AOA3 is a rare type of autosomal recessive cerebellar ataxia. Other disorders in this group include Spinocerebellar Ataxia, Autosomal Recessive 1, Ataxia with Oculomotor Apraxia Type 1, Ataxia-Telangiectasia and Ataxia-Telangiectasia-Like-Disorder. The disease is characterized by ataxia, dysmetria, peripheral neuropathy, areflexia, cerebellar atrophy, oculomotor apraxia and raised alpha-fetoprotein levels. Symptoms usually surface in the second decade of life and follow a highly rapid progression. Patients may hence become wheelchair-bound by the third or fourth decade of life. AOA3 has so far been diagnosed in only a single Saudi Arab family.
AOA3 follows an autosomal recessive pattern of inheritance and is caused by mutations in the PIK3R5 gene. This gene encodes a regulatory subunit of the PI3K gamma complex, a family of lipid kinases involved in cell growth, proliferation, differentiation, motility, survival and intracellular trafficking. Expression of the gene is found to be high in both the fetal and adult human brain.