American Speech-Language-Hearing Association

Communication Facts: Special Populations: Autism - 2008 Edition

Autism is a neurodevelopmental disorder defined by impairments in social and communication development, accompanied by stereotyped patterns of behavior and interest (1). ASHA-certified speech-language pathologists screen for, evaluate, and treat speech and language disorders secondary to the primary diagnosis of autism. Speech-language pathologists may also be part of the interdisciplinary team involved with the diagnosis of autism (2).

General Demographics

Controversy surrounds reports on the incidence and prevalence of autism and autistic spectrum disorders. Even more confusing is the concern regarding an apparent increase in the prevalence of the condition, often attributed to a variety of possible causes. Several possible explanations exist, including changes in diagnostic criteria, variations in case finding and identification between different epidemiologic studies, genetic and/or environmental sources, greater public and professional awareness, wider availability of treatment services, and increases in the actual incidence of the disorders (3-8).

  • Prevalence figures vary widely within the medical and allied health literature. The stated range for the prevalence of autism may be from less than 1 to 1,300 per 10,000 individuals (4, 6, 7, 9-14).
  • Autism is three to five times more common in males than in females (15).
  • Evidence is growing to strongly support genetic inheritance as an important contributor to autism. Scientists estimate that, in families with one child with autism, the risk of having a second child with the disorder is approximately 2% to 8%, which is greater than the risk for the general population (16-18).
  • The number of children with disabilities, ages 3-21, served in the public schools under the Individuals with Disabilities Education Act (IDEA) Part B in Fall 2002 was 6,606,702 (in the 50 states, D.C., and P.R.). Of these children, 136,986 (2%) received services for autism-related disorders (19). Data by disability are not reported by the Department of Education for children between birth and age 3.

Pervasive Developmental Disorder

Pervasive Developmental Disorder (PDD) includes five diagnoses under the autism spectrum: autistic disorder, Asperger's syndrome, childhood disintegrative disorder, Rett's Syndrome, and Pervasive Developmental Disorder-Not Specified (PDD-NOS) (2, 18).

  • PDD is characterized by severe and pervasive impairment in general areas of development, including reciprocal social interaction skills and communication skills (20).
  • Actual speech production may be impaired: speech may be robotic, monotonous, and with little change in pitch or expression. There can also be problems with pronunciation (21).
  • Prevalence rates for PDD vary widely within the pertinent literature, ranging from 18.7 to 60 per 10,000 (22, 23).
  • Estimating the prevalence of PDD in children and adolescents with mental retardation is complicated. The literature reports prevalence rates ranging from 3% through 50%. The differences in the estimated prevalence rates are related, in part, to the concept of PDD (24).

Autistic Disorder

Autistic Disorder begins in childhood. It is marked by the presence of markedly abnormal or impaired development in social interaction and communication and a markedly restricted repertoire of activity and interest. When speech develops, the pitch, intonation, rate, rhythm, or stress may be abnormal (e.g., monotony, inappropriate tone with context) (20). Manifestations of the disorder vary greatly depending on the developmental level and chronological age of the individual (11). Several studies indicate that the prevalence rate for autistic disorder ranges from between .2 and .6 per 10,000 individuals (10, 11, 20).

Asperger's Syndrome

The essential features of Asperger's Syndrome are severe and sustained impairment in social interaction, and the development of restricted, repetitive patterns of behavior, interests, and activities. There are no clinically significant delays or deviance in language acquisition, although more subtle aspects of social communication may be affected. Variability of cognitive functioning may be observed, often with strengths in areas of verbal ability, and weakness in non-verbal areas (20).

  • The prevalence rate of Asperger's syndrome is not well established, with estimates ranging from 2 to 97 per 10,000 individuals (23, 25).
  • A much greater frequency of autistic psychopathy is present in boys than girls (17).
  • Asperger Syndrome is a pervasive developmental disorder or an autism spectrum disorder that is thought to have a higher incidence than that of autism. Asperger Syndrome is different from autism, with a lack of delayed language as the most distinct difference (26).

Childhood Disintegrative Disorder

Childhood disintegrative disorder is a rare condition characterized by marked severe and prolonged regression in multiple areas of functioning following a period of at least two years of apparently normal development. It occurs in the absence of an associated medical condition. A loss of skills occurs in at least two of the following areas: expressive or receptive language, social skills or adaptive behavior, bowel or bladder control, play, or motor skills. Childhood disintegrative disorder is associated with severe cognitive impairment. Behavioral features of autistic disorder must be present in at least two of the following areas: qualitative impairment in social interaction; qualitative impairment in communication and play; restricted repetitive and stereotyped patterns of behavior (2, 20). The prevalence of childhood disintegrative disorder is not widely reported in the medical and allied health literature. Three studies suggest that the prevalence ranges from 0.2 to 1.7 per 10,000 individuals (23, 27, 28).

Rett's Syndrome

Rett's syndrome is a progressive neurological disorder that has almost exclusively occurred in girls (29, 30). There is a period of normal development and then beginning at the age of 1 to 4 years, a loss of previously acquired skills with a loss of purposeful hand skills, replaced with repetitive hand movements, such as wringing, washing, licking, or clapping (2). Other features include diminished ability to express feelings, avoidance of eye contact, a lag in brain and head growth, gait abnormalities, and seizures. The loss of muscle tone is usually the first symptom (31). There is also severe impairment in expressive and receptive language development (20).

  • The syndrome affects approximately 1 in every 10,000-23,000 live female births (17, 31).
  • Reports suggest that the cause for Rett's syndrome is a mutation on the X chromosome at the gene MECP2 (17).


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  2. Filipek, P.A., et. al. (1999). The screening and diagnosis of autistic spectrum disorders. Journal of Autism and Developmental Disorders, 29 (6): 439-484.
  3. Barbaresi, W.J., Katusic, S.K., & Voigt, R.G. (2006, November). Autism: A review of the state of the science for pediatric primary health care clinicians. Archives of Pediatric & Adolescent Medicine, 160 (11): 1167-1175.
  4. Rogel-Ortiz, F.J. (2005-March-April). Autism. Gacenta Medica de Mexico, 141 (2): 143-147. [Article in Spanish]
  5. Coury, F.L., & Nash, P.L. (2003, October). Epidemiology and etiology of autistic spectrum disorders difficult to determine. Pediatric Annals, 32 (10): 696-700.
  6. Rutter, M. (2005, January). Incidence of autism spectrum disorders: changes over time and their meaning. Acta Paediatrica, 94 (1): 2-15.
  7. Blaxill, M.F. (2004, November-December). What's going on? The question of time trends in autism. Public Health Reports, 119 (6): 536-551.
  8. Volkmar, F.R., Lord, C., Bailey, A., Schultz, R.T., & Klin, A. (2004, January). Autism and pervasive developmental disorders. Journal of Child Psychology and Psychiatry, and Allied Disciplines, 45 (1): 135-170.
  9. Centers for Disease Control & Prevention (2007, February 9). Prevalence of autism spectrum disorders - Autism & developmental disabilities monitoring network, six sites, Unites States, 2000. MMWR Surveillance Summaries, 56 (1): 1-11.
  10. Charman, T. (2002, December). The prevalence of autism spectrum disorders: Recent evidence and future challenges. European Child & Adolescent Psychiatry, 11 (6): 249-256.
  11. Wing, L., & Potter, D. (2002). The epidemiology of autistic spectrum disorders: Is the prevalence rising? Mental Retardation and Developmental Disabilities Research Reviews, 8 (3): 151-161.
  12. Gadia, C.A., Tuchman, R., & Rotta, N.T. (2004, April). Autism and pervasive developmental disorders. Jornal de Pediatria, 80 (2 Suppl.): S83-S94. [Article in Portuguese]
  13. Williams, J.G., Higgins, J.P., & Brayne, C.E. (2006, January). Systematic review of prevalence studies of autism spectrum disorders. Archives of Diseases in Childhood, 91 (1): 2-5.
  14. Centers for Disease Control & Prevention (2007, February 9). Prevalence of autism spectrum disorders - Autism & developmental disabilities monitoring network, 14 sites, Unites States, 2002. MMWR Surveillance Summaries, 56 (1): 12-28.
  15. Carter, A.S., et. al. (2007, January). Sex differences in toddlers with autism spectrum disorders. Journal of Autism and Developmental Disorders, 37 (1): 86-97.
  16. Hu-Lince, D., Craig, D.W., Huentelman, M.J., & Stephan, D.A. (2005). The Autism Genome Project: goals and strategies. American Journal of Pharmacogenomics, 5 (4): 233-246.
  17. Rau, J.D. (2003, April). Is it autism? Contemporary Pediatrics, 20 (4): 54-82.
  18. Muhle, R., Trentacoste, S.V., & Rapin, I. (2004, May). The genetics of autism. Pediatrics, 113 (5): e472-e486.
  19. U.S. Department of Education. (2003). To assure the free appropriate public education of all Americans: Twenty-sixth annual report to Congress on the implementation of the Individuals with Disabilities Education Act. <Accessed June 8, 2007,>.
  20. Diagnostic and Statistical Manual of Mental Health Disorders, Fourth Edition, Text Revision. Washington, DC, American Psychiatric Association, 2000.
  21. National Dissemination Center for Children with Disabilities. (1998). Pervasive Developmental Disorders (Fact Sheet 20 - FS20). Washington, DC: Author.
  22. Mugno, D., et. al. (2007, April 27). Impairment of quality of life in parents of children and adolescents with pervasive developmental disorder. Health and Quality of Life Outcomes, 5, 22.
  23. Fombonne, E. (2003, August). Epidemiological surveys of autism and other pervasive developmental disorders: An update. Journal of Autism and Developmental Disorders, 33 (4): 365-382.
  24. de Bildt, A., Sytema, S., Kraijer, D., & Minderaa, R. (2005, March). Prevalence of pervasive developmental disorders in children and adolescents with mental retardation. Journal of Child Psychology and Psychiatry, and Allied Disciplines, 46 (3): 275-286.
  25. Elder, L.M., et. al. (2006). The efficacy of social skills. Treatment for children with Asperger syndrome. Education and Treatment of Children, 29 (4): 635-663.
  26. Schnur, J. (2005, August). Asperger syndrome in children. Journal of the American Academy of Nurse Practitioners, 17 (8): 302-308.
  27. Fombonne, E. (2002, June). Prevalence of childhood disintegrative disorder. Autism, 6 (2): 149-157.
  28. Agarwal, V., Sitholey, P., & Mohan, I. (2005, December). Childhood disintegrative disorder, an atypical presentation: A case report. Journal of Autism and Developmental Disorders, 35 (6): 873-874.
  29. Leonard, H., Silberstein, J., Falk, R., et. al. (2001, May). Occurrence of Rett syndrome in boys. Journal of Child Neurology, 16 (5): 333-338.
  30. Leonard, H., Fyfe, S., Dye, D., & Leonard, S. (2000, January). Using genetic epidemiology to study Rett syndrome: The design of a case-control study. Paediatric and Perinatal Epidemiology, 14 (1): 85-89.
  31. Jellinger, K.A. (2005, November). Rett disorder and the developing brain. European Journal of Neurology, 12 (11): 919-920.

Compiled by Andrea Castrogiovanni * American Speech-Language-Hearing Association * 2200 Research Boulevard, Rockville, MD 20850 *

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