Diagnostic Criteria

Autism is a severe disruption of the normal developmental processes that occurs in the first three years of life. It leads to impaired language, play, cognitive, social and adaptive functioning, causing children to fall farther and farther behind their peers as they grow older. The cause is unknown, but evidence points to physiological causes such as neurological abnormalities in certain areas of the brain.

Autistic children do not learn in the same way that children normally learn. They seem to not understand simple verbal and nonverbal communication, respond differently to sensory input, and withdraw in varying degrees from people and the world around them. They show little interest in other children and tend not to learn by observing and imitating others. They become preoccupied with certain activities and objects that interfere with development of play.

Although children with Autism Spectrum Disorder (ASD) exhibit common behavioral deficits (e.g., communication and social) and excesses of stereotypic sensory behaviors, there are tremendous differences among children. For example, although many children have limited understanding and use of language, there are children with ASD who may be able to understand complex language, express their needs or even converse. Their language deficit may involve difficulties of grammar or speaking in a robotic fashion. Children with ASD also demonstrate a variety of social deficits. Whereas some children may reject all social contact, there are children who are quite social. However, they may only be social around adults and have no interest in children. Or the may be interested in children but do not initiate or sustain interactions. Similarly there are tremendous differences among children’s self-stimulatory behaviors. Some children may exhibit repetitive body movement while others line up objects, tap surfaces repetitively, or rewind a DVD to endlessly watch a particular scene. Some children may not demonstrate any noticeable motor stereotypies but have complex and obsessive rules.

The constellation of behaviors seen with ASD can be quite baffling to parents and professionals alike. Therefore, a diagnostician with tremendous experience is necessary to make this complex diagnosis.


With the advancement in diagnostic tools, most children with ASD can be reliably diagnosed by the age of 3, although earlier diagnosis is possible even as young as 12 months. Parents are usually the first to notice the difference in their child. These children do not follow the typical patterns of child development. Some of these peculiarities are noted as early as the first few months after birth, but most often are noted between the ages of 1 and 3. Some parents report a sudden regression and onset of social aloofness, while other parents report a lack of progress after the child has reached certain developmental milestones. In her paper, “Practice Parameter: Screening & Diagnosis of Autism,” Dr. Filipek, et al., listed some indicators warranting further evaluation:

  • No babbling, no pointing or other gesture by 12 months
  • No single words by 16 months
  • No 2-word spontaneous (not echolaliac) phrases by 24 months
  • Any loss of any language or social skills at any age

The six items in the Modified Checklist for Autism in Toddlers (M-CHAT) that are found to have the best discriminability between children diagnosed with and without autism/PDD are:

  • Lack of interest in other children
  • Not using index finger to point, to indicate interest in anything
  • Not bringing objects over to parents to show them
  • Lack of imitation Failure to respond to his/her name when called
  • Not following other’s pointing at a toy across the room by looking at it
  • Young children who are noted to have these symptoms are urgently need comprehensive professional evaluation to rule out the diagnosis of ASD


The U.S. Centers for Disease Control in 2007 reported a prevalence of Autistic Spectrum Disorder (ASD) at 6.7 children per 1,000, significantly higher than other conditions affecting children including childhood cancer and Downs Syndrome. Boys are affected by autism at a much higher rate than girls, for reasons that are not entirely clear. A similar pattern is seen in other childhood disorders such as Attention Deficit Disorder.

It is generally believed that the prevalence is similar across countries and cultures, although the numbers obtained in prevalence studies vary according to the methodology and diagnostic criteria used. In the U.K., the National Autism Society estimates between 5.5 and 9.1 children per 1,000 have ASD, depending on the diagnostic criteria used. A 2007 study published in Hong Kong found a prevalence rate of 1.6 per 1,000 children. In Canada the prevalence rate was reported to be 5 per 1,000 in 2003.

There are a variety of factors that appear to contribute to the increase in ASD. The diagnostic criteria for ASD has widened significantly over the years. Fifteen years ago if a child was conversational or affectionate, it was unlikely they would have received a diagnosis of ASD. More recently there is an understanding that autism occurs in many forms and therefore children who present as “high functioning” should still receive the diagnosis of ASD. In previous years many children received the diagnosis of mental retardation; however, today these children are properly diagnosed with ASD. Another factor contributing to higher reported prevalence is the increased availability of diagnosticians who are qualified to provide an appropriate diagnosis. Finally, due to massive media attention there is a greater awareness of ASD among parents and professionals.