- Ataxia (HP:0001251): Ataxia refers to impaired coordination of voluntary muscle movement. 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). Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:79136)
- Abnormality of ocular smooth pursuit (HP:0000617): An abnormality of eye movement characterized by impaired smooth-pursuit eye movements. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:79136)
- Gaze-evoked nystagmus (HP:0000640): Nystagmus made apparent by looking to the right or to the left. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:79136)
- Diplopia (HP:0000651): Diplopia is a condition in which a single object is perceived as two images, it is also known as double vision. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:79136)
- Postural instability (HP:0002172): A tendency to fall or the inability to keep oneself from falling; imbalance. The retropulsion test is widely regarded as the gold standard to evaluate postural instability, Use of the retropulsion test includes a rapid balance perturbation in the backward direction, and the number of balance correcting steps (or total absence thereof) is used to rate the degree of postural instability. Healthy subjects correct such perturbations with either one or two large steps, or without taking any steps, hinging rapidly at the hips while swinging the arms forward as a counterweight. In patients with balance impairment, balance correcting steps are often too small, forcing patients to take more than two steps. Taking three or more steps is generally considered to be abnormal, and taking more than five steps is regarded as being clearly abnormal. Markedly affected patients continue to step backward without ever regaining their balance and must be caught by the examiner (this would be called true retropulsion). Even more severely affected patients fail to correct entirely, and fall backward like a pushed toy soldier, without taking any corrective steps. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:79136)
- Incoordination (HP:0002311): A deficit in coordination of muscle movements. Coordination is defined as the orchestrated movement of multiple body parts as required to accomplish intended actions, like walking. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:79136)
- Vertigo (HP:0002321): An abnormal sensation of spinning while the body is actually stationary. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:79136)
- Frequent falls (HP:0002359). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:79136)
- Abnormal head movements (HP:0002457). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:79136)
- Nausea (HP:0002018): A sensation of unease in the stomach together with an urge to vomit. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:79136)
These phenotypes are associated with the disease Episodic ataxia type 4 (ORPHA:79136).