Neuropathy, ataxia and retinitis pigmentosa (NARP)
Incidence
It is a mtDNA point mutation. NARP is associated with mutations in the ATPase 6 gene (subunit 6 of complex V) with mitochondrial heteroplasmy < than 90%..
Clinical Characteristics
NARP is characterized by developmental delay, seizures, proximal neurogenic muscle weakness, ataxia, dementia, sensory neuropathy and retinitis pigmentosa. The onset is usually in young adulthood and the course is slowly progressive. Ragged-red fibers (RRF) are absent but electronic microscopy (EM) of muscle biopsy has revealed small subsarcolemmal aggregates of mitochondria with abnormal cristae. Muscle fibers are COX-positive, but a subset of fibers may be either negative or deficient for mitochondrial ATPase.
Precipitants
Infections may worsen the condition.
Provocation Tests
no
Diagnostic Procedures
DB-W, DB-F (DNA testing for point mutation)