C9Orf72 Repeat Expansion In Als plays an important role in the study of neurodegenerative diseases. This page provides comprehensive information about this topic, including its mechanisms, significance in disease processes, and therapeutic implications.
The C9orf72 hexanucleotide repeat expansion is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), accounting for approximately 40% of familial ALS cases and 5-10% of sporadic ALS cases[1][2]. This expansion represents a critical therapeutic target and has revolutionized our understanding of the ALS-FTD disease spectrum.
The C9orf72 gene is located on chromosome 9p21.1 and encodes a DENN (Differentially Expressed in Normal and Neoplasia) domain protein involved in:
The gene spans approximately 6.7 kb and contains 12 exons. The pathogenic expansion occurs in the first intron, within a GC-rich region[3].
| Repeat Length | Classification | Clinical Significance |
|---|---|---|
| <10 | Normal | No disease risk |
| 10-30 | Intermediate | Uncertain significance |
| 30-60 | Penetrance uncertain | May be pathogenic |
| >60 | Pathogenic | Disease-causing |
| Hundreds to thousands | Full penetrance | Classic ALS/FTD |
The expansion is meotically unstable and can expand further in successive generations, explaining anticipation in some families[4].
The C9orf72 expansion leads to disease through three interconnected mechanisms:
The expanded RNA transcript forms toxic RNA foci that sequester essential RNA-binding proteins:
This sequestration disrupts normal RNA processing, splicing, and transport[5].
Non-ATG (RAN) translation of the expanded repeat produces five different dipeptide repeat (DPR) proteins:
| DPR Species | Toxicity Mechanism |
|---|---|
| Poly-GA | Proteasome impairment, aggregation |
| Poly-GP | Less toxic, potential protective role |
| Poly-GR | Translation inhibition, nucleolar stress |
| Poly-PR | Translation inhibition, DNA damage |
| Poly-PA | Less characterized |
The poly-GA species is most abundant in patient brains and forms inclusions that impair proteostasis[6].
Reduced C9orf72 protein expression due to:
This loss affects endolysosomal trafficking and autophagy, contributing to neurodegeneration[7].
Patients with C9orf72 expansions typically present with:
Approximately 30% of C9orf72 carriers develop FTD:
| Approach | Target | Status |
|---|---|---|
| ASO therapy | C9orf72 mRNA | Preclinical/Phase 1 |
| Small molecules | DPR aggregation | Discovery |
| Gene therapy | Viral delivery | Preclinical |
C9Orf72 Repeat Expansion In Als plays an important role in the study of neurodegenerative diseases. This page provides comprehensive information about this topic, including its mechanisms, significance in disease processes, and therapeutic implications.
The study of C9Orf72 Repeat Expansion In Als has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
DeJesus-Hernandez et al., 2011 - Expanded GGGGCC hexanucleotide repeat in noncoding region of C9ORF72 causes chromosome 9p-linked FTD and ALS ↩︎
Renton et al., 2011 - A hexanucleotide repeat expansion in C9ORF72 is the cause of chromosome 9p21-linked ALS-FTD ↩︎
Balendra & Isaacs, 2018 - C9orf72-mediated ALS and FTD: multiple pathways to disease ↩︎
Gomez-Tortosa et al., 2017 - C9orf72 repeat expansion length and anticipation ↩︎
Lee et al., 2013 - Molecular dissection of C9orf72 toxic proteins ↩︎