Individuals with Asperger syndrome share the social deficits, restricted and repetitive behaviors and interests, and impairments in theory of mind and executive function characteristic of autism 2 , 3.
Individuals with Asperger syndrome typically have an intense interest in a few topics. They focus on these topics so intensely that they become expert in these areas.
This characteristic of Asperger syndrome has given rise to the mistaken popular notion that all individuals with the syndrome are savants. People with Asperger syndrome often have difficulty initiating or maintaining a reciprocal conversation, partly due to their intense focus on a few favored topics. Studies have shown Asperger syndrome is up to 10 times more common in males than females. However, this skewed gender ratio may reflect difficulties in identifying the disorder in girls and women.
An emerging body of research indicates that girls with the disorder tend to be diagnosed later in life, perhaps because they are better at masking their symptoms 7. Functional impairment had to be obvious before age three. The newly created category of AS required at least two symptoms of social interaction deficits and one symptom of behavioral and interest restriction, normal cognitive, and linguistic development before age 3, and age-adequate adaptive functioning in areas other than social interaction.
Onset before age three was not mandatory. Importantly, the subject should not meet diagnostic criteria for Autistic Disorder — in which case the latter diagnosis should be given precedence, implying a differential diagnosis between AS and autism without cognitive delay, also called high-functioning autism HFA; Klin et al. Diagnosis required all six. There was no clause precluding a diagnosis of autism, and no mention of a minimum age limit or periods of normal development.
Although not exactly contradictory, these several diagnostic schemes nevertheless produced a bewildering semiologic cacophony. Mandatory diagnostic criteria for Asperger Syndrome according to Szatmari et al. The consecration of AS as a distinct diagnosis was surrounded by controversy from the outset.
The main problem was the precedence given to a diagnosis of autism. It soon became clear that most patients with significant impairments in social interaction and restriction of interests and activities also fulfill criteria for autistic disorder, thus precluding a diagnosis of AS. The requirement of normal cognitive and linguistic development failed to rescue a diagnosis of AS for the simple reason that cognitive and linguistic delay are not mandatory for diagnosing autistic disorder Mayes et al.
Moreover, it is often difficult to establish retrospectively if a patient had normal language before the age of three, and full-scale IQ is seldom a useful measure in AS, given the typically heterogeneous IQ profile Gillberg, ; Spek et al. Consequences of this conundrum soon became visible in research. Importantly albeit inconsequently , Klin proposed a reversal of the precedence rule: in the presence of criteria for both HFA and AS, As should be diagnosed.
Eventually, the controversy gradually converged onto knowing if AS and HFA can be distinguished qualitatively suggesting different etiological and neurobiological mechanisms for each syndrome , or if they merely differ quantitatively and should therefore be regarded as variants of a single disorder Macintosh and Dissanayake, Most studies used cross-sectional comparisons between subjects with either diagnosis to answer this question. AS subjects have earlier language development, more appropriate intonation and pitch, and more pedantic speech and idiosyncratic vocabulary, while HFA subjects show more echolalia, pronoun reversal, and neologisms Eisenmajer et al.
AS children also display more imitative social play, attention and help-seeking, and reciprocal social interactions than HFA children Prior et al. Yet, these superior linguistic and social skills of AS children do not translate into superior ability to make friends or engage in reciprocal conversation. By adolescence, differences are no longer obvious, although AS subjects still show more sophisticated vocabulary and greater desire for friendship Eisenmajer et al.
Cognitively, and as a group, AS subjects typically show a combination of superior verbal performance and visual-spatial, perceptual, and motor deficits non-verbal learning disability profile , while the opposite profile characterizes HFA Gillberg, ; Chiang et al.
However, individual variability is huge, and it is difficult to control for the biasing effects of a differential diagnosis based on differences in language development Klin et al. Studies that looked at theory of mind performance found mainly quantitative differences, with AS subjects scoring intermediately between HFA and healthy controls Prior et al.
Although many authors consider clumsiness as typical of AS, studies on motor control and gait have only found subtle differences in comparisons with HFA Macintosh and Dissanayake, ; Rinehart et al. Again, differences decrease with age Iwanaga et al. Finally, AS subjects show more intense preoccupations and circumscribed interests, while individuals with HFA have poorer imaginative play and more stereotyped behaviors, such as body rocking Macintosh and Dissanayake, ; South et al.
In terms of global functioning, AS subjects fare significantly better academically, but not in terms of employment or independent living Tantam, ; Howlin, An obvious approach to the question of whether or not AS and HFA are distinct entities is to look for biological differences between them. Despite the accumulated evidence on neurophysiological abnormalities in autism spectrum disorders ASD as a group, few data are available on possible differences between AS and HFA, apart from subtle differences in EEG connectivity patterns and left-hemisphere intra-cortical inhibition abnormally decreased in HFA but not in AS; Duffy et al.
Genetic studies have likewise produced little support for a discrimination between AS and HFA, although this must be tempered by growing evidence of a common genetic susceptibility shared by neurodevelopmental disorders in general, rather than a specific genetic etiology for each disorder Lichtenstein et al. Structural MRI studies comparing AS and HFA have produced contradictory results, with two recent meta-analyses and a recent systematic review reaching three different conclusions Via et al.
The most consistent positive findings come from studies that differentiated AS from HFA based on language acquisition history: compared to AS and typical controls, HFA subjects have lower gray matter and white matter volumes, increased gyrification, and abnormal cortical folding in inferior frontal areas including the pars opercularis; Nordahl et al.
However, these qualitative neuroanatomical differences are contradicted by studies that only found quantitative differences, with AS intermediately positioned between HFA and typical subjects Lotspeich et al. Many differences are quantitative rather than qualitative, and are distinctly more pronounced at younger ages, although the same might be said of many differences that discriminate HFA from typically developing subjects Luckhardt et al.
Moreover, research has been systematically plagued by difficulties ensuring independence between selection criteria and outcome measures Macintosh and Dissanayake, At this time, researchers did not consider the biology or genetics involved, but only looked at the impact of life experiences. To this end, it was differentiated from the diagnosis of childhood schizophrenia.
The manual also included a checklist for diagnostic criteria in order to eliminate the lack of consistency between diagnoses made by clinicians. This made it easy for autistic children to get special education services.
Temple Grandin , an American scientist and animal behaviorist, wrote Emergence - Labeled Autistic, which described her life with autism. Later on, many other studies quickly debunked this theory and the article was retracted, however, the idea that vaccines cause autism is still somewhat of a popular misconception.
The previous statistics suggested in , this rate was 1 in However, the increase in the prevalence of autism was attributed by the CDC to the advancements in diagnostic and screening techniques. Autism Spectrum Disorder is now defined by two categories, namely the impaired social communication and restricted and repetitive behaviors. This article is examined by Clinical Child Psychologist and Ph.
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