What is Autism Spectrum Disorder?
Autism Spectrum Disorder is a disabling disorder in children characterised by deficits in brain development that results in problematic behaviour such as difficulty in social settings, communication problems in terms of language and deficits in perception and motor development. The onset of Autism Spectrum Disorder is in the early childhood years when the child starts showing symptoms and gradually deficits in his/her social, emotional and motor functioning becomes apparent.
What are its sub-categories?
Autism Spectrum Disorder is a ‘spectrum’ of disorders where different types of Autism are clubbed together. The spectrum covers the following conditions:

1. Aspergers Syndrome: 

A milder form of the disorders of the autism spectrum, a child with Aspergers can have a good intellectual functioning but have deficits in the social functioning.

2. Pervasive Developmental Disorder, Not Otherwise Specified (PDD-NOS):

It is a condition that lies between Aspergers syndrome and Autistic disorder in severity. Thus, children with this condition have symptoms more severe than Aspergers Syndrome but less severe than Autistic Disorder.

3. Autistic Disorder: 

This condition has more severe symptoms than the above two along the Autism Spectrum Disorders.

4. Childhood Disintegrative Disorder: 

This is rare but most severe among the disorders in this spectrum children with Childhood Disintegrative Disorder develop normally in the early years but suddenly start showing symptoms between the age 2-4, where they begin to lose communicative, social, motor and mental skills rapidly.

What are the symptoms in Autism Spectrum Disorder?
Deficits in Social Interactions: Children with Autism Spectrum disorder show a marked deficit in social interactions. These deficits include failure to initiate conversations a lack of response and an inability to get into a back-and-forth conversation. This extends to non-verbal communication as well, where the child shows a lack of facial expressions, eye contact and deficits in bodily gestures. Additionally a deficit in developing social relationships such as making friends or belonging to peer group is difficult or absent.
Absence of speech: Children with autism have difficulty learning the basics of speech and as a result show very limited use of speech. They would speak in a very basic manner often restricted to just ‘yes’ or ‘no’. Another characteristic feature would be ‘Echolalia’ - where the child repetitively speaks the same thing like a parrot.
Repetitive Behaviour: Children with autism exhibit a ‘sameness’ in behaviour where they may seem to be stuck with a limited routine and follow it ritualistically. Any change in this routine or change in their surroundings can cause them extreme distress and they can show this in the form of marked agitation or violent bouts of shouting and crying. They may also develop a pattern of repetitive movements such as spinning, rocking and many other such behaviours and continue to do them for hours without stopping.
Intellectual Deficits: Children with Autism show marked impairment in their cognitive and mental abilities. Their performance in cognitive tasks is below the other children their age. In fact Intellectual Disability and Autism Spectrum Disorder often co-occur.
What are the Causes?
Brain Abnormality:  The exact cause of Autism Spectrum Disorder is not known but most of the researchers agree on brain abnormality as the main underlying cause. This abnormality is inborn and hampers the child’s ability to make sense of the incoming information or relate to the world.
Genes: Genetics are widely implied in Autism Spectrum Disorder (Smoller et al., 2008) but the exact mechanism is still unknown. According to the Autism Genome Project, 2007 (an extensive project for understanding the genetics of Autism) autism results from a faulty wiring pattern during the early stages of development and in this the neurotransmitter Glutamate is implicated for Glutamate plays an essential role in the wiring of the brain during the early developmental stages.
How can it be treated?
Medicines: As far as medical treatment is concerned, there is no sure shot treatment for Autism Spectrum Disorder. Usually medication is prescribed based on the dominant symptoms and can vary from antipsychotics to antidepressants to medicines for aggression. However, the effectiveness of these drugs cannot be extended to the fact they they treat Autism Spectrum Disorder. In fact there is no such medicine that can totally qualify as a treatment for autism.
Psychological Interventions: With the absence of sure shot medical procedures to treat Autism Spectrum Disorder, the next best treatment lies in the Psychological interventions. Such interventions address the behavioural aspects of autism and emphasise the development of the behaviours that would help the child to function in the society. These behaviours range from basic communication skills such as  interacting in the real world to forming social relationships (in short, areas where such children show a marked difficulty). Research suggests a positive outcome from such psychological interventions especially when parents are involved in such programmes (Siegel, 2003).