One of the most frequent questions I'm asked by parents of young children is whether I believe there is a greater prevalence of kids being diagnosed with Autism now compared to earlier years. Anecdotally there is a sense that people regard this disorder to be on the increase.
A key question is whether more kids are being labeled with autism today due to a true increase of the disorder or whether factors such as greater awareness by doctors and the public, a broader definition of it, better diagnostic instruments, and changes in diagnostic criteria are contributing to this perception.
According to Dr. Chris Johnson, a professor of pediatrics at the University of Texas Health Sciences Center at San Antonio and co-chair of the American Academy of Pediatrics Autism Expert Panel there may be a chance we’re seeing a true rise, but right now he doesn’t think anybody can answer that question for sure. Some parents have been or are of the belief that the disorder is increasing due to some modern hazard that is damaging the children’s brains.
This theory was aided by a paper in The Lancet, a British medical journal in the late 1990’s. In that, a connection between vaccines and autism were raised – the MMR vaccine controversy claimed that autism spectrum disorders can be caused by the MMR vaccine, an immunisation against measles, mumps and rubella. In 2011 the research was declared fraudulent and The Lancet paper was partially retracted in 2004 and fully retracted in 2010. Scientific consensus is that no evidence links the vaccine to the development of autism, and that the vaccine's benefits greatly outweigh its risks.
Studies in the 1960s indicated that autism was quite rare, affecting only about one person in every 2,000 to 2,500, according to the Centers for Disease Control and Prevention. Other research in 1970 put the figure at one case per 10,000, according to Johnson. Precisely how many people have autism today is unknown. Estimates suggest there are five to six cases of autism spectrum disorders per 1,000 people or roughly as many as one case out of every 166 people.
A relatively recent report commissioned by Autism Advisory Board on Autism Spectrum Disorders found that there is one child with autism spectrum disorder on average in every 160 children.
It is however difficult to make comparisons across decades. Diagnostic criteria changed dramatically in the late 1980’s, broadening the number of people who could be considered to have autism spectrum disorder. In earlier years, only those with severe autistic characteristics would be diagnosed with autism; and others might have been categorized as individuals with intellectual disabilities.
The idea that changes in diagnostic criteria and greater awareness leading to an increase in the incidence of autism was examined by W. Barbaresi and colleagues (Mayo Clinic Child Development Research Group) in an important study looking at the Incidence of Autism in Olmsted County, Minnesota, 1976-1997.
Using data on every child living in the county during those years, the researchers used modern diagnostic criteria to conclude that the incidence of autism specifically rose dramatically, from 5.5 cases per 100,000 children from 1980 to 1983, to 44.9 cases from 1995 to 1997. A sharp increase started between 1988 and 1991, a period during which broader diagnostic criteria for autism were newly in use and increased awareness of the disorder occurred.
The findings of the study was published in the January issue of the Archives of Pediatrics and Adolescent Medicine, and highlighted by Time Magazine as one of the most important medical studies published in 2005.
More recently, numerous studies attempting to better understand the causes, and hopefully improving diagnosis and treatment have focused on genetic underpinnings of the disorders that may play a role in a significant number of cases. The US federal government, has, for example organized an international coalition to explore the genetics.
Many scientists believe that autism is largely caused by genes. Studies have shown, for instance, that if one identical twin has autism the second twin is very likely to also have the disorder. But the risk isn't 100 percent, suggesting that other factors can contribute, even if they aren't the main cause.