- Hypertonia (HP:0001276): A condition in which there is increased muscle tone so that arms or legs, for example, are stiff and difficult to move. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:163985)
- Exaggerated startle response (HP:0002267): An exaggerated startle reaction in response to a sudden unexpected visual or acoustic stimulus, or a quick movement near the face. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:163985)
- Developmental regression (HP:0002376): Loss of developmental skills, as manifested by loss of developmental milestones. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:163985)
- Focal impaired awareness seizure (HP:0002384): Focal impaired awareness seizure (or focal seizure with impaired or lost awareness) is a type of focal-onset seizure characterized by some degree (which may be partial) of impairment of the person's awareness of themselves or their surroundings at any point during the seizure. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:163985)
- Hypoplasia of the frontal lobes (HP:0007333): Underdevelopment of the frontal lobe of the cerebrum. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:163985)
- Generalized tonic seizure (HP:0010818): A generalized tonic seizure is a type of generalized motor seizure characterized by bilateral limb stiffening or elevation, often with neck stiffening without a subsequent clonic phase. The tonic activity can be a sustained abnormal posture, either in extension or flexion, sometimes accompanied by tremor of the extremities. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:163985)
- EEG with temporal focal spikes (HP:0012018): EEG with focal sharp transient waves of a duration less than 80 msec in the temporal region. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:163985)
- 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: Frequent (HP:0040282). (ORPHA:163985)
- Trigonocephaly (HP:0000243): Wedge-shaped, or triangular head, with the apex of the triangle at the midline of the forehead and the base of the triangle at the occiput. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:163985)
These phenotypes are associated with the disease Hyperekplexia-epilepsy syndrome (ORPHA:163985).