Autism is one of the pervasive developmental disorders (PDD), a group of conditions that also includes Asperger syndrome, pervasive developmental disorder not otherwise specified (PDD-NOS), Rett syndrome, and childhood disintegrative disorder. Collectively, autism, Asperger syndrome, and PDD-NOS are often referred to as "autistic spectrum disorders" (ASDs). However, Rett syndrome and childhood disintegrative disorder fall outside the autistic spectrum. Autism is characterised by qualitative impairments in communication and social interaction, and by restricted, repetitive, and stereotyped patterns of behaviours and interests. Abnormal development is present before the age of 3 years. The clinical features required for a diagnosis of autism to be made are set out in International classification of diseases
and Diagnostic and statistical manual of mental disorders 4th ed
For ICD-10 criteria
. Individuals with autism have a history of language delay (single word or phrase speech delay), and a quarter lose previously acquired skills (regression), most commonly in the second year of life.
A third of individuals develop epilepsy,
and three quarters have mental retardation.
Males are affected more commonly than females (3.5–4.0:1).
The findings of this review apply to children and adolescents with autism, and results may not be generalisable to children with other ASDs. Diagnosis:
The generally accepted "gold standard" assessment tools for autism are the Autism Diagnostic Interview-Revised (ADI-R),
a semistructured, interviewer-based schedule administered to the primary caregiver, and the Autism Diagnostic Observational Schedule,
a semistructured assessment carried out with the individuals themselves. Although these schedules are informative for the clinician, autism remains a clinical diagnosis.
Table 1 Diagnostic criteria for childhood autism − International Classification of Diseases (ICD-10) issued by the WHO
The detected prevalence of autism has increased in recent years, and a recent high-quality UK study found 40/10,000 children to have childhood autism.
The prevalence of autism for studies published between 1977 and 1991 was 4.4/10,000, whereas that for the studies published during the period 1992 to 2001 was 12.7/10,000.
When considering all autism spectrum disorders, findings suggest the prevalence rises to 120/10,000; many of these people have PDD-NOS.
Evidence from twin and family studies suggests that most cases of autism arise because of a combination of genetic factors.
Family studies indicate that the rate of autism in siblings of autistic individuals is about 2.2%,
and the sibling recurrence rate for all PDDs is 5% to 6%
— significantly greater than that of the general population. Monozygotic twin studies show 60% to 91% concordance for autism, and therefore it is likely that most cases arise on the basis of multiple susceptibility genes, with influence from environmental or other factors.
A minority of cases of autism can be attributed to genetic disorders, including chromosomal abnormalities, fragile X syndrome, tuberose sclerosis, neurofibromatosis type 1, and a variety of other medical conditions.
Although perinatal factors have been implicated, it is unlikely that they have a causal role.
Research evidence suggests that autism is not caused by the MMR vaccine, or by thimerosal (mercury) in vaccines (see review on measles, mumps, and rubella: prevention).
There is strong evidence supporting a neurobiological basis of autism.
Ongoing research into the relationship between neurophysiology, neuroanatomy, neurochemistry, and genetic factors is likely to increase our understanding, and represents the best chance of unravelling the complex aetiology of ASD. The presence of phenotypic and genetic heterogeneity may have significant implications for studies of interventions/treatments for autism, as efficacy may vary with phenotype.
Autism is a lifelong condition with a highly variable clinical course throughout childhood and adolescence.
Many adults with autism require lifelong full-time care. About 15% of adults with autism will live independent lives, whereas 15% to 20% will live alone with community support.
Verbal and overall cognitive capacity seem the most important predictors of ability to live independently as an adult.
To improve social function, communication, cognitive ability, and reduce the repetitive, obsessional, and comorbid behaviours seen in autism, with minimal adverse effects of treatment.
Social function; behavioural function; cognitive function; communication; repetitive behaviour; global function; self care; family function; and adverse effects of treatment.
Clinical Evidence search and appraisal May 2009. For this review various sources were used for the identification of studies: Medline 1986 to May 2009, Embase 1986 to April 2009, and The Cochrane Library, Issue 2, 2009. Additional searches were carried out on the NHS Centre for Reviews and Dissemination (CRD), Database of Abstracts of Reviews of Effects (DARE), Health Technology Assessment (HTA), Turning Research into Practice (TRIP), and National Institute for Health and Clinical Excellence (NICE) websites. Abstracts of studies retrieved in the search were assessed independently by two information specialists. Predetermined criteria were used to identify relevant studies. Study design criteria included: systematic reviews; RCTs; quasi-randomised trials; controlled clinical trials; and prospective and retrospective cohort studies. Prospective and retrospective cohort studies were included only for interventions for which we could find no RCTs. We included studies with at least 20 participants. There was no minimum level or length of follow-up. We included open-label studies for interventions that could not be blinded. We only included studies of children or adolescents with autism; if studies included individuals with other ASDs, those which provided a subgroup analysis of at least 20 individuals with autism were included. Limitations of the research: The guidance included in this review is applicable to children with autism rather than other ASDs. Many excluded studies have included small numbers of participants, with a range of ASD diagnoses and therefore a range of abilities; combining data on the outcome of individuals with autism and those individuals with other PDDs is unlikely to be either scientifically valid or clinically useful. In addition, participants in studies have frequently been diagnosed using clinical criteria, without standardised assessment tools, and outcomes have been assessed using a variety of measures, often after a short follow-up period. Much of the research is observational and few RCTs were found. Only by conducting well-designed RCTs in large samples of people characterised as having autism using standardised assessment tools, and by measuring outcomes using standardised measures after an acceptable time period, will the effect of interventions be robustly proved. Applying the evidence in practice: For clinicians and parents, various factors require consideration when deciding whether an intervention or treatment may be of benefit to a child with autism. As described, the limitations of the research have led to weaknesses in the evidence base for many established interventions. Some studies have appropriately measured outcome using standardised assessment tools; however, improvements in scale scores on such assessments do not necessarily translate into obvious functional improvements in the everyday life of a child with autism. Longitudinal studies and data on long-term outcome after interventions are lacking; for some children, improvements in outcome may be moderate, and there is at present no way of ascertaining whether a particular group of children may benefit from a specific intervention. In addition to considering the possible adverse effects of treatment, the wider cost of interventions should be considered. Many interventions are expensive, and costs may not necessarily be covered by state funding. Some interventions are administered by (or in conjunction with) parents and may be carried out in the home. Consideration of the direct financial costs, indirect costs (through possible lost earnings), and the impact on relationships within the family (to siblings or spouse) must be balanced against likely and possible improvements in outcome for the individual with autism. To aid readability of the numerical data in our reviews, we round many percentages to the nearest whole number. Readers should be aware of this when relating percentages to summary statistics such as relative risks (RRs) and odds ratios (ORs). The categorisation of the quality of the evidence (into high, moderate, low, or very low) reflects the quality of evidence available for our chosen outcomes in our defined populations of interest. These categorisations are not necessarily a reflection of the overall methodological quality of any individual study, because the Clinical Evidence population and outcome of choice may represent only a small subset of the total outcomes reported, and population included, in any individual trial. For further details of how we perform the GRADE evaluation and the scoring system we use, please see our website (www.clinicalevidence.com). We have performed a GRADE evaluation of the quality of evidence for interventions included in this review (
GRADE evaluation of interventions for autism.