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Preprint WatchMildOctober 23rd, 2026

Multi-level repression ensures tight translation control of C9ORF72

Haizel, S.; Ko, A. N.; Manning, L.; Ge, X.; Zou, H.; Cheng, R. C.; Widjaja, A.; Jean-Baptiste, J.; Khazhinsky, S.; Spealman, P.; Vogel, C.

Translation of C9ORF72 is held down by multiple layers of repression in the mRNA leader, and the pathogenic intronic repeat expansion sits inside that same regulated leader.

Mild contradiction

1 prior failure

One documented clinical failure (Phase 1 or 2) overlaps with the claimed mechanism.

This preprint reports that C9ORF72 translation is tightly repressed at several levels within the mRNA leader that also carries the pathogenic repeat expansion. Claidex holds one documented C9ORF72 programme failure, wve-004-c9orf72-als-ftd-phase1-2-translational-mismatch, in which an antisense oligonucleotide aimed at the repeat-containing transcript was classified as a translational mismatch. A mechanism in which baseline C9ORF72 output is already constrained by layered translational control bears directly on how much additional knockdown of a specific transcript variant can be expected to change protein levels in patients. The flag is MILD because the single matching claim is not an efficacy failure, and because this is molecular work in cells rather than a clinical contradiction.

Abstract excerpt

C9ORF72 is involved in multiple neuronal functions and a major factor in Amyotrophic Lateral Sclerosis, a fatal neurodegenerative disease. Pathogenicity is implemented through an intronic repeat expansion in the mRNA leader of a gene that produces long, repetitive RNA and dipeptides when translated through repeat associated non-canonical translation. The expanded repeat also suppresses transcription of the major transcript variant (Variant 2) which comprises 90% of the C9ORF72 levels in healthy cells, leading to an additional loss-of-function effect. Examining the sequence, structure, and ribosome occupancy of the Variant 2 mRNA leader in detail, we found that translation of C9ORF72 is tightly regulated through a multi-layered system. To deconvolute this system, we conducted a mutant screen and developed a method to evaluate the results quantitatively. We found that near-cognate start codons in all three frames, a start-stop element in frame 2, a uTranslon in frame 1, and secondary structures cooperate to keep baseline C9ORF72 translation low. Further, initiation at upstream near-cognate start codons reduces the impact of both the start-stop and the uTranslon, effectively buffering their repressive function and creating a feedforward loop. A strong secondary structure in the Variant 2-specific sequence further modulates initiation at all the elements. We hypothesize that this buffered repressor system has evolved to ensure reliable, noise-insensitive expression of this critical regulator of neuronal function. Finally, we used ADAR-based RNA editing of specific sites in the Variant 2 mRNA leader, increasing translation of the gene and providing a novel avenue to rescue the loss-of-function phenotype in disease.

Matching Claidex post-mortems

1 of 1 indexed

This is an automated contradiction flag, not an editorial judgment on the preprint's quality. Flags identify where the preclinical literature and the clinical failure record diverge.