Children and adults with autism spectrum disorder (ASD) have social communication and interaction difficulties and show restricted, repetitive, and stereotyped patterns of behaviours, interests, or activities.
Social communication impairments and ASD behaviours are present during early childhood, but may only become manifest later.
ASD is caused by genetic and non-genetic factors; other factors are also likely to have a role in causing ASD.
Boys are affected more frequently than girls (4:1).
Around 20% to 30% of people with ASD have epilepsy.
Around 50% of people with ASD have intellectual disability; others have ability in the average or above average range. However, many people have an uneven cognitive profile, and show relative cognitive strengths and weaknesses on cognitive testing.
Long-term outcome in adulthood is variable. Many people live either in 24-hour care or with community support; however, some people with ASD live independent lives, and some have jobs and families.
Autism spectrum disorder (ASD) is characterised by persistent impairments in social communication, and restricted, repetitive, and stereotyped patterns of behaviours, interests, or activities.  Abnormal development is present during early childhood, but may only become manifest later.  There may be a history of language delay (single-word or phrase speech delay) and 25% of children lose previously acquired acquired language skills (regression).   Children who meet the criteria have a diagnosis of 'autism spectrum disorder', additionally qualified by level of severity.  Approximately 20% to 30% of children develop epilepsy and 50% have intellectual disability;  others have ability in the average or above average range. However, many people have an uneven cognitive profile, and show relative cognitive strengths and weaknesses on cognitive testing. In addition to the core symptoms of ASD, the majority of people have coexisting conditions (e.g., difficulties with sleep). Many young people and adults with ASD have mental health problems such as anxiety. These associated conditions are often more challenging to manage than ASD itself. 
Clinical Senior Lecturer/Hon Consultant
Institute of Neuroscience
JP is an author of a number of references cited in this monograph.
Department of Psychiatry & Behavioural Neurosciences and Pediatrics
MWS has received financial support from Bristol-Myers Squibb in connection with presentations at meetings. MWS is the co-author of references cited in this monograph.
Senior Lecturer & Honorary Consultant
Department of Forensic and Neurodevelopmental Sciences
Institute of Psychiatry
De Crespigny Park
MC declares that he has no competing interests.
Associate Clinical Professor of Psychiatry and Pediatrics
Vanderbilt Department of Psychiatry
KS declares that he has no competing interests.
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