Autism is a complex disorder that is not completely understood. There are many areas of active research trying to discover what factors may put a child at risk for autism.
The main risk factor for autism is heredity. Autism spectrum disorders are thought to be caused by multiple genes.
Autism is a multifactorial condition, which means that more than one thing is responsible, probably many different things. Autism is also a spectrum disorder, meaning that there is wide variation in how severely people with autism are affected. The term autism spectrum disorder is often used, or ASD.
The main risk factor for autism is heredity. Autism spectrum disorders are thought to be caused by multiple genes. Research is ongoing, looking for the genes. Because multiple genes are involved, and because other factors may play a role, family members with the same genes do not show the exact same symptoms. With autism, it may “run in the family,” but every case will be different, and many people will not be affected.
If one child in a family has a condition anywhere on the autism spectrum, the chances of a sibling having autism are approximately 5 to 6%. If two children have autism, the risk for another child is even higher. If one of two identical twins has ASD, the other twin has an 80 to 90% of developing autism. Male children are much more likely to be affected than female children by a ratio of at least 4 to 1.
There are certain environmental or external forces that may increase the likelihood that a child with a genetic predisposition to autism will actually have the disorder.
There are risk factors at work before birth, which include:
- An older father and/or an older mother.
- Drugs taken during pregnancy, especially those known to cause damage to the fetus, like valproic acid.
- Maternal illness during the pregnancy, including German measles, which can cause Congenital Rubella syndrome.
Probably less than 10% of autism cases are caused or associated with another more serious condition or syndrome. These are usually inherited. In most of these cases, there will be obvious and visible problems besides the autism. Often this means some degree of mental retardation. Some of the syndromes include:
- Fragile X syndrome. This syndrome includes mental retardation and specific anatomic abnormalities. This is the most common cause of both autism and mental retardation in males. 10 to 15 % of children with fragile X syndrome have some of the symptoms of autism. 5% of autistic children have Fragile X Syndrome. Patients with this diagnosis need genetic testing. If parents have a child with Fragile X as well as autism, there is a 50% chance that other boys born to these parents will have Fragile X.
- Neurocutaneous disorders.
- Tuberous sclerosis is a disease in which there are multiple spots or growths on various parts of the body, including the skin, kidneys, and brain. Children with this disorder may have mental retardation, seizures, and attention deficit/hyperactivity-disorder, as well as autism. Tuberous sclerosis can be inherited or caused by a new mutation. Between 1 and 4% of patients with autism have tuberous sclerosis.
- Neurofibromatosis is the disease that was depicted in the play and movie “The Elephant Man.” People with this disorder often have multiple large tumors on the skin and in the nervous system. This disorder is also hereditary, but can be caused by a new mutation in a specific gene. Most patients with neurofibromatosis have normal intelligence and behavior, but there are some who show symptoms of autism and/or mental retardation.
- PKU, or phenylketonuria, can cause autism, but since babies are checked for this at birth and treated, it is now a rare condition in the United States.
- There are a number of other rare syndromes that can be associated with autism. Children with these disorders will have other very obvious problems.
Other risk factors for autism are very controversial and provoke extreme reactions and deep feelings in parents of autistic children. These include:
- The MMR (measles, mumps, and German measles) vaccine. There has in fact been no association proven between vaccination with the vaccine and autism. This issue has been essentially resolved in the scientific community, but is not necessarily settled in the view of parents with autistic children.
- Mercury, in vaccines as the preservative thimerosal, or from the environment. Again, thimerosal in the MMR vaccine has been eliminated as an issue from a scientific point of view. However, many agree that mercury in the environment may be a problem.
- Other environmental factors have been suggested, from fluoride in toothpaste and water, food, including wheat gluten and dairy products, to a wide range of environmental contaminants. There are those in the autism community who believe that there are many risk factors that can be eliminated or reduced by the use of certain diets, toxin removal by chelation, and various other interventions. People who advocate the diets and treatment truly believe that they know better than the medical establishment.
There may be environmental factors that increase the risk of autism, but these have not yet been proven. Examples of toxins that may very well increase the risk are heavy metals such as mercury. As stated above, thimerosal in vaccines has not been associated with ASD. However, mercury contamination in the environment may actual pose a risk to children.
There is active research trying to better define all the risks, be they genetic, infectious, or environmental.