MedGen

Mitochondrial DNA (mtDNA)-associated Leigh syndrome and NARP (neurogenic muscle weakness, ataxia, and retinitis pigmentosa) are part of a continuum of progressive neurodegenerative disorders caused by abnormalities of mitochondrial energy generation. Leigh syndrome (or subacute necrotizing encephalomyelopathy) is characterized by onset of symptoms typically between ages three and 12 months, often following a viral infection. Decompensation (often with elevated lactate levels in blood and/or CSF) during an intercurrent illness is typically associated with psychomotor retardation or regression. Neurologic features include hypotonia, spasticity, movement disorders (including chorea), cerebellar ataxia, and peripheral neuropathy. Extraneurologic manifestations may include hypertrophic cardiomyopathy. About 50% of affected individuals die by age three years, most often as a result of respiratory or cardiac failure. NARP is characterized by proximal neurogenic muscle weakness with sensory neuropathy, ataxia, and pigmentary retinopathy. Onset of symptoms, particularly ataxia and learning difficulties, is often in early childhood. Individuals with NARP can be relatively stable for many years, but may suffer episodic deterioration, often in association with viral illnesses. [from GeneReviews]

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. [from HPO]

A reduction in the number of axons in the peripheral nervous system. [from HPO]

Abnormal cognition is characterized by deficits in thinking, reasoning, or remembering. [from HPO]

A type of ataxia characterized by the impairment of the ability to smoothly perform the elements of a voluntary movement in the appropriate order and speed. With dyssynergia, a voluntary movement appears broken down into its component parts. [from HPO]

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). [from HPO]

A kind of ataxia that affects movements of the extremities. [from HPO]

Hemiballismus is a rare movement disorder that is caused primarily by damage to various areas in the basal ganglia. Hemiballismus is usually characterized by involuntary flinging motions of the extremities. The movements are often violent and have wide amplitudes of motion. They are continuous and random and can involve proximal and/or distal muscles on one side of the body, while some cases even include the facial muscles. The more a patient is active, the more the movements increase. With relaxation comes a decrease in movements. [from HPO]

Incoordination of movement caused by a deficit in the sensory nervous system. Sensory ataxia can be distinguished from cerebellar ataxia by asking the patient to close his or her eyes. Persons with cerebellar ataxia show only a minimal worsening of symptoms, whereas persons with sensory ataxia show a marked worsening of symptoms. [from HPO]

A type of myopathy associated with mitochondrial disease and characterized by findings on biopsy such as ragged red muscle fibers. [from HPO]

A nonspecific term denoting degeneration of the retinal pigment epithelium and/or retinal photoreceptor cells. [from HPO]

Retinitis pigmentosa (RP) refers to a heterogeneous group of inherited ocular diseases that result in a progressive retinal degeneration affecting 1 in 3,000 to 5,000 people (Veltel et al., 2008). Symptoms include night blindness, the development of tunnel vision, and slowly progressive decreased central vision starting at approximately 20 years of age. Upon examination, patients have decreased visual acuity, constricted visual fields, dyschromatopsia (tritanopic; see 190900), and the classic fundus appearance with dark pigmentary clumps in the midperiphery and perivenous areas ('bone spicules'), attenuated retinal vessels, cystoid macular edema, fine pigmented vitreous cells, and waxy optic disc pallor. RP is associated with posterior subcapsular cataracts in 39 to 72% of patients, high myopia, astigmatism, keratoconus, and mild hearing loss in 30% of patients (excluding patients with Usher syndrome; see 276900). Fifty percent of female carriers of X-linked RP have a golden reflex in the posterior pole (summary by Kaiser et al., 2004). Juvenile Retinitis Pigmentosa Autosomal recessive childhood-onset severe retinal dystrophy is a heterogeneous group of disorders affecting rod and cone photoreceptors simultaneously. The most severe cases are termed Leber congenital amaurosis (see 204000), whereas the less aggressive forms are usually considered juvenile retinitis pigmentosa (Gu et al., 1997). Autosomal recessive forms of juvenile retinitis pigmentosa can be caused by mutation in the SPATA7 (609868), LRAT (604863), and TULP1 (602280) genes (see LCA3, 604232, LCA14, 613341, and LCA15, 613843, respectively). An autosomal dominant form of juvenile retinitis pigmentosa (see 604393) is caused by mutation in the AIPL1 gene (604392). [from OMIM]

A movement disorder which consists of effects including diminished voluntary movements and the presence of involuntary movements. [from HPO]

The presence of characteristic findings of denervation on electromyography (fibrillations, positive sharp waves, and giant motor unit potentials). [from HPO]

A reduction in the number of nerve cells in the basal ganglia. [from HPO]

Degenerative changes of the peripheral retina consisting of close-packed tiny cystic spaces at the outer plexiform/inner nuclear retinal level. The degeneration is very common in adult eyes and starts adjacent to the ora serrata and extends circumferentially and posteriorly. [from HPO]