Hypermethylation of repeat expanded C9orf72 is a clinical and molecular disease modifier.
C9orf72 promoter hypermethylation inhibits the accumulation of pathologies which have been postulated to be neurotoxic. We tested here whether C9orf72 hypermethylation is associated with prolonged disease in C9orf72 mutation carriers. C9orf72 methylation was quantified from brain or blood using methylation-sensitive restriction enzyme digest-qPCR in a cross-sectional cohort of 118 C9orf72 repeat expansion carriers and 19 non-carrier family members. Multivariate regression models were used to determine whether C9orf72 hypermethylation was associated with age at onset, disease duration, age at death, or hexanucleotide repeat expansion size. Permutation analysis was performed to determine whether C9orf72 methylation is heritable. We observed a high correlation between C9orf72 methylation across tissues including cerebellum, frontal cortex, spinal cord and peripheral blood. While C9orf72 methylation was not significantly different between ALS and FTD and did not predict age at onset, brain and blood C9orf72 hypermethylation was associated with later age at death in FTD (brain: β = 0.18, p = 0.006; blood: β = 0.15, p < 0.001), and blood C9orf72 hypermethylation was associated with longer disease duration in FTD (β = 0.03, p = 0.007). Furthermore, C9orf72 hypermethylation was associated with smaller hexanucleotide repeat length (β = -16.69, p = 0.033). Finally, analysis of pedigrees with multiple mutation carriers demonstrated a significant association between C9orf72 methylation and family relatedness (p < 0.0001). C9orf72 hypermethylation is associated with prolonged disease in C9orf72 repeat expansion carriers with FTD. The attenuated clinical phenotype associated with C9orf72 hypermethylation suggests that slower clinical progression in FTD is associated with reduced expression of mutant C9orf72. These results support the hypothesis that expression of the hexanucleotide repeat expansion is associated with a toxic gain of function.
Translational Neuropathology Research Laboratory, Department of Pathology and Laboratory Medicine, Perelman School of Medicine at the University of Pennsylvania, 605B Stellar Chance Laboratories, 422 Curie Blvd, Philadelphia, PA, 19104, USA.
Jenny
J
Russ
Elaine Y
EY
Liu
Kathryn
K
Wu
Donald
D
Neal
EunRan
E
Suh
David J
DJ
Irwin
Corey T
CT
McMillan
Matthew B
MB
Harms
Nigel J
NJ
Cairns
Elisabeth M
EM
Wood
Sharon X
SX
Xie
Lauren
L
Elman
Leo
L
McCluskey
Murray
M
Grossman
Vivianna M
VM
Van Deerlin
Edward B
EB
Lee
D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism; D001921:Brain / Q000378:metabolism; D000073885:C9orf72 Protein; D003072:Cognition Disorders / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D019175:DNA Methylation; D042622:DNA Repeat Expansion; D005260:Female; D057174:Frontotemporal Lobar Degeneration / Q000175:diagnosis / Q000235:genetics / Q000378:metabolism; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009154:Mutation; D011379:Prognosis; D011401:Promoter Regions, Genetic; D011506:Proteins / Q000235:genetics* / Q000378:metabolism
D000073885:C9orf72 Protein; C568651:C9orf72 protein, human; D011506:Proteins