Pervasive Developmental Disorder 

Pervasive developmental disorders (PDDs) include a spectrum of behavioral problems commonly associated with autism. The Diagnostic and Statistical Manual of Mental Disorders, 4th Edition (DSM-IV) includes autistic disorder, Rett syndrome, childhood disintegrative disorder, Asperger disorder, and PDD not otherwise specified under the spectrum of PDD.^[1]

The DSM-IV groups these disorders together because they share behavioral problems in the area of social interaction and communication. Other symptoms include stereotyped behaviors, restrictive interests or activities, and cognitive deficits. (See History.)

Autistic disorder in its most severe presentation may describe a child aged 3 years who presents with no expressive language, who seeks comfort from parents in atypical ways, who engages in repetitive hand flapping, and who makes no eye contact. In the mildest presentation, PDD not otherwise specified may describe a child aged 9 years with poor peer interactions, normal verbal abilities, and mild nonverbal disabilities. The mild nonverbal disabilities make it difficult for the child to follow subtle social cues that most children easily interpret as anxiety, anger, or sadness. The child's preoccupation with a restricted interest and attention to detail often tires the patience of peers with similar interests who are developing normally. (See History, Etiology.)

Symptoms of PDDs that may begin during the first year of life include lack of joint attention. A normally developing 1-year-old infant would make eye contact with a parent, point at an object for the parent to see, and smile responsively if the parent identifies the object. A child at risk for PDD often lacks these behaviors. Some such children may escape clinical attention until adolescence. Adolescents with normal development begin to use abstract thinking, realize that people have differing opinions, and learn to accept them. Adolescents with PDD often present with rigid thinking, are unable to accept other's opinions, and explode behaviorally when they cannot convince others to adhere only to their opinion.

DSM-V may exclude Rett syndrome from the group of PDDs, because a genetic etiology has been identified for this disorder. For this reason, the association of fragile X syndrome and autistic disorder has been debated.^[2] Some clinicians and researchers argue that, because fragile X syndrome is a genetic disorder, individuals with this syndrome cannot have autistic disorder. Alternatively, some propose that the frequency of autistic disorder among individuals with fragile X syndrome is similar to that in individuals with intellectual disability.

Go to Autism, Asperger Syndrome, and PET Scanning in Autism Spectrum Disorders for complete information on these topics.

Associated morbidities

Identified organic disorders that occur with PDD include epilepsy (the most common medical condition associated with PDD), cerebral palsy, fragile X syndrome, fragile X premutation involvement, tuberous sclerosis, phenylketonuria, neurofibromatosis, Down syndrome, and congenital rubella. Roughly 30% of patients with PDD present with a known medical disorder.^[3] Seizures are the most frequent comorbidity. Deletions or duplications (eg, 15q duplication) are the most common genetic abnormality associated with PDD.^[4] (See Etiology.)

Autistic disorder is commonly comorbid with intellectual disability. Fragile X syndrome is the most common genetic cause of intellectual disability. Therefore, autistic disorder should be common in those with fragile X syndrome. Several studies have demonstrated an excess of autistic symptom clusters and clinical findings, such as larger head circumference, in individuals with fragile X syndrome greater than would be expected among persons with intellectual disability without a genetic etiology.^[5] These features are absent in cases of fragile X syndrome without autism. Therefore, a subtype of fragile X syndrome may be a PDD behavioral phenotype. As evidence mounts that PDDs have biological origins, these genetic syndromes may be used as models to develop new treatment strategies for PDD. (See Etiology.)

Symptoms of obsessive-compulsive disorder (OCD) and attention deficit hyperactivity disorder (ADHD) are often present in patients with PDD. Some clinicians label the OCD and ADHD symptoms separately, whereas others include them as part of the presentation of PDD. Regardless of the approach, the symptoms of OCD and ADHD may be disabling and require treatment with standard approaches that include, but are not limited to, medications and behavioral therapy.

Aggression is a symptom not specific to any particular psychiatric disorder. The etiologies are broad and include constipation, depression, anxiety, psychosis, or adjustment disorder. Treatment requires clarification of etiology to help select medications and other appropriate therapies.

Sensory integrations disorder is not found in the DSM-IV or the International Statistical Classification of Diseases and Related Health Problems, 10th revision (ICD-10) but best captures the behavioral problems that result when individuals with PDD become disruptive because they react adversely to loud noises, tags on clothing, or textures of food. They may also be disruptive while trying to seek alternative methods of self-soothing, such as swinging, wrapping themselves in heavy blankets, or eating nonnutritive items. Identification of these sensory needs or deficits is integral to the behavioral management of individuals with PDD.

Milestone regression

Regression, or the loss of developmental milestones, was once a controversial finding in autistic disorder. Today, differing degrees of regression are recognized as part of the developmental presentation of autistic disorder.^[6]

Major losses of developmental milestones suggest Rett Syndrome, childhood disintegrative disorder, or Landau-Kleffner syndrome.

Also see Acquired Epileptic Aphasia.

Researchers continue to identify multiple etiologies for the underlying pathophysiology of pervasive developmental disorder (PDD). Different levels of dysfunction in CNS systems are most likely involved. For example, at the molecular level, the type of serotonin-transporter gene promoter may modulate the severity of PDD or increase the risk for development of PDD.^[7] Data from a blood genomic study have suggested that the immune system plays a role.^[8] At the neuroanatomic level, preliminary brain imaging studies have shown differences that may manifest clinically as a larger head size.^[9]

Environmental factors may also contribute to development of PDD, although mercury exposure and vaccinations have mostly been dismissed.

Changes in culture may explain some of the increased rates of PDD not otherwise specified. A study correlated increased time spent indoors with increased rates of PDD and suggested that this was caused by increased television viewing.^[10] Television may reinforce repetitive behaviors in vulnerable children who, in a different era, would not have spent so much time with computer games and television programming that detract from interpersonal interactions.

Children with PDD may have other specific cognitive deficits, including central auditory processing problems, which imply distorted pathways between hearing and cortical processing. They may also have specific cognitive strengths. In isolated cases, these special cognitive talents lead to these individuals being labeled savants.

Some of these deficits and strengths may manifest as sensory integration issues. For example, children with PDD may have hyperacoustic hearing, predisposing them to act erratically around loud noises. The hyperacoustic hearing may enable some children with PDD to be gifted musicians.^[11] Temple Grandin, a distinguished author and professor with Asperger disorder, writes about her need for increased tactile stimulation, which helped her develop a more humane way to move cattle.^[12]

Children with fragile X syndrome have many of these cognitive deficits. The genetic and molecular basis of fragile X syndrome has been described in detail, supporting the premise that deficits in the protein encoded by the fragile X syndrome gene result in glutamate disturbance and abnormal neuronal axonal development.^[13] The protein FMRP, encoded by the fragile X syndrome gene, may interact with other neurotransmitters or processes to cause autistic symptoms in fragile X syndrome more often than in other genetic syndromes or nonsyndromic intellectual disability.

Since the identification of the genetic abnormality in Rett syndrome, milder cases of Rett syndrome with smaller deletions have been identified.^[14] Individuals with milder cases of Rett syndrome have better intellectual ability and more classic symptoms of autistic disorder. The genetic defect in Rett syndrome results in alterations in the power center equivalents of brain cells, also known as mitochondria.^[15]

Incidence in the United States

A survey of existing literature by Fombonne in 2003 indicated that the rate for all forms of pervasive developmental disorder (PDD) was 30-60 cases per 10,000 population, while the rate for Asperger disorder was 2.5 cases for 10,000 population and the rate for childhood disintegrative disorder was 0.2 case per 10,000 population. Fombonne attributed an increase in prevalences over time to changes in case definitions and to improved awareness.^[16]

An epidemiologic survey confirmed the prevalence of PDD disorders to be 1 in 150 children.^[17]

The increase in reported cases of PDD probably results from an increased identification of cases that do not meet specific criteria for autistic disorder or Asperger disorder but are diagnosed as PDD not otherwise specified.

Available surveys lack sufficient proof to support an increase in the prevalence of autistic disorder.

International incidence

No evidence suggests that the international prevalence of PDD differs from the prevalence in the United States. However, the literature indicates that these disorders are identified at a later age in specific regions of the United States than in other countries.^[18]

Race predilection

Race has not been implicated as a risk factor for PDD.

Sex predilection

Sex bias for PDD is significant. Autism and PDD not otherwise specified may be 5 times more common in boys than in girls. Asperger syndrome may be 10 times more common in boys than in girls.

Only Rett syndrome affects more girls than boys; in fact, Rett syndrome is rarely diagnosed in boys. However, new molecular testing for Rett syndrome indicates that the incidence of the condition is greater in boys than previously reported.

Age predilection

Autistic disorder carries an onset criterion; evidence of the disorder must be present by age 3 years. Rett syndrome and childhood disintegrative disorder are also usually apparent by age 3 years.

As noted earlier, PDDs are diagnosed relatively late in United States compared with other countries.^[18] Within the United States, geographical differences in age of diagnosis present a significant public health challenge as evidence mounts to support early diagnosis and intervention.

Many parents of children with pervasive developmental disorder (PDD) need legal guidance to help them understand their legal rights to benefits and services available from public schools and from the medical system.

For patient education information, see the Brain and Nervous System Center, as well as Autism and Asperger Syndrome.