ASDs are notoriously heterogeneous in their presentation: there may be variability in the particular symptoms manifested in any individual at a given point in time and there may be significant levels of comorbidity. Accurate diagnosis requires that the clini-cian looks for the particular symptoms and signs that character-ize it: peculiar and deficient modes of social interaction, deficits in communication and the focused behaviors and interests.
Many consider the disturbance of social development, in-cluding difficulty in developing meaningful attachments and interpersonal reciprocity, to be the central impairment in ASD. While many children with ASD will seem aloof and unattached totheir parents, many will display age-appropriate separation anxi-ety. Typically, a child with autistic disorder has abnormal patterns of eye contact and facial expression. When compared with normal children, children with autism fail consistently to maintain eye contact or vary facial expression to establish social. These chil-dren seem to have considerable difficulty effectively coordinating social cues. They have difficulty demonstrating empathy or per-ceiving or anticipating others’ moods or responses The child with ASD often acts in a socially inappropriate manner or lacks the social responsiveness needed to succeed in social settings, leading to difficulty in the development of close, meaningful relationships. Some children with ASD eventually develop warm, friendly rela-tionships with family while their relationships with peers lag be-hind considerably, and these deficits typically persist across time.
It is estimated that only about half of children with autistic disorder develop functional speech. If autistic children do begin to speak, their babble is frequently decreased in quantity and lacking in vocal experimentation. When children with autistic disorder do acquire some speech, it is often peculiar and lacking in social per spective. Some children with autistic disorder are even loquacious, although their speech tends to be repetitious and self-directed rather than aimed at maintaining a reciprocal dialogue. People with autistic disorder commonly make use of stereotyped speech, including immediate and delayed echolalia, pronoun reversal and neologisms. Speech usage is often idiosyncratic, may consist of concrete and poorly constructed grammar, may not be used to con-vey social meaning, and is often literal, lacking in inference, and lacking in imagination. The delivery of speech is frequently ab-normal with atypical tone, pitch and cadence. Paradoxically, chil-dren with autistic disorder often have echolalia, in which prosody and other aspects of speech are frequently imitated verbatim.
Individuals with autistic disorder routinely engage in unu-sual patterns of behavior. Most people with ASD also resist or have significant difficulty with new experiences or transitions. They are commonly resistant to changes in their environment. They often repeatedly perform stereotyped motor acts such as hand clapping or flapping, or peculiar finger movements. These movements frequently occur at the periphery of their vision near their own face. Some children with autistic disorder engage in self-injurious behaviors including biting or striking themselves or banging their heads. This is most likely to occur with severe or profound mental retardation but is also seen in children with autistic disorder without mental retardation. Their play only oc-casionally involves traditional toys, and objects may be used in ways other than intended (for instance, a doll is used as a ham-mer), and there is a paucity of make-believe play. Individuals with autistic disorder seem to have unusual sensitivity to some sensory experiences, particularly specific sounds.
Other problems in ASD include impair ment in “joint at-tention”, the sharing or mutual focus on an object or event by two or more people, and the ability to shift attention when the social situation calls for it. Many children with ASD also have symptoms of hyperactivity and difficulty sustaining attention, but these should be distinguished from the joint attentional dys-function found in all patients with autistic disorder. Examples of joint attention include social exchanges that require pointing, referential gaze and gestures showing interest.
Children with Asperger’s disorder begin to speak at about the same time as other children do and eventually gain a full complement of language and syntax. However, they display un-usual use of pronouns, continuous repetition of certain words or phrases, and exhaustive focus of speech on particular topics. These children have difficulty in social reciprocity, engage in repetitive play and focus on certain interests excessively. Thus, the predominant differentiating feature between autistic disor-der and Asperger’s disorder is that those with Asperger’s dis-order do not have a delay in general (i.e., nonsocial) language development.
Rett’s disorder is a developmental disorder that preferen-tially strikes girls and differs substantially from autistic disorder past the toddler stage. The disorder was first described by Rett when 22 patients were reported in 1966 (Rett, 1966). Typically, a child with Rett’s disorder has an uneventful prenatal and peri-natal course that continues through at least the first 6 months. With onset of the classic form of the disease, there is decelera-tion of head growth, usually between 5 months and 4 years of age. In toddlerhood, the manifestations can be similar to autistic disorder in which there is frequently impairment in language and social development, along with the presence of stereotyped mo-tor movements. In particular, there is a loss of acquired language, restricted interest in social contact or interactions, and the start of handwringing, clapping, or tapping in the midline of the body. This type of activity begins after purposeful hand movement is lost. Serious psychomotor retardation sets in as well as recep-tive and expressive language impairments. Between the ages of 1 and 4 years, truncal apraxia and gait apraxia typically ensue. Since the vast majority of Rett’s disorder cases have mutations in MECP2, it has been possible to confirm that many variants of Rett’s disorder, including those with preserved ambulation and preserved speech, are due to mutations in the same gene (Amir et al., 1999; Kim and Cook, 2000).
Childhood disintegrative disorder and autistic disorder share some similar deficits in social interaction and communi-cation as well as repetitive behaviors. However, the symptoms of childhood disintegrative disorder appear abruptly or in the period of a few months’ time after 2 years or more of normal de-velopment. There is generally no prior serious illness or insult, although a few cases have been linked to certain brain ailments such as measles, encephalitis, leukodystrophies, or other dis-eases. With the onset of childhood disintegrative disorder, the child loses previously mastered cognitive, language and mo-tor skills and regresses to such a degree that there is loss of bowel and bladder control (Volkmar and Cohen, 1989). Children with childhood disintegrative disorder tend to lose abilities that would normally allow them to take care of themselves, and their motor activity contains fewer complex, repetitive behaviors than autistic disorder. Some children with this disorder experi-ence regression that occurs for a time and then becomes stable. Another group of children has a poorer outcome, with onset of fo-cal neurological findings and seizures in the face of a worsening course and greater motor impairment. The majority of children with this disorder deteriorate to a severe level of mental retarda-tion; a few retain selected abilities in specific areas. Differential diagnosis of childhood disintegrative disorder requires obtain-ing a particularly thorough developmental history, history of course of illness and an extensive neurological evaluation and testing.
PDD NOS or atypical autism should be reserved for cases in which there are qualitative impairments in reciprocal social development, and either communication or imaginative and flex-ible interests are met, but not full criteria for a specific PDD.