The pervasive developmental disorders, or PDDs, are a group of childhood disorders that manifest during the first years of the child's life. They are marked by severe weaknesses in several areas of development: social interaction, communication, or the appearance of stereotyped behavior patterns and interests. The PDDs are also known as autistic spectrum disorders. As the phrase spectrum disorder suggests, persons with these disorders fall at different points along a fairly wide continuum of disabilities and associated disorders. As defined by DSM-IV, the pervasive developmental disorders include:
pervasive developmental disorder not otherwise specified (PDD-NOS)
Description
The PDDs form a diagnostic category intended to identify children with delays in or deviant forms of social, linguistic, cognitive, and motor (muscular movement) development. The category covers children with a wide variety of developmental delays of differing severity in these four broad areas. The precise cause(s) of the PDDs are still obscure, but are assumed to be abnormalities of the central nervous system.
Autistic disorder
Autistic disorder, or autism, was first described in 1943. Autistic children are characterized by severe impairment in their interactions with others and delayed or abnormal patterns of communication; about 50% of autistic children do not speak at all. These abnormalities begin in the first weeks of life; it is not unusual for the parents of an autistic child to say that they "knew something was wrong" quite early in the child's development. Another characteristic symptom has been termed "insistence on sameness;" that is, these children may become extremely upset by trivial changes in their environment or daily routine—such as a new picture on the wall or taking a different route to the grocery store. Autistic children often make repetitive or stereotyped gestures or movements with their hands or bodies. Their behavioral symptoms may also include impulsivity, aggressiveness, temper tantrums, and self-biting or other forms of self-injury.
About 75% of children diagnosed with autism are also diagnosed with moderate mental retardation (IQ between 35 and 50). Their cognitive skills frequently develop unevenly, regardless of their general intelligence level. A minority of autistic children have IQs above 70; their condition is sometimes called high-functioning autism, or HFA. In addition to mental retardation, autism is frequently associated with other neurological or medical conditions, including encephalitis, phenylketonuria, tuberous sclerosis, fragile X syndrome, and underdeveloped reflexes. About 25% of autistic children develop seizure disorders, most often in adolescence.
Rett syndrome
Unlike autism, Rett syndrome has a very distinctive onset and course. The child develops normally during the first five months of life; after the fifth month, head growth slows down and the child loses whatever purposeful hand movements she had developed during the first five months. After 30 months, the child frequently develops repetitive hand-washing or hand-wringing gestures; over 50% of children with the disorder will develop seizure disorders. Rett syndrome is also associated with severe or profound mental retardation. As of 2001, this disorder has been diagnosed only in females.
Childhood disintegrative disorder, or CDD, was first described by an educator named Theodore Heller in 1908. He referred to it as dementia infantilis. Children with CDD have apparently normal development during the first two years of life. Between two and ten years of age, the child loses two or more previously acquired skills, including language skills, social skills, toileting, self-help skills, or motor skills. The child may also lose interest in his or her surroundings, and often comes to "look autistic." The data available as of 2001 indicate that CDD has several different patterns of onset and development; it may develop rapidly (within weeks) or more slowly (over a period of months).
CDD is frequently associated with severe mental retardation. In addition, children with CDD have a higher risk of seizures. CDD is occasionally associated with general medical conditions (metachromatic leukodystrophy or Schilder's disease) that could account for the developmental losses, but in most cases there is no known medical cause of the child's symptoms.
Asperger syndrome
Asperger syndrome (AS) was first identified in 1944 by a Viennese psychiatrist. It is sometimes called autistic psychopathy. AS is distinguished from autism by later onset of symptoms; these children usually develop normally for the first few years of life and retain relatively strong verbal and self-help skills. They are often physically clumsy or awkward, however, and this symptom may be noticed before the child starts school. AS is diagnosed most frequently when the child is between five and nine years of age. One of the distinctive features of Asperger syndrome is an abnormal degree of fascination or preoccupation with a limited or restricted subject of interest, such as railroad timetables, the weather, astronomical data, French verb forms, etc. In addition, the child's knowledge of the topic reflects rote memorization of facts rather than deep understanding.
Unlike autism, AS does not appear to be associated with a higher risk of seizure disorders or such general conditions as fragile X syndrome.
Pervasive developmental disorder not otherwise specified
PDD-NOS is regarded as a "sub-threshold" category, which means that it covers cases in which the child has some impairment of social interaction and communication, or has some stereotyped patterns of behavior, but does not meet the full criteria for another PDD. PDDNOS is sometimes referred to as atypical personality development, atypical autism, or atypical PDD. No diagnostic criteria specific to this category are provided in DSM-IV. Little research has been done on children diagnosed with PDD-NOS because the condition has no clear definition. The available data indicate that children placed in this category are diagnosed at later ages than children with autism, and are less likely to have mental impairment.
Genetic profile
Of the PDDs, autism has the best-documented genetic component, although more research is required. It is known that the degree of similarity in a pair of twins with respect to autism is significantly higher in identical than in fraternal twins. The likelihood of the biological parents of an autistic child having another child with the disorder is thought to be about 1:20. It is possible that the actual rate is higher, since many parents of one autistic child decide against having more children.
The genetic profile of Asperger syndrome is less well known, although the disorder appears to run in families—most commonly families with histories of depression or bipolar disorder. Rett syndrome is known only from case studies, so data about its genetic profile is not available as of 2001. The same lack of information is true also of CDD—partly because the disorder was first reported in 1966 and has only been officially recognized since 1994, and partly because the condition has been frequently misdiagnosed.
Demographics
Autism is thought to affect between two and five children out of every 10,000. Childhood disintegrative disorder is much less frequent, perhaps only a tenth as common as autism. Rett syndrome is also very rare, and is known only from case series reported in the medical literature. The incidence of Asperger syndrome is not definitely known as of 2001, but is thought to lie somewhere between 0.024% and 0.36% of the general population.
Some of the PDDs are considerably more common in boys than in girls. The male to female sex ratio in autism is variously given as 4:1 or 5:1. Less is known about the incidence of Asperger syndrome, but one study reported a male/female ratio of 4:1. Initial studies of CDD suggested an equal sex ratio, but more recent data indicate that the disorder is more common among males. Rett syndrome, on the other hand, has been reported only in females.
Signs and symptoms
The signs and symptoms of each PDD are included in its description.
Diagnosis
The differential diagnosis of autistic spectrum disorders is complicated by several factors. One is the wide variation in normal rates of children's development. In addition, because some of the symptoms of autism are present in mental retardation, it can be difficult to determine which condition is present in a specific child, or whether both conditions are present. A definitive diagnosis of autism is rarely given to children below the age of three years. Delays or abnormal patterns in cognitive and social development can be more accurately assessed in children age three or four; children with AS or PDDNOS may not be diagnosed until age five or later. A third factor is the tangled history of differential diagnosis of childhood disorders. Autism was first described by a physician named Leo Kanner in 1943. For several decades after Kanner's initial observations, researchers assumed that there was an association or continuity between autism in children and schizophrenia in adults. In fact, the term autism was first used to describe the self-focused thinking that characterizes schizophrenia; it was only later that the word was applied to the severe impairment of social behaviors that is a major symptom of autistic disorder. It took years of further research to establish clear diagnostic distinctions between autism and schizophrenia. Furthermore, the early assumption of a connection between autism and schizophrenia led to the hypothesis that autism was caused by painful experiences in early childhood. It is now known that autism and the other PDDs are essentially neurological disturbances.
Medical or laboratory testing
As of 2001, there are no brain imaging studies or laboratory tests that can be performed to diagnose a pervasive developmental disorder. The examiner may, however, recommend a hearing test to rule out deafness as a possible cause of a child's failure to respond to the environment, or a brain scan to rule out other physical conditions.
Diagnostic interviews
A PDD may be diagnosed by a pediatrician, pediatric neurologist, psychologist, or specialist in child psychiatry. The diagnosis is usually based on a combination of the child's medical and developmental history and clinical interviews or observations of the child. Children who cannot talk can be evaluated for their patterns of nonverbal communication with familiar as well as unfamiliar people. The parents may be asked to describe the child's use of eye contact, gestures, facial expressions, and body language. A clinical psychologist can administer special tests designed to evaluate the child's problem-solving abilities without the use of language.
Diagnostic questionnaires and other tools
The examiner may use a diagnostic checklist or screener such as the Childhood Autism Rating Scale, or CARS, which was developed in 1993. In addition, the Autism Research Institute (ARI) distributes a Form E-2 questionnaire that can be completed by the parents of a child with a PDD and returned to ARI. Form E-2 is not a diagnostic instrument as such but a checklist that assists ARI in the compilation of a database of symptoms and behaviors associated with autistic spectrum disorders. Parents who complete the form will receive a brief report about their child. Researchers expect that the database will help to improve the accuracy of differential diagnosis as well as contribute to more effective treatments for children with PDDs.
Treatment and management
The treatment and management of children with PDDs will vary considerably according to the severity of the child's impairment and the specific areas of impairment.
Medications
As of 2001, there are no medications that can cure any of the PDDs, and no single medication that is recommended for the symptoms of all children with PDDs. In addition, there are few comparative medication studies of children with autistic spectrum disorders. The five sites (UCLA, University of Indiana, Ohio State, Yale, and the Kennedy-Krieger Institute) involved in the Research Units in Pediatric Psychopharmacology (RUPP) Program are currently conducting a study of respiridone in PDD children with behavioral problems. The RUPP sites are also testing medications approved for use in adults with self-injuring behaviors, anxiety, aggressive behavior, and obsessive-compulsive disorder on children with PDDs. This research is expected to improve the available treatments for children with these disorders.
Psychotherapy
The only PDD patients who benefit from individual psychotherapy are persons with AS or with HFA who are intelligent enough to have some insight into their condition. Typically they become depressed in adolescence or adult life when they recognize the nature and extent of their social disabiliities.
Educational considerations
Most children with AS and some children with high-functioning autism are educable. Many people with AS, in fact, successfully complete graduate or professional school. Only a small percentage of autistic children, however, complete enough schooling to be able to live independently as adults. Children with CDD must be placed in schools for the severely disabled.
Employment
Most children with AS can finish school and enter the job market. They do best, however, in occupations that have regular routines or allow them to work in isolation. Only a few high-functioning autistic children are potentially employable.
Prognosis
The PDDs as a group are lifelong disorders, but the prognoses vary according to the child's degree of impairment. As a general rule, language skills and the child's overall IQ are the most important factors in the prognosis. Children with AS have the most favorable educational prognosis but usually retain some degree of social impairment even as adults. Of autistic children, only about one-third achieve partial or complete independence in adult life. The prognoses for Rett syndrome and CDD are worse than that for autism, as the skill levels of these children often continue to deteriorate. Some, however, make very modest developmental gains in adolescence. Lastly, current information about the prognoses of children with PDDs is derived from treatments given to patients in the 1970s or 1980s. As knowledge of effective treatments for PDDs continues to accumulate, children with these disorders receive treatment earlier than they did two decades ago. It is likely that future prognoses for the PDDs will reflect these improvements.
BOOKS
American Psychiatric Association Staff. Diagnostic and Statistical Manual of Mental Disorders. 4th ed, revised. Washington, DC: American Psychiatric Association, 2000.
"Psychiatric Conditions in Childhood and Adolescence." In The Merck Manual of Diagnosis and Therapy. Edited by Mark H. Beers, MD, and Robert Berkow, MD. Whitehouse Station, NJ: Merck Research Laboratories, 1999.
Waltz, Mitzi. Pervasive Developmental Disorders: Finding a Diagnosis and Getting Help. New York: O'Reilly & Associates, Inc., 1999.
PERIODICALS
Autism Research Institute. Autism Research Review International. San Diego, Calif.: 1987.
ORGANIZATIONS
Autism Research Institute. 4182 Adams Ave., San Diego, 92116. Fax: (619) 563-6840.
National Organization for Rare Disorders (NORD). PO Box 8923, New Fairfield, CT 06812-8923. (203) 746-6518 or (800) 999-6673. Fax: (203) 746-6481. <http://www.rarediseases.org>.
Yale-LDA Social Learning Disabilities Project. Yale Child Study Center, 230 South Frontage Road, New Haven, CT 06520-7900. (203) 785-3488. <http://info.med.Yale.edu/chldstdy/autism>.
WEBSITES
Center for the Study of Autism Home Page, maintained by Stephen Edelson, PhD. <http://www.autism.org>.
