Long-read sequencing revealed complex biallelic pentanucleotide repeat expansions in RFC1-related Parkinson's disease

Biallelic intronic pentanucleotide repeat expansions, mainly (AAGGG)exp and/or (ACAGG)exp in RFC1, are detected in cerebellar ataxia, neuropathy and vestibular areflexia syndrome, late-onset ataxia, and in a wide disease spectrum including Charcot-Marie-Tooth disease, multiple system atrophy, and Parkinson's disease (PD). However, the genotype-phenotype correlation and underlying mechanism are mostly unknown. We screened RFC1-repeat expansions in 1445 patients with parkinsonism. Comprehensive genetic and clinical, and pathological assessments were performed. We report two early-onset patients with PD carrying complex biallelic pentanucleotide repeat expansions in RFC1. Long-read sequencing revealed a novel repeat configuration of (AGGGG)exp(AAGGG)₁₄ and a possible somatic variant of (AAGGG)exp(AATGG)exp(AAGGG)exp in the (AAGGG)exp alleles in two RFC1-related PD patients. RNA foci were detected in the (AGGGG)exp-expressed HEK293T cell line as well as (AAGGG)exp and (ACAGG)exp, supporting (AGGGG)exp as a novel pathogenic repeat motif. This work revealed complex genotypes with novel repeat configuration of (AGGGG)exp and possible somatic (AATGG)exp insertion in RFC1-related PD.