PPP2R2B and cerebellar ataxia: PPP2R2B, encoding the B55β subunit, was implicated as causative in spinocerebellar ataxia 12, with patients presenting with upper extremity tremor, progressing to head tremor, gait ataxia, dysmetria, dysdiadokinesis, hyperreflexia, paucity of movement, and abnormal eye movements - eventually developing dementia.