© Mike Connor 2007.
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This set of summaries begins with references to the possibility of identifying autism in very young children (at or before 2 years of age), and to a recommendation for autism screening of all infants at the time of routine 18 month and 24 month examinations.
The next section discusses the possibility that pre-natal exposure to agricultural pesticides can be a risk factor for autism spectrum disorders.
There follows a description of comparisons between children with ASD (and other developmental disorders) and typically-developing children in respect of hyper-responsive patterns and of repetitive behaviours.
The final section refers to the nature of autism in adulthood and to those symptoms remaining stable, and those moderating, since the time of formal diagnosis during childhood.
Early Detection/Screening
The recent work completed by Landa et al (2007) set out to determine how early it is possible to detect signs of autism and ASD in children.
The target group of children who were monitored comprised 107 siblings of children already identified with ASD and, therefore, deemed to be at heightened risk for ASD themselves, together with a group of 18 children of low risk.
The authors noted that autism is most commonly identified after the age of 2 years, but earlier identification has been a consistent goal for research. Accordingly, this sample of children were enrolled as participants in the study before the age of 14 months and periodically assessed for motor skills, language, and cognitive development (and rated on ASD screening instruments) from that time.
The final evaluation was carried out by a different group of clinicians when the children were aged between 30 and 36 months; and the diagnostic groupings (ASD, broader autism phenotype, or non autistic) were used retrospectively to assess the significance of the earlier test results.
Existing evidence indicates that children identified with autism and ASD have deficits in a number of areas, such as language, which can be recognised by the age of 18 months, but this has emerged from retrospective rather than prospective studies.
In this current study, ASD was diagnosed in 30 of the children’s siblings by 30 to 36 months, and 16 were given the diagnosis following the 14-month follow-up. Meanwhile, those not diagnosed at that early stage and only identified with ASD by the later follow-up did show some impairments at 14 months, such as an absence of gaze shifting, but were not significantly different from controls. It was by 24 months that the performance showed significant differences compared to that of control children.
The early-diagnosis group showed multiple impairments including language deficits, limited joint attention, and fewer shared-play activities.
The conclusion highlighted the finding that, for some children eventually diagnosed with autism, diagnostic features are observable at age 14 months; but other children diagnosed later with autism are not distinguishable at that age from normally-developing children.
(A commentary on these findings by Basco (2007) noted the point that, early diagnosis or not, many of the children presented behaviours that were a source of concern to parents at 14 months. This could suggest a higher awareness on the part of parents who had an older child already diagnosed with autism, so that these current results reflect a “selective” population.
However, it could also be interpreted as supporting the view that there is a continuum of ASD symptoms among the siblings of children with ASD ... ie such children may commonly exhibit a degree of impairment in certain areas [ a broader autism phenotype ], albeit not matching the criteria for a formal diagnosis.
What matters is that the siblings of children with ASD are a higher-risk group with the implication of careful monitoring, with the suggestion of formal developmental screening from the first and second birthdays.)
In respect of the issue of wider screening for autism, one notes the recommendation by the American Academy of Pediatrics (October 2007) that a formal assessment of signs and symptoms of autism and ASD should become a routine part of the examinations of infants at 18 and 24 months.
This recommendation reflects the apparently marked increase in the incidence of (formally-diagnosed) ASD, with a current estimate referring to 1 in 150 children; and the converging evidence that a critical element of successful intervention is its early initiation. While there is no cure for ASD, and despite the lack of clarity concerning aetiology, it is clear that appropriate intervention can produce a reduction in those symptoms which inhibit day to day functioning (and, one might suggest, ensure awareness among significant others about the means of modifying the environment and the management of the child further to reduce the impact of the ASD).
The lead author of the AAP statement (Dr Chris Johnson) suggests that no action would be taken if the possibility of ASD is ruled out, but any doubts would trigger follow-up actions including a referral to an autism-specialist clinic for a definitive evaluation, an audiological assessment by which to check for the possible effect of hearing problems, and consideration of the appropriateness of a specific programme of intervention.
The recommendation includes information about signs and symptoms of ASD to guide the early evaluations. Language delay is cited as a common source of concern to parents, but earlier and subtle signs could lead to a diagnosis.
Such signs include the lack of any response to a parent saying ... “ Look at ...”; not pointing at some object or action to show parents something interesting; lack of babbling; smiling late; and failure to make eye contact.
There is also a highlighting of the enhanced risk for ASD among the siblings of those children already diagnosed.
The issue of early and structured and intensive intervention, involving the family, is repeated when it comes to discussing action, with the advice offered about initiating a programme as soon as a diagnosis is being seriously considered rather than deferring action until a definitive diagnosis has been set down (especially if this may only be achieved after a delay resulting from the need for multi-disciplinary input and from the limited availability of specialist staff such that long waiting lists may develop).
A Further Risk Factor (“Trigger”?) : Exposure to Agricultural Pesticide
The report of the study completed by Roberts et al (2007) begins with a reference to the increase since around the start of the 1990s in the numbers of children diagnosed with ASD. At least part of this apparent rise in incidence can be attributed to shifts in diagnostic criteria and procedures, but the pattern is inconsistent ... (and the questions remain whether autism can be triggered by some event or experience and whether vulnerability in children has become greater as a result of an enhanced number/intensity of potential triggering factors).
In any event, the authors note that a diagnosis does not usually occur until the symptoms are readily evident ... during early childhood ... but cite converging evidence (such as that of Arndt et al [2005] among others) which is consistent with some pathological process starting during pre-natal development.
Much of this evidence relates to some functional deficit caused by an alteration to specific brain structures occurring during foetal life and which might be attributable to genetic factors, environmental “trauma”, or a combination. The eventual diagnoses of ASD may well reflect idiosyncratic permutations of causal features.
As a preface to their own study, Roberts et al cite the growing evidence for adverse neurological effects of widely-used agricultural pesticides, raising the question whether these compounds could be implicated in the aetiology of ASD and other neuro-developmental disorders.
There is further evidence that these compounds are likely to drift and they may be detected for extended periods in air samples taken at locations beyond the site of application.
The concern is that various toxic compounds may be conveyed through the placenta, and that the blood-brain barrier remains relatively permeable to many of them until well into the first year of life.
Their own study involved an evaluation of a range of hypothesised associations between living near to sites where pesticides are applied and the incidence of ASD by means of a retrospective case-control design.
The study population included nearly 270,000 children born between January 1996 and December 1998 in the areas of California making up the Central Valley.
Children with ASD were identified through existing health records; and, for each case identified, 15 control cases were selected from typically-developing children born at the same time.
Records were obtained from the California Department of Pesticide Regulation to highlight the temporal and geographical patterns of pesticide use.
Inspection of data plus statistical analysis indicated that the association between organochlorine pesticide applications immediately before the beginning of foetal life, and during foetal life, and risk for ASD was such to merit concern and to justify further investigation.
The association was strongest for residences closest to the areas where pesticides were used and attenuated with increasing distance.
The critical period for the possible effect of pre-natal exposure to pesticides appeared to be the 8 weeks immediately following neural tube closure.
The authors are careful in recommending that their findings require replication, and also recognise the small number of participants classified as “exposed” under their procedures which highlighted the greatest magnitude of ASD risk (ie living with 500 metres of the field[s] involved and with the child’s foetal age concurring with the maximal temporal influence).
A further limitation was the lack of information over and above basic demographics to describe the mothers and the children so that there was no opportunity to adjust their own data for potentially confounding factors (such as diet) relevant to the child’s early neurodevelopment ... and while anecdotal evidence suggested that the sample covered a range of socio-economic backgrounds, it cannot be ruled out that the mothers were disproportionately employed in the agricultural work and subject to pesticide exposure beyond “drift”.
Nevertheless, the authors’ conclusion restated that risk for ASD appeared to be consistently associated with living close to areas where organochlorine pesticides are used around the time of the CNS embryogenesis. The evidence suggests some association between risk for ASD and pre-natal exposure to pesticides, and the recommendation is for further study by which to seek to replicate the findings.
Hyper-responsive Sensory Patterns
Unusual sensory behaviour, be it hypo-responsiveness or hyper-responsiveness, may not be universal among children with autism and ASD, but they are very common and may be relevant to a formal diagnosis.
Baranek et al (2007) cite parental reports to the effect that the impact of the child’s unusual sensory responses can interfere with daily routines in the family, such as having to restrict diets, or to avoid certain sounds or textures. The number of shared social experiences within the family may also be inhibited; and the child is likely to be restricted in the exploration of the environment and associated learning opportunities.
Hyper-responsiveness refers to a pattern of exaggerated behavioural reactions to sensory stimuli.
The prevalence of such behaviours among children with autism is not easily established because of differences among studies in respect of the methodology adopted, context, particular behaviour sampled, and the source of ratings (parents or teachers). For example, survey results can produce wide variation in the percentages within samples of children with autism of hyper-responsiveness to auditory stimuli.
Baranek et al summarise the existing data about prevalence, across sensory modalities and contexts, by citing a figure of around 56% of hyper-responsiveness among children with autism between the ages of 1 and 6 years. Mental age appears to be a mediating factor.
However, the authors point out that much of the information upon which this estimate is based emerges from ratings provided by parents or carers rather than from more direct observation.
Meanwhile, it is noted that hyper-responsive sensory behaviours may be observed among children with developmental delays not attributable to autism. They may, for example, be part of the symptomatology of Fragile X Syndrome or of ADHD.
There have been few studies which directly compared children with autism against children with other developmental conditions in respect of hyper-responsiveness, but the prevalence of this behaviour in other clinical groupings raises questions about the specificity of hyper-responsiveness to autism, the role of general maturational factors upon the presentation of such reactions, and the underlying mechanisms.
Debate continues about the significance of sensory features, including hyper-responsiveness, in autism.
One school of thought (as represented by Happé 1996) emphasises weak central coherence (ie local, part by part processing of incoming stimuli rather than gaining a global impression) which can result in enhanced perceptual discrimination but no capacity for integrating the stimuli into meaningful units of information.
An alternative view involves neurobiological mechanisms as the source of the hyper-responsiveness in autism.
A review of relevant studies indicates that this pattern has implicated dysfunction in the parasympathetic nervous system including the frontal lobes, limbic system (hippocampus); and cerebellum. There is no consensus over precisely where the sensory processing or integration breaks down ... but the sensory features linked with autism are not attributed to peripheral deficits such as a lack of visual or auditory acuity.
Baranek et al comment further that the existing neuro-cognitive or neuro-biological theories do not fully account for the role of developmental maturation on the reactivity to sensory stimuli. The questions remain whether hyper-responsiveness is a generalised phenomenon among clinical groups, and to what extent this behaviour is present across different stimuli and environmental contexts.
Therefore, the purpose of their own study was to examine the prevalence and nature of hyper-responsiveness to incoming stimuli among children with autism compared to children with other developmental delays and to typically-developing children.
Three groups of participants were involved in this study ... 56 children with ASD; 30 children with developmental delay; and 33 children demonstrating typical development. The age range was from 5 to 83 months.
The assessment instruments included the Sensory Processing Assessment for Young Children ... a play-based observation schedule; and the Vineland Adaptive Behaviour Scales ... a parent-report system for assessing functional communication, social behaviour, competence in daily routines, and motor skills. The Mullen Scales of Early Learning were the principal means of gaining a measure of cognitive functioning; but the Leiter Scales or Bayley Scales were also used in some (older) cases.
The overall findings were taken as support for the effects of developmental maturation upon hyper-responsive sensory patterns such as sensory aversion or avoidance. Such patterns were found to diminish in line with increasing mental age, and this association was observed in all three groups of children.
Further, it was noted that chronological age had a similar effect to that of mental age in that older children showed less sensory aversion than younger children ... although this effect markedly diminished when controls were put in place for mental age.
The interpretation held that neurobiological maturation, life experiences, and/or acquired cognitive abilities appear to provide children with an increased tolerance to sensory input.
It was further held that sensory hyper-responsiveness is a general deficit associated with various developmental disabilities and is not specific to autism.
While existing research evidence (eg Mottron et al 2003) does suggest enhanced sensory-perceptual discrimination to be a specific feature of autism, it is thought likely that this kind of behaviour is different from the sensory aversion or avoidance described in this current study.
It is speculated that one area of difference could lie in the distinction between neuro-cognitive mechanisms associated with perception (temporal and parietal cortex functioning) or attention (implicating the dorso-lateral prefrontal cortex and cerebellum) and affective mechanisms associated with the modulation of aversive experiences (involving the limbic system and amygdale).
The kind of hyper-responsive patterns observed in this current study can be linked to physiological over-arousal in various clinical groups. Further, there appears to be an interaction between physiology and development in that the more mature children are better able to assimilate incoming information, and link it with existing experience, thus adapting more readily to novel sensory input and avoiding any fight or flight reaction.
The authors had not expected that habituation response patterns would show no differences across their groups of participants; and they concluded that some generalised habituation deficit cannot explain the subtleties associated with sensory hyper-responsiveness in young children.
On the other hand, the probability of some response rather than no response did differ by groups in that a greater percentage of the children with ASD fell into a non-responding category, especially at lower mental age levels. Such a finding is consistent with existing evidence for deficits in young children with autism in respect of orienting towards social and non-social sensory stimuli, and underlines the diagnostic significance of such behaviour.
Among typically-developing children, this orienting response appears early in infancy and is a basis for engagement with events in the environment and for social learning. The present sample of children with autism at the lower mental age levels lacked the expected orienting response to auditory stimuli but those with greater maturational abilities (and perhaps with more experience of intervention) showed a greater response to novel or salient stimuli. This general pattern was not observed among children in the developmental delay or typical development groups, all of whom appeared to have intact orienting responses across a range of mental age levels.
The authors acknowledge some limitations in their study such as the smaller number of participants in the developmental delay group but the greater mix in respect of socio-economic status of the families. It was also not possible, on ethical grounds, deliberately to expose the children to stimuli likely to evoke very aversive reactions; but this may have affected the sensitivity of the assessment measures.
The final concern was about the difficulty in measuring response patterns across a wide range of ages and functioning levels.
However, Baranek et al concluded that their findings indicated that hyper-responsive patterns appear characteristic of developmental delay in general, thus challenging the theory of specificity of such behaviour in children with autism. Mental age was cited as a strong predictor of aversive and avoidant responses to novel stimuli as well as of habituation to repeated stimuli.
Therefore, while
hyper-responsiveness may not be a means of achieving differential diagnoses, it
may still carry significant implications for development, adaptive behaviour,
and social interaction.
They cite the importance of further research to assess the impact of
interventions such as gradual exposure to novel sensory experiences
(desensitization) and direct teaching of coping strategies to mitigate the
effects of this hyper-responsiveness in various settings.
Repetitive Play and Behaviour
Honey et al (2007) introduce their work by describing repetitive behaviour as being characterised by sameness and rigidity, and as consistently observed among children with ASD, albeit varying in type and degree across individuals and showing changes over time.
It is further noted that such behaviour may be a defining feature of ASD but may also be observed in other children including those displaying other developmental or neurological conditions (and those showing typical development).
Repetitive behaviour is commonly reported to be associated with impairment in imaginative activities (and this combination is one element of the perceived “triad” of core characteristics of ASD).
However, this is not how international classifications of autism (DSM-IV or ICD-10) set out diagnostic criteria. Rather, they offer a separate category for repetitive behaviours while including impairments of imagination as part of communication deficits. It is, accordingly, possible to diagnose autism in a child with significant repetitiveness of behaviour and impaired communication but satisfactory symbolic play skills.
Honey et al recognise that there are few hard data about the relationship between repetitive behaviour and imagination, either in autism or typical development.
What evidence does exist demonstrates that repetitive behaviours are common among children until around 4 years of age when they gradually decline as emotional, social, and communication skills become increasingly mature. However, among an autistic population, repetitive behaviour is maintained and is marked by more frequent and longer bouts; and this characteristic is seen to be a pervasive part of autism.
Meanwhile, among typically-developing children, the onset of pretend play can be observed at around 18 months ... but such play has been shown to be limited or impaired among children with autism. Even non-symbolic play is usually delayed in this population; and less functional play is noted compared to what may be observed among typically-developing children and children with learning difficulties. What functional play there is tends, too, to be less elaborate or varied.
However, some studies have found no differences between the functional play of children with ASD compared to that of other children.
The aim of the study by Honey et al was to assess the relationship between repetitive behaviour and play to determine whether this relationship is general or specific to certain forms of play.
The methodology involved the use of a parent-report measure to examine repetitive behaviour and play in a sample of children with ASD and a sample of children showing typical development.
Information was gathered for 79 children with ASD and 117 control children, drawn from two age groups, 2-4 years, and 6-8 years.
The prime measure was the Activities and Play Questionnaire, specifically developed to assess, via parental reports, the play and repetitive behaviours of children. This measure was derived from the Repetitive Behaviour Questionnaire (Turner 1996) and DISCO (an interview schedule devised by Wing et al [2002]).
Language level was separately recorded, using appropriate subsections of the DISCO.
The findings, exploring the hypothesis that repetitive behaviours replace imaginative activities in children with autism, indicated that the association between repetitive behaviour was found only in the ASD sample. The further implication drawn was that children with ASD who engage in only a few repetitive behaviours are likely to engage in more play activities than other children with ASD who frequently engage in repetitive behaviours.
In typically-developing children, play was predicted only by language level; for children with ASD aged between 2 and 8 years, play was also predicted by the level of repetitive behaviour.
Such findings support the presently-perceived triad of impairments; but also offer support for the view that play in ASD (and in typical development) is highly related to levels of communication and language so that it is reasonable that the ICD criteria regard imaginative impairments as a component of communication difficulties.
The authors suggest that the best way of representing the relationships is that of a 3-way association between repetitive behaviour and imagination and communication.
The association between repetitive behaviour and imagination has not featured much in previous research possible because of methodological difficulties including the varying visibility of some of the relevant behaviours. Mannerisms, for example, can be recorded, but certain routines and rituals may not be readily evident by a researcher given that they may be linked to some specific context such as bedtime or mealtime. It may also be the case that comparative ratings are skewed by the greater awareness on the part of parents of children with ASD of the particular behaviours that mark out their children as special. Parents of typically-developing children may be less attuned to signs of repetitive behaviour.
Nevertheless, the authors accept that their own study had limitations that might have been compensated at least in part by the use of observational methods. This may be particularly relevant to the recording and classifying of play (pretend, functional, and exploratory).
It is also accepted that the findings would have had a stronger foundation had there been a more accurate measure of language performance and more data about the level of severity of autism among the target group.
The final point by Honey et al refers to the need for longitudinal research in both typically-developing children and those with ASD to determine whether the relationship between repetitive behaviour and imagination remains stable or changes from early to later childhood.
Early Predictors of Autistic Symptoms in Adulthood
As a result of a brief review of relevant evidence, Billstedt et al (2007) report that classic and severe cases of autism usually persist across the life span, and that most individuals diagnosed in childhood continue to meet the criteria for the disorder as adults. There is long term persistence of the triad of impairments in social interaction, reciprocal communication, and restricted activity patterns.
However, the precise nature of symptoms appear to differ at different ages; and symptoms typical of the young child may take a different quality, or no longer be evident, in the adult.
These authors completed a follow-up study into adulthood of individuals diagnosed with ASD in childhood to assess distinctive symptoms and symptom clusters. The main source of information was a structured interview (DISCO) with informants who knew the person with autism well during the years from late adolescence to mid-adulthood.
The ASD sample comprised 84 males and 36 females, born between 1962 and 1984, followed up for a period of 13 to 22 years with an evaluation at a mean age of 17·8 and again at a mean age of 25·5 (range 17-40 years).
(Some families declined further participation, and 6 individuals had died at the time of the second evaluation, so that 105 individuals were included within the full study.)
At the follow-up, 89 of the 105 participants continued to be clinically diagnosable as having ASD; 15 were diagnosed with atypical autism; and 1 individual no longer met the criteria for ASD.
So, with that one exception, the late-adolescent or adult individuals included in this present study still met the clinical criteria for autism at the time of re-evaluation.
However, there was found to be wide variation in the pattern of symptoms.
The authors compared their findings with those of Seltzer et al (2003) who had compared adolescent and adult symptomatology.
This previous set of findings also highlighted the continuing manifestation of symptoms that would justify a diagnosis of ASD. The adult cohort revealed a less severe impairment in behaviours, such as repetitive activity, than that observed in the adolescent cohort. It was speculated by this research team that the developmental course of the condition is a matter of abatement of symptoms over time; although the adolescent group appeared less impaired than the adult group in the display of pro-social behaviours.
The findings of Billstedt et al partly support these earlier results (ie sharing the finding of an abatement of certain abnormal behaviours) and partly contradict them
(ie not sharing the finding of a generally large improvement across a range of domains of functioning).
There is converging evidence that IQ and language performance are predictors of outcomes in autism.
The present findings support both of these factors, particularly underlining the salience of speech before the age of 5 years as a predictor of all the triad features of autism.
Epilepsy, with an onset before 5 years, has also featured as a predictor, but the present findings suggest that a generally poorer level of intellectual functioning is a common denominator for epilepsy and other medical disorders, and a key to the apparent predictive power of such variables.
The authors acknowledge that their findings probably generalise only to low- and middle-functioning individuals with autism, although in some areas of functioning, notably those concerned with reciprocity of interaction, it is likely that the pattern will be very similar among all levels of ASD functioning (including Asperger syndrome).
In other words, the developmental trajectory may be thought partly independent of IQ.
Their summary highlighted the finding that there was much more homogeneity in respect of social interaction and one-sided social approaches, while other autistic symptoms, such as maladaptive and stereotyped behaviour, were much more variable in this adult group. The implication includes the need for ongoing support in respect of these social communication problems.
The finding of pervasive sensory problems in adulthood raised the question whether such symptoms should be considered as core elements of ASD; but the final point highlighted the many different patterns of symptoms and behaviours among adults with ASD with implications for individual evaluation and ongoing monitoring to determine how best to organise support.
* * * * * *
M.J.Connor November 2007
REFERENCES
American Academy of Pediatrics - Johnson C. et al (2007) Recommendation for autism screening for all infants. Presentation to the AAP National Conference : San Francisco (30/10/07)
Arndt T., Stodgell C., and Rodier P. 2005 the teratology of autism. International Journal of Developmental Neuroscience 23(2-3) 189-199
Baranek G., Boyd B., Poe M., David F., and Watson L. 2007 Hyper-responsive sensory patterns in young children with autism, developmental delay, and typical development. American Journal on Mental Retardation 112(4) 233-245
Basco W. 2007 Can we detect signs of autism in very young children ? A commentary on the Landa et al (2007) study. Medscape Pediatrics : 17/10/07
Billstedt E., Gillberg C., and Gillberg C. 2007 Autism in adults : symptom patterns and early childhood predictors. Journal of Child Psychology and Psychiatry 48(11) 1102-1110
Happé F. 1996 Studying weak central coherence at low levels. Journal of Child Psychology and Psychiatry 37 873-876
Honey E., Leekam S., Turner M., and McConachie H. 2007 Repetitive behaviour and play in typically developing children and children with autism spectrum disorders. Journal of Autism and Developmental Disorders 37 1107-1115
Landa R., Holman K. and Garrett-Mayer E. 2007 Social and communication development in toddlers with early and later diagnosis of autism spectrum disorders. Archives of General Psychiatry 64 853-864
Mottron L., Burack J., Iarocci G., Belleville S., and Enns J. 2003 Locally oriented perception with intact global processing among adolescents with high-functioning autism. Journal of Child Psychology and Psychiatry 44 904-913
Roberts E., English P., Grether J., Windham G., Somberg L., and Wolff C. 2007 Maternal residence near agricultural pesticide applications and autistic spectrum disorders among children in California Central Valley. Environmental Health Perspectives 115(10) 1482-1489
Seltzer M., Krauss M., Shattuck P., Orsmund G., Swe A., and Lord C. 2003 The symptoms of autistic spectrum disorder in adolescence and adulthood. Journal of Autism and Developmental Disorders 33 565-581
Turner M. 1999 Annotation : repetitive behaviour in autism. In J. Russell (Ed) Executive Function and Autism. New York : Oxford University Press
Wing L., Leekam S., Libby S., Gould J., and Larcombe M. 2002 The diagnostic interview for social and communicative disorder. Journal of Clinical Psychology and Psychiatry 43(3) 307-325
© Mike Connor 2007.
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