Biallelic intronic repeat expansions (a series of repeating nucleotide sequences) in the
replication factor C subunit 1 (RFC1) gene causes
cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS). Within the poly(A) tail of an AluSx3 element in
RFC1, there are eleven repeats of the pentanucleotide "AAAAG". Repeat expansion and polymorphic configuration are observed in part of the population, with increased number of repeats associated to alternative "AAAGG", "AAGGG" and "ACAGG" pentanucleotides. In particular, biallelic "AAGGG" and "ACAGG" repeat expansion have disproportionately been observed in patients with CANVAS. Biallelic "AAGGG" repeat expansion is also reported in a high number of sporadic cases of late-onset ataxia, and, less frequently, isolate cerebellar ataxia. Due to a diagnostic overlap with CANVAS, researchers have also investigated the presence of
RFC1 expansions in pathologically confirmed
multiple system atrophy (MSA) but found a similar alteration frequency (0.7%) to a healthy population, suggesting
RFC1 does not have a role in this disease. Mutant biallelic intronic repeat expansions do not affect
RFC1 expression in patient peripheral and brain tissue, suggesting no overt loss of function of this gene. == References ==