This is a relatively uncommon inherited disorder, primarily of the nervous system. It is unusual for the causative mutation is found in mitochondrial DNA (as opposed to DNA found in the nucleus of the cell). Mitochondria are the small organelles in the cell responsible for generating energy for cell functions.
The first symptoms often occur in childhood. Irritability, delayed development and psychomotor retardation can be evident in the first decade of life. Night blindness and loss of side vision are symptoms in the next decade when some unsteadiness (ataxia) is often noted. Vision loss is progressive and blindness is often the result among young adults. An eye examination reveals evidence of retinitis pigmentosa, a progressive deterioration of the retina of the eye. Numbness, tingling, and pain in the arms and legs are common and some patients have seizures. Muscle weakness is experienced by many patients and older individuals may have frank dementia. Some patients experience hearing loss.
This disorder results from a mutation in the DNA of mitochondria. Since mitochondria are transmitted to the next generation only through the mother, the pedigree pattern is one of maternal transmission (to both sexes) only. Fathers with mitochondrial mutations do not transmit these to their offspring.
The diagnosis is most likely made by a pediatric neurologist. The ophthalmologist can diagnose the retinitis pigmentosa picture in the retina and the combination of neurological deterioration from childhood with progressive vision loss and pigmentary changes in the retina generally suggest this disorder. Blindness and physical disabilities eventually occur. There is no effective treatment for the disease although low vision aids can be helpful in early stages of vision loss.