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Autism Spectrum Disorders (ASD) are developmental disabilities characterized by difficulties with social interactions, impairment in verbal and/or nonverbal communication, and the development of repetitive, unusual, or highly-specialized interests. The pathology underlying the condition is based in the brain, although the precise disease mechanism behind ASD has yet to be described. ASDs are typically diagnosed in early childhood with functional impairment persisting throughout life.
ASDs include a number of specific diagnoses. Autistic Disorder (AD) is the best-described and most severe of these. Others include Asperger Syndrome, Pervasive Developmental Disability – Not Otherwise Specified (PDD-NOS), Rett’s Syndrome, and Childhood Disintegrative Disorder. The general term “autism” is often used either specifically to refer to AD or more generally to refer to ASD. Another term that is often used synonomously with ASD is Pervasive Developmental Disorders (PDD). This term is the diagnostic category heading under which the five specific diagnoses mentioned above are listed. We prefer ASD over PDD because it emphasizes the common “autism-like” features of all of these specific diagnoses and, at the same time reflects the wide variation in the manner and severity that individuals are affected.
The main symptoms of ASD are particular social and language problems. Often, but not always, children with ASDs will have delays developing spoken language. Some individuals with ASD remain non-verbal throughout their life. Currently, language delays are the symptom that most commonly captures the attention of parents or pediatricians and, consequently, children are infrequently diagnosed before the age of 3 or 4 years. However, problems in other social and communication behaviors, such as imitation and use of gestures, may hold the key to being able to recognize the behavioral signs of ASD at earlier ages.
The specialized interests that develop in persons with ASD can be quite varied. In young children this can first appear as constant lining up of, rather than playing with, toys or obsessive watching and re-watching of segments of a particular video/DVD. Older, verbal children with ASD may show a strong tendency to talk, regardless of the setting or context, about particular topics of interest.
There are no definitive biologic signs or symptoms of ASD and it is diagnosed only based on careful observation/assessment of behavior and knowledge of the individual’s developmental history. There is no medical test that can diagnose ASD.
Children with ASD often have other associated problems that can include, sensory impairment, gastrointestinal problems, sleep disturbances, and seizure disorders, as well as often appearing to have cognitive impairment. At the same time, they may also show special skills in certain areas like drawing, math, music, or memory. It is unclear to what extent these problems or skills are caused by the same process that leads to ASD.
There is still much confusion about the difference between Asperger Syndrome and PDD NOS. Individuals with both of these diagnoses are similar in that they do not have sufficient or severe enough impairment in each of the characteristic ASD areas (social, communication, specialized interests) to warrant an autistic disorder diagnosis. Children with Asperger Syndrome, however, typically do not have language delays and might read precociously or have extraordinarily rich vocabularies for their age. However, these children still struggle with the social aspects of language and nonverbal communication and can have all the other attendent problems of ASD. Children with Asperger Syndrome have normal or above normal IQ – but so too do many children with PDD NOS (although these children have typically had some language delay). Children with ASD who have normal to above normal IQ (which includes those with Asperger Syndrome, many with PDD NOS, and some with autistic disorder) and whose behaviors are less of an impediment in their daily activities are often referred to as having “High Functioning Autism.” While much time and effort can be spent sorting through the criteria for these different labels, it is still not clear to what extent these distinctions reflect important differences in the causes behind, or the interventions best suited for, the underlying disorder.
ASD affects persons of any race, socioeconomic status, and gender, although it is more prevalent in boys than in girls – for example, there are 4 boys for every 1 girl with autistic disorder.
Better data are available on the prevalence of autistic disorder than other ASDs, or ASDs overall. That said, there are still many challenges to accurately measuring the prevalence of autistic disorder in populations. Most of the autistic disorder prevalence estimates coming from recent studies (those completed in the mid-to-late 1990s) fall between 15 and 30 per 10,000. Recent estimates for all ASDs combined tend to fall between 20 and 80 per 10,000. Most of these studies were more likely to be affected by challenges that would lead to under-, rather than over-estimation, of prevalence. The Centers for Disease Control and Prevention includes on its autism resource page, a prevalence estimate of 3-7 cases of ASDs per 1,000 children.
Unquestionably, there are more children being diagnosed with ASD today than ever before. This, in and of itself, presents a major public health challenge. It is, however, very difficult to determine why this is occurring. We know that there have been changes in diagnostic criteria and the manner and frequency with which criteria are applied. Consequently, there is no way of accurately determining how much of the increase in ASD prevalence seen over the last decade is attributable to diagnostic issues and how much is attributable to a real increase in risk.
At present, we do not know exactly what causes ASD. It is certain that genetics plays a large role. However, we do not know what proportion of ASD cases have some inherited susceptibility nor do we know how large a proportion of autism cases are entirely caused by inherited genetic factors. Further, while genetic risk factors are important, this does not rule out a potential major role for non-heritable risk factors. That said, there is little conclusive evidence supporting a prominent role for any particular non-genetic risk factor. However, part of the reason why no other risk factors have been identified may be that genetic and non-genetic factors need to be studied together in order to get a clear picture. In other words, only when studying ASD cases with a certain genetic background may we be able to see that a particular non-genetic trigger was important. Studies like this are only just now getting underway.
There has been much recent discussion over a potential link between vaccines and ASD. Concern has been expressed over the MMR (measles/mumps/rubella) vaccine and vaccines that contain a preservative, thimerosal (which contains a form of mercury.) A number of epidemiologic studies of MMR vaccination and ASD have now been completed with none finding evidence of a link between MMR vaccination and ASD. Epidemiologic data has recently become available on the potential association between thimerosal and autism. These data do not support an association. While it appears that there is no link between thimerosal exposure and autism risk at the population level, there may still be small groups of individuals susceptible to neurodevelopmental effects of low-dose mercury. Research is underway exploring the possible mechanisms. In sum, the available epidemiologic data suggest no link between childhood vaccination and autism - these data offer no reason why immunization should be avoided or postponed. Dr. Leo Kanner, a physician at Johns Hopkins Hospital, published the first paper describing autism in 1943. At virtually the same time, an Austrian psychologist, Hans Asperger, described a similar group of patients. Although ASD has been recognized as a medical condition only in modern times, there are many historical accounts pointing to the existence of autism well before the 20th century. There is no known cure for autism. However, early behavioral-based interventions can help children to better develop the communication and social skills needed to improve their functional abilities. Although a number of different specific behavioral and educational techniques are currently used as part of interventions for individual children with autism, these techniques are grounded in a vast body of research based on a common set of behavioral and learning principles. Early intervention programs generally emphasize attending to social stimuli, imitation skills, language comprehension and usage, appropriate play skills, and social interaction. For certain subgroups of children with ASD, drug therapy may be available that reduce problematic behaviors. However, of the numerous other interventions that have been proposed over the years, none have been proven effective. |
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