Aggressive behavior can denote verbal aggression, physical aggression against objects, physical aggression against people, and may also include aggression towards oneself.

Cerebellar ataxia refers to ataxia due to dysfunction of the cerebellum. This causes a variety of elementary neurological deficits including asynergy (lack of coordination between muscles, limbs and joints), dysmetria (lack of ability to judge distances that can lead to under- or overshoot in grasping movements), and dysdiadochokinesia (inability to perform rapid movements requiring antagonizing muscle groups to be switched on and off repeatedly).

Language impairment is a deficit in comprehension or production of language that includes reduced vocabulary, limited sentence structure or impairments in written or spoken communication. Language abilities are substantially and quantifiably below age expectations.

A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes.

A seizure is an intermittent abnormality of nervous system physiology characterised by a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain.

A stereotypy is a repetitive, simple movement that can be voluntarily suppressed. Stereotypies are typically simple back-and-forth movements such as waving of flapping the hands or arms, and they do not involve complex sequences or movement fragments. Movement is often but not always rhythmic and may involve fingers, wrists, or more proximal portions of the upper extremity. The lower extremity is not typically involved. Stereotypies are more commonly bilateral than unilateral.

Difficulty in social interactions related to an impairment of characteristics such as eye contact, smiling, appropriate facial expressions, and body postures and characterized by difficulty in forming peer relationships and forming friendships.

Abnormality observed by electroencephalogram (EEG), which is used to record of the brain's spontaneous electrical activity from multiple electrodes placed on the scalp.

A generalized-onset seizure is a type of seizure originating at some point within, and rapidly engaging, bilaterally distributed networks. The networks may include cortical and subcortical structures but not necessarily the entire cortex.

Hyperactivity is a state of constantly being unusually or abnormally active, including in situations in which it is not appropriate.

The presence of developmental dysplasia of the cerebral cortex.

A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age.

Reduction of neurologic reflexes such as the knee-jerk reaction.

A focal-onset seizure is a type of seizure originating within networks limited to one hemisphere. They may be discretely localized or more widely distributed, and may originate in subcortical structures.

A type of motor delay characterized by a delay in acquiring the ability to control the large muscles of the body for walking, running, sitting, and crawling.

Progressive loss of previously present language abilities.

Complete lack of development of speech and language abilities.

Diminution of tendon reflexes, which is an invariable sign of peripheral nerve disease.

A type of malformation of cortical development that primarily affects areas of neocortex. It can be identified on conventional magnetic resonance imaging as focal cortical thickening, abnormal gyration, and blurring between gray and white matter, often associated with clusters of heterotopic neurons.

Subnormal intellectual functioning which originates during the developmental period. Intellectual disability, previously referred to as mental retardation, has been defined as an IQ score below 70.

Generalized muscular hypotonia (abnormally low muscle tone).

Occipitofrontal (head) circumference greater than 97th centile compared to appropriate, age matched, sex-matched normal standards. Alternatively, a apparently increased size of the cranium.

Hyperventilation refers to an increased pulmonary ventilation rate that is faster than necessary for the exchange of gases. Hyperventilation can result from increased frequency of breathing, an increased tidal volume, or both, and leads to an excess intake of oxygen and the blowing off of carbon dioxide.

Absence of fine and sharp appearance of brows, nose, lips, mouth, and chin, usually because of rounded and heavy features or thickened skin with or without thickening of subcutaneous and bony tissues.