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Neuropathy ataxia retinitis pigmentosa (NARP) syndrome is characterized by a variety of signs and symptoms that mainly affect the nervous system. Beginning in childhood or early adulthood, most people with NARP experience numbness, tingling, or pain in the arms and legs (sensory neuropathy); muscle weakness; and problems with balance and coordination (ataxia). Affected individuals may also have vision loss caused by a condition called retinitis pigmentosa. Other features of NARP include learning disabilities, developmental delay, seizures, dementia, hearing loss, and cardiac conduction defects. Mutations in the MT-ATP6 gene cause NARP syndrome. This gene is located within mitochondrial DNA (mtDNA). Most individuals with NARP have a specific MT-ATP6 mutation in 70 percent to 90 percent of their mitochondria. NARP syndrome is inherited from the mother (maternal inheritance) because only females pass mitochondrial DNA to their children.
Source: GARD Last updated on 05-01-20
NARP and mitochondrial DNA-associated Leigh syndrome are part of a continuum of progressive neurodegenerative disorders.
These conditions affect mitochondria, which are structures within cells that convert the energy from food into a form that cells can use. NARP and MILS can be caused by mutations in the MT-ATP6 gene, which is contained within mitochondrial DNA. Although most DNA is packaged in chromosomes within the nucleus, mitochondria also have a small amount of their own DNA. The most common genetic change in the MT-ATP6 gene replaces the DNA building block thymine with guanosine at position 8993 (written as T8993G).
Most of the body's cells contain thousands of mitochondria, each with one or more copies of mitochondrial DNA. The severity of some mitochondrial disorders is associated with the percentage of mitochondria in each cell that has a particular genetic mutation. Most individuals with NARP have the T8993G mutation in 70 to 90 percent of their mitochondria. When this mutation is present in a higher percentage of a person's mitochondria—greater than 90 percent—it causes the more severe features of mitochondrial DNA- associated Leigh syndrome. Because these two conditions can result from the same genetic changes and can occur in different members of a single family, researchers believe that they represent a spectrum of overlapping features instead of two distinct syndromes.
Last updated on 05-01-20
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