No abstract

GGGGCC (G 4 C 2 ) hexanucleotide repeat expansion (HRE) in the first intron of the C9ORF72 (C9) gene is the most common genetic cause of ALS and FTD, two devastating adult-onset neurodegenerative disorders 1,2 . Proposed disease mechanisms include a partial loss of the C9ORF72 protein function (C9ORF72 haploinsufficiency) and acquired toxicity of the repeat expansion 3 . Transcription of the C9ORF72 gene generates three transcript variants: V1, V2 and V3 (Fig. 1a). V1 is translated to produce a short protein isoform (222 amino acids), whereas V2 and V3 generate the most predominant C9ORF72 protein (481 amino acids), which functions in vesicular trafficking 4 . Located adjacent to the promoter region of the most abundant V2 transcript variant, the G 4 C 2 repeat expansion impairs its transcription, leading to C9ORF72 protein haploinsufficiency 5,6 , impaired function of myeloid cells 7,8 and diminished neuronal viability 9 . Both sense and antisense transcripts encompassing the HRE in V1 and V3 generate RNA foci and undergo translation into atypical, aggregation-prone dipeptide repeat (DPR) proteins in all open reading frames 10,11 . These unusual DPRs are toxic in several experimental model systems [12][13][14][15] . Despite important advances in elucidating the molecular pathology of the expanded hexanucleotide repeats, there are no meaningful therapies for C9ORF72-related ALS or FTD.ASOs can drive therapeutic effects by mechanisms that include splice-modulation or, if the ASO contains DNA, activation of endogenous RNase H 16 to degrade the target RNA. The broad bioavailability of ASOs in the central nervous system (CNS), including both neurons and glial cells 17 , has prompted development of ASOs as therapy for dominantly transmitted genetic disorders of the CNS (for example, ALS caused by mutations in the SOD1 gene).Here we report development of ASOs targeting C9ORF72 to treat ALS and FTD. Using different C9-related model systems, including patient-derived samples and two C9BAC transgenic mouse models 18,19 , we generated ASOs that specifically reduce levels of the transcripts harboring the HRE as well as their DPR products, with minimal effects on the most abundant V2 isoform, which does not contain the HRE. We show that modification of a subset of the phosphodiester internucleoside linkages significantly improves ASO tolerability without impairing potency. We demonstrate that, in a single patient harboring mutant C9ORF72 with the G 4 C 2 repeat expressions, repeated intrathecal dosing of the optimal ASO was well tolerated and led to significant and durable reduction in levels of cerebrospinal fluid (CSF) poly(GP). Results ASO suppresses C9ORF72 in fibroblasts and mouse neurons.Because haploinsufficiency of C9ORF72 is thought to be adverse, we developed ASOs that target only the 5′ end of transcripts V1 and V3 that bear the G 4 C 2 repeat expansion, sparing transcript V2. As it is not fully clear whether the repeat-containing intron is retained or spliced out, we focused our effort on ASO sequences targeting ...

Tay-Sachs Disease (TSD) is an inherited neurological disorder caused by deficiency of hexosaminidase A (HexA). Preclinical work demonstrated safety and efficacy of CNS gene therapy using AAVrh8-HEXA/HEXB. Here we describe an expanded access trial in two patients with infantile TSD (IND 18225).Case TSD-001 demonstrated neurodevelopmental regression by 8 months of age and severe seizures by 1 year was treated at 30 months. An equimolar mix of AAVrh8-HEXA and AAVrh8-HEXB (now AXO-AAV-GM2) was administered intrathecally (IT), with 75% of the dose (1x10 14 vg) delivered to the cisterna magna and 25% at the thoraco-lumbar junction. The second patient (TSD-002) was treated at 7 months of age with 4•2x10 13 vg by a combination of bilateral thalamic (0•18 mL; 1•5x10 12 vg per thalamus), and IT infusion (3•9x10 13 vg). Both patients underwent immunosuppression with sirolimus, corticosteroids, and rituximab.Injection procedures were well tolerated and have shown no vector-related adverse events to date. CSF HexA activity nearly doubled from baseline and remained stable. In TSD-002 (now 16 months of age), MRI showed stabilization of disease by 3 months post-injection; there now appeared to temporarily deviate from the natural history of infantile TSD but declined again 6 months post-treatment. TSD-001 (now 4.5 years of age remains seizure-free on the same anticonvulsant therapy as pre-therapy, but TSD-002 developed seizures between 13 and 17 months post-treatment (by 2 years of age).Administration of AXO-AAV-GM2 by IT and thalamic injections was safe, HexA activity increased in CSF and ongoing myelination was apparent in the younger patient treated at an early symptomatic stage. This study provides early safety and proof-of-concept in humans for treatment of TSD patients by AAV gene therapy.

ObjectiveTo define the natural history of the C9orf72 amyotrophic lateral sclerosis (C9ALS) patient population, develop disease biomarkers, and characterize patient pathologies.MethodsWe prospectively collected clinical and demographic data from 116 symptomatic C9ALS and 12 non–amyotrophic lateral sclerosis (ALS) full expansion carriers across 7 institutions in the United States and the Netherlands. In addition, we collected blood samples for DNA repeat size assessment, CSF samples for biomarker identification, and autopsy samples for dipeptide repeat protein (DPR) size determination. Finally, we collected retrospective clinical data via chart review from 208 individuals with C9ALS and 450 individuals with singleton ALS.ResultsThe mean age at onset in the symptomatic prospective cohort was 57.9 ± 8.3 years, and median duration of survival after onset was 36.9 months. The monthly change was −1.8 ± 1.7 for ALS Functional Rating Scale–Revised and −1.4% ± 3.24% of predicted for slow vital capacity. In blood DNA, we found that G4C2 repeat size correlates positively with age. In CSF, we observed that concentrations of poly(GP) negatively correlate with DNA expansion size but do not correlate with measures of disease progression. Finally, we found that size of poly(GP) dipeptides in the brain can reach large sizes similar to that of their DNA repeat derivatives.ConclusionsWe present a thorough investigation of C9ALS natural history, providing the basis for C9ALS clinical trial design. We found that clinical features of this genetic subset are less variant than in singleton ALS. In addition, we identified important correlations of C9ALS patient pathologies with clinical and demographic data.

GGGGCC repeat expansion in C9ORF72, which can be translated in both sense and antisense directions into five dipeptide repeat (DPR) proteins, including poly(GP), poly(GR), and poly(GA), is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Here we developed sensitive assays that can detect poly(GA) and poly(GR) in the cerebrospinal fluid (CSF) of patients with C9ORF72 mutations. CSF poly(GA) and poly(GR) levels did not correlate with age at disease onset, disease duration, or rate of decline of ALS Functional Rating Scale, and the average levels of these DPR proteins were similar in symptomatic and pre-symptomatic patients with C9ORF72 mutations. However, in a patient with C9ORF72-ALS who was treated with antisense oligonucleotide (ASO) targeting the aberrant C9ORF72 transcript, CSF poly(GA) and poly(GR) levels decreased approximately 50% within 6 weeks, indicating they may serve as sensitive fluid-based biomarkers in studies directed against the production of GGGGCC repeat RNAs or DPR proteins.

Since the discovery of the chromosome 9 open reading frame 72 (C9orf72) repeat expansion mutation in 2011 as the most common genetic abnormality in amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease) and frontotemporal dementia (FTD), progress in understanding the signaling pathways related to this mutation can only be described as intriguing. Two major theories have been suggested—(i) loss of function or haploinsufficiency and (ii) toxic gain of function from either C9orf72 repeat RNA or dipeptide repeat proteins (DPRs) generated from repeat-associated non-ATG (RAN) translation. Each theory has provided various signaling pathways that potentially participate in the disease progression. Dysregulation of the immune system, particularly glial cell dysfunction (mainly microglia and astrocytes), is demonstrated to play a pivotal role in both loss and gain of function theories of C9orf72 pathogenesis. In this review, we discuss the pathogenic roles of glial cells in C9orf72 ALS/FTD as evidenced by pre-clinical and clinical studies showing the presence of gliosis in C9orf72 ALS/FTD, pathologic hallmarks in glial cells, including TAR DNA-binding protein 43 (TDP-43) and p62 aggregates, and toxicity of C9orf72 glial cells. A better understanding of these pathways can provide new insights into the development of therapies targeting glial cell abnormalities in C9orf72 ALS/FTD.

Objective: To measure the correlation between single breath counting (SBC) and forced vital capacity (liters, FVC L ) in amyotrophic lateral sclerosis (ALS) patients and to define the utility of SBC for determining when patients meet the threshold for initiation of noninvasive positive pressure ventilation (FVC < 50% predicted [FVC pred ]). Methods: Both patient paced (SBCpp) or externally paced (SBCep) counting along with FVC Lþpred and standard clinical data were collected. Linear regression was used to examine SBCpp and SBCep as a predictor of FVC L . Receiver operating characteristic curve analysis evaluated the sensitivity and specificity of SBC categorically predicting FVC pred of 50%. Results: In 30 ALS patients, SBC explained a moderate proportion of the variance in FVC L (SBCpp: R 2 ¼ 0.431, p < 0.001; SBCep: R 2 ¼ 0.511, p < 0.01); this proportion improved when including covariates (SBCpp: R 2 ¼ 0.635, p < 0.01; SBCep: R 2 ¼ 0.657, p < 0.01). Patients with minimal speech involvement performed similarly in unadjusted (SBCpp: R 2 ¼ 0.511, p < 0.01; SBCep: R 2 ¼ 0.595, p < 0.01) and adjusted (SBCpp: R 2 ¼ 0.634, p < 0.01; SBCep: R 2 ¼ 0.650, p < 0.01) models. SBCpp had 100% sensitivity and 60% specificity (area under curve (AUC) ¼ 0.696) for predicting FVC pred <50%. SBCep had 100% sensitivity and 56% specificity (AUC ¼ 0.696). With minimal speech involvement SBCpp and SBCep both had 100% sensitivity and 76.1% specificity (SPCpp: AUC ¼ 0.845; SBCep: AUC ¼ 0.857). Conclusions: SBC explains a moderate proportion of variance in FVC and is an extremely sensitive marker of poor FVC. When FVC cannot be obtained, such as during the current COVID-19 pandemic, SBC is helpful in directing patient care.

Expansions of a G4C2 repeat in the C9ORF72 gene are the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), two devastating adult-onset neurodegenerative disorders. Proposed disease mechanisms include a gain of toxic functions of the G4C2 repeats, implying that selective reduction in levels of the repeat-containing transcripts would represent a treatment strategy for this disorder. In the present study, using C9-ALS/FTD patient derived cells and C9ORF72 BAC transgenic mice, we have generated and optimized antisense oligonucleotides (ASOs) that selectively blunt expression of G4C2 repeat containing transcripts in both the sense and anti-sense strands of C9ORF72 and effectively suppress tissue levels of polyGP dipeptides. In a single patient harboring mutant C9ORF72 with the G4C2 repeat expressions, repeated dosing by intrathecal delivery of the optimal ASO was well tolerated, leading to significant reductions in levels of CSF polyGP.