Ataxia with Oculomotor Apraxia Type 1 – RETIRED CHAPTER, FOR HISTORICAL REFERENCE ONLY

NOTE: THIS PUBLICATION HAS BEEN RETIRED. THIS ARCHIVAL VERSION IS FOR HISTORICAL REFERENCE ONLY, AND THE INFORMATION MAY BE OUT OF DATE.

Clinical characteristics: Ataxia with oculomotor apraxia type 1 (AOA1) is characterized by childhood onset of slowly progressive cerebellar ataxia, followed by oculomotor apraxia and a severe primary motor peripheral axonal motor neuropathy. The first manifestation is progressive gait imbalance (mean age of onset: 4.3 years; range: 2-10 years), followed by dysarthria, then upper-limb dysmetria with mild intention tremor. Oculomotor apraxia, usually noticed a few years after the onset of ataxia, progresses to external ophthalmoplegia. All affected individuals have generalized areflexia followed by a peripheral neuropathy and quadriplegia with loss of ambulation about seven to ten years after onset. Hands and feet are short and atrophic. Chorea and upper-limb dystonia are common. Intellect remains normal in some individuals; in others, different degrees of cognitive impairment have been observed.

Diagnosis/testing: The diagnosis of AOA1 is based on clinical findings (including family history) and exclusion of the diagnosis of ataxia-telangiectasia. Cerebellar atrophy is visible on MRI in all affected individuals. EMG reveals axonal neuropathy in 100% of individuals with AOA1. APTX is the only gene known to be associated with AOA1.

Management: Treatment of manifestations: May include physical therapy, particularly for disabilities resulting from peripheral neuropathy; a wheelchair for mobility, usually by age 15-20 years; educational support for difficulties with speaking, reading, and writing.

Prevention of secondary complications: High-protein diet to prevent edema by restoring serum albumin concentration; low-cholesterol diet.

Surveillance: Routine follow up with a neurologist.

Genetic counseling: AOA1 is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being neither affected nor a carrier. Carrier testing for at-risk family members and prenatal testing for pregnancies at increased risk are possible if both pathogenic variants in a family have been identified.