What is Autism Spectrum Disorder?

Autism is referred to as a spectrum disorder because it presents very differently in different people, and ranges greatly in severity. This is how it is defined on the website of Autism Speaks:

Autism spectrum disorder (ASD) and autism are both general terms for a group of complex disorders of brain development. These disorders are characterized, in varying degrees, by difficulties in social interaction, verbal and nonverbal communication and repetitive behaviors. With the May 2013 publication of the DSM-5 diagnostic manual, all autism disorders were merged into one umbrella diagnosis of ASD. Previously, they were recognized as distinct subtypes, including autistic disorder, childhood disintegrative disorder, pervasive developmental disorder-not otherwise specified (PDD-NOS) and Asperger syndrome. 

Autism versus Asperger’s Syndromes

One of the key characteristics for diagnosing autism is a significant delay in the onset of speech.  Intellectual ability on the autism spectrum can range from very low to very high.

The Austrian psychiatrist Hans Asperger first wrote about a group of children of average to above-average intelligence who displayed normal language development; however, they shared many of the characteristic atypical behaviors of those with autism.  To differentiate this subset, they were given the label of Asperger’s Syndrome.