Further Thoughts on Autism Disorder Subtypes


(Notes for the Policy and Performance Department, Surrey LEA)



A common classification cited by many writers on autism involves a tri-partite type system. 


Temple Grandin, for example, puts classical autism and Asperger Syndrome (AS) into the same category, while contrasting this joint category with epileptic or regressive autism, and with pervasive developmental disorders not otherwise specified (PDD-NOS).


Others might prefer to separate classical autism (sometimes called Kanner autism) and Asperger syndrome, and the trend in research data or informed opinion is towards this distinction.

Nevertheless, it is acknowledged that classical autism and AS do share many signs and symptoms and defining features.  These would include the “triad” of characteristics involving impairments in social skills and interaction, communication, and (imaginative) play, reflected in relatively solitary activities, stereotyped and repetitive interests and behaviours, and some rigidity of thought. 

The two conditions appear also to share cerebellar impairments resulting in sensory anomalies such as hypersensitivity to sensory input and a deficit in managing such input… often leading to a withdrawal from those settings where the input is complex and diffuse (as might well be the case in a school playground). 

Amygdala impairments, too, may be common to both conditions.

They both are likely to involve poor and slow processing of information, especially verbal information, which will further inhibit communication including the interpretation and following of directions, with an implication for taking nothing for granted and for being very specific in the use of language when posing questions and giving directions and in checking the understanding thereof … especially if the children concerned will not learn “incidentally” from listening to the other children and from watching their responses.


Classical autism and AS do appear differentiable in terms of better performance among the AS population in language, some greater skills in respect of reading theory of mind cues and non-verbal language, and higher scores in cognitive tests.  General level of functioning is higher and such children tend to respond better to day to day community demands, and to placement in a school setting.

The problem is that adequate expressive language and vocabulary may sometimes lead to an over-estimation of general communication skills when the AS children may not all have comparable skills in receptive language and comprehension or in the rate of processing … with implications for limited fluency or bi-directionality of conversations, and, consequently, for social interaction. 

Further, the children may have the capacity to recognise their own difficulties or disadvantages or differences, especially in terms of peer relationships, but to be unaware of how to act, and this may be one factor behind their increased susceptibility to emotional and psychiatric problems.


A further type is referred to in some classification systems … the regressive or epileptic type.  The autistic signs and symptoms may be of relatively late onset, after a period of apparently normal development. 

Speech and language typically regress sharply, which is the most clearly observable marker of the onset of the condition, and many of the children are left with significant disabilities.


It is suggested that at least some of these cases reflect a situation where a (genetic) susceptibility is present and which is triggered by some environmental event, such as exposure to allergens or toxins (but almost certainly not the MMR injections). 


These cases may be marked by more evident neurological problems, and particularly poor understanding of speech (or limited capacity to make out and interpret speech sounds … like a central auditory processing disorder).  There are commonly severe problems with managing or filtering sensory input. 

There may well be signs of subtle epileptic seizure activity, or episodes of apparent aggressiveness which actually reflect frontal or temporal lobe seizure activity.


In many cases, the children are low functioning, but it may happen that low observable or measurable ability, and an assumption of generally low functioning, will be attributed as a result of the immediately observable sensory and communication problems.


The notes by Lars Perner (2006) of the University of Southern California may be thought representative of many contributors to this field in citing 3 basic types :

To this trio, there could be added Rett Syndrome, albeit not often bracketed with autism given the severe physiological impairments; or Childhood Integrative Disorder, albeit relatively rare.


Perner comments that the major problem with this, or any, basic sub-division is that differences within groups may be larger than the average differences between groups.

Many more subtypes could probably be identified, with significant differences between the various groups in terms of their specific nature or severity of symptoms and their response to given interventions.

Further, whatever the diagnostic classification, some individuals are more vulnerable to gastro-intestinal problems, and others to anxiety or self-injurious behaviour.  


He argues that there are two significant problems in seeking to establish meaningful subtypes.


Firstly, it is likely that within-group variance (in response to intervention, for example) will be large given the tendency for individuals with autism to cluster around one or other extreme of some characteristic.  Therefore, mean differences between groups may not be observed even if there are wide differences across individuals, or sub-groups of individuals, and these (mean) results may conceal significant effects.

This may be described as “aggregation bias” whereby misleading conclusions may be set down as a result of averaging the group observations.


Secondly, there will arise problems in identifying promising interventions for a given individual.  Comparison of groups, comprising participants who may vary widely in various attributes one from another, is likely to fail to recognise the individual characteristics predictive of a successful outcome of an intervention. 

This, in turn, could mean that there is a delay in the identification of effective interventions, or the emergence of negative outcomes from adopting interventions that are not effective, together with the stress impacting upon both child and family during the process of trialling a number of approaches, especially if the children in question cannot articulate their experiences and feelings.


With regard to PDD-NOS, the problem is that this is a kind of “residual” category for various children whose symptoms are of an autistic type but who do not fully match the criteria for either classical autism or Asperger Syndrome. 

Meanwhile, individuals diagnosed with autistic disorder who receive intensive treatment as a result of which they no longer meet the original diagnostic criteria, could be reclassified as PDD.


Further, Rett Syndrome and Childhood Integrative Disorder appear qualitatively different from autism, but may still be discussed alongside classical autism or Asperger syndrome, or be classified as forms of PDD and thus somehow equated with autism.

The regressive type of autism, identified by the dramatic regression in developmental skills, notably language, and the emergence of stereotypic and repetitive behaviours during the second year, is experienced by a minority of cases (20% +). 


Relevant to all this is the ongoing work among researchers at the University of British Columbia and Simon Fraser University which has involved a cluster analysis of data gathered from a large sample of children with autistic spectrum disorders. 

They describe 4 meaningful subtypes as emerging from the analysis.


This study emphasised the range and significance of differences among the children identified with autistic disorder, and noted the relationship between cognitive functioning and subtypes of the condition. 


Commonly comorbid and confounding conditions would usefully be listed in order to seek to highlight what are primary autistic characteristics while also acknowledging the overlap between autistic disorder and other conditions.  These include specific language disorder, reactive attachment disorder, central auditory processing disorder, anxiety, avoidant behaviour, anxiety, etc.

At this point, it would be reasonable to cite the current concern about the use of diagnostic labels, sometimes applied on the basis of less than comprehensive assessments or observations or ratings, and which pathologise children (as having Asperger Syndrome ?) when the presenting issues may be little more than a degree of shyness or of eccentricity.  Once a label is attached, it can happen that all the negative characteristics, and severe levels of symptomatology, are attributed to a child despite the heterogeneity of symptoms and behaviours among the children who are legitimate candidates for an autistic diagnosis.


This heterogeneity would usefully be emphasised; and one could  highlight the many areas of functioning where the performances of children with autistic disorder vary widely … such as expressive language, receptive language, sensory sensitivity, aggressive behaviour, externalising behaviour, self injury, sleep patterns, eating patterns, symptoms of stress, etc.   


Finally, one should mention the ongoing Autism Phenome Project (M.I.N.D. Institute, Sacramento, California) which is exploring the nature and aetiology of autism which currently is marked by its bewildering heterogeneity. 

The project involves 1800 children, aged between 2 and 4 years at the start of the exercise, across multiple sites across the country, subject to a medical evaluation

(including the assessment of metabolic and genetic features); behavioural observations; epidemiological investigation to determine, for example, whether some children are more susceptible to certain forms of autism and how the susceptibility is translated (via environmental exposure to toxins?) into diagnosable autistic disorder; genomic evaluation to determine which genes are implicated; examination of brain structure and functioning via MRI; immune function analysis; plus a search for biological “markers” (such as the variable expression of certain proteins)  for subtypes of autism, or observable genetic and physiological patterns which may be linked to definable subtypes of autism.



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M.J.Connor                                                                                    September 7th 2007



This article is reproduced by kind permission of the author.

© Mike Connor 2007.

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