Autism spectrum disorder refers to disorders that meet criteria in two broad symptom categories:
-    Deficits in social communication and social interaction
There must be deficits in social-emotional reciprocity (1), non-verbal communication (2) and the development and maintenance of relationships (3). 
-    Restricted repetitive patterns of behaviour
There must be two of four symptoms present (i.e. motor movements; rituals; fixated interests; hyper/hypo response to sensory information). 
75% of the people diagnosed with autism also have an intellectual disability. However, this may be different in the DSM-5. The onset of ASD is during early development, around 2 years of age. Symptoms may not manifest until later in people with mild versions of the disorder or manifest earlier in people with more severe variants of the disorder.
The prevalence of autism is 1% and 4 times more males than females are diagnosed. The prevalence rate of ASD has been increasing but it is unclear whether this is due to an actual increase or differences in diagnostics. It is likely that the increase is due to better methodology and improved awareness.
Asperger’s syndrome may be a less severe type of autism though it may also be a separate category due to differences in language development. These children tend to have more verbal rituals and ask odd questions. The group with high-functioning autism (HFA) demonstrates more atypical speech patterns (e.g. echolalia, noun reversal, atypical gestures). It is difficult to differentiate high-functioning autism and Asperger’s syndrome solely on the basis of diagnosis. 
Children with autism have difficulties with theory of mind. However, children with mild autism are able to solve these problems while children with more severe autism cannot. 
Symptom category    Examples
Qualitative and persistent impairment in social interaction and communication across three broad areas (three symptoms).    •    Social reciprocity: sharing, social referencing, initiating, maintaining interaction.
•    Non-verbal communication: lack of eye contact, gestures, facial expression.
•    Maintaining and developing social interactions: deficits in adapting behaviour to context, imaginary play, engaging with peers
Restricted, repetitive patterns of behaviour or activities (2 symptoms).    •    Repetitive speech, non-functional activities, echolalia.
•    Need for sameness: rituals.
•    Preoccupation and fixedness on topics or parts of objects or themes.
•    Hyper- or hypo-responsiveness to sensory stimuli.

Referential looking refers to shifting the gaze between the caregiver and the object of interest. This occurs around six to nine months of age and is followed by the active use of gestures to engage adults in reciprocal interaction. Children with autism may find comfort in hyper-focusing on a repetitive, non-functional task when their senses are overwhelmed.
It was first believed that autism was caused by a cold and non-nurturing way of raising the child (i.e. refrigerator mother). However, this is not the case. There is a strong genetic component of autism. In the case of twins, the chance is 1/3 that the other twin has autism as well. If this twin does not have autism, then the child will show minor autistic features.
To assess whether a child has ASD, behaviour rating scales can be used. It is also useful to use medical and family history and obtain information regarding comorbid disorders.
Instrument and age level    Assessment    Measures
Gilliam Autism Rating Scale (GARS). Three years to 22.    Behaviour rating scale.    Autism quotient, four scales: stereotyped behaviours (1), social interaction (2), communication (3) and developmental disturbance (4).
Childhood Autism Rating Scale (CARS). 2 years and older.    Behaviour rating scale.    Classifies autistic symptoms into mild-moderate-severe range.
Asperger Syndrome Diagnostic Scale (ASDS). Five years to 18 years.    Behaviour rating scale    Asperger quotient, five scales: cognitive (1), maladaptive (2), language (3), social (4) and sensorimotor (5).
Gilliam Asperger’s Disorder Scale (GADS). Three years to 22.    Behaviour rating scale.    Four scales.

Most children with ASD will demonstrate difficulties conform the key symptom clusters. However, the symptomatology and severity varies. Targeting specific deficits (1), use of a highly structured and predictable programme with a low teacher/student ratio (2), integration of programmes across situations (3), engagement of parents as co-therapists (4) and careful monitoring of transition between programmes (5) may be characteristics of successful treatment programmes for ASD. Early intervention is effective. Educational programmes should provide opportunities for intense engagement in the process of learning (1), individualized and systematic instruction (2) and parental involvement (3). 
The treatment and education for autistic and related communication handicapped children (TEACCH) programme focuses on close collaboration between parents and professionals. It is based on the idea that children are motivated to learn language as intentional communication. The programme contextualizes language and integrates it into ongoing daily activities. It also translates abstract concepts into visually meaningful alternatives.