Neurogenic weakness, Ataxia, and Retinitis Pigmentosa (NARP)
This syndrome describes a group of patients who have a combination of features including weakness, unsteadiness of movement, impaired sensation (neuropathy) and visual disturbance. The weakness is usually found in the muscles around the large joints such as the hip and shoulder, rather than the hands or feet (proximal myopathy). Additional features include developmental delay or dementia and those children with very high levels of mutated mitochondrial DNA develop Leigh syndrome. The mutations responsible for NARP are found in the ATPase genes of mitochondrial DNA (maternally inherited) and two of the most commonly reported sites are8993T>G/C and 9176T>G/C. These mutations affect complex V, responsible for the final step in the energy conversion process. Routine testing of muscle will often not reveal any abnormality, because activity of complex V is difficult to demonstrate in the tests that we do. If we suspect NARP from the information we gather by talking to and examining the patient, then we identify the coding sequence in the ATPase genes and compare it to normal.