Elevated methylation levels, reduced expression levels, and frequent contractions in a clinical cohort of C9orf72 expansion carriers

Abstract

Background: A repeat expansion in the C9orf72-SMCR8 complex subunit (C9orf72) is the most common genetic cause of two debilitating neurodegenerative diseases: amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Currently, much remains unknown about which variables may modify these diseases. We sought to investigate associations between C9orf72 promoter methylation, RNA expression levels, and repeat length, their potential effects on disease features, as well as changes over time and within families.Methods: All samples were obtained through the ALS Center at Mayo Clinic Florida. Our primary cohort included 75 unrelated patients with an expanded C9orf72 repeat, 33 patients who did not possess this expansion, and 20 control subjects without neurodegenerative diseases. Additionally, 67 members from 17 independent C9orf72 families were selected of whom 33 harbored this expansion. Longitudinally collected samples were available for 35 C9orf72 expansion carriers. To increase our understanding of C9orf72-related diseases, we performed quantitative methylation-sensitive restriction enzyme-based assays, digital molecular barcoding, quantitative real-time PCR, and Southern blotting.

Truncated stathmin-2 is a marker of TDP-43 pathology in frontotemporal dementia

“…Transcript level abundance was determined using nSolver 4.0 analyses software (NanoString technologies) and normalized to HTRP1, a housekeeping gene that was unaltered across disease subtypes in our dataset, and previously used to normalize human brain transcripts (72).…”

Insights into disease mechanisms and potential therapeutics for C9orf72-related amyotrophic lateral sclerosis/frontotemporal dementia

“…Somatic instability can explain why the detection of intermediate expansion in blood samples may correspond to massive repeats in the brain (Rohrer et al, 2015). Besides, fluctuations in repeat length have been reported in parental-offspring transmission as well, with a tendency towards a contraction in repeat length over successive generations (Jackson et al, 2020).…”

“…Though controversial, there is little evidence in support of disease anticipation, such as a significant decrease in age at onset (Mossevelde et al, 2017), longer repeat size and increased CpG methylation in the offspring (Gijselinck et al, 2016). Another work reports a contraction in repeat length within successive generations, arguing against anticipation (Jackson et al, 2020).…”

C9orf72 loss-of-function: a trivial, stand-alone or additive mechanism in C9 ALS/FTD?

“…DNA methylation and histone modifications [46]. Several studies investigated methylation levels of the C9orf72 promoter and the repeat expansion itself in genomic DNA from the patient brain and/or blood samples [8,45,53,70,80,94,121]. Hypermethylation of CpG sites in the promoter region of the C9orf72 gene, leading to decreased promoter activity, is associated with shorter disease duration (i.e.…”

“…Hypermethylation of CpG sites in the promoter region of the C9orf72 gene, leading to decreased promoter activity, is associated with shorter disease duration (i.e. a more aggressive disease course) [45,53,70], supporting LOF. However, other studies contradict this finding and suggest an association of C9orf72 promoter hypermethylation with increased survival [80,94].…”