Complex molecules in cells that contain the instructions necessary in the development and functioning of all living organisms. DNA consists of long twisted strands, each composed of a precise sequence of units. Sections of these units form genes.

Describes a condition or process which unfolds during child development. Development may reflect a typical pattern in which certain skills and behaviours are attained, following broadly the same time frame in different children. In atypical development, for instance in autism, certain key processes such as language and communication develop at a different rate, in a different way or not at all. (See also developmental trajectory.)

A term for the developmental sequence. This emphasises two facets of typical development: (1) There is a characteristic sequence of 'milestones' such as crawling, sitting up and walking. (2) Early developmental skills such as pointing and looking are thought to lay the foundations for later more sophisticated skills such as play with siblings, friendships with peers, or the complex relationships of the teenage years and adulthood. The idea of an atypical developmental trajectory is an important concept in work on autism.

The American Psychiatric Association's formal system for the classification and diagnosis of psychiatric, mental health and developmental conditions, which includes criteria for diagnosing autism. The 5^th edition, published in 2013, dispensed with the diagnostic sub-types of autism (e.g. Asperger Syndrome) seen in earlier versions. The DSM-5 approach to classifying and diagnosing autism treats it as a continuous spectrum and uses severity scores and specifiers to characterise each individual’s strengths and weaknesses.

Formal descriptions of medical, psychiatric and developmental conditions, used in making diagnoses. The criteria comprise a list of symptoms or features that an individual must have for a condition or problem to be diagnosed, and in some cases specify additional symptoms that should not be present. (See also DSM and ICD.)

A set of systematic procedures used to diagnose conditions like autism, for which no medical test can be applied. Diagnostic instruments involve questionnaires, observations of the person and interviews with the family (where possible). The instruments are designed such that the diagnostic criteria are applied in a standard consistent way.

An interview designed for use with the parents of children or adults who are being assessed for an autism spectrum diagnosis. The interview offers a 'dimensional' framework, allowing for ‘graded’ evaluation of how closely an individual matches the criteria for a pervasive developmental disorder, as defined in the ICD and DSM systems.

A specific developmental condition characterised by problems with reading, writing and spelling as a result of underlying difficulties in processing and remembering information. It is not linked to intelligence.