Clinical Characteristics
Ocular Features
This condition has its onset in young adults. Early ocular signs are gaze-evoked horizontal nystagmus and defective ocular pursuit movements with the full range of extraocular movements. Some patients but not all have optic atrophy. Ptosis is not present.
Systemic Features
Gait disturbances have their onset in the first or second decades of life. The gait may be broad-based. Intermittent hemiparesis with headache, nausea and vomiting has been reported in some individuals. Absent ankle jerks and extensor plantar responses have been noted but general muscle tone and strength is usually normal. An axonal sensorimotor neuropathy may be present in midlife as documented by nerve conduction studies. MRIs of the brain may reveal cerebellar atrophy.
Mild cognitive problems have been reported in a few individuals.
Genetics
Inheritance
This is a mitochondrial disorder secondary to mutations in the mitochondrial MT-ATP6 gene.