Terms and Definitions

Terms used to refer to various Autism Spectrum Disorders (ASDs) can be very confusing at first: one will hear terms such as:

• autism, classic autism, high functioning autism
• Autistic Disorder
• Asperger Syndrome or Asperger's Disorder
• Pervasive Developmental Disorder (PDD), and/or Autism Spectrum Disorder (ASD)

A note on terms and labels
It is important to distinguish between the clinical terms and descriptions of ASD and our understanding and knowledge of people who live with ASD. We need to understand clinical terms used in medical settings, during diagnosis, and in certain treatment or intervention settings. However, it is wise to keep in mind that these terms may also be seen as limiting labels to some people on the spectrum who feel that ASDs have been "medicalized" to the point where individuals who are unique in their skills, abilities and value to their communities, have been forgotten or eclipsed by the "disorder".

All are commonly used terms and may be interpreted differently in various settings. The term "autism" is often used in two different ways. It is used to refer specifically to Autistic Disorder and it is also used more generally to refer to all ASDs. 

The term "spectrum" refers to a continuum of severity or developmental impairment. Children and adults with ASDs usually have particular communication and social characteristics in common, but the conditions cover a wide spectrum, with individual differences in:

• Number and particular kinds of symptoms
• Severity - mild to severe
• Age of onset
• Levels of functioning
• Challenges with social interactions

There are in fact five Autism Spectrum Disorders described under this diagnostic category of Pervasive Developmental Disorders (PDD) that appear in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) of the American Psychiatric Association. While the DSM-IV still categorizes autism as a mental health disorder, there is debate about whether this classification is appropriate.

When speaking of ASDs, most people are referring to three of the PDDs that are most common:

• Autistic Disorder (also called autism, classic autism and AD)
• PDD-NOS (Pervasive Developmental Disorder - Not Otherwise Specified)
• Asperger's Disorder (also called AS, Asperger's Syndrome and Asperger Syndrome)

Individuals with ASDs have varying degrees of difficulty in social interaction and communication and may show repetitive behaviours and have unusual attachments to objects or routines.

Autism is the most common neurological disorder affecting children and one of the most common developmental disabilities affecting Canadians in general. ASDs change the way the brain processes information and can affect all aspects of a person's development. Classic autism usually appears during the first three years of life. Autism is four times more common in boys than girls.

Each individual is unique - no one person with an ASD responds or behaves exactly like another with the same diagnosis.

Childhood Disintegrative Disorder (CDD)

• Rare: ~0.2 in 10,000 Canadians
• Significant losses in social behaviour, language, play and adaptive behaviour after period of normal development of 3 or more years
• Severe deficits in cognitive ability

Rett Syndrome (RTT)

• Rare: ~1 in 10,000 female births
• A developmental disorder found almost exclusively in girls
• Symptoms appear after an early period of apparently normal or near normal development until six to eighteen months of life, when there is a slowing down or stagnation of skills
• Often misdiagnosed as autism or cerebral palsy
• RTT causes problems in cognitive, sensory, emotional, motor and autonomic function. Can affect learning, speech and communication, sensory sensations, mood, movement, breathing, cardiac function and psycho-motor skills
• Disabilities caused by Rett Syndrome range from mild to severe.
  
• More on Rett Syndrome

Autistic Disorder (AD)

• Most common: ~20 in 10,000 Canadians
• Cognitive impairments
• Deficits in verbal and non-verbal communication
• Deficits in social understanding
• Unusual behaviours, restricted activities

Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS)

• Common: ~15 in 10,000 Canadians
• Also called atypical autism
• Severe and pervasive impairment in some areas such as reciprocal social interaction, or restricted activities and interests but the strict criteria for autistic disorder are not met

Asperger Disorder (also called Asperger's Syndrome, Asperger Syndrome, and AS)

• Common: ~5 in 10,000 Canadians
• Mild to severe impairments in social interaction and understanding
• Restricted and repetitive activities and interests
• Language and cognitive development not delayed
• Deficits in communication

Reference for prevalence:
Fombonne, E., 2003: Modern Views of Autism, Can. J. Psychiatry, 48:503-505.
Fombonne, E., 2003: Epidemiology of autism and other pervasive developmental disorders: an update. J. Autism.Dev. Disord. 33:365-381

Related Conditions

• Several other medical conditions also include some features of PDD, such as Down Syndrome, Prader-Willi Syndrome, Fragile X Syndrome, Landau-Kleffner Syndrome, William's Syndrome or Tourette's Syndrome but PDD does not actually include these medical conditions.