Autism affects children of all races and nationalities, but certain factors are known to increase a child's risk. They include:

• Your child's gender. Studies show that boys are three to four times more likely to develop low functioning autism than girls are, and potentially up to 10 times more likely to develop Asperger's Syndrome.
• Family history. Families who have one child with autism have an increased risk of having another child with the disorder. It is very common for the parents or relatives of an autistic child to have minor or major problems with social or communication skills themselves or to engage in certain autistic behaviors. Relatives of autistic children are greatly overrepresented in fields where systemitizing ability is valuable, such as math, science and computer engineering.
• Other disorders. Children with certain medical conditions have a higher than normal risk of having autism. These conditions include fragile X syndrome, an inherited disorder that causes intellectual impairment; tuberous sclerosis, a condition in which benign tumors develop in the brain; the neurological disorder Tourette syndrome; and epilepsy, which causes seizures.
• Environmental Exposures: There are certain environmental exposures that greatly increase the likelihood a child will develop autism. The most dangerous condition is fetal exposure to alcohol. Other risky exposures include prenatal exposure to thalidomide, valproic acid, and ethyl mercury.
• Maternal Illness:  Maternal illness during pregnancy with various infectious diseases such as rubella, influenza, urinary or vaginal infections, and encephalitis, results in a statistically significant increase in autism diagnosis in the child postnatally.
• Maternal Major Stressor:  Women who have had a major stressful event - death of a spouse, job loss, or a long-distance move - midway through their pregnancy may have a greater chance of having an autistic child. Research has shown that these women were more likely to have experienced a major stressor the 24th through 28th weeks of their pregnancy. The timing of the stressful events recorded for the study seem to mesh well, timewise, with the periods of development of the fetal cerebellum - a key portion of the brain that is structurally different in autistic children.
• Paternal age. Research increasingly suggests that having an older father may increase a child's risk of autism. One large study showed that children born to men 40 years or older were almost six times more likely to have autism spectrum disorder than were children born to men younger than 30 years. Maternal age, accordint to a recent study, has a more limited impact.