What Causes Autism?

Autism is a brain disorder or unknown etiology - which means, in layman's terms "We don't know what causes it." There are a number of theories, and a lot of controversy surrounding the causes of autism, and some of it is wrapped up in the controversy surrounding just how common autism is, and whether or not there's been a sharp increase in actual cases of autism in the past ten years.

For parents, one of the most important things to know is that autism is NOT a psychological disorder. Researchers have long since put to rest the theory that autism is caused by the lack of a nurturing mother, but the belief still persists in some circles. If your child has been diagnosed with autism, rest assured that it is not because you were a bad parent.

The Genetic Link
There's a great deal of research that strongly suggests a genetic basis for autism. For instance, the incidence of autism in the general population is approximately 1.5 in 1000 people, but parents who have one autistic child have a 1 in 20 chance of having another autistic child. In fact, neurobiologists believe that autism is the most heritable of all the neurobiological conditions. The most persuasive evidence is the research done in twins. Twin studies can help establish a genetic link for a condition by examining the difference in prevalence of the condition in identical (monozygotic) and fraternal (dizygotic) twins. If a condition is genetic in origin, the prevalence will be markedly higher in monozygotic twins, since they share the exact same chromosomes. In most twin studies that have been done for autism, the prevalence of autism is as much as 90% higher in monozygotic twins than in dizygotic twins.

On the other hand, the studies raise other questions. The fact that not one of the studies showed 100% concordance in monozygotic twins suggests that there are other factors at play in the causes of autism, for instance. And other familial studies have noted common characteristics - for instance, that autism is more common in families of physicists and engineers, giving rise to the term 'the geek syndrome' to identify autism.

Environmental Factors
A number of researchers believe that there may be an environmental factor in the development of autism. Dr. Bernard Rimland, for instance, proposed in 1967 that autism may be a result of mercury and heavy metal toxicity to which some children have a genetic sensitivity. His treatment of autistic children with a gluten-free, casein-free diet and mercury chelation therapy (removal of mercury from the system) has shown some success with some children.

Other environmental factors that have been suggested to play a part are viral or bacterial infections, vaccines and thalidomide.

The Supermale Brain Theory
One particularly interesting recent theory about the etiology of autism is that it's caused by high levels of testosterone during development. A study in England measured the testosterone level of the amniotic fluid in mothers, then followed up with testing of children after birth and at four years. They found that the babies with the highest levels of testosterone pre-birth had a smaller vocabulary and made eye contact less often at a year old, and were less socially developed at age four. The theory holds that high testosterone levels in the brain support the development of 'male skills' like analysis of systems and seeing patterns, but repress the development of 'female skills' like communication and empathy.