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Psychiatric disorders are central nervous system diseases characterized by disturbances in emotion, cognition, motivation, and socialization. As a result of their high prevalence, early onset, and persistence, they contribute substantially to the burden of illness worldwide. Most psychiatric disorders are heterogeneous syndromes that currently lack well-defined neuropathology and bona fidebiological markers. Therefore, diagnoses continue to be made solely from clinical observations using criteria in the Diagnostic and Statistical Manual of Mental Disorders of the American Psychiatric Association (2000), 4th edition, text revision (DSM-IVTR). Recent advances in neuroimaging are beginning to provide evidence of brain pathology, which may one day be used for diagnosis and for following treatment. Family, twin, and adoption studies have shown that all common psychiatric syndromes are highly heritable, with genetic risk comprising 20–90% of disease vulnerability. The epidemiology, genetics, and biology of four common psychiatric disorders—autism, schizophrenia, mood disorders, and drug addiction—are presented below. A detailed discussion of the clinical manifestations and treatment of schizophrenia and mood disorders can be found in Chap. 391. Further discussion of alcoholism can be found in Chap. 392, opiate addiction in Chap. 393, cocaine and other drugs of abuse in Chap. 394, and nicotine addiction in Chap. 395.

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The DSM-IVTR criteria for Autism Spectrum Disorders (ASDs) require delays or abnormal functioning in social interactions, language as used in social communication, and symbolic or imaginative play, with onset prior to age 3. In addition to abnormal social behavior, ASDs are frequently, but not always, associated with reduced IQ and epilepsy. Individuals who exhibit some autism-like symptoms with relatively preserved cognitive functioning and language skills are described as having Asperger's syndrome.

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Epidemiology

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There has been a dramatic increase in the diagnosis of ASDs, from ∼1/1000 (1950s–1990s) to a current level of ∼1/150. Whether this increase reflects increased disease prevalence remains uncertain; ongoing studies are searching for genetic, environmental, and sociologic mechanisms that may have contributed to this change. In the 1950s–1960s, psychological factors were held to underlie autism. This conception was largely debunked by the 1970s, with the demonstration that prenatal rubella and phenylketonuria can cause ASDs, and with evidence for the genetic etiology of ASDs from twin studies. There is ongoing public concern that vaccines in general, or mercury-based preservatives in vaccines, can cause ASDs; however, large epidemiologic analyses have not supported this as an etiology. Whether environmental factors, such as perinatal infection and various toxins, for example, ethanol, illicit drugs, medications, and mutagenic agents, play a role is unclear.

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Neuropathology and Neuroimaging

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ASDs show no defining neuroanatomic phenotype that would indicate neurodevelopmental abnormalities. However, structural neuroimaging and histologic studies of postmortem brain provide evidence for anatomic defects. There is a modest increase in cerebrum growth (∼10%; affecting both the white and grey matter) during early childhood (years 1–3), with the largest effect in the frontal lobes; the growth rate then decreases with age. ...

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