- Nystagmus (HP:0000639): Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:280210)
- Lower limb spasticity (HP:0002061): Spasticity (velocity-dependent increase in tonic stretch reflexes with increased muscle tone and hyperexcitable tendon reflexes) in the muscles of the lower limbs, hips, and pelvis. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:280210)
- Gliosis (HP:0002171): Gliosis is the focal proliferation of glial cells in the central nervous system. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:280210)
- Cerebral hypomyelination (HP:0006808): Reduced amount of myelin in the nervous system resulting from defective myelinogenesis in the white matter of the central nervous system. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:280210)
- Lower limb amyotrophy (HP:0007210): Muscular atrophy affecting the lower limb. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:280210)
- Severe intellectual disability (HP:0010864): Severe intellectual disability (ID) is defined as a type of ID characterized by severely sub-average adaptive functioning and intellectual functioning, with an intelligence quotient (IQ) the range of 20-34. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:280210)
- Abnormal myelination (HP:0012447): Any anomaly in the process by which myelin sheaths are formed and maintained around neurons. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:280210)
- 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: Frequent (HP:0040282). (ORPHA:280210)
- 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: Frequent (HP:0040282). (ORPHA:280210)
- Dysarthria (HP:0001260): Dysarthric speech is a general description referring to a neurological speech disorder characterized by poor articulation. Depending on the involved neurological structures, dysarthria may be further classified as spastic, flaccid, ataxic, hyperkinetic and hypokinetic, or mixed. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Pachygyria (HP:0001302): Pachygyria is a malformation of cortical development with abnormally wide gyri with sulci 1,5-3 cm apart and abnormally thick cortex measuring more than 5 mm (radiological definition). See also neuropathological definitions for 2-, 3-, and 4-layered lissencephaly. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Absent speech (HP:0001344): Complete lack of development of speech and language abilities. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Poor head control (HP:0002421): 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. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Inability to walk (HP:0002540): Incapability to ambulate. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Functional motor deficit (HP:0004302). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Laryngeal stridor (HP:0006511): An abnormal high-pitched noisy sound, occurring during inhalation or exhalation caused by the incomplete obstruction in the throat. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Pendular nystagmus (HP:0012043): Rhythmic, involuntary sinusoidal oscillations of one or both eyes. The waveform of pendular nystagmus may occur in any direction. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Titubation (HP:0030187): Nodding movement of the head or body. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Dystonic gait (HP:0031954): Dystonic gait disorders frequently appear bizarre, particularly because activity increases dystonic tonus and posture. The abnormal posture of the foot in dystonic gait typically involves inversion, plantar flexion and tonic extension of the big toe. In many patients complex types of walking, such as walking backwards and running are paradoxically less impaired than walking forward and may seem completely unaffected. Sensory tricks, for instance, if the affected individual rests a hand on his or her neck, may improve or even normalize dystonic gait in some patients. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Confluent hyperintensity of cerebral white matter on MRI (HP:0040330): Areas of brighter than expected MRI signal in the white matter of the brain whereby individual patches run together. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Abnormal morphology of musculature of pharynx (HP:0430015): An abnormality of any of the muscles of the pharynx. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:280210)
- Gait disturbance (HP:0001288): The term gait disturbance can refer to any disruption of the ability to walk. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:280210)
- Cerebellar hypoplasia (HP:0001321): Cerebellar hypoplasia is a descriptive term implying a cerebellum with a reduced volume, but a normal shape and is stable over time. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:280210)
- Failure to thrive (HP:0001508): Failure to thrive (FTT) refers to a child whose physical growth is substantially below the norm. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:280210)
- Respiratory failure (HP:0002878): A severe form of respiratory insufficiency characterized by inadequate gas exchange such that the levels of oxygen or carbon dioxide cannot be maintained within normal limits. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:280210)
- Short stature (HP:0004322): A height below that which is expected according to age and gender norms. Although there is no universally accepted definition of short stature, many refer to "short stature" as height more than 2 standard deviations below the mean for age and gender (or below the 3rd percentile for age and gender dependent norms). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:280210)
- Nasogastric tube feeding (HP:0040288): The condition of inability to eat normally treated by placement of a thin tube through the nose into the stomach that is then used to carry food. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:280210)
These phenotypes are associated with the disease Pelizaeus-Merzbacher disease, connatal form (ORPHA:280210).