Understanding the Five Types of Pervasive Developmental Disorders

Types of PDD In the 1980’s there were only two subtypes of PDD-one being a severe form of autism called “infantile autism ” or “Kanner’s syndrome” and the other Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS). Understanding the neurological basis of PDD and the five disorders currently included under this heading is key for researchers who seek prevention and treatment. These disorders are:

· Autism

· Rett’s syndrome

· Childhood Disintegrative Disorder (CDD)

· Asperger’s syndrome

· Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS)

According to the authors of “Autism: A Comprehensive Occupational Therapy Approach” (Kuhaneck & Watling, 2010), the fourth edition of the Diagnostic and Statistic Manual of Mental Disorders (DSM) published in 1994 was revised to further distinguish the disorders of autism and PDD-NOS because they differed in onset, severity of symptoms, age of onset, gender affected and prognosis. To make matters more confusing- according to Psychology Today blogger Jean Mercer, Ph.D., the asperger’s diagnosis may be eliminated from the DSM 2014 edition and instead placed under a “high functioning” autism heading.

Classical Autism

Children on the severe end of the autism spectrum may be said to have “classical autism” also known as “infantile autism” or “Kanner’s syndrome”. Diagnostic criteria in the DSM include impairments in social and communication skills and repetitive, stereotypical behaviors. Psychiatrist Leo Kanner created quite a stir when he wrote in 1949 that autism appeared to be caused by “cold” unaffectionate parents. However, by the 1960’s the psychologist Bernard Rimland- himself the father of an autistic child debunked this notion- concluding that autism is a neurologically based disorder with strong genetic links. According to The National Institutes of Health, Eunice Kennedy Shriver Center, classical autism primarily affects boys, siblings of those with autism and people with other developmental disorders such as Fragile X.

Neurologiocal Differences in the Autistic Brain

According to Kuhaneck and Watling, a unified neurodevelopmental theory of the autism spectrum disorders remains elusive. However, research into brain functioning and specific neural structures find consistent differences in the brains of individuals on the spectrum when compared to typcially developing children. Some notable differences in early brain development of children with autism include:

· Larger head size

· Overgrowth in the cerebellum, frontal and temporal lobes-impacting higher cognitive functions

· Mirror neurons (brain cells that react when we observe something) don’t perform normally.

· Decreased cerebral blood flow in specific brain areas

· Differences in the limbic system ‘”which is responsible for memory, emotion and facial identification.

· Increased serotonin synthesis- impacting mood regulation

Occupational therapists such as me have a deep interest in understanding the neurological basis of PDD-including autism as we provide sensorimotor activities that impact brain function with goals to improve focus, sensory processing and managing multiple sensory stimuli. Gail Richard- author of The source for Autism (Richard, 1997) succinctly describes the confusing neurological system of a person with these differences. “This confusion leads to sensory defensiveness. The sensory defensiveness ranges anywhere on a continuum from mild to severe.”

Rett’s-the”Girl’s Syndrome”

Children with Rett’s syndrome begin life with apparent normal development and head circumference. Then at around 12-18 months of age they dramatically regress-losing previously learned skills. Symptoms include cognitive and communication delays, small head circumference, unusual hand and eye movements, balance and coordination difficulties and seizures. According to Gail J. Richard and Debra Reichert Hoge, authors of “The Source for Syndromes”, Rett’s is a genetic disability that appears to be caused by an X chromosome mutation that only affects females. Diagnosis is made by ruling out other disorders, identifying criteria symptoms and confirmed by genetic tests. Fortunately, Rett’s syndrome is rare. However, therapeutic and educational intervention is challenging since these children experience progressive loss of mobility, muscle wasting and scoliosis.

Childhood Disintegrative Disorder

Childhood Disintegrative Disorder (CDD) has been referred to as a “regressive autism” because the child appears to develop normally for two years and then begins losing abilities such as bowel and bladder control, language, social and motor skills. These children differ from those on the autism spectrum because they can often speak in full sentences before the deterioration and then over time lose all ability to speak. According to the Mayo Clinic there is no known cause. However, it is theorized that contributing factors include:

· An abnormal gene

· Environmental toxins

· Autoimmune responses

In addition, CDD often co-exists with the conditions of:

· Tuberous sclerosis (tumors in the brain)

· Lipid storage disease (a metabolic disorder)

· Subacute sclerosing panencephalitis (a chronic brain infection)

Asperger’s Syndrome

In 1994 Dr. Hans Asperger published his findings describing children with social deficits, clumsiness and strange obsessions in bizarre subjects (Richard & Hoge, 1999). He theorized that there was a genetic transmission of the disorder, especially amongst males. Children with this diagnosis differ from those with “high functioning autism ” (HFA) in that they demonstrate deficits associated with right hemisphere deficits-(i.e. visual processing deficits but good language development); whereas children with HFA demonstrate characteristics seen in a left-hemisphere language impairment.

Understanding the neurological basis for PDD as pertains to Asperger’s Syndrome (AS) involves studying the frequently coexisting conditions of obsessive compulsive disorder, anxiety, depression and sensory processing disorders. According to the National Institute of Neurological Disorders and Stroke, current research points the cause of AS to brain abnormalities-including structural and functional differences. AS tends to run in families and certain groups of genes may make a person vulnerable to developing the disorder.

Pervasive Developmental Disorder-Not Otherwise Specified

The diagnosis of Pervasive Developmental Disorder-Not Otherwise Specificed (PDD-NOS) demonstrates just how confusing diagnosis can be since PDD-NOS falls under the umbrella of PDD. According to Kuhaneck and Watling, the term PDD is used more within the medical context, whereas the term autism spectrum disorders (ASD) is widely used within the educational context and meant to include children with either diagnoses. Regardless of terminology, both ASD and PDD are neurological in nature and vary in severity.

Understanding Neurological Disorders

As an occupational therapist I have found that the most successful treatment approaches combine use of behavior modification and sensory integration modalities. Children learn best when their sensory needs are being met and they are rewarded for positive actions. Higher functioning students- such as those with Asperger’s Syndrome often demonstrate quirky behaviors that are not immediately attributed to a neurological disorder, but attributed instead to lack of discipline or poor parenting. I believe that this demonstrates how misdiagnosis or lack of diagnosis can be harmful. Current research strongly points to a neurological basis for sensory sensitivities and sensory processing challenges. Hopefully, understanding this will enable society, including educators and employers better accept and meet the needs of individuals with PDD.


Kuhaneck, H.M. & Watling, R. Autism: A Comprehensive Occupational Therapy Approach. AOTA Press, 2010.

Richard, G. The Source for Autism. LinguiSystems,1997.

Richard, G. & Hoge, D. R. The Source for Syndromes. Lingui Systems. 1999.