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Abstract 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.

Abstract Elevated neurofilament light chain (NfL) levels have been associated with dementia in idiopathic Parkinson’s disease (iPD). To examine the baseline and longitudinal changes in NfL levels in GBA-PD, SNCA-PD, and LRRK2-PD and further investigate the association between these genetic mutations, NfL, and dementia in PD. We analyzed data from the Parkinson’s Progression Markers Initiative (PPMI), including 184 healthy controls (HC) and 617 PD categorized as iPD (n = 381), LRRK2-PD (n = 142), GBA-PD (n = 76) and SNCA-PD (n = 18). Analysis of covariance (ANCOVA) or linear mixed-effect models were used to compare the baseline or dynamic NfL levels between groups. We then explored the relationship between genetic mutations, serum NfL levels, and conversion to dementia using mediation analysis. After adjusting for confounding factors, SNCA-PD exhibited higher baseline serum NfL levels than iPD. Regarding longitudinal changes, SNCA-PD showed the highest increase rate in estimated NfL levels (2.43 pg/mL per year), while LRRK2-PD experienced the slowest increase rate (0.52 pg/mL per year). Mediation analysis indicated that higher estimated NfL level changes were associated with faster cognitive decline (β = 0.591, p = 0.026). Specifically, the relationship between LRRK2 and dementia was mediated by the estimated NfL level change (β = −0.717, p