Pervasive Developmental Disorders, which Autism Spectrum Disorders fall under are characterized by severe and widespread impairments in several areas of development: reciprocal social interaction skills, communication skills, or the presence of stereotyped behavior, interests and activities. (See What is Autism page for more details)

There are 6 types of Pervasive Developmental Disorders:

Autistic Disorder

Some professionals consider "Autistic Disorder" appropriate only for those who show extreme symptoms in every one of several developmental areas related to autism. Other professionals are more comfortable with the term Autistic Disorder and use it to cover a broad range of symptoms connected with language and social dysfunction. Therefore, an individual may be diagnosed by one practitioner as having Autistic Disorder and by another practitioner as having PDD-NOS (Pervasive Developmental Disorder - Not Otherwise Specified) or PDD, if the practitioner is abbreviating for PDD-NOS.

Asperger’s Disorder

Cognitive, social and communication skills tend to be less impaired than those of the autistic individual.

Rett’s Disorder

High functioning autism; Rett’s disorder occurs only in females while autism occurs in both males and females and motor skills tend to be significantly impaired.

Childhood Disintegrative Disorder

Characterized by apparently normal development for at least the first two years of life and lose previously acquired skills.

Pervasive Developmental Disorder - Not Otherwise Specified (PDD-NOS) This diagnosis is generally reserved for those children who display impairments in language, social skills and behavior but who do not meet the specific criteria for autism.

FRAGILE X

Represents a subtype of autism with a known etiology (genetic disorder).

Genetic Factors:

Although research has failed to find a specific gene marker for autism, findings of familial studies and the greater prevalence in males than females strongly suggest a possible genetic involvement. Among identical twins both are afflicted with autism in about 82-86% of cases. The rate among fraternal twins is 25%. The syndrome of autism has been found to be more common in the siblings of a child with the disorder than in the general population. That is, if parents have one child with autism, they have an increased chance of having another child with the same disorder (i.e., the rate of autism amongst siblings is approximately 2%). In 7 to 10 percent of the autistic population, a syndrome called Fragile X has been identified, involving a break or weakness in the formation of the X chromosome. The correlation between Fragile X syndrome and autism has not been proven.

Family/Genetic Information

Among identical twins both are afflicted in about 82 - 86% of cases

the rate among fraternal twins is 25%

2/100 siblings of autistic children are also later diagnosed with autism

Diagnosing PDD

Generally, a total of six (or more) items from (1), (2), and (3), with at least two from (1), and one each from (2) and (3)must be observed by numerous parties (usually parents and teachers because they spend the most time with the child)

(1) qualitative impairment in social interaction, as manifested by at least two of the following: 
(a) marked impairment in the use of multiple nonverbal behaviors such as eye-to-eye gaze, facial expression, body postures, and gestures to regulate social interaction 
(b) failure to develop peer relationships appropriate to developmental level 
(c) a lack of spontaneous seeking to share enjoyment, interests, or achievements with other people (e.g., by a lack of showing, bringing, or pointing out objects of interest) 
(d) lack of social or emotional reciprocity 

(2) qualitative impairments in communication, as manifested by at least one of the following: 
(a) delay in, or total lack of, the development of spoken language (not accompanied by an attempt to compensate through alternative modes of communication such as gesture or mime) 
(b) in individuals with adequate speech, marked impairment in the ability to initiate or sustain a conversation with others 
(c) stereotyped and repetitive use of language or idiosyncratic language 
(d) lack of varied, spontaneous make-believe play or social imitative play appropriate to developmental level 

(3) restricted repetitive and stereotyped patterns of behavior, interests, and activities, as manifested by at least one of the following: 
(a) encompassing preoccupation with one or more stereotyped and restricted patterns of interest that is abnormal either in intensity or focus 
(b) apparently inflexible adherence to specific, nonfunctional routines or rituals 
(c) stereotyped and repetitive motor mannerisms (e.g., hand or finger flapping or twisting, or complex whole-body movements) 
(d) persistent preoccupation with parts of objects