Studies suggest the prevalence is somewhere between 1 in 200 - 500. In recent years there has been a large increase in the number of children diagnosed with ASD, particularly those in the high functioning category. This is probably due to a broadening of the criteria for diagnosis, and better diagnostics methods enabling detection at a very young age.

The role of mercury as a risk factor for childhood autism is not fully understood; however, it has been shown that mercury can interfere with the signaling pathways in a child’s developing brain and the modulation of proteins that regulate the immune system (see Understanding Mercury, Understanding Autism by Ellen Silbergeld, Ph.D., and Jennifer Nyland, Ph.D.).

Findings indicate that many children with autism or those who are at risk of developing autism have a metabolic impairment that reduces their ability to rid their bodies of heavy metals and other toxins. Build-up of these toxins in the body can lead to brain and nervous system damage and developmental delays (see We’re Loaded with Toxins: Analyzing the Toxic Body Burden of Americans by Judy Chinitz Gorman).

Some children who are genetically at risk for ASD may be more susceptible to the adverse effects of pesticide exposure. Research shows that several genes associated with autism risk encode for proteins that regulate excitation/inhibition within the central nervous system. Several of these neurotransmitter systems are known to be targets of pesticides frequently found in children (see Can Exposure to Environmental Toxicants Influence Autism Susceptibility? by Isaac N. Pessah, Ph.D.).

Autoimmunity is a condition in which the immune system attacks the body’s own tissues. Several studies show that autoimmune activity can be associated with ASD in some cases, but it has not been determined if this activity contributes to the development of the disorder or if it is a consequence of the disease (see Autism Spectrum Disorders and the Immune System by Paula Goines, B.S., Paul Ashwood, Ph.D., and Judy Van de Water, Ph.D.).

There are reported cases that some children with autism have substantially or completely recovered. Commonweal, a non-profit health and environmental research institute, is conducting an autism recovery documentation project that will provide a detailed report of a number of verifiable recoveries from ASD (see Helping to Shift the Paradigm: Learning More About Recovery in Autism by Robert Sinaiko).

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The specific cause of ASD is not known however researchers around the world are exploring different theories and trying to identify the specific gene or genes that may cause autism. It is known that there are biological or neurological differences in the brains of people with autism. There are several outdated theories concerning the cause of ASD; it is not caused by bad parenting and it is not a mental illness.

In many families, there is a pattern of ASD or related disabilities, suggesting that there is a genetic basis to the disorder. There is some tendency for ASD to cluster in families with the incidence rate amongst siblings 50 times that of the general population.

Autism is diagnosed by examining the child’s development and behaviours. Sometimes autism can be difficult to diagnose so it is important to have a comprehensive assessment to distinguish ASD from a range of other difficulties. assessment by a paediatrician is required prior to an assessment for ASD in order to rule out other factors including medical conditions that may be affecting the child’s development and behaviour. A hearing assessment may also be required.

The term "incidence" refers to the number of newly diagnosed cases of a disease occurring in a specific population during a specific time period. The incidence rate is the number of newly diagnosed cases in a specific population during a specific time period per "x" number of people; usually the time period is one year and "x" number of people is 100,000. Such an incidence rate is "crude", is not age adjusted (see #11 below) and therefore cannot be used to compare different populations.

Texas Cancer Information expects to add incidence data in the fall of 2007. There is currently limited incidence and survival data available in the on-line publication of Texas Cancer Facts & Figures 2004 , a publication made possible through the collaborative efforts of the American Cancer Society, Texas Division, Inc.

Some of these bacterially produced compounds (mentioned above), known as short-chain fatty acids, when injected in small amounts into the brains of experimental rodents, produce bouts of hyperactivity and repetitive behavior resembling those seen in ASDs. Research shows that repeated exposure to these compounds can exert permanent effects on brain and behavior (see Canadian Study: Is There a Digestive Link to Autism? by Kulani Mahikoa).