No single cause of autism has been identified so far.  However, the developmental disorder may be due to several different causes. Years ago, parental practices were largely thought to cause autism; this has now been disproved.  Today, combinations of genetic and environmental factors are thought to play a role in causing autism; several genes have been discovered that are connected to autism.

There has been a great deal of discussion and controversy over whether or not some vaccinations cause autism, especially those for the measles-mumps-rubella (MMR) vaccine, and vaccinations that contain the preservative thimerosal.  However, there has been no conclusive evidence showing this.  

Possible causes of autism include:

1. Environmental causes - Viral infections and pollutants may play some role in autism.
2. Genetic causes - Inheritance of certain genetic errors is strongly suspected to play a role in causing autism.  
3. Miscellaneous causes - A variety of other possible causes are being investigated, including: damage to the amygdala (an area of the brain); immune system problems; and difficulties during the birth of a child.

Risk factors
Autism usually begins before the age of 3, and affects anywhere from 3 to 6 children for every 1000 children in the US.  It affects people across ethnic lines. However, autism disproportionately affects males: for every 1 girl who is diagnosed with autism, 4 boys are diagnosed.  Additionally, conditions statistically more likely for the development of autism include the following: 

• Conception - Children born to fathers over the age of 40 may be more likely to develop autism.
• Family history - Having a sibling or parent who has autism.
• Gender - Males are significantly more likely than females to develop autism.

Related health conditions
People diagnosed with autism are usually diagnosed with other, related health issues.  Because of the relatively high correlation of autism, and the occurrence of other condition, additional treatment options may be needed for each.  Or, preventative steps may be necessary. Health issues related to autism include:

Fragile X syndrome - This inherited form of mental retardation affects the X chromosomes of approximately 5% of autistic suffers.  

Mental retardation - This disorder may impair a child's mental abilities within a subject area for a child with autism. 

Sensory problems - Children with autism may be highly sensitive to any sensory perception, even to the point where some sensations may be extremely painful to the child.  Other children with autism develop insensitivity to sense and may not feel other sensory perceptions, even when it would normally be very painful.  For example, an autistic child may break a leg, and not act in pain.  

Seizures - Approximately 25% of children with autism experience seizures, which may begin during childhood, or during adolescence.  

Tuberous sclerosis - Approximately 1-4% of autistics are diagnosed with this genetic disorder, which causes benign tumors to grow in the brain and other vital organs of the body. 

Because the symptoms of autism can vary in intensity and type, it's important to become aware of the signs and symptoms of autism, especially during a child's early years.  This is even more important, if a parent or sibling has been diagnosed with autism.  To get an autism symptoms checklist, continue reading our next section on Autism Symptoms now.