Types of Autism

The diagnostic category pervasive developmental disorders (PDD), as opposed to specific developmental disorders (SDD), refers to a group of five disorders characterized by delays in the development of multiple basic functions including socialization and communication. The pervasive developmental disorders are:

Autism Spectrum Disorder (ASD)

Is a disorder of neural development characterized by impaired social interaction and communication, and by restricted and repetitive behavior. The diagnostic criteria require that symptoms become apparent before a child is three years old. Autism affects information processing in the brain by altering how nerve cells and their synapses connect and organize; how this occurs is not well understood. It is one of three recognized disorders in the autism spectrum (ASDs), the other two being Asperger syndrome, which lacks delays in cognitive development and language, and pervasive developmental disorder, not otherwise specified (commonly abbreviated as PDD-NOS), which is diagnosed when the full set of criteria for autism or Asperger syndrome are not met. Autism has a strong genetic basis, although the genetics of autism are complex and it is unclear whether ASD is explained more by rare mutations, or by rare combinations of common genetic variants. In rare cases, autism is strongly associated with agents that cause birth defects. Controversies surround other proposed environmental causes, such as heavy metals, pesticides or childhood vaccines; the vaccine hypotheses are biologically implausible and lack convincing scientific evidence. The prevalence of autism is about 1–2 per 1,000 people worldwide, and the Centers for Disease Control and Prevention (CDC) report 11 per 1,000 children in the United States are diagnosed with ASD as of 2008. The number of people diagnosed with autism has increased dramatically since the 1980s, partly due to changes in diagnostic practice; the question of whether actual prevalence has increased is unresolved. Parents usually notice signs in the first two years of their child’s life. The signs usually develop gradually, but some autistic children first develop more normally and then regress. Early behavioral or cognitive intervention can help autistic children gain self-care, social, and communication skills. Although there is no known cure, there have been reported cases of children who recovered. Not many children with autism live independently after reaching adulthood, though some become successful. An autistic culture has developed, with some individuals seeking a cure and others believing autism should be accepted as a difference and not treated as a disorder.

Asperger's Syndrome (AS)

Also known as Asperger’s syndrome or Asperger Disorder (AD), is an autism spectrum disorder (ASD) that is characterized by significant difficulties in social interaction, alongside restricted and repetitive patterns of behavior and interests. It differs from other autism spectrum disorders by its relative preservation of linguistic and cognitive development. Although not required for diagnosis, physical clumsiness and atypical (peculiar, odd) use of language are frequently reported. The syndrome is named after the Austrian pediatrician Hans Asperger who, in 1944, studied and described children in his practice who lacked nonverbal communication skills, demonstrated limited empathy with their peers, and were physically clumsy. The modern conception of Asperger syndrome came into existence in 1981 and went through a period of popularization, becoming standardized as a diagnosis in the early 1990s. Many questions remain about aspects of the disorder. There is doubt about whether it is distinct from high-functioning autism (HFA); partly because of this, its prevalence is not firmly established. It has been decided that the diagnosis of Asperger’s be eliminated in DSM-5, to be replaced by a diagnosis of autism spectrum disorder on a severity scale. The exact cause is unknown. Although research suggests the likelihood of a genetic basis, there is no known genetic etiology and brain imaging techniques have not identified a clear common pathology. There is no single treatment, and the effectiveness of particular interventions is supported by only limited data. Intervention is aimed at improving symptoms and function. The mainstay of management is behavioral therapy, focusing on specific deficits to address poor communication skills, obsessive or repetitive routines, and physical clumsiness. Most children improve as they mature to adulthood, but social and communication difficulties may persist. Some researchers and people with Asperger’s have advocated a shift in attitudes toward the view that it is a difference, rather than a disability that must be treated or cured.

Pervasive Development Disorder - Not Otherwise Specified (PDD-NOS)

The diagnostic category pervasive developmental disorders (PDD), as opposed to specific developmental disorders (SDD), refers to a group of five disorders characterized by delays in the development of multiple basic functions including socialization and communication. The pervasive developmental disorders are: Pervasive developmental disorder not otherwise specified (PDD-NOS), which includes atypical autism, and is the most common; Autism, the best-known; Asperger syndrome; Rett syndrome; and Childhood disintegrative disorder (CDD). The first three of these disorders are commonly called the autism spectrum disorders; the last two disorders are much rarer, and are sometimes placed in the autism spectrum and sometimes not. Parents may note symptoms of PDD as early as infancy and typically onset is prior to three years of age. PDD itself does not affect life expectancy. There is a division among doctors on the use of the term PDD. Many use the term PDD as a short way of saying PDD-NOS. Others use the general category label of PDD because they are hesitant to diagnose very young children with a specific type of PDD, such as autism. Both approaches contribute to confusion about the term, because the term PDD actually refers to a category of disorders and is not a diagnostic label.

Childhood Disintegrative Disorder (CDD)

Also known as Heller’s syndrome and disintegrative psychosis, is a rare (1.7 cases per 100,000[1]) condition characterized by late onset (>3 years of age) of developmental delays in language, social function, and motor skills. Researchers have not been successful in finding a cause for the disorder. CDD has some similarity to autism, and is sometimes considered a low-functioning form of it, but an apparent period of fairly normal development is often noted before a regression in skills or a series of regressions in skills. Many children are already somewhat delayed when the disorder becomes apparent, but these delays are not always obvious in young children. The age at which this regression can occur varies, and can be from age 2-10 with the definition of this onset depending largely on opinion. The regression can be so dramatic, that the child may be aware of it, and in its beginning he may even ask, vocally, what is happening to him. Some children describe or appear to be reacting to hallucinations, but the most obvious symptom is that skills apparently attained are lost. This has been described by many writers as a devastating condition, affecting both the family and the individual’s future. As is the case with all pervasive developmental disorder categories, there is considerable controversy about the right treatment for CDD. The syndrome was originally described by Austrian educator Theodor Heller in 1908, 35 years before Leo Kanner and Hans Asperger described autism, but it has not been officially recognised until recently.

Rett Syndrome

Originally termed as cerebroatrophic hyperammonemia, is a neurodevelopmental disorder of the grey matter of the brain that almost exclusively affects females but has also been found in male patients. The clinical features include small hands and feet and a deceleration of the rate of head growth (including microcephaly in some). Repetitive stereotyped hand movements, such as wringing and/or repeatedly putting hands into the mouth, are also noted. People with Rett syndrome are prone to gastrointestinal disorders and up to 80% have seizures. They typically have no verbal skills, and about 50% of individuals affected are not ambulatory. Scoliosis, growth failure, and constipation are very common and can be problematic. The signs of this disorder are most easily confused with those of Angelman syndrome, cerebral palsy and autism. In DSM-IV-TR Rett’s disorder is listed under the broad category of pervasive developmental disorders, together with the autism spectrum disorders and childhood disintegrative disorder. Some argue that it is misclassified in this group, as it is similar to non-autistic spectrum disorders such as fragile X syndrome, tuberous sclerosis, or Down syndrome where one can see autistic features. Its removal from DSM-5 has been proposed because it has a specific etiology. It has also been argued that Rett Syndrome is in fact a neurodegenerative condition as opposed to a neurodevelopmental condition. This was shown by the fact that mice with induced Rett Syndrome can have their neurons completely restored and a normal phenotype by adding the MECP2 gene back to their genome. This information has also helped lead to further studies in curing or treating the disorder. It was first described by Austrian pediatrician Andreas Rett in 1966.