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

An unintentional, oscillating to-and-fro muscle movement about a joint axis.

A failure to achieve the ability to walk at an appropriate developmental stage. Most children learn to walk in a series of stages, and learn to walk short distances independently between 12 and 15 months.

A degree of language development that is significantly below the norm for a child of a specified age.

A condition in which epileptiform abnormalities are believed to contribute to the progressive disturbance in cerebral function. Epileptic encephalaopathy is characterized by (1) electrographic EEG paroxysmal activity that is often aggressive, (2) seizures that are usually multiform and intractable, (3) cognitive, behavioral and neurological deficits that may be relentless, and (4) sometimes early death.

Incapability to ambulate.

Habitual clasping and wringing of the hands in the middle of the body, similar to a hand-washing movement.

Hypsarrhythmia is abnormal interictal high amplitude waves and a background of irregular spikes. There is continuous (during wakefulness), high-amplitude (>200 Hz), generalized polymorphic slowing with no organized background and multifocal spikes demonstrated by electroencephalography (EEG).

Persistent deficits in social interaction and communication and interaction as well as a markedly restricted repertoire of activity and interest as well as repetitive patterns of behavior.

A sudden flexion, extension, or mixed extension-flexion of predominantly proximal and truncal muscles that is usually more sustained than a myoclonic movement but not as sustained as a tonic seizure. Limited forms may occur

An increase in size of the ventricular system of the brain.

Intellectual disability, previously referred to as mental retardation, is characterized by subnormal intellectual functioning that occurs during the developmental period. It is defined by an IQ score below 70.

A failure to achieve the ability to sit at an appropriate developmental stage. Most children sit with support at 6 months of age and sit steadily without support at 9 months of age.

Delayed achievement of the ability to roll front to back and back to front.

A failure to achieve the ability to crawl at an appropriate developmental stage. Normal infant motor development is marked by a series of postural milestones including learning to crawl on hands and knees between the ages of 6 and 10 months.

Hypotonia is an abnormally low muscle tone (the amount of tension or resistance to movement in a muscle). Even when relaxed, muscles have a continuous and passive partial contraction which provides some resistance to passive stretching. Hypotonia thus manifests as diminished resistance to passive stretching. Hypotonia is not the same as muscle weakness, although the two conditions can co-exist.

Difficulty to maintain correct position of the head while standing or sitting. Infant head lag is observed when the head seems to flop around or lags posteriorly behind the trunk. Several articles have maintained that head lag should be absent by age 3 to 4 months.

Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms.