RFC1 -related ataxia is a mimic of early multiple system atrophy

Multiple systems atrophy (MSA) is a rare neurodegenerative disorder combining varying presentations of cerebellar impairment, parkinsonism and autonomic dysfunction that relies on pathological examination for a definitive diagnosis.1 2 The second consensus diagnostic criteria (SCDC) subdivide patients into two groups based on a predominance of either parkinsonism (MSA-P) or cerebellar impairment (MSA-C).2 MSA is frequently misdiagnosed, especially early in the disease course, with only 60% of possible and probable MSA meeting the pathological criteria.2 3 A recessive intronic expansion in replication factor C subunit 1 ( RFC1 ) has been found to be a cause of late-onset ataxia and cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS),4 Due to the overlapping clinical features of MSA and CANVAS, we hypothesised that the recessive RFC1 expansion may be implicated in patients that atypically fit the diagnostic criteria for MSA. Here, we present three cases with biallelic RFC1 expansions: two clinically diagnosed with ‘probable’ MSA and one with ‘probable’ based on the SCDC for MSA.2 ### Samples We enrolled 207 patients with ‘possible’ and ‘probable’ MSA, from the National Hospital for Neurology and Neurosurgery (NHNN). MSA diagnosis based on the SCDC for MSA.2 ### Genetic testing Genomic DNA was extracted from blood and investigated under approval of the joint ethics committee of the UCL Institute of Neurology and The NHNN, London, UK (UCLH: 04/N034). Flanking PCR, repeat-primed PCR and Southern blot were performed on all samples as previously described4 (figure 1A). Figure 1 Clinical presentation of affected patients. (A) Workflow of RFC1 screen; clinical screening of cohort leads to sample gDNA undergoing flanking PCR and those with no amplifiable product and potential carriers are taken forward for RPPCR. Samples with a positive RPPCR trace (hallmark sawtooth pattern) are then Southern blotted, confirming size of expansion. (B) CANVAS RPPCR positive fragment analysis traces for patients …