A novel RFC1 repeat motif (ACAGG) in two Asia-Pacific CANVAS families

Abstract

Cerebellar ataxia, neuropathy and vestibular areflexia syndrome (CANVAS) is a progressive late-onset, neurological disease. Recently, a pentanucleotide expansion in intron 2 of RFC1 was identified as the genetic cause of CANVAS. We screened an Asian-Pacific cohort for CANVAS and identified a novel RFC1 repeat expansion motif, (ACAGG)exp, in three affected individuals. This motif was associated with additional clinical features including fasciculations and elevated serum creatine kinase. These features have not previously been described in individuals with genetically-confirmed CANVAS. Haplotype analysis showed our patients shared the same core haplotype as previously published, supporting the possibility of a single origin of the RFC1 disease allele. We analysed data from >26 000 genetically diverse individuals in gnomAD to show enrichment of (ACAGG) in non-European populations.

Keywords: neuropathy; sensory neuropathy; cerebellar ataxia; vestibular areflexia syndrome; CANVAS; RFC1; repeat expansion.

Figure 1

Novel configuration of the RFC1 expansion in an Asian Pacific family. (A) Pedigree of Family Indo1. Half-shaded symbols represent individuals identified as (ACAGG) repeat expansion carriers by flanking PCR and RP-PCR. (B) Representative Sanger chromatogram of long-range, nested PCR products containing the novel (ACAGG) expansion at the RFC1 locus. The grey shaded region indicates the (ACAGG) repeat sequence. (C) Representative positive RP-PCR fragment analysis result for the (ACAGG) repeat expansion.

Figure 2

Visualization of the (ACAGG) repeat expansion from whole genome sequencing of Patient N1. Reads containing the RFC1 intron 2 (ACAGG) motif are visible with soft-clipping enabled on IGV. This shows the patient is homozygous for the (ACAGG) motif.