- Ragged-red muscle fibers (HP:0003200, a Human Phenotype Ontology term): 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. (OMIM:545000)
- Generalized myoclonic seizure (HP:0002123, a Human Phenotype Ontology term): 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. (OMIM:545000)
- Increased circulating pyruvate concentration (HP:0003542, a Human Phenotype Ontology term): The concentration of pyruvate in the blood circulation is above the upper limit of normal. Evidence: TAS. (OMIM:545000)
- Seizure (HP:0001250, a Human Phenotype Ontology term): 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: IEA. (OMIM:545000)
- Myopathy (HP:0003198, a Human Phenotype Ontology term): A disorder of muscle unrelated to impairment of innervation or neuromuscular junction. Evidence: IEA. (OMIM:545000)
- Sensorineural hearing impairment (HP:0000407, a Human Phenotype Ontology term): A type of hearing impairment in one or both ears related to an abnormal functionality of the cochlear nerve. Evidence: IEA. (OMIM:545000)
- Increased circulating lactate concentration (HP:0002151, a Human Phenotype Ontology term): 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. (OMIM:545000)
- Ataxia (HP:0001251, a Human Phenotype Ontology term): 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: IEA. (OMIM:545000)
- Mitochondrial inheritance (HP:0001427, a Human Phenotype Ontology term): A mode of inheritance that is observed for traits related to a gene encoded on the mitochondrial genome. Because the mitochondrial genome is essentially always maternally inherited, a mitochondrial condition can only be transmitted by females, although the condition can affect both sexes. The proportion of mutant mitochondria can vary (heteroplasmy). Evidence: IEA. (OMIM:545000)
- Muscle weakness (HP:0001324, a Human Phenotype Ontology term): Reduced strength of muscles. Evidence: IEA. (OMIM:545000)
- Spasticity (HP:0001257, a Human Phenotype Ontology term): A motor disorder characterized by a velocity-dependent increase in tonic stretch reflexes with increased muscle tone, exaggerated (hyperexcitable) tendon reflexes. Evidence: IEA. (OMIM:545000)
- Myoclonus (HP:0001336, a Human Phenotype Ontology term): Very brief, involuntary random muscular contractions occurring at rest, in response to sensory stimuli, or accompanying voluntary movements. Evidence: IEA. (OMIM:545000)
These phenotypes are associated with the disease MERRF syndrome (OMIM:545000, an entry in Online Mendelian Inheritance in Man).