Genome sequencing has ferreted out mutations in more than 65 genes that increase the risk of developing autism. Hundreds of others will likely be implicated as well. Some genetic mutations are passed from the DNA of the mother, the father or, sometimes, from both parents to the child. Others arise spontaneously, meaning they aren’t present in either parent’s genetic makeup. To date, genetic causes have been pinpointed in only about 20 percent of autism cases, usually those that are associated with certain rare diseases, such as Fragile X syndrome. But there’s no smoking gun for the remaining cases. It’s still largely unknown which genes drive the development of the disorder.
The number of genetic mutations that contribute to autism is manifold, on the order of several hundreds, perhaps even a thousand. That means the likelihood that any two patients will have a mutation in the same gene is very low. That’s why autism, now diagnosed in one in every 68 children in the United States, is no longer considered one condition but rather a spectrum of related but distinct disorders.
Genetics alone do not account for all instances of autism. The increasing prevalence of autism has generated great interest in the potential involvement of toxins in our environment. Autism is caused by a combination of genetics and a “vast array” of environmental factors—from a child’s exposure to certain toxins to overweight parents. Our best guess is that in many individuals, autism is caused by genes interacting with not only other genes but with an unknown number of potential environmental factors too.
12-13% of ASD among children in U.S. was related to being born too early, too small, and/or by Cesarean delivery. If it were possible to eliminate the many different reasons children are born too early, too small, and/or delivered by Cesarean, the number of children with ASD would be reduced by 12-13%.
Other risk factors include (1) parental age at conception, (2) maternal nutrition, (3) infection during pregnancy, (4) prematurity, (5) maternal obesity, (6) maternal diabetes, (7) air pollution, (8) anti-epileptic drug valproate during pregnancy, (9) fevers during pregnancy, (10) prenatal exposure to the chemicals thalidomide and valproic acid, (11) severe infections that affect the brain (meningitis, celiac disease, encephalitis, etc.), and (12) exposure to toxins or illness during pregnancy (rubella, chemicals, etc.).
SOURCE FOR THE INFORMATION PROVIDED ABOVE: Centers for Disease Control and Prevention