Parkinson's disease is a common, progressive neurodegenerative disease, with typical tremor, bradykinesia and muscle rigidity, and non-motor symptoms. The cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) is a rarer type of late-onset ataxia, some of whose symptoms, such as movement, balance and sensory problems, may overlap with Parkinson’s disease. While genetic causes can be established in approximately 10 % of patients with Parkinson’s disease, the genetic cause of CANVAS has been identified only recently. CANVAS is now understood to be caused by biallelic pathogenic (AAGGG)n repeat expansions in the RFC1 gene. The pathogenic expansion differs in nucleotide sequence and size from the reference allele (AAAAG)11. Only large biallelic expansion with the (AAGGG)exp or (AAAGG)exp (over 400 repeats) sequence are considered to be pathogenic. In 2022, it was shown for the first time that pathogenic expansions associated with CANVAS may also be present in patients clinically diagnosed as Parkinson's patients. Because the percent of Parkinson’s disease patients explained by genetic testing is low, while CANVAS was relatively unknown until recently, the possibility exists that there may be CANVAS patients among the undiagnosed Parkinson’s disease patients, a hypothesis that has not yet been tested in Slovenia. Our aim was to determine the possible presence of CANVAS-specific pathogenic expansions in a cohort of Parkinson's disease patients. We performed CANVAS testing by using a two-step fluorescent polymerase chain reaction (PCR), based on the initial exclusion of long expansions in CANVAS, and a second stage confirmation of long pathogenic expansions, with the detection based on fragment analysis. By applying this method, we found two patients with homozygous pathogenic expansions in RFC1 in our cohort of patients with Parkinson’s disease. The percent of such patients in Slovenia is similar to that reported in other European populations.
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