Autistic disorder is the most common of the pervasive developmental disorders of childhood onset.
It is characterized by the triad of impaired social interactions, impaired ability to communicate, and restricted repertoire of activities and interests.

Etiology
Autistic disorder is familial. Genetic studies demonstrate incomplete penetrance (36% concordance rate in monozygotic twins), although a specific genetic defect has not been discovered. A small percentage of those with autistic disorder have a fragile X chromosome, and a high rate of autism exists with tuberous sclerosis.

Epidemiology
Autistic disorder is rare. It occurs in two to five children per 10,000 live births. The male-female sex ratio is 3-4 : 1.

Clinical Manifestations
History, Mental Status Examination, and Laboratory Tests
Abnormal development is usually first noted soon after birth. Commonly, the first sign is impairment in social interactions (failure to develop a social smile, facial expressions, or eye-to-eye gaze). Older children often fail to develop nonverbal forms of communication (e.g., body postures and gestures) and may seem to have no desire or to lack the skills to form friendships. There is also a lack of seeking to share enjoyment (i.e., not showing, sharing, or pointing out objects they find interesting). By definition, findings must be present before age 3.

Autistic disorder is also characterized by a marked impairment in communication. There may be delay in or total lack of language development. Those children who do develop language show impairment in the ability to initiate and sustain conversations and use repetitive or idiosyncratic language. Language may also be abnormal in pitch, intonation, rate, rhythm, or stress.

Finally, there are usually restrictive, repetitive, or stereotyped patterns of behavior, interests, or activities. There may be an encompassing preoccupation with one or more stereotyped and restricted patterns of interest (e.g., amassing baseball trivia), an inflexible adherence to specific nonfunctional routines or rituals (e.g., eating the same meal in the same place at the same time each day), stereotyped or repetitive motor mannerisms (e.g., whole-body rocking), and a persistent preoccupation with the parts of objects (e.g., buttons).

Approximately 25% of children with autistic disorder have comorbid seizures; approximately 75% have mental retardation (the moderate type is most common). EEGs and intelligence testing are typically part of the initial evaluation. Rarely, specific special skills are present, e.g., calendar calculation.

Differenual Diagnosis
The diagnosis is usually clear after careful history, mental status examination, and developmental monitoring. However, childhood psychosis, mental retardation ( alone), language disorders, and congenital deafness or blindness must all be ruled out.

Management
Autistic disorder is a chronic lifelong disorder with relatively severe morbidity. Very few individuals with autism will ever live independently. Once the diagnosis is made, parents should be informed that their child has a neurodevelopmental disorder (not a behavioral disorder that they might feel responsible for creating). They will have to learn behavioral management techniques designed to reduce the rigid and stereotyped behaviors of the disorder and improve social functioning. Many children with autism require special education or specialized day programs for behavior management.

Autistic children with a comorbid seizure disorder are treated with anticonvulsants. Low doses of neuroleptics (e.g., haloperidol) and some mood stabilizers and antidepressants have been shown to help decrease aggressive or self-harming behaviors.