MitAtax - Hereditary Ataxias in Northern Finland

Hereditary ataxias are a group of rare neurological disorders, affecting the cerebellum and its afferent and efferent pathways. To date, more than 100 causative genes have been identified.
We ascertained a cohort of 96 patients with either known or suspected hereditary ataxia to study the genetic background and clinical features of Finnish ataxia. Molecular testing for common pathogenic variants known to cause ataxia was performed. Whole exome sequencing and mitochondrial DNA sequencing was performed for selected patients. A genetic diagnosis was found for 34 patients.
Polyglutamine expansions in ATXN8(OS) causing SCA8 was the most common form of dominantly inherited ataxia. The recently described intronic (AAGGG)exp pentanucleotide expansion in RFC1 causing CANVAS and homozygous p.Trp748Ser variant in POLG causing mitochondrial ataxia-polyneuropathy spectrum disorders are the most common forms of recessive ataxia in Finland. Nineteen probands were clinically evaluated using clinical scales SARA and INAS. The probands and 21 healthy controls then performed instrumented versions of the finger-to-nose test, utilizing kinetic sensors to quantify upper limb ataxia. The performance of probands in the finger-to-nose test was compared with their SARA scores and the performance of healthy controls. We found that ataxic patients slow down their movements in order to gain accuracy, resulting in highly variable slow movements, but the end-point accuracy remains fairly intact.