Loren Flynn PhD

With the disease modifying therapy Qalsody (tofersen) which targets the RNA product of the SOD1 gene, having been shown effective in amyotrophic lateral sclerosis (ALS), the present perspective seeks to explore progress towards the implementation of precision medicine principles in ALS drug development. We address the advances in our understanding of the complex genetic architecture of ALS, including the varying models of genetic contribution to disease, and the importance of understanding population genetics and genetic testing when considering patient selection for clinical studies. Additionally, we discuss the advances in long-read whole-genome sequencing technology and how this method can improve streamlined genetic testing and our understanding of the genetic heterogeneity in ALS. We highlight the recent advances in omics-data for understanding ALS patient sub-groups and how this knowledge should be applied to pre-clinical drug development in a proposed patient profiling workflow, particularly for gene targeted therapies. Finally, we summarise key ethical considerations that are pertinent to equitable care for patients, as we enter the era of precision medicine to treat ALS.

Key points
1. Precision medicine means giving the right drug to the right patient at the right time. With the emergence of antisense oligonucleotide technologies, additional gene targeted therapies will soon enter the market for ALS.

2. The improved understanding of the complex genetic architecture of ALS and pathophysiological mechanisms involved in disease has increased the number of validated drug targets for ALS.

3. Long-read sequencing will revolutionise our understanding of ALS genetics through the comprehensive mapping of genetic variation. Long read sequencing has enabled the complete sequence of a human genome and subsequently, the first human global and population-specific pan-genome references, adding hundreds of millions of bases that were not present in the previous human genome reference.

4. Leveraging omics data and machine learning methodologies will improve our understanding of both ALS phenotype and the underlying molecular heterogeneity between ALS patients, enhancing patient stratification through the detection of specific sub-groups of patients.

5. Comprehensive patient profiling through the collection of full omics data will be critical to define responder populations. A patient profiling workflow is proposed to conduct in vitro trials alongside early clinical studies as more antisense therapies begin entering the clinic.

6. Ethical strategies to consider for population targeted therapeutic development include tiered pricing models, public-private partnerships, and global distribution initiatives, all of which may be valuable for facilitating access to genetic therapies, thereby reducing inequalities in ALS care.

Pathogenic variations in the fused in sarcoma (FUS) gene are associated with rare and aggressive forms of amyotrophic lateral sclerosis (ALS). As FUS-ALS is a dominant disease, a targeted, allele-selective approach to FUS knockdown is most suitable. Antisense oligonucleotides (AOs) are a promising therapeutic platform for treating such diseases. In this study, we have explored the potential for allele-selective knockdown of FUS. Gapmer-type AOs targeted to two common neutral polymorphisms in FUS were designed and evaluated in human fibroblasts. AOs had either methoxyethyl (MOE) or thiomorpholino (TMO) modifications. We found that the TMO modification improved allele selectivity and efficacy for the lead sequences when compared to the MOE counterparts. After TMO-modified gapmer knockdown of the target allele, up to 93% of FUS transcripts detected were from the non-target allele. Compared to MOE-modified AOs, the TMO-modified AOs also demonstrated reduced formation of structured nuclear inclusions and SFPQ aggregation that can be triggered by phosphorothioate-containing AOs. How overall length and gap length of the TMO-modified AOs affected allele selectivity, efficiency and off-target gene knockdown was also evaluated. We have shown that allele-selective knockdown of FUS may be a viable therapeutic strategy for treating FUS-ALS and demonstrated the benefits of the TMO modification for allele-selective applications.

Background. Inclusions of Sequestosome1 (SQSTM1/p62) within muscle fibers are a pathological hallmark of sporadic inclusion body myositis (sIBM) with p62 overexpression reported in patients. Mounting evidence suggests a role for p62 expression and/or variation in sIBM pathology, due to the presence of rare and potentially pathogenic missense variants (A117V, G194R, K238E, P392L). Consequently, we hypothesized that genetic modifiers of SQSTM1 may present a critical missing link for sIBM pathology and contribute to disease expres¬sion. Short structural variants (SSVs) are a class of genetic variation that can be difficult to characterized due to their highly repetitive and complex nature. Evidence that SSVs play an important role in complex diseases such as Alzhei¬mer’s Disease, Amyotrophic lateral sclerosis, Spinocerebellar Ataxia type 2, and Huntington’s disease is now confirmed and further investigations of this type of genetic variation is necessary to uncover missing heritability in complex dis¬eases. We and others have previously reported an SSV within SQSTM1 that is associated with altered expression of p62. The SSV rs60327661 is a CAAA in¬sertion/deletion within intron 5 of SQSTM1, which also confers risk for familial Amyotrophic lateral sclerosis. Due to the role of the SSV in Amyotrophic lateral sclerosis and altered p62 expression, we hypothesized the SSV rs60327661 may have disease-modifying effects in a longitudinal cohort of sIBM patients.

Methods. DNA samples from 218 sIBM patients and 242 healthy controls were received from The Institute for Immunology and Infectious Diseases, Murdoch, Western Australia, and the NINDS Repository, Coriell Institute for Medical Research, New Jersey. Genomic DNA samples were systematically assessed through polymerase chain reaction, capillary separation, and Sanger sequencing for rs60327661 allele genotyping.

Results: In the present study, when controlling for self-declared ancestry, car¬riage of the D/D genotype is associated with sIBM disease expression (p<0.05). Both the case and control groups did not violate Hardy-Weinberg equilibrium (p=0.99, p=0.98; respectively. Intriguingly, patients who were CN1A seroposi¬tive were more likely carry the D allele (n=18) when compared to patients with-out a D allele (n=3; p<0.047). Patients classified as fast progressors (n=2) carried only the D/D genotype.

Conclusion. In this study, we present the first report of an association between the SQSTM1 insertion/deletion and sIBM disease expression. We provide evi¬dence that the investigation of genetic variants outside of the HLA region is war¬ranted, and that such investigations are likely to uncover critical information for sIBM. We present the SSV rs60327661 as a novel disease modifying variant for sIBM which is functionally linked to p62 by altering protein expression. Our data adds to growing evidence that examination of SSVs may uncover novel genetic risk markers, and consequently further understanding of the pathogenic mechanisms at play.

There is considerable variability in disease progression for patients with amyotrophic lateral sclerosis (ALS) including the age of disease onset, site of disease onset, and survival time. There is growing evidence that short structural variations (SSVs) residing in frequently overlooked genomic regions can contribute to complex disease mechanisms and can explain, in part, the phenotypic variability in ALS patients. Here, we discuss SSVs recently characterized by our laboratory and how these discoveries integrate into the current literature on ALS, particularly in the context of application to future clinical trials. These markers may help to identify and differentiate patients for clinical trials that have a similar ALS disease mechanism(s), thereby reducing the impact of participant heterogeneity. As evidence accumulates for the genetic markers discovered in SQSTM1, SCAF4, and STMN2, we hope to improve the outcomes of future ALS clinical trials.

Amyotrophic lateral sclerosis (ALS) is the most common adult-onset motor neuron disease classified as both a neurodegenerative and neuromuscular disorder. With a complex aetiology and no current cure for ALS, broadening the understanding of disease pathology and therapeutic avenues is required to progress with patient care. Alpha-synuclein (αSyn) is a hallmark for disease in neurodegenerative disorders, such as Parkinson’s disease, Lewy body dementia, and multiple system atrophy. A growing body of evidence now suggests that αSyn may also play a pathological role in ALS, with αSyn-positive Lewy bodies co-aggregating alongside known ALS pathogenic proteins, such as SOD1 and TDP-43. This review endeavours to capture the scope of literature regarding the aetiology and development of ALS and its commonalities with “synucleinopathy disorders”. We will discuss the involvement of αSyn in ALS and motor neuron disease pathology, and the current theories and strategies for therapeutics in ALS treatment, as well as those targeting αSyn for synucleinopathies, with a core focus on small molecule RNA technologies.

Oligonucleotides and nucleic acid analogues that alter gene expression are now showing therapeutic promise in human disease. Whilst the modification of synthetic nucleic acids to protect against nuclease degradation and to influence drug function is common practice, such modifications may also confer unexpected physicochemical and biological properties. Gapmer mixed-modified and DNA oligonucleotides on a phosphorothioate backbone can bind non-specifically to intracellular proteins to form a variety of toxic inclusions, driven by the phosphorothioate linkages, but also influenced by the oligonucleotide sequence. Recently, the non-antisense or other off-target effects of 2′ O- fully modified phosphorothioate linkage oligonucleotides are becoming better understood. Here, we report chemistry-specific effects of oligonucleotides composed of modified or unmodified bases, with phosphorothioate linkages, on subnuclear organelles and show altered distribution of nuclear proteins, the appearance of highly stable and strikingly structured nuclear inclusions, and disturbed RNA processing in primary human fibroblasts and other cultured cells. Phosphodiester, phosphorodiamidate morpholino oligomers, and annealed complimentary phosphorothioate oligomer duplexes elicited no such consequences. Disruption of subnuclear structures and proteins elicit severe phenotypic disturbances, revealed by transcriptomic analysis of transfected fibroblasts exhibiting such disruption. Our data add to the growing body of evidence of off-target effects of some phosphorothioate nucleic acid drugs in primary cells and suggest alternative approaches to mitigate these effects.

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) that exist on a spectrum of neurodegenerative disease. A hallmark of pathology is cytoplasmic TDP-43 aggregates within neurons, observed in 97% of ALS cases and ~ 50% of FTLD cases. This mislocalisation from the nucleus into the cytoplasm and TDP-43 cleavage are associated with pathology, however, the drivers of these changes are unknown. p62 is invariably also present within these aggregates. We show that p62 overexpression causes TDP-43 mislocalisation into cytoplasmic aggregates, and aberrant TDP-43 cleavage that was dependent on both the PB1 and ubiquitin-associated (UBA) domains of p62. We further show that p62 overexpression induces neuron death. We found that stressors (proteasome inhibition and arsenic) increased p62 expression and that this shifted the nuclear:cytoplasmic TDP-43 ratio. Overall, our study suggests that environmental factors that increase p62 may thereby contribute to TDP-43 pathology in ALS and FTLD.

Objective: There is a critical need to establish genetic markers that explain the complex phenotypes and pathogenicity of ALS. This study identified a polymorphism in the Stathmin-2 gene and investigated its association with sporadic ALS (sALS) disease risk, age-of onset and survival duration.

Methods: The candidate CA repeat was systematically analyzed using PCR, Sanger sequencing and high throughput capillary separation for genotyping. Stathmin-2 expression was investigated using RT-PCR in patient olfactory neurosphere-derived (ONS) cells and RNA sequencing in laser-captured spinal motor neurons.

Results: In a case-control analysis of a combined North American sALS cohort (n = 321) and population control group (n = 332), long/long CA genotypes were significantly associated with disease risk (p = 0.042), and most strongly when one allele was a 24 CA repeat (p = 0.0023). In addition, longer CA allele length was associated with earlier age-of-onset (p = 0.039), and shorter survival duration in bulbar-onset cases (p = 0.006). In an Australian longitudinal sALS cohort (n = 67), ALS functional rating scale scores were significantly lower in carriers of the long/long genotype (p = 0.034). Stathmin-2 mRNA expression was reduced in sporadic patient ONS cells. Additionally, sALS patients and controls exhibited variable expression of Stathmin-2 mRNA according to CA genotype in laser-captured spinal motor neurons.

Conclusions: We report a novel non-coding CA repeat in Stathmin-2 which is associated with sALS disease risk and has disease modifying effects. The potential value of this variant as a disease marker and tool for cohort enrichment in clinical trials warrants further investigation.

The literature surrounding the use of antisense oligonucleotides continues to grow, with new disease and mechanistic applications constantly evolving. Furthermore, the discovery and advancement of novel chemistries continues to improve antisense delivery, stability and effectiveness. For each new application, a rational sequence design is recommended for each oligomer, as is chemistry and delivery optimization. To confirm oligomer delivery and antisense activity, a positive control AO sequence with well characterized target-specific effects is recommended. Here, we describe splice-switching antisense oligomer sequences targeting the ubiquitously expressed human and mouse SMN and Smn genes for use as control AOs for this purpose. We report two AO sequences that induce targeted skipping of SMN1/SMN2 exon 7 and two sequences targeting the Smn gene, that induce skipping of exon 5 and exon 7. These antisense sequences proved effective in inducing alternative splicing in both in vitro and in vivo models and are therefore broadly applicable as controls. Not surprisingly, we discovered a number of differences in efficiency of exon removal between the two species, further highlighting the differences in splice regulation between species.

The underlying genetic and molecular mechanisms that drive amyotrophic lateral sclerosis (ALS) remain poorly understood. Structural variants within the genome can play a significant role in neurodegenerative disease risk, such as the repeat expansion in C9orf72 and the tri-nucleotide repeat in ATXN2, both of which are associated with familial and sporadic ALS. Many such structural variants reside in uncharacterized regions of the human genome, and have been under studied. Therefore, characterization of structural variants located in and around genes associated with ALS could provide insight into disease pathogenesis, and lead to the discovery of highly informative genetic tools for stratification in clinical trials. Such genomic variants may provide a deeper understanding of how gene expression can affect disease etiology, disease severity and trajectory, patient response to treatment, and may hold the key to understanding the genetics of sporadic ALS. This article outlines the current understanding of amyotrophic lateral sclerosis genetics and how structural variations may underpin some of the missing heritability of this disease.