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Video Tapes are now available of Jane M. El-Dahr, M.D.,  Head of Pediatric Allergy/
Rheumatology,  Tulane University Health Sciences Center lecturing on "Autism and immunology effects---The heavy metal connection."


Boyd E. Haley, Ph.D., Professor and Chairman, Chemistry Department, University of Kentucky, lecturing on "The biochemical interrelationships of Vitamin C, melatonin, glutathione and other redox compounds."

Rising Autistic Spectrum Disorder Rates


  • Pervasive Developmental Disorders in Preschool Children

    • Suniti Chakrabarti, MD, MRCP; Eric Fombonne, MD, FRCPsych

    • JAMA, Vol. 285 No. 24, June 27, 2001


  • Autism on the Rise, Multidisciplinary efforts aim at finding the biological basis for a complex disease

    • The Scientist 15[10]:16, May 14, 2001

    • By Laura DeFrancesco



Pervasive Developmental Disorders in Preschool Children  

 Suniti Chakrabarti, MD, MRCP; Eric Fombonne, MD, FRCPsych

JAMA, Vol. 285 No. 24, June 27, 2001

Context  Prevalence rates of autism-spectrum disorders are uncertain, and speculation that their incidence is increasing continues to cause concern.

Objective  To estimate the prevalence of pervasive developmental disorders (PDDs) in a geographically defined population of preschool children.

Design, Setting, and Participants  Survey conducted July 1998 to June 1999 in Staffordshire, England. The area's 15 500 children aged 2.5 to 6.5 years were screened for developmental problems. Children with symptoms suggestive of a PDD were intensively assessed by a multidisciplinary team, which conducted standardized diagnostic interviews and administered psychometric tests.

Main Outcome Measure  Prevalence estimates for subtypes of PDDs.

Results  A total of 97 children (79.4% male) were confirmed to have a PDD. The prevalence of PDDs was estimated to be 62.6 (95% confidence interval, 50.8-76.3) per 10 000 children. Prevalences were 16.8 per 10 000 for autistic disorder and 45.8 per 10 000 for other PDDs. The mean age at diagnosis was 41 months, and 81% were originally referred by health visitors (nurse specialists). Of the 97 children with a PDD, 25.8% had some degree of mental retardation and 9.3% had an associated medical condition.

Conclusions  Our results suggest that rates of PDD are higher than previously reported. Methodological limitations in existing epidemiological investigations preclude interpretation of recent high rates as indicative of increased incidence of these disorders although this hypothesis requires further rigorous testing. Attention is nevertheless drawn to the important needs of a substantial minority of preschool children.

JAMA. 2001;285:3093-3099

Autism is a severe developmental disorder involving deviance and often delay in the development of language or communication skills; social interactions and reciprocity; and imagination, play, and interests.1 Since the first epidemiological survey of autism was conducted in the mid 1960s in England,2 more than 30 surveys have been performed worldwide.3, 4 Rates of autism typically have been reported in the range of 4 to 6 per 10 000 although these figures increased in surveys conducted in the last 15 years.4, 5 These estimates do not account for a large group of children falling short of strict diagnostic criteria for autism (pervasive developmental disorders [PDDs]) and whose development poses similar assessment and educational challenges.

Although the apparent increased prevalence of autism may reflect improved detection and recognition of autism and its variants, it might also index a secular change in the incidence of the disorder. The role of genetic factors in the origin of autism does not favor such a hypothesis,6 however. Moreover, no survey has thus far concentrated specifically on preschool children. Obtaining a reliable estimate in this age group is particularly important since early intensive preschool education might improve the outcome in autism.7, 8 Accordingly, the goals of this study were to estimate the prevalence of PDDs in preschool children in a geographically defined population.


Site and Target Population

The study was conducted at the child development centers in Stafford, Cannock, and Wightwick in the Midlands, England, and it received approval from the South Staffordshire Health Authority local ethics committee. These child development centers serve the entire preschool and early school population of one National Health Service Trust. The survey was conducted from July 1998 to June 1999 although some initial clinical assessments were performed from 1994 onward. The area is a mixture of urban, rural, and semi-industrial areas. There is a stable population of indigenous British people with a small (1.4%), mostly Asian, immigrant population. The total population living in the area covered by the National Health Service Trust was 320 000 people in June 1998. The target population included all children (N = 15 500) born between January 1, 1992, and December 31, 1995, living within the target area on June 6, 1998.

Case Identification and Definition: 4 Stages

Stage 1

The national framework of Child Health Surveillance recommends the screening by health professionals of all UK children at birth; at age 6 weeks; between ages 6 and 9 months, 18 and 24 months, and 3¼ and 3½ years. In the study population, all the neonatal and 6-week screenings were performed by pediatricians or general practitioners and the 7-month screening by health visitors, who are nurse specialists experienced in working with children and families. Health visitors or physicians performed the 18- to 24-month and 3¼- to 3½-year screening. Screening was conducted in accordance with the guidelines of the "Health for All Children" report,9 which emphasizes continuity of care, making observations, checking history, eliciting parental concerns, offering health advice and guidance, and moving away from prescriptive tests. The primary care worker may also have had the opportunity to listen to and discuss any concerns about the child's progress during the immunization visits at 2, 3, 4, and 13 months. Besides health visitors, speech and language therapists, pediatricians, general practitioners, and other professionals contributed to the referral process, especially for children older than 3 years. The study was coordinated through the child development centers that processed all the referrals of preschool children.

The participating professionals underwent training sessions on early identification of developmental problems and received written guidelines for referral of children with developmental or behavioral problems. The guidance to those making referrals for the initial screenings was left purposefully general to include children with any likely serious developmental, behavioral, or physical problems. This procedure also ensured maximal sensitivity for PDD case finding. The guidelines for the initial screen were to refer all children with more than mild or transient problems in one or more areas of development, including personal-social, fine or gross motor, speech and language, play skills and attention, concentration, and behavioral difficulties. Referrals were sought as soon as any problem was identified, usually by the age of 2 to 2½ years or earlier.

Stage 2

Children referred at this initial stage underwent a second screening carried out by a developmental pediatrician (S.C.) or by the child development team, consisting of a pediatrician, a specialist health visitor, and speech and language, physical, occupational, and play therapists. Parents or main caretakers were involved in each stage of the screening. Any urgent referrals were fast-tracked to the developmental pediatrician or a multidisciplinary team.

Stage 3

Children who failed the second screening were selected for a 2-week assessment conducted by a multidisciplinary team. During these assessments, a play therapist led a group of 4 children with their participating parents in 2-hour sessions of structured activities as well as free play. A developmental pediatrician (S.C.) took a detailed developmental history and conducted a comprehensive medical and neurodevelopmental examination. Children were assessed by a speech and language therapist, a pediatric physical therapist, an occupational therapist, a dental nurse, a dietitian, and a nurse specialist trained in behavioral intervention for children with PDDs and other learning problems. Hearing was assessed by an audiological physician, and vision was screened by an orthoptist. At the end of this assessment, a clinical diagnostic formulation was made by the lead pediatrician.

All screening and evaluation steps undertaken at stages 1, 2, and 3 were part of a normal screening procedure implemented by the local service. Permission for extra data collection associated with research was sought either at the end of stage 3 or shortly after entering stage 4. About 75% of parents provided written informed consent. The rest provided oral informed consent.

Stage 4

Children strongly suspected of having a PDD diagnosis were further assessed with standardized diagnostic measures and psychometric assessments. The Autism Diagnostic Interview-Revised (ADI-R)10-12 is a semistructured diagnostic interview for use with caregivers of children with a possible PDD diagnosis. The ADI-R was administered by the developmental pediatrician (S.C.), who has been trained in its use. The ADI-R algorithm generates scores for the areas of social interaction, communication (verbal and nonverbal), repetitive behaviors, and age of recognition of first abnormalities for which appropriate cutoff points are available. The ADI-R algorithm is compatible with Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV) diagnostic criteria. A total ADI-R score is obtained by summing the scores in the 3 domains of developmental deviance.

Children diagnosed as having a PDD subsequently underwent a formal psychometric assessment by a senior educational psychologist. All tests were performed in 1999 and early 2000. The tests used were the Wechsler Preschool and Primary Scale of Intelligence13 and the Merrill-Palmer14 tests. Intellectual functioning was estimated according to performances on the nonverbal scales of the Wechsler Preschool and Primary Scale of Intelligence or with the quotient derived from the Merrill-Palmer test. Mental retardation was defined according to conventional levels of severity (ie, mild, 50-69; moderate, 35-49; severe, 20-34; and profound, <20).

The final diagnostic determination was derived from a review of all existing data by the pediatrician who knew all children well. Diagnosis was made with DSM-IV diagnostic criteria1 for PDD including autistic disorder (AD), Asperger syndrome, Rett syndrome, childhood disintegrative disorder, and pervasive developmental disorder-not otherwise specified (PDD-NOS).

Reliability Study

All ADI-R interviews were videotaped or audiotaped. A subset of 38 ADI-R videotapes was selected at random and blindly rated by 3 trained raters (including E.F.). Interrater reliability for domain scores as measured by the intraclass correlation coefficient15 was 0.82 for social interactions, 0.87 for nonverbal communication, 0.85 for verbal communication (based on a subset of 28 children with a sufficient language level), 0.59 for repetitive behaviors, and 0.86 for the total ADI-R score. Agreement on the proportion of subjects scoring higher than each of the predetermined cutoffs was high for all domains (social interactions, 92.1%; nonverbal communication, 90.0%; verbal communication, 85.7%; repetitive behavior, 81.6%; and onset before age 3 years, 97.4%). Blinded raters were also asked to provide an independent global diagnostic judgment about the presence or absence of a PDD based on the parental interview. Independent raters confirmed the presence of a PDD in all 38 children, yielding a 100% agreement with the original pediatrician's diagnoses.

Biological Investigations

Following the 2-week assessment, systematic laboratory investigations were performed, which included full blood cell count; plasma chemistry; serum calcium, thyrotropin and thyroxine, and creatine kinase levels; plasma and urine amino acid chromatogram; urine organic acids; chromosomes; fragile X testing; and electroencephalogram. The skin of children with suggestive birthmarks was examined with UV light to detect markers of tuberous sclerosis. In a small number of cases, brain imaging using computed tomographic or magnetic resonance imaging scans was performed on clinical suspicion of a possible neurological problem.

Statistical Analyses

Between-group comparisons for continuous variables were performed with both nonparametric (Kruskal-Wallis) and parametric 1-way analyses of variance followed by post hoc Scheffé pairwise comparisons. Because P values were almost identical, the results of parametric analyses are subsequently presented. chi2 tests were used for categorical variables. Throughout, a conventional P value of .05 was retained as the level of statistical significance. Asymptotic 95% confidence intervals (CIs) for prevalence estimates were obtained with STATA software version 6.16



The details of case ascertainment in this investigation are summarized in Figure 1. Of the 576 children referred to a child development center for a stage 1 assessment, 103 children were clinically diagnosed as having PDD at the stage 3 assessment. Of these 103 children, 99 parents agreed to take part in the ADI-R interview and 4 parents refused. One interview was deferred indefinitely for external circumstances, and 98 interviews were finally carried out (95 videotaped, 3 audiotaped).

Pervasive Developmental Disorders in Preschool Children (JAMA. 2001;285:3093-3099)

Of the 5 children who did not receive an ADI-R interview, a final PDD diagnosis was subsequently confirmed by an independent educational psychologist or child psychiatrist (2, AD; 3, PDD-NOS). Of the 98 children with ADI-R data, 6 children did not fulfill strict ADI-R diagnostic criteria for a PDD at stage 4. Thus, at the completion of stage 4, 97 children were diagnosed as having PDD, resulting in a prevalence estimate of 62.6 (95% CI, 50.8-76.3) per 10 000 children for all PDDs. Further analysis by PDD subtype led to the following estimates: for 26 children with AD, the prevalence was 16.8 (95% CI, 11.0-24.6) per 10 000; for 13 with Asperger syndrome, 8.4 (95% CI, 4.5-14.3) per 10 000; for 1 girl with Rett syndrome, 0.6 (95% CI, 0.02-3.6) per 10 000; for 1 boy with childhood disintegrative disorder, 0.6 (95% CI, 0.02-3.6) per 10 000; and for 56 with PDD-NOS, 36.1 (95% CI, 27.3-46.9) per 10 000. For the 71 children with a PDD diagnosis other than AD, the prevalence was 45.8 (95% CI, 35.8-57.7) per 10 000 children.

ADI-R Mean Scores

The mean (SD) age of 92 children with available ADI data was 58.1 (13.0) months at interview. Excluding the boy with childhood disintegrative disorder and the girl with Rett syndrome, comparison of scores across the 3 remaining diagnostic subgroups yielded significant differences in all domains except for the repetitive behaviors domain (Table 1). Post hoc tests showed that children with AD had consistently higher scores than the 2 other groups, which in turn did not differ from each other. All children met the requirement of an onset before age 3 years.

Table 1. Mean Autism Diagnostic Interview-Revised (ADI-R) Scores by Diagnostic Subgroup*


Referral Source and Age at Diagnosis

Thirty-four percent of the 97 referrals came from pediatricians, 32.9% from speech and language therapists, 21.6% from health visitors, 5.1% from general practitioners, and 6.2% from miscellaneous sources. However, a closer look at referral patterns showed that most of the referrals to pediatricians and speech therapists were initiated by health visitors; thus, taking these data in combination, 79 (81%) of the 97 children were originally identified by the health visitor as having a problem requiring further assessment. The average age of children at referral was 35.7 months (range, 11-63 months), and the average age at initial clinical diagnosis was 41 months (range, 21-78 months). Analyses of variance were performed to test for differences in age at referral and age at diagnosis in the 95 children with AD, Asperger syndrome, or PDD-NOS diagnoses. A significant effect of diagnosis was found for age at referral (F2,92 = 11.3; P<.001). Pairwise comparisons showed that mean age at referral for children with AD (30.0 months) was significantly lower than for children with PDD-NOS (37.2 months; P = .03) or with Asperger syndrome (47.5 months; P<.001). Age at referral of children with PDD-NOS was also significantly lower than in those children with Asperger syndrome (P = .01). For age at diagnosis, a significant effect of diagnostic subgroup was also found (F2,92 = 12.0; P<.001). Post hoc Scheffé tests similarly indicated significantly lower mean age at diagnosis for children with AD (34.6 months) vs children with PDD-NOS (43.1 months; P = .005) and lower age at diagnosis for children with Asperger syndrome (51.8 months; P<.001), whereas children with PDD-NOS had significantly lower mean age at diagnosis than those with Asperger syndrome (P = .04).

Clinical Correlates

The sample included 77 boys (79.4%) with no significant difference (chi22 = 0.33; P = .85) in the proportion of boys in the AD (76.9%), Asperger syndrome (84.6%), and PDD-NOS (80.4%) groups. Of the 97 children, 29 (29.9%) had no functional use of language defined as the daily spontaneous use of 3-word phrases. The proportion of children without functional language was however strongly associated with diagnostic subtype (AD, 69.2%; Asperger syndrome, 0%; PDD-NOS, 16.1%; chi22 = 30.6; P<.001).

Of the 97 children, 37 children underwent Merrill-Palmer testing and 56, Wechsler Preschool and Primary Scale of Intelligence testing. Four children could not be tested for practical reasons. Overall, 24 (25.8%) of 93 children had some degree of mental retardation. The 2 children with childhood disintegrative disorder and Rett syndrome scored in the moderate range of mental retardation. However, patterns of cognitive functioning varied according to diagnosis (Table 2) and, combining together all levels of mental retardation, a significant difference was found for the presence or absence of mental retardation between the 3 PDD subtypes (chi22 = 40.6; P<.001), the AD group having more frequent and severe cognitive delays than the Asperger syndrome and PDD-NOS groups.

Table 2. Intellectual Functioning by Diagnostic Subgroup*

In the sample, 5 children had a sibling with another PDD (including 1 twin pair). Four of the sibling pairs were in the age range of this study and were included in the prevalence pool. Of the sibling pairs, 3 sets were diagnosed with both pairs having PDD-NOS, 1 set with AD and PDD-NOS, and 1 set with Asperger syndrome and AD. Based on the total number of siblings across all 93 families (n = 220, including the 97 participating children), the sibling risk is estimated at 3.94% (5/127) in this study.

Associated Medical Conditions

The results of medical investigations in this sample are summarized in Table 3. There was no case of deafness, blindness, or fragile X disorder, and only 1 child had tuberous sclerosis. Six of 8 children with an abnormal medical result had mental retardation. Overall, the proportion of children with any abnormal medical result was 9.3%.

Table 3. Associated Medical Conditions in Children With Pervasive Developmental Disorder


Most other surveys5, 17 estimated the prevalence of children with PDD to be nearer to 20 per 10 000 children than the 62.6 per 10 000 prevalence in our study. This rate is, however, consistent with the 57.9 and 67.4 per 10 000 estimates reported in 2 recent investigations.18, 19 These 3 surveys have all used intensive screening procedures, focused on children younger than 10 years, and used modern standardized diagnostic measures such as the ADI-R10-12 or the Autism Diagnostic Observation Schedule-Generic.20 The somewhat lower estimate of 26.1 per 10 000 (and 30.1 per 10 000 among children aged 5 to 9 years) obtained in another UK survey21 probably reflects methodological differences in an investigation that was focusing primarily on common childhood psychiatric disorders. Thus, the latter survey did not rely on screening procedures and diagnostic measures specific to PDDs. It is worth noting that 4 UK surveys of children in the same age groups conducted at the same time and in the same country showed a 6-fold variation in prevalence rates, emphasizing how powerfully various methods used in a survey affect prevalence estimates.4 The findings also point to the probable lack of sensitivity of case finding procedures in earlier surveys resulting in underestimation of rates. Therefore, the prevalence of PDDs seems to be about 60 per 10 000 children, an estimate that draws attention to the needs of a substantial minority of children.

Whether the higher prevalence rates reported recently arise from a secular increase in the incidence of the disorder or merely reflect a broadening of the concept of PDD together with improved detection and recognition cannot be assessed from these data. Comparison of prevalence rates obtained from cross-sectional surveys conducted at different times are confounded by changes in diagnostic concepts and criteria, changes in the efficiency of case finding procedures (as already shown above), and improved awareness in both the lay and professional public about the autism-spectrum conditions.4 In 1 survey, comparison of rates between successive birth cohorts was performed holding constant case definition and identification methods, and no evidence could be produced of an increase over time.22 Reports of increased numbers of children with PDD by providers of educational services have also been quoted as evidence of an epidemic of autism23, 24 although several analyses of these claims refuted their validity.25-27 One factor accounting for increased rates lies in the decreasing age at diagnosis, which occurred during the last 30 years.23, 25, 28 Assuming no change in the underlying incidence and a steady prevalence pool, this trend could explain the increasing numbers of young children seen in clinical settings and identified in surveys, particularly since those surveys usually relied on service providers to detect known cases rather than on systematic population screening.

In our survey, AD accounted for only 27% of the cases with these children showing much greater cognitive and language impairments. By contrast, the majority of cases was found at the mild end of the autistic spectrum, with the PDD-NOS and Asperger syndrome groups accounting for 71.1% of the cases. High proportions of PDDs were also found in recent surveys (46.8%18 and 40%19). Prior surveys focused on a narrow definition, which led to the exclusion of these milder forms although it has been recognized for some time that they represented a group as sizable if not bigger than that of autism.5 The inclusion of these milder variants certainly may account for a substantial part of the increase in prevalence rates.

Children with a PDD thus present as a whole as less impaired than what has been classically described. Although the average rate of mental retardation was near 75% in previous autism surveys,5 this rate has fallen to much lower figures of 40%18 and 55%19 in large epidemiological series of PDD and was 26% in this survey. Moreover, there appears to be a downward trend for the rate of mental retardation within the group narrowly defined as autism (ie, 50% in the Brick Township study among 3- to 10-year-olds19 and 25% among 3- to 5-year-olds in a Finnish survey29).

This shift has important implications for intervention since the majority of these children will require education in mainstream schools with provision of individual support. In addition, it is possible that very early intervention in autism and PDD might be associated with a much better cognitive outcome in the short term. Evidence of the beneficial impact of intensive educational programs between the ages of 2 and 4 years has accumulated recently,7, 8 and the notion of a critical period for a maximal effect of intensive educational interventions clearly requires further examination. Parents recognize the first developmental abnormalities before the second birthday in the majority of cases,30, 31 and one encouraging result from this survey was that four fifths of PDD cases were identified at a very early age by trained health visitors, indicating that early population screening programs could detect a high proportion of children with PDDs before the age of 2 years. Instruments with adequate levels of sensitivity and specificity are currently being developed,18, 32, 33 which may make that goal attainable. Such screening must be supported with appropriate assessment services combining special expertise in autism and multidisciplinary skills,32 as was the case in our population.

Consistent with a major role of genetic factors in PDD,6, 34 identified medical abnormalities were found in less than 10% of our sample. Moreover, the abnormalities reported in this sample might not be causally implicated in the development of PDD and might have occurred simply as random findings in a population submitted to intensive medical work-up. Nevertheless, the rate of 10% for medical abnormalities of potential etiological significance is consistent with prior findings deriving from both clinical35, 36 and epidemiological surveys.3, 5 The rate of sibling recurrence obtained in this study is also consistent with figures of 3% to 7% reported by other investigators,34 and although the absolute magnitude of the risk remains small, a comparison with the population prevalence points toward a large increase in the risk of autism or PDD in families with an already affected child.

Some limitations of this study must be mentioned. First, clinical assessment of children was not performed with standardized diagnostic techniques although such instruments were available for parental interviews and cognitive testing. It is unlikely that this would affect the prevalence estimates obtained in this study since experienced clinicians agreed 100% on the presence of a PDD in the whole sample. Availability of these assessments might nevertheless have provided a different breakdown of the diagnosis into various diagnostic subcategories. Assessing young children with PDDs is a complex task and guidelines to draw the line between high-functioning autism, Asperger syndrome, and PDD-NOS remain to be firmly established. Second, there is a possibility that some children might have been missed despite the intensive screening efforts used in the survey. This might particularly apply to some cases of Asperger syndrome who are sometimes not detected before school age and might have led to some underestimation of the prevalence. Conversely, some children diagnosed as having mild forms of PDD-NOS may turn out on follow-up assessments to have more transient developmental problems. This might have produced an inflation of the prevalence estimate. Whether these 2 problems might cancel each other remains to be seen, but we are committed to reassess this sample at age 8 to 10 years to address these issues and to obtain a more stable estimate.

Author/Article Information

Author Affiliations: Child Development Centre, Central Clinic, Stafford, England (Dr Chakrabarti); and Department of Child & Adolescent Psychiatry, MRC Child Psychiatry Unit, Institute of Psychiatry, King's College, London, England (Dr Fombonne).

Corresponding Author and Reprints: Eric Fombonne, MD, FRCPsych, MRC Child Psychiatry Unit, Institute of Psychiatry/King's College London, Denmark Hill, London SE5 8AF, England (e-mail: e.fombonne@iop.kcl.ac.uk).

Author Contributions: Study concept and design, analysis and interpretation of data, drafting of the manuscript, critical revision of the manuscript for important intellectual content, and administrative, technical, or material support: Chakrabarti, Fombonne.

Acquisition of data and obtained funding: Chakrabarti.

Statistical expertise and supervision: Fombonne.

Funding/Support: Funding for this study was provided by the First Community Health Trust.

Acknowledgment: We are grateful to the First Community Trust board and its executive directors for supporting this research. We especially thank the parents and children in the research group without whose cooperation and help this research would not have been possible. We also thank all the staff of the child development centers for their support and Sally Williams, BSc, senior educational psychologist of Staffordshire LEA, who conducted all the psychometric assessments of the children. Frank Devine, RGN, RNM, behavior nurse specialist, helped enormously by his meticulous observation and recording of the children's behavior, as well as by providing support to the children's families. We also thank Marianne Murin and Simon Wallace for taking part in the reliability study.


1.American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition. Washington, DC: American Psychiatric Association; 1994. 

2.Lotter V. Epidemiology of autistic conditions in young children, I: prevalence. Soc Psych. 1966;1:124-137.

3.Fombonne E. Epidemiological surveys of autism: a review. Psychol Med. 1999;29:769-786. MEDLINE

4.Fombonne E. Epidemiological estimates and time trends in rates of autism. Mol Psychiatry. In press. 

5.Fombonne E. Epidemiological investigations of autism and other pervasive developmental disorders. In: Lord C, ed. Educating Children With Autism. Washington, DC: National Academy of Sciences Press; 2001.

6.Bailey A, Le Couteur A, Gottesman I, et al. Autism as a strongly genetic disorder: evidence from a British twin study. Psychol Med. 1995;25:63-77. MEDLINE

7.Rogers S. Brief report: early intervention in autism. J Autism Dev Disord. 1996;26:243-246. MEDLINE

8.National Academy of Sciences. Report of the Committee on Educational Interventions in Children With Autism: Educating Children With Autism. Washington, DC: National Academy of Sciences Press; 2001. 

9.Hall D, ed. Health for All Children: Report of the Third Joint Working Party on Child Health Surveillance. 3rd ed. Oxford, England: Oxford University Press; 1996.

10.Lord C, Rutter M, Le Couteur A. Autism Diagnostic Interview-Revised: a revised version of a diagnostic interview for caregivers of individuals with possible pervasive developmental disorders. J Autism Dev Disord. 1994;24:659-685. MEDLINE

11.Le Couteur A, Rutter M, Lord C, et al. Autism Diagnostic Interview: a standardized investigator-based instrument. J Autism Dev Disord. 1989;19:363-387. MEDLINE

12.Fombonne E. Diagnostic assessment in a sample of autistic and developmentally impaired adolescents. J Autism Dev Disord. 1992;22:563-581. MEDLINE

13.Weschler D. Manual for Wechsler Pre-school and Primary Scale of Intelligence-Revised (British Amendments). Kent, England: The Psychological Corp; 1990.

14.Stutsman R. Merrill-Palmer Scale of Mental Tests. Preprints of Part III, Mental Measurement of Pre-school Children. Chicago, Ill: Stoelting Co; 1948.

15.Bartko J. On various intraclass correlation reliability coefficients. Psychol Bull. 1976;83:762-765.

16.STATA Corp. Statistic/Data Analysis. College Station, Tex: STATA Press; 1997.

17.Wing L, Gould J. Severe impairments of social interaction and associated abnormalities in children: epidemiology and classification. J Autism Dev Disord. 1979;9:11-29. MEDLINE

18.Baird G, Charman T, Baron-Cohen S, et al. A screening instrument for autism at 18 months of age: a 6 year follow-up study. J Am Acad Child Adolesc Psychiatry. 2000;39:694-702. MEDLINE

19.Centers for Disease Control and Prevention. Prevalence of Autism in Brick Township, New Jersey, 1998. Atlanta, Ga: Centers for Disease Control and Prevention; 2000. Community Report. Available at: http://www.cdc.gov/ncbddd/dd/rpttoc.htm. Accessibility verified May 15, 2001.

20.Lord C, Risi S, Lambrecht L, et al. The Autism Diagnostic Observation Schedule-Generic: a standard measure of social and communication deficits associated with the spectrum of autism. J Autism Dev Disord. 2000;30:205-223. MEDLINE

21.Fombonne E, Simmons H, Ford T, Meltzer H, Goodman R. Prevalence of pervasive developmental disorders in the British nationwide survey of child mental health. J Am Acad Child Adolesc Psychiatry. In press.

22.Fombonne E, du Mazaubrun C, Cans H, Grandjean H. Autism and associated medical disorders in a large French epidemiological sample. J Am Acad Child Adolesc Psychiatry. 1997;36:1561-1569. MEDLINE

23.California Department of Developmental Services. Changes in the Population of Persons With Autism and Pervasive Developmental Disorders in California's Developmental Services System: 1987 Through 1998. Report to the Legislature; March 1, 1999. Available at: http://www.dds.ca.gov. Accessibility verified May 30, 2001.

24.Wakefield A. MMR vaccination and autism [letter]. Lancet. 1999;354:949-950. MEDLINE

25.Fombonne E. Is there an epidemic of autism? Pediatrics. 2001;107:411-413. MEDLINE

26.Dales L, Hammer SJ, Smith NJ. Time trends in autism and MMR immunization coverage in California. JAMA. 2001;285:1183-1185. ABSTRACT  |  FULL TEXT  |  PDF  |  MEDLINE

27.Immunization Safety Review Committee. Measles-Mumps-Rubella Vaccine and Autism. Washington, DC: Institute of Medicine; 2001.

28.Howlin P, Moore A. Diagnosis in autism: a survey of over 1200 patients in the UK. Autism. 1997;1:135-162.

29.Kielinen M, Linna SL, Moilanen I. Autism in northern Finland. Eur Child Adolesc Psychiatry. 2000;9:162-167. MEDLINE

30.De Giacomo A, Fombonne E. Parental recognition of developmental abnormalities in autism. Eur Child Adolesc Psychiatry. 1998;7:131-136. MEDLINE

31.Rogers JS, Di Lalla D. Age of symptom onset in young children with pervasive developmental disorders. J Am Acad Child Adolesc Psychiatry. 1990;29:207-216.

32.Filipek PA, Accardo PJ, Baranek GT, et al. The screening and diagnosis of autistic spectrum disorders. J Autism Dev Disord. 1999;29:439-484. [published correction appears in J Autism Dev Disord. 2000;30:81]. MEDLINE

33.Stone W, Coonrod E, Ousley O. Screening tool for autism in two-year-olds (STAT): development and preliminary data. J Autism Dev Disord. 2000;30:607-612. MEDLINE

34.Szatmari P, Jones M, Zwaigenbaum L, MacLean J. Genetics of autism: overview and new directions. J Autism Dev Disord. 1998;28:351-368. MEDLINE

35.Barton M, Volkmar F. How commonly are known medical conditions associated with autism? J Autism Dev Disord. 1998;28:273-278. MEDLINE

36.Rutter M, Bailey A, Bolton P, Le Couteur A. Autism and known medical conditions: myth and substance. J Child Psychol Psychiatry. 1994;35:311-322. MEDLINE

The Scientist 15[10]:16, May 14, 2001

Autism on the Rise

Multidisciplinary efforts aim at finding the biological basis for a complex disease

By Laura DeFrancesco


The rate of autism is rising. The number of reported cases has increased 10-fold in the last few decades, from 1 in 2,500 in the 1970s to 1 in 250 in the 1990s. Researchers are looking everywhere for the reason--from drinking water to the womb--with no clear-cut answer to date. In part, the increased incidence can be attributed to a broader definition of autism, which now includes milder forms of the disorder,1 as well as to better diagnostics and greater public awareness.2 But scientists don't know if these reasons explain the entire increase.

At a late-April conference entitled "Autism: Deciphering the Puzzle," developmental biologists, geneticists, and neurobiologists gathered to talk about this complex disease. While scientists attending the conference at the California Institute of Technology could not explain the huge jump in incidence, they did voice some hope: there is progress in understanding the condition's biological basis, along with the development of experimental models, and it could lead to better treatments.

A Neurologist's Nightmare

Described by one participant as "a neurologist's nightmare," autism affects a cohort of complex behaviors, involving impaired language development, the inability to interact socially, and repetitive and restrictive behaviors. Generally, autism is diagnosed in children aged 2 and older because the behaviors can't be observed at an earlier age. But researchers are working on improving the tools for diagnosing autism, particularly in young children. As with many neurological diseases, including apraxia and fetal alcohol syndrome, early intervention improves the prognosis.

Patricia Rodier, professor of obstetrics and gynecology at the University of Rochester, described an early intervention test at the conference that is used with infants. Devised by Susan Bryson of York University in Toronto, this test measures a child's ability to shift focus from one stimulus to another. In the first part of the test, one light is turned on, and then as a second light is turned on, the first is shut off. All children will shift their focus from the first to the second light. In the second part of the test, the first light is left on. Here, normal children will disengage from the first to the second light, but autistic children cannot make that shift. Rodier showed dramatic video footage of a 5-year-old autistic child attempting this task. A look of panic came across the child's face, as he realized that he couldn't take his eyes off the first light. In contrast, a severely retarded 6-month-old could refocus her gaze with no problem.

The above image shows positive functional activity in the fusiform gyrus (FG) and superior temporal sulcus (STS) in a group of normal subjects in response to faces, in comparison to the lack of functional activity noted in these regions in autistic patients (left image). The T value is a metric of the functional NMR signal intensity in relation to the variance. Courtesy Karen Pierce

One research tool that has eluded workers in this field is an experimental animal model for autism, because the diagnosis relies on human terms such as eye contact, facial expressions, and speech. Bryson's test may be just the ticket; it provides a glimpse into the nervous system but doesn't require learning or intelligence.

In the Mind's Eye

Many parents of autistic children suffer a heart-breaking burden: often, their youngsters are not emotionally connected to them. A recent University of Washington study, presented to the Society for Research in Child Development, showed that autistic children don't respond to faces, which could explain the emotional distance from their parents. Measuring brain activity with a net of external electrodes, Geraldine Dawson, director of the University of Washington Autism Center, found that the brains of autistic children were electrophysiologically silent when shown pictures of their mothers, while they did respond to other pictures, such as their favorite toys.

At the Caltech conference, Eric Courchesne, professor of neurosciences at the University of California, San Diego, presented live, deep-brain scans that back Dawson's work. Using imaging techniques, Courchesne and co-workers showed that the fusiform gyrus, the part of the brain involved with face recognition, is not active when autistic children are shown pictures of faces. Instead, in autistic children, each child displays a different electrophysiological pattern. Why there is decreased activity in the fusiform gyrus is unknown, but Karen Pierce, the principal investigator, offers several explanations. "One possibility is that limited exposure to faces in patients with autism (perhaps due to innate preference, biases of processing style, or learning) results in an underdevelopment or maldevelopment of face-processing systems. Another reason is that the neural substrates involved in face processing (e.g., fusiform gyrus or amygdala) is abnormal in autism." She made her comments after the conference.

Thalidomide Revisited

Most everyone is familiar with the haunting pictures from the 1960s of so-called thalidomide babies, who were born with deformed limbs after their mothers took this sedative while pregnant. Overlooked in the early studies is that many thalidomide children are autistic--missed, no doubt, because their parents and doctors were dealing with the more obvious and dramatic limb deformities. But in 1994, Swedish researchers reported the surprising finding that thalidomide children had a high incidence of autism,3 and for developmental biologist Rodier, this was helpful news, because the Swedish researchers identified when, during their pregnancies, the women took the drug.

Armed with these results, Rodier is developing an animal model for the kinds of brain abnormalities observed with autism, since she knows exactly when in the developmental program she needs to intervene. And she has the environmental agents to do it. Though thalidomide doesn't affect rodents in the same way as humans, Rodier has found that valproic acid, a common anti-seizure drug known to induce autism, causes brain damage in rodents, and precisely in the places expected, based on what's known about this disease.

Meeting organizer Paul Patterson describes a promising experimental system being developed in his lab at Caltech that is based on studies linking prenatal infections and immune dysfunction with mental illness. In developing a system that assesses how interactions between the immune system and nervous system affect brain development, Patterson has observed autistic-like behaviors in mice born to mothers exposed to influenza during pregnancy using a battery of behavioral tests. In one experiment, mice are dropped into a box. While normal mice move around the box, frequently stretching to sniff the environment, mice born to infected mothers stay in the corner, clinging to the wall and sniffing only occasionally. Using this test and others, Patterson intends to pick apart the immune response to see what proteins or factors might be involved in explaining the offspring's odd behavior.

The evidence for a genetic component to autism is overwhelming and indisputable.4 Consider, for example, that the parents of an autistic child are more likely to have a second autistic child, as opposed to those who have unaffected children. In a normal family, the likelihood is 0.4 percent; if there already is an autistic child, the odds grow to 2 to 3 percent. With identical twins, if one is autistic, the likelihood that the second will have some form of autism is a staggering 90 percent; with fraternal twins, the odds shrink to 2 to 3 percent.

Strong sentiment exists, particularly among the parents of autistic children, that environmental factors also are involved here. One popular theory links immunizations, particularly measles, mumps, rubella (MMR), with the onset of autism. Researchers at the Caltech meeting summarily dismissed this notion, because scientific evidence, they say, does not exist. Several recent studies, including an Institute of Medicine report issued April 23, did not show a correlation between MMR immunization and autism.5 In a study published last February in the British Medical Journal,6 there was no abrupt increase in the incidence of autism after the MMR vaccine was introduced.

What about other environmental factors? Eric Hollander, professor of psychiatry at the Mt. Sinai School of Medicine and Clinical Director of the Seaver Autism Research Center in New York City, is looking at several factors. Noting that an unusually large number of women at his clinic had pitocin-induced labor, Hollander is currently conducting a survey of some 58,000 births recorded in a national perinatal database to look for a connection between that drug and autism. Hollander also is investigating the possibility that an infectious agent is involved. He has found that in autistic children, a high expression level exists of a particular B-cell marker, D8/17, which is associated with altered sensitivity to streptococcus A.

Though much research has been carried out, there is still no complete answer, or answers, as to why more autistic children exist today. "Cautious folks will say that it is really impossible to say for sure what the reason is at this point," Patterson says. "Given the broadening of the diagnostic criteria, the heightened recognition of the disorder by doctors, and the fact that parents only get state funds to help with special education ... if the child has a diagnosis of a severe disorder such as autism, we'll only be able to tell if this is a true rise in incidence after the dust has settled."

Laura DeFrancesco can be contacted at defrancesco1@earthlink.net.


1. E. Fombonne, "The epidemiology of autism: a review," Psychological Medicine, 29: 769-86, 2000.

2. C. Lord et al., "Autism spectrum disorders," Neuron 28(2): 355-63, 2001.

3. K. Strömland, K. et al., "Autism in thalidomide embryopathy: A population study," Developmental Medicine and Child Neurology, 36: 351-6, 1994.

4. A. Bailey, "Autism as a strongly genetic disorder: evidence from a British twin study," Psychological Medicine, 25:63-77, 1995.

5. "Immunization Safety Review: Measles-Mumps-Rubella Vaccine and Autism," Institute of Medicine, April 23, 2001.

6. J.A. Kaye et al., "Mumps, measles, and rubella vaccine and the incidence of autism recorded by general practitioners; a time trend analysis," British Medical Journal, 322:460-3, 2001.

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