Kleffner syndrome, almost invariably produces side effects, which may include weight gain, high blood pressure, diabetes, growth failure, stomach ulcers, irritability, mood swings, hyperactivity, destruction of the hip joint, and susceptibility to infectious disease (suppressed immune system). While most of these side effects are reversible, some of the complications of high-dose prednisone therapy can be irreversible and even fatal.
Other treatments ranging from common anticonvulsant therapy to surgery have been proposed and are being tried for Landau-Kleffner syndrome. It is difficult to evaluate the true effects of any treatment for Landau-Kleffner syndrome due to the high rate of spontaneous resolution of symptoms (remission).
Is autism genetic?
Because many different disorders can result in autism, this question is complex. Certainly, disorders such as the fragile X syndrome and tuberous sclerosis, which are both associated with autism, are inherited. There are many families with more than one child with autism where the autism is not clearly due to another cause. Recent studies have found that the gene for at least one kind of familial autism may be on chromosome 13. In some families, autism seems to be passed from generation to generation. In other families, autism is not found in prior generations, but affects multiple siblings (brothers or sisters). The results of this research make it likely that at least one "autism gene" will eventually be found.
However, the majority of individuals with autism do NOT have a strong family history, which supports the premise that environmental or a combination of environmental and genetic factors contribute to the development of autism. In this context, environmental is meant to indicate any nongenetic factor, including infections, toxins, nutrition, or others.