- Apnea (HP:0002104): Lack of breathing with no movement of the respiratory muscles and no exchange of air in the lungs. This term refers to a disposition to have recurrent episodes of apnea rather than to a single event. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Hepatomegaly (HP:0002240): Abnormally increased size of the liver. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Developmental regression (HP:0002376): Loss of developmental skills, as manifested by loss of developmental milestones. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Bulbar signs (HP:0002483). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Hyperventilation (HP:0002883): Hyperventilation refers to an increased pulmonary ventilation rate that is faster than necessary for the exchange of gases. Hyperventilation can result from increased frequency of breathing, an increased tidal volume, or both, and leads to an excess intake of oxygen and the blowing off of carbon dioxide. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Hyperalaninemia (HP:0003348): An increased concentration of alanine in the blood. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Segmental peripheral demyelination/remyelination (HP:0003481): A segmental pattern of demyelination and regeneration (remyelination) affecting peripheral nerves. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Mitochondrial myopathy (HP:0003737): A type of myopathy associated with mitochondrial disease and characterized by findings on biopsy such as ragged red muscle fibers. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Episodic respiratory distress (HP:0004885). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Demyelinating peripheral neuropathy (HP:0007108): Demyelinating neuropathy is characterized by slow nerve conduction velocities with reduced amplitudes of sensory/motor nerve conduction and prolonged distal latencies. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Infantile spasms (HP:0012469): Infantile spasms represent a subset of "epileptic spasms". Infantile Spasms are epileptic spasms starting in the first year of life (infancy). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Abnormal prosody (HP:0031434): Prosody refers to the patterns of rhythm, stress, and intonation in spoken language. Abnormal prosody refers to abnormalities in the patterns of rhythm, stress, or intonation of speech or vocalization that can be heard by the observer. In general, this refers to overt and clear deviations in patterns from culturally accepted norms but many also include differences noted in comparison to the usual patterns of the individual (a quiet person suddenly becomes loud or vice versa). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Cardiac conduction abnormality (HP:0031546): Any anomaly of the progression of electrical impulses through the heart. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Multiple glomerular cysts (HP:0100611): The presence of many cysts in the glomerulus of the kidney related to dilatation of the Bowman's capsule. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Ragged-red muscle fibers (HP:0003200): An abnormal appearance of muscle fibers observed on muscle biopsy. Ragged red fibers can be visualized with Gomori trichrome staining as irregular and intensely red subsarcolemmal zones, whereas the normal myofibrils are green. The margins of affect fibers appear red and ragged. The ragged-red is due to the accumulation of abnormal mitochondria below the plasma membrane of the muscle fiber, leading to the appearance of a red rim and speckled sarcoplasm. Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:255210)
- Low plasma citrulline (HP:0003572): A decreased concentration of citrulline in the blood. Evidence: TAS. Frequency: Very rare (HP:0040284). (ORPHA:255210)
- Abnormality of Krebs cycle metabolism (HP:0000816): An abnormality of the tricarboxylic acid cycle. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:255210)
- Increased CSF lactate (HP:0002490): Increased concentration of lactate in the cerebrospinal fluid. Evidence: TAS. Frequency: Very frequent (HP:0040281). (ORPHA:255210)
- Pigmentary retinopathy (HP:0000580): An abnormality of the retina characterized by pigment deposition. It is typically associated with migration and proliferation of macrophages or retinal pigment epithelial cells into the retina; melanin from these cells causes the pigmentary changes. Pigmentary retinopathy is a common final pathway of many retinal conditions and is often associated with visual loss. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Ophthalmoparesis (HP:0000597): Ophthalmoplegia is a paralysis or weakness of one or more of the muscles that control eye movement. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- 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:255210)
- 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:255210)
- Spasticity (HP:0001257): A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- 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:255210)
- Muscle weakness (HP:0001324): Reduced strength of muscles. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Dystonia (HP:0001332): An abnormally increased muscular tone that causes fixed abnormal postures. There is a slow, intermittent twisting motion that leads to exaggerated turning and posture of the extremities and trunk. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- 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:255210)
- Gait ataxia (HP:0002066): A type of ataxia characterized by the impairment of the ability to coordinate the movements required for normal walking. Gait ataxia is characteirzed by a wide-based staggering gait with a tendency to fall. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Bilateral tonic-clonic seizure (HP:0002069): A bilateral tonic-clonic seizure is a seizure defined by a tonic (bilateral increased tone, lasting seconds to minutes) and then a clonic (bilateral sustained rhythmic jerking) phase. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Chorea (HP:0002072): Chorea (Greek for 'dance') refers to widespread arrhythmic involuntary movements of a forcible, jerky and restless fashion. It is a random-appearing sequence of one or more discrete involuntary movements or movement fragments. Movements appear random because of variability in timing, duration or location. Each movement may have a distinct start and end. However, movements may be strung together and thus may appear to flow randomly from one muscle group to another. Chorea can involve the trunk, neck, face, tongue, and extremities. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Generalized myoclonic seizure (HP:0002123): A generalized myoclonic seizure is a type of generalized motor seizure characterized by bilateral, sudden, brief (<100 ms) involuntary single or multiple contraction of muscles or muscle groups of variable topography (axial, proximal limb, distal). Myoclonus is less regularly repetitive and less sustained than is clonus. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Increased circulating lactate concentration (HP:0002151): Abnormally increased level of blood lactate (2-hydroxypropanoic acid). Lactate is produced from pyruvate by lactate dehydrogenase during normal metabolism. The terms lactate and lactic acid are often used interchangeably but lactate (the component measured in blood) is strictly a weak base whereas lactic acid is the corresponding acid. Lactic acidosis is often used clinically to describe elevated lactate but should be reserved for cases where there is a corresponding acidosis (pH below 7.35). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Episodic vomiting (HP:0002572): Paroxysmal, recurrent episodes of vomiting. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Lacticaciduria (HP:0003648): An increased concentration of lactic acid in the urine. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Sensorimotor neuropathy (HP:0007141). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Focal T2 hyperintense basal ganglia lesion (HP:0007183): A lighter than expected T2 signal on magnetic resonance imaging (MRI) of the basal ganglia. This term refers to a localized hyperintensity affecting a particular region of the basal ganglia. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Floppy infant (HP:0008947): Floppiness/hypotonia is defined as reduced resistance to passive movement of joints. Physical examination of floppy/hypotonic infants shows head lag, lack of shoulder and elbow muscle contraction on traction response, inability to tighten the shoulder girdle muscles (or slipping through) when held under the axillae, scarf sign (when the arm is pulled to the opposite side, the arm wraps around the neck with the elbow crossing midline), hyperdorsiflexion of the feet, easy apposition of the thumb against the forearm, feet touching the cheek with ease and without discomfort, frog leg position, and inverted U sign on ventral suspension (head, arms, and legs hanging down without elbow or knee flexion and the trunk rounded in a dome shape). Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- 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: Frequent (HP:0040282). (ORPHA:255210)
- Dyskinesia (HP:0100660): A movement disorder which consists of effects including diminished voluntary movements and the presence of involuntary movements. Evidence: TAS. Frequency: Frequent (HP:0040282). (ORPHA:255210)
- Abnormal renal tubule morphology (HP:0000091): An abnormality of the renal tubules. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- 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: Occasional (HP:0040283). (ORPHA:255210)
- Rod-cone dystrophy (HP:0000510): An inherited retinal disease subtype in which the rod photoreceptors appear to be more severely affected than the cone photoreceptors. Typical presentation is with nyctalopia (due to rod dysfunction) followed by loss of mid-peripheral field of vision, which gradually extends and leaves many patients with a small central island of vision due to the preservation of macular cones. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Nystagmus (HP:0000639): Rhythmic, involuntary oscillations of one or both eyes related to abnormality in fixation, conjugate gaze, or vestibular mechanisms. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Optic atrophy (HP:0000648): Atrophy of the optic nerve. Optic atrophy results from the death of the retinal ganglion cell axons that comprise the optic nerve and manifesting as a pale optic nerve on fundoscopy. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Hyporeflexia (HP:0001265): Reduction of neurologic reflexes such as the knee-jerk reaction. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Hyperreflexia (HP:0001347): Hyperreflexia is the presence of hyperactive stretch reflexes of the muscles. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Hepatic failure (HP:0001399). Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Hypertrophic cardiomyopathy (HP:0001639): Hypertrophic cardiomyopathy (HCM) is defined by the presence of increased ventricular wall thickness or mass in the absence of loading conditions (hypertension, valve disease) sufficient to cause the observed abnormality. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Dilated cardiomyopathy (HP:0001644): Dilated cardiomyopathy (DCM) is defined by the presence of left ventricular dilatation and left ventricular systolic dysfunction in the absence of abnormal loading conditions (hypertension, valve disease) or coronary artery disease sufficient to cause global systolic impairment. Right ventricular dilation and dysfunction may be present but are not necessary for the diagnosis. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Fever (HP:0001945): Body temperature elevated above the normal range. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Dysphagia (HP:0002015): Difficulty in swallowing. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Hypothermia (HP:0002045): Reduced body temperature due to failed thermoregulation. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
- Dyspnea (HP:0002094): Difficult or labored breathing. Dyspnea is a subjective feeling only the patient can rate, e.g., on a Borg scale. Evidence: TAS. Frequency: Occasional (HP:0040283). (ORPHA:255210)
These phenotypes are associated with the disease Mitochondrial DNA-associated Leigh syndrome (ORPHA:255210).