The National Institute of Neurological Disorders and Stroke (branch of NIH) describes Autism Spectrum Disorder (ASD) as a "range of complex neurodevelopmental disorders, characterized by social impairment, communication difficulties, and restricted, repetitive, and stereotyped pattern of behavior.
They note that it is found in "all ethnic and socioeconomic groups." Roughly one out of 88 children by age 8 will have ASD. It is four times as common in males than females. Individuals with ASD commonly have a variety of other health problems such as learning disabilities, ADHD, Tourette Syndrome, tuberous sclerosis, and others. Epileptic seizures are especially common such that 20-30% have a seizure disorder by adulthood.
What was just called Autism is now named Autism Spectrum Disorder because it is now believed that a variety of different diagnoses such as Asperger Syndrome are all part of the same category of illnesses that represent different levels of severity.
The ultimate cause of ASD is unknown. However, there is good evidence to believe that it is a combination of genetic and environmental factors. What we do know for sure is that it is not caused by parenting types such as a "refrigerator" mother (cold and distant from her child). This is a totally discredited theory from the past.
We also know that it is not caused by vaccines including MMR (measles, mumps, rubella). This debunked theory was promoted by a British physician who published a paper showing a connection. However, sometime after publication, it was discovered that he had made up some of the data. He lost his medical license as a result.
Nevertheless, there are people including celebrities who continue to promote this false association. Multiple studies since the fake paper by the British physician have all shown that here is no connection between ASD and vaccines, and the Institute of Medicine in 2011 made a strong statement that MMR is not associated with autism or childhood diabetes (some people had thought diabetes could be caused by the MMR vaccine).
It appears that a large number of genes are involved in making a person vulnerable to getting ASD (polygenic disorder). There are some families in which autism runs in the family.
An epidemiological study in Sweden involving 417,000 children showed that the risk of ASD rises sharply if the mother is over the age of 30. Also, the incidence is much higher in the offspring of men over age 45, and it continually rises as men get older. These findings are consistent with genetic factors playing a significant role. It is known, for example, that there are more genetic mutations during sperm development in men as they age.
Studies of twins show that the odds of an identical twin having ASD is 70% if the other twin has it. In contrast, fraternal twins have only a 35% chance. Identical twins have 100% of the same genes, whereas fraternal twins only have 50%. Non-twin siblings have a likelihood of ASD if a sibling has it 3-14% of the time.
Environmental factors seem necessary to explain why some people with the same genetic makeup do not get it. Some suggested factors include exposure to excess alcohol while in utero, exposure to certain medications, viral infections, and others. There is no definitive proof for any of these.
One intriguing possibility has been identified at the University of North Carolina medical school. There are a group of enzymes called topoisomerases that may play an important role. These enzymes are necessary for normal brain development, among other things. We do know that some chemicals such as topotecan, an anti-cancer drug, inhibit these enzymes and would be expected to adversely affect brain development in a fetus. Topotecan is known to inhibit about 50 of the genes associated with ASD. it may be that there are chemicals to which a pregnant woman or very young child can be exposed to that may inhibit this class of enzymes. Clearly, much more research needs to be done on this topic.
The bottom line is that ASD represent a group of neurodevelopmental disorders of varying severity. There is no known cause, but abundant evidence demonstrates a combined role for multiple genes and environmental factors. Families affected by ASD anxiously await further research and understanding of ASD with the hope that more effective treatments will follow.
Peter M. Hartmann, MD
