- Epileptic encephalopathy (HP:0200134): 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. Evidence: TAS. Frequency: Obligate (HP:0040280). (ORPHA:2066)
- Hypotonia (HP:0001252): 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. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:2066)
- EEG abnormality (HP:0002353): Abnormality observed by electroencephalogram (EEG), which is used to record of the brain's spontaneous electrical activity from multiple electrodes placed on the scalp. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:2066)
- Cerebral dysmyelination (HP:0007266): Defective structure and function of myelin sheaths of the white matter of the brain. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:2066)
- Severe global developmental delay (HP:0011344): A severe delay in the achievement of motor or mental milestones in the domains of development of a child. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:2066)
- Elevated CSF gamma-aminobutyric acid concentration (HP:0032531). Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:2066)
- Elevated circulating gamma-aminobutyric acid concentration (HP:0410053): An increase in the level of Gamma-aminobutyric acid (GABA) in the blood circulation. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:2066)
- Increased level of gamma-aminobutyric acid in urine (HP:0500253): Elevated concentration of gamma-aminobutyric acid in the urine. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:2066)
- Tall stature (HP:0000098): A height above that which is expected according to age and gender norms. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- Elevated circulating growth hormone concentration (HP:0000845): Acromegaly is a condition resulting from overproduction of growth hormone by the pituitary gland in persons with closed epiphyses, and consists chiefly in the enlargement of the distal parts of the body. The circumference of the skull increases, the nose becomes broad, the tongue becomes enlarged, the facial features become coarsened, the mandible grows excessively, and the teeth become separated. The fingers and toes grow chiefly in thickness. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- Seizure (HP:0001250): 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. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- Choreoathetosis (HP:0001266): Involuntary movements characterized by both athetosis (inability to sustain muscles in a fixed position) and chorea (widespread jerky arrhythmic movements). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- Hyperreflexia (HP:0001347): Hyperreflexia is the presence of hyperactive stretch reflexes of the muscles. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- Failure to thrive (HP:0001508): Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- Cerebral atrophy (HP:0002059): Atrophy (wasting, decrease in size of cells or tissue) affecting the cerebrum. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- Progressive psychomotor deterioration (HP:0007272). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- Feeding difficulties in infancy (HP:0008872): Impaired feeding performance of an infant as manifested by difficulties such as weak and ineffective sucking, brief bursts of sucking, and falling asleep during sucking. There may be difficulties with chewing or maintaining attention. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- High-pitched cry (HP:0025430): A type of crying in an abnormally high-pitched voice. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- Excessive daytime somnolence (HP:0001262): A state of abnormally strong desire for sleep during the daytime. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:2066)
- Lethargy (HP:0001254): A state of fatigue, either physical or mental slowness and sluggishness, with difficulties in initiating or performing simple tasks. Distinguished from apathy which implies indifference and a lack of desire or interest in the task. A person with lethargy may have the desire, but not the energy to engage in personal or socially relevant tasks. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2066)
- Cerebellar atrophy (HP:0001272): Cerebellar atrophy is defined as a cerebellum with initially normal structures, in a posterior fossa with normal size, which displays enlarged fissures (interfolial spaces) in comparison to the foliae secondary to loss of tissue. Cerebellar atrophy implies irreversible loss of tissue and result from an ongoing progressive disease until a final stage is reached or a single injury, e.g. an intoxication or infectious event. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2066)
- Abnormal corpus callosum morphology (HP:0001273): Abnormality of the corpus callosum. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:2066)
These phenotypes are associated with the disease Gamma-aminobutyric acid transaminase deficiency (ORPHA:2066).