Frequency of GAA- FGF14 Ataxia in a Large Cohort of Brazilian Patients With Unsolved Adult-Onset Cerebellar Ataxia

Intronic GAA repeat expansions have recently been found to be a common cause of hereditary ataxia (GAA- ataxia; SCA27B). The global epidemiology and regional prevalence of this newly reported disorder remain to be established. In this study, we investigated the frequency of GAA- ataxia in a large cohort of Brazilian patients with unsolved adult-onset ataxia. We recruited 93 index patients with genetically unsolved adult-onset ataxia despite extensive genetic investigation and genotyped the repeat locus. Patients were recruited across 4 different regions of Brazil. Of the 93 index patients, 8 (9%) carried an (GAA) expansion. The expansion was also identified in 1 affected relative. Seven patients were of European descent, 1 was of African descent, and 1was of admixed American ancestry. One patient carrying a (GAA) expansion developed ataxia at age 28 years, confirming that GAA- ataxia can occur before the age of 30 years. One patient displayed episodic symptoms, while none had downbeat nystagmus. Cerebellar atrophy was observed on brain MRI in 7 of 8 patients (87%). Our results suggest that GAA- ataxia is a common cause of adult-onset ataxia in the Brazilian population, although larger studies are needed to fully define its epidemiology.