Friedreich ataxia (FRDA) is the most common recessive ataxia in Caucasians. Over 95% of patients are homozygous for the hyperexpansion of a GAA triplet repeat in the first intron of the frataxin (FXN) gene, which represses FXN expression via an epigenetic mechanism. Most residual FXN expression comes from the chromosome with the shortest repeat (GAA1), whose length has been shown to correlate with age at symptom onset and with disease severity. Clinically, FRDA is dominated by a tabeto-cerebellar ataxic pattern, associated with pyramidal signs and various systemic manifestations. FRDA patients may present subtle signs of proprioceptive loss, such as loss of tendon reflexes and a Romberg sign, before they become frankly symptomatic. However, FRDA patients become overtly ataxic only when cerebellar symptoms appear. Most items in the scales for the assessment of neurological deficits in FRDA (e.g., Scale for the Assessment and Rating of Ataxia (SARA) or the Friedreich Ataxia Rating Scale) are performed under patients’ visual control and mainly reflect cerebellar dysfunction rather than afferent proprioceptive ataxia. Neuroimaging studies show progressive thinning of the cervical spinal cord, but to what extent this is due to shrinking of pyramidal tracts or the posterior columns is unclear (Koeppen et al., 2017, Dogan et al., 2019).
- Friedreich's ataxia
- Cortico-kinematic coherence