- Microcephaly (HP:0000252): Head circumference below 2 standard deviations below the mean for age and gender. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Sensorineural hearing impairment (HP:0000407): A type of hearing impairment in one or both ears related to an abnormal functionality of the cochlear nerve. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Visual impairment (HP:0000505): Visual impairment (or vision impairment) is vision loss (of a person) to such a degree as to qualify as an additional support need through a significant limitation of visual capability resulting from either disease, trauma, or congenital or degenerative conditions that cannot be corrected by conventional means, such as refractive correction, medication, or surgery. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Ptosis (HP:0000508): The upper eyelid margin is positioned 3 mm or more lower than usual and covers the superior portion of the iris (objective); or, the upper lid margin obscures at least part of the pupil (subjective). Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Abnormal electroretinogram (HP:0000512): Any abnormality of the electrical responses of various cell types in the retina as measured by electroretinography. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Abnormality of visual evoked potentials (HP:0000649): An anomaly of visually evoked potentials (VEP), which are electrical potentials, initiated by brief visual stimuli, which are recorded from the scalp overlying the visual cortex. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Atypical behavior (HP:0000708): Atypical behavior is an abnormality in a person's actions that can be controlled or modulated by the will of the individual. While abnormal behaviors can be difficult to control, they are distinct from other abnormal actions that cannot be affected by the individual's will. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Decreased nerve conduction velocity (HP:0000762): A reduction in the speed at which electrical signals propagate along the axon of a neuron. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- 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: Very frequent (HP:0040281). (ORPHA:1933)
- 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:1933)
- Global developmental delay (HP:0001263): A delay in the achievement of motor or mental milestones in the domains of development of a child, including motor skills, speech and language, cognitive skills, and social and emotional skills. This term should only be used to describe children younger than five years of age. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Hyporeflexia (HP:0001265): Reduction of neurologic reflexes such as the knee-jerk reaction. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Ventriculomegaly (HP:0002119): An increase in size of the ventricular system of the brain. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Delayed gross motor development (HP:0002194): A type of motor delay characterized by a delay in acquiring the ability to control the large muscles of the body for walking, running, sitting, and crawling. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Generalized hirsutism (HP:0002230): Abnormally increased hair growth over much of the entire body. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Cerebral calcification (HP:0002514): The presence of calcium deposition within the cerebrum. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Skeletal muscle atrophy (HP:0003202): The presence of skeletal muscular atrophy (which is also known as amyotrophy). Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Elevated circulating creatine kinase activity (HP:0003236): The activity of creatine kinase in the blood circulation is above the upper limit of normal. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Aminoaciduria (HP:0003355): An increased concentration of an amino acid in the urine. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- 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: Very frequent (HP:0040281). (ORPHA:1933)
- Cachexia (HP:0004326): Severe weight loss, wasting of muscle, loss of appetite, and general debility related to a chronic disease. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Intellectual disability (HP:0001249): The term intellectual disability or intellectual developmental disorder is used to describe significantly sub-average intellectual and adaptive functioning based on clinical assessment and as measured by individually administered, appropriately normed, standardized and validated tests of intellectual functioning and adaptive behavior, with onset during the developmental period from infancy through adolescence. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
- Methylmalonic aciduria (HP:0012120): Increased concentration of methylmalonic acid in the urine. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:1933)
These phenotypes are associated with the disease Mitochondrial DNA depletion syndrome, encephalomyopathic form with methylmalonic aciduria (ORPHA:1933).