**3. Autism: Aetiology, diagnosis and prevalence**

The term 'autism' has been attributed to the Austrian-American psychiatrist Kanner in the early 1940s, although individual cases had been described well before that time. While Kanner's work was written in English and has been recognised widely, his predecessor, the Swiss psychiatrist Bleuler, who coined the term 'autism', and his contemporary, the Austrian paediatrician Asperger, both writing in German, were virtually ignored. Asperger was eventually recognised when his writings were translated into English posthumously. Subsequently, the body of research grew until the diagnostic classification was formalised for the first time in 1980 in the Diagnostic and Statistical Manual of Mental Disorders (DSM-III) [11].

The diagnostic category changed over time, from 'Pervasive Developmental Disorders' that including autistic disorder, Rhett's disorder, childhood disintegrative disorder, Asperger's disorder, and pervasive developmental disorder – not otherwise specified (PDD-NOS) in the DSM-IV-TR [12] to the single category 'Autism Spectrum Disorders (ASD)' in the DSM-5 [13]. The diagnosis of ASD is based on two symptom domains, i.e., impaired social/communication and restricted, repetitive behaviours, and three levels of support needs. Autism was recognised as a heterogeneous condition with many presentations, i.e., each person with autism affected in different ways.

The exact causes of autism are unknown and are likely to concern genetic vulnerabilities coupled with environmental risk factors. It is likely that there are a variety of aetiologies that lead to a variety of 'autisms' [14].

Rising rates of autism are associated with increased costs to society and quality-of-life for individuals and their families. Autism prevalence rates in children in the USA have risen from 1 per 110 (0.90%) to 1:50 [15] and even higher prevalence rates have been reported in South Korea (2.64%) [16] and the United Kingdom (3.5%) [17]. The individual lifetime support cost for someone with autism is estimated between USA\$1.4 and USA\$2.4 million (UK£0.9-UK£1.5 million) depending on the level of support needs. Assuming a prevalence of 60% co-occurring intellectual disability, 'the total annual costs are £3.4 billion (USA \$5 billion) per year in the United Kingdom and \$66 billion per year in the United States' [18]. Effective interventions can do much to ameliorate the situation for individuals with autism and their families.
