The Changing Face of Autism

The diagnosis of autism spectrum disorders (ASD) has been on the rise in Hong Kong and around the world since the mid 1990s. In the upcoming version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V), research evidence is indicating that autism is not a black or white categorically defined condition, but something that is on a spectrum and has grades of severity. Persons on the autism spectrum range from severely impaired with low cognitive ability, minimal or no verbal skills and a high degree of rigid restricted behaviours, social deficits and difficulties with emotional control, to those at the higher end (most commonly referred to as Aspergers Syndrome) who have cognitive ability that is in the average range or above but still have social impairment and rigid restricted behaviours and interests as well as difficulty with emotional control.

One of the most important defining characteristic of ASD is social problems, which is now being viewed as a quantitative trait that is genetic in origin. Much of the research establishing autism as a quantifiable genetic disorder is reviewed in a study published by Dr John Constantino in the Journal of Paediatric Research.

This research is having a profound impact on the conceptualisation of autistic disorders as part of a continuum of social variation in nature and views autism as fundamentally a quantitative disorder. In order words, the symptoms and traits of ASD are distributed normally in the population and this research has also been validated in cross cultural studies outside of North America.

The reason for the rise in diagnosis of autism spectrum disorders has been documented as being due to changes in diagnostic criteria in the middle of 1990s in which higher functioning individuals (particularly Aspergers Syndrome) were being listed as persons on the autism spectrum. Environmental causes such as the MMR vaccine were implicated as causing a rise in autism but subsequent research in several different countries over the last decade suggested that the rise was due in part to the change in diagnostic criteria.

More and more genetic studies are providing evidence that autism is clearly an inherited disorder. A lot of this evidence comes from family and twin studies. The concordance rate for autism in identical twins is about 88% and 30% in non identicals. It is also found that siblings of children diagnosed with autism have about 15% chance of also being diagnosed on the autism spectrum. Current studies now suggest that 90% of autism symptoms are inherited though it is possible for the genes to skip a generation and some researchers have theorised that the gene can sometimes be dormant (particularly in females) and skip a generation before being expressed. It is believed that 5% to 10% cases of children that are diagnosed with autism may be due to what is known as a genetic “denovo mutation” in which there can be no traceable hereditary link. In cases of denovo mutation it is also suggested that the chances of a child having autism are increased with advanced paternal or maternal age. In other words, the older the age of the parent the higher the chance that the child may have autism. This does not completely rule out the possibility for environmental causes but it is postulated that they only account for a very small number of the cases of children that are diagnosed on the spectrum.

Because there are now reliable quantitative measures such as the Social Responsiveness Scale that provide a valid estimate of the severity of an autism spectrum disorder, it is becoming much easier to carry out genetic and population study research and sheds light on some possible causes for the increase besides diagnostic criteria. One theory put forward is that the selection of mates or partners is different now than it was in the 1950s to 1970s. Dr Constantino suggests that one possible factor is that persons with similar autistic traits may be drawn to each other and with increasing numbers of women attending university and joining the work force since the 1960s as well as social networking on the internet, it increases the odds for “birds of feather flocking together” so to speak. The idea behind this as being one causative factor for the increase is due to research that utilizes Social Responsiveness Scale adult ratings and self-report measures. The outcomes suggest that parents of autistic children will often rate themselves and each other as having autistic like traits and this can be correlated with the degree of autism that may be expressed in their child.

Taken together this information gives professionals better insight into the causes of autism spectrum disorders. Hopefully this will lead to preventative treatment measures in the future as well as giving us better tools for early identification which significantly increases the chance for a positive outcome.

References:
The Quantitative Nature of Autistic Social Impairment, Constantino, J. 2012, Pediatric Research.
http://www.ncbi.nlm.nih.gov/pubmed/21289537