UNC13A influences survival in Italian amyotrophic lateral sclerosis patients: a population-based study

Synaptopathy: presynaptic convergence in frontotemporal dementia and amyotrophic lateral sclerosis

Frontotemporal dementia and amyotrophic lateral sclerosis are common forms of neurodegenerative disease that share overlapping genetics and pathologies. Crucially, no significantly disease-modifying treatments are available for either disease. Identifying the earliest changes that initiate neuronal dysfunction is important for designing effective intervention therapeutics. The genes mutated in genetic forms of frontotemporal dementia and amyotrophic lateral sclerosis have diverse cellular functions, and multiple disease mechanisms have been proposed for both. Identification of a convergent disease mechanism in frontotemporal dementia and amyotrophic lateral sclerosis would focus research for a targetable pathway, which could potentially effectively treat all forms of frontotemporal dementia and amyotrophic lateral sclerosis (both familial and sporadic). Synaptopathies are diseases resulting from physiological dysfunction of synapses, and define the earliest stages in multiple neuronal diseases, with synapse loss a key feature in dementia. At the presynapse, the process of synaptic vesicle recruitment, fusion and recycling is necessary for activity-dependent neurotransmitter release. The unique distal location of the presynaptic terminal means the tight spatio-temporal control of presynaptic homeostasis is dependent on efficient local protein translation and degradation. Recently, numerous publications have shown that mutations associated with frontotemporal dementia and amyotrophic lateral sclerosis present with synaptopathy characterized by presynaptic dysfunction. This review will describe the complex local signalling and membrane trafficking events that occur at the presynapse to facilitate neurotransmission and will summarize recent publications linking frontotemporal dementia/amyotrophic lateral sclerosis genetic mutations to presynaptic function. This evidence indicates that presynaptic synaptopathy is an early and convergent event in frontotemporal dementia and amyotrophic lateral sclerosis and illustrates the need for further research in this area, to identify potential therapeutic targets with the ability to impact this convergent pathomechanism.

Rare and common genetic determinants of mitochondrial function determine severity but not risk of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease involving selective vulnerability of energy-intensive motor neurons (MNs). It has been unclear whether mitochondrial function is an upstream driver or a downstream modifier of neurotoxicity. We separated upstream genetic determinants of mitochondrial function, including genetic variation within the mitochondrial genome or autosomes; from downstream changeable factors including mitochondrial DNA copy number (mtCN). Across three cohorts including 6,437 ALS patients, we discovered that a set of mitochondrial haplotypes, chosen because they are linked to measurements of mitochondrial function, are a determinant of ALS survival following disease onset, but do not modify ALS risk. One particular haplotype appeared to be neuroprotective and was significantly over-represented in two cohorts of long-surviving ALS patients. Causal inference for mitochondrial function was achievable using mitochondrial haplotypes, but not autosomal SNPs in traditional Mendelian randomization (MR). Furthermore, rare loss-of-function genetic variants within, and reduced MN expression of, ACADM and DNA2 lead to ∼50 % shorter ALS survival; both proteins are implicated in mitochondrial function. Both mtCN and cellular vulnerability are linked to DNA2 function in ALS patient-derived neurons. Finally, MtCN responds dynamically to the onset of ALS independently of mitochondrial haplotype, and is correlated with disease severity. We conclude that, based on the genetic measures we have employed, mitochondrial function is a therapeutic target for amelioration of disease severity but not prevention of ALS.

Intermediate Repeat Expansion in the ATXN2 Gene as a Risk Factor in the ALS and FTD Spanish Population

Intermediate CAG expansions in the gene ataxin-2 (ATXN2) are a known risk factor for ALS, but little is known about their role in FTD risk. Moreover, their contribution to the risk and phenotype of patients might vary in populations with different genetic backgrounds. The aim of this study was to assess the relationship of intermediate CAG expansions in ATXN2 with the risk and phenotype of ALS and FTD in the Spanish population. Repeat-primed PCR was performed in 620 ALS and 137 FTD patients in three referral centers in Spain to determine the exact number of CAG repeats. In our cohort, ≥27 CAG repeats in ATXN2 were associated with a higher risk of developing ALS (odds ratio [OR] = 2.666 [1.471-4.882]; p = 0.0013) but not FTD (odds ratio [OR] = 1.446 [0.558-3.574]; p = 0.44). Moreover, ALS patients with ≥27 CAG repeats in ATXN2 showed a shorter survival rate compared to those with <27 repeats (hazard ratio [HR] 1.74 [1.18, 2.56], p = 0.005), more frequent limb onset (odds ratio [OR] = 2.34 [1.093-4.936]; p = 0.028) and a family history of ALS (odds ratio [OR] = 2.538 [1.375-4.634]; p = 0.002). Intermediate CAG expansions of ≥27 repeats in ATXN2 are associated with ALS risk but not with FTD in the Spanish population. ALS patients carrying an intermediate expansion in ATXN2 show more frequent limb onset but a worse prognosis than those without expansions. In patients carrying C9orf72 expansions, the intermediate ATXN2 expansion might increase the penetrance and modify the phenotype.

Disease survival and progression in TARDBP ALS patients from Sardinia, Italy

BACKGROUND

Common genes implicated in amyotrophic lateral sclerosis (ALS) development may also influence its progression rate. The C9orf72 mutations featured a faster progression rate while the European SOD1 mutations were associated with a slower progression. In this study, we assessed the relationship between TARDBP and ALS progression/survival.

METHODS

ALS incident patients (2010-2019) were diagnosed by El Escorial revised criteria and staged over the disease course by the King's staging system. Disease progression was analysed by Kaplan-Meier survival curves and Cox regression models, with survival measured from symptom onset to death/tracheostomy or censor date.

RESULTS

The study population included 76 patients carrying TARDBP mutations (A382T/G295S), 28 patients carrying the C9orf72 GGGGCC expansion, and 158 patients who had no evidence of causative genetic mutations (nmALS group). TARDBP patients reached death/tracheostomy later than C9orf72 and nmALS patients, independently of possible prognostic indicators (sex, age at ALS onset, diagnostic delay, phenotype at onset, and family history of ALS). On King's staging, the time elapsed between disease onset (King's stage 1) and involvement of the second body region (King's stage 2B) was similar in TARDBP and nmALS patients but longer in TARDBP than in C9orf72 patients. TARDBP patients reached King's stages 3 and 4 later than C9orf72 and nmALS patients.

CONCLUSIONS

TARDBP patients have a better survival/prognosis than C9orf72-positive and nmALS patients. King's staging also suggested that the higher survival rate and the slower progression associated with the TARDBP mutation could mainly be attributed to the longer time elapsed between King's stages 2B to 3.

Role of the UNC13 family in human diseases: A literature review

This literature review explores the pivotal roles of the Uncoordinated-13 (UNC13) protein family, encompassing UNC13A, UNC13B, UNC13C, and UNC13D, in the pathogenesis of various human diseases. These proteins, which are evolutionarily conserved and crucial for synaptic vesicle priming and exocytosis, have been implicated in a range of disorders, spanning from neurodegenerative diseases like amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) to immune-related conditions such as familial hemophagocytic lymphohistiocytosis (FHL). The involvement of UNC13A in neurotransmitter release and synaptic plasticity is linked to ALS and FTD, with genetic variations affecting disease progression. UNC13B, which is closely related to UNC13A, plays a role in autism spectrum disorders (ASD), epilepsy, and schizophrenia. UNC13C is implicated in oral squamous cell carcinoma (OSCC) and hepatocellular carcinoma (HCC), and has a neuroprotective role in Alzheimer's disease (AD). UNC13D has an essential role in immune cell function, making it a key player in FHL. This review highlights the distinct molecular functions of each UNC13 family member and their implications in disease contexts, shedding light on potential therapeutic strategies and avenues for future research. Understanding these proteins' roles offers new insights into the management and treatment of neurological and immunological disorders.

Genomic and transcriptomic advances in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disorder and the most common motor neuron disease. ALS shows substantial clinical and molecular heterogeneity. In vitro and in vivo models coupled with multiomic techniques have provided important contributions to unraveling the pathomechanisms underlying ALS. To date, despite promising results and accumulating knowledge, an effective treatment is still lacking. Here, we provide an overview of the literature on the use of genomics, epigenomics, transcriptomics and microRNAs to deeply investigate the molecular mechanisms developing and sustaining ALS. We report the most relevant genes implicated in ALS pathogenesis, discussing the use of different high-throughput sequencing techniques and the role of epigenomic modifications. Furthermore, we present transcriptomic studies discussing the most recent advances, from microarrays to bulk and single-cell RNA sequencing. Finally, we discuss the use of microRNAs as potential biomarkers and promising tools for molecular intervention. The integration of data from multiple omic approaches may provide new insights into pathogenic pathways in ALS by shedding light on diagnostic and prognostic biomarkers, helping to stratify patients into clinically relevant subgroups, revealing novel therapeutic targets and supporting the development of new effective therapies.

UNC13A in amyotrophic lateral sclerosis: from genetic association to therapeutic target

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with limited treatment options and an incompletely understood pathophysiology. Although genomewide association studies (GWAS) have advanced our understanding of the disease, the precise manner in which risk polymorphisms contribute to disease pathogenesis remains unclear. Of relevance, GWAS have shown that a polymorphism (rs12608932) in the UNC13A gene is associated with risk for both ALS and frontotemporal dementia (FTD). Homozygosity for the C-allele at rs12608932 modifies the ALS phenotype, as these patients are more likely to have bulbar-onset disease, cognitive impairment and FTD at baseline as well as shorter survival. UNC13A is expressed in neuronal tissue and is involved in maintaining synaptic active zones, by enabling the priming and docking of synaptic vesicles. In the absence of functional TDP-43, risk variants in UNC13A lead to the inclusion of a cryptic exon in UNC13A messenger RNA, subsequently leading to nonsense mediated decay, with loss of functional protein. Depletion of UNC13A leads to impaired neurotransmission. Recent discoveries have identified UNC13A as a potential target for therapy development in ALS, with a confirmatory trial with lithium carbonate in UNC13A cases now underway and future approaches with antisense oligonucleotides currently under consideration. Considering UNC13A is a potent phenotypic modifier, it may also impact clinical trial outcomes. This present review describes the path from the initial discovery of UNC13A as a risk gene in ALS to the current therapeutic options being explored and how knowledge of its distinct phenotype needs to be taken into account in future trials.

The era of cryptic exons: implications for ALS-FTD

TDP-43 is an RNA-binding protein with a crucial nuclear role in splicing, and mislocalises from the nucleus to the cytoplasm in a range of neurodegenerative disorders. TDP-43 proteinopathy spans a spectrum of incurable, heterogeneous, and increasingly prevalent neurodegenerative diseases, including the amyotrophic lateral sclerosis and frontotemporal dementia disease spectrum and a significant fraction of Alzheimer's disease. There are currently no directed disease-modifying therapies for TDP-43 proteinopathies, and no way to distinguish who is affected before death. It is now clear that TDP-43 proteinopathy leads to a number of molecular changes, including the de-repression and inclusion of cryptic exons. Importantly, some of these cryptic exons lead to the loss of crucial neuronal proteins and have been shown to be key pathogenic players in disease pathogenesis (e.g., STMN2), as well as being able to modify disease progression (e.g., UNC13A). Thus, these aberrant splicing events make promising novel therapeutic targets to restore functional gene expression. Moreover, presence of these cryptic exons is highly specific to patients and areas of the brain affected by TDP-43 proteinopathy, offering the potential to develop biomarkers for early detection and stratification of patients. In summary, the discovery of cryptic exons gives hope for novel diagnostics and therapeutics on the horizon for TDP-43 proteinopathies.

Association of the risk factor UNC13A with survival and upper motor neuron involvement in amyotrophic lateral sclerosis

Background

The UNC13A gene is an established susceptibility locus for amyotrophic lateral sclerosis (ALS) and a determinant of shorter survival after disease onset, with up to 33.0 months difference in life expectancy for carriers of the rs12608932 risk genotype. However, its overall effect on other clinical features and ALS phenotypic variability is controversial.

Methods

Genotype data of the UNC13A rs12608932 SNP (A-major allele; C-minor allele) was obtained from a cohort of 972 ALS patients. Demographic and clinical variables were collected, including cognitive and behavioral profiles, evaluated through the Edinburgh Cognitive and Behavioral ALS Screen (ECAS) - Italian version and the Frontal Behavioral Inventory (FBI); upper and lower motor neuron involvement, assessed by the Penn Upper Motor Neuron Score (PUMNS) and the Lower Motor Neuron Score (LMNS)/Medical Research Council (MRC) scores, respectively; the ALS Functional Rating Scale Revised (ALSFRS-R) score at evaluation and progression rate; age and site of onset; survival. The comparison between the three rs12608932 genotypes (AA, AC, and CC) was performed using the additive, dominant, and recessive genetic models.

Results

The rs12608932 minor allele frequency was 0.31 in our ALS cohort, in comparison to 0.33-0.41 reported in other Caucasian ALS populations. Carriers of at least one minor C allele (AC + CC genotypes) had a shorter median survival than patients with the wild-type AA genotype (-11.7 months, p = 0.013), even after adjusting for age and site of onset, C9orf72 mutational status and gender. Patients harboring at least one major A allele (AA + AC genotypes) and particularly those with the wild-type AA genotype showed a significantly higher PUMNS compared to CC carriers (p = 0.015 and p_adj = 0.037, respectively), thus indicating a more severe upper motor neuron involvement. Our analysis did not detect significant associations with all the other clinical parameters considered.

Conclusion

Overall, our findings confirm the role of UNC13A as a determinant of survival in ALS patients and show the association of this locus also with upper motor neuron involvement.

Advances in sequencing technologies for amyotrophic lateral sclerosis research

Amyotrophic lateral sclerosis (ALS) is caused by upper and lower motor neuron loss and has a fairly rapid disease progression, leading to fatality in an average of 2-5 years after symptom onset. Numerous genes have been implicated in this disease; however, many cases remain unexplained. Several technologies are being used to identify regions of interest and investigate candidate genes. Initial approaches to detect ALS genes include, among others, linkage analysis, Sanger sequencing, and genome-wide association studies. More recently, next-generation sequencing methods, such as whole-exome and whole-genome sequencing, have been introduced. While those methods have been particularly useful in discovering new ALS-linked genes, methodological advances are becoming increasingly important, especially given the complex genetics of ALS. Novel sequencing technologies, like long-read sequencing, are beginning to be used to uncover the contribution of repeat expansions and other types of structural variation, which may help explain missing heritability in ALS. In this review, we discuss how popular and/or upcoming methods are being used to discover ALS genes, highlighting emerging long-read sequencing platforms and their role in aiding our understanding of this challenging disease.

Atypical TDP-43 protein expression in an ALS pedigree carrying a p.Y374X truncation mutation in TARDBP

We describe an autosomal dominant, multi-generational, amyotrophic lateral sclerosis (ALS) pedigree in which disease co-segregates with a heterozygous p.Y374X nonsense mutation within TDP-43. Mislocalization of TDP-43 and formation of insoluble TDP-43-positive neuronal cytoplasmic inclusions is the hallmark pathology in >95% of ALS patients. Neuropathological examination of the single case for which CNS tissue was available indicated typical TDP-43 pathology within lower motor neurons, but classical TDP-43-positive inclusions were absent from motor cortex. The mutated allele is transcribed and translated in patient fibroblasts and motor cortex tissue, but overall TDP-43 protein expression is reduced compared to wild-type controls. Despite absence of TDP-43-positive inclusions we confirmed deficient TDP-43 splicing function within motor cortex tissue. Furthermore, urea fractionation and mass spectrometry of motor cortex tissue carrying the mutation revealed atypical TDP-43 protein species but not typical C-terminal fragments. We conclude that the p.Y374X mutation underpins a monogenic, fully penetrant form of ALS. Reduced expression of TDP-43 combined with atypical TDP-43 protein species and absent C-terminal fragments extends the molecular phenotypes associated with TDP-43 mutations and with ALS more broadly. Future work will need to include the findings from this pedigree in dissecting the mechanisms of TDP-43-mediated toxicity.

Clinical and Metabolic Signature of UNC13A rs12608932 Variant in Amyotrophic Lateral Sclerosis

Background and Objectives

To characterize the clinical and cognitive behavioral phenotype and brain ¹⁸F-2-fluoro-2-deoxy-d-glucose-PET (¹⁸F-FDG-PET) metabolism of patients with amyotrophic lateral sclerosis (ALS) carrying the rs12608932 variant of the UNC13A gene.

Methods

The study population included 1,409 patients with ALS without C9orf72, SOD1, TARDBP, and FUS mutations identified through a prospective epidemiologic ALS register. Control participants included 1,012 geographically matched, age-matched, and sex-matched participants. Clinical and cognitive differences between patients carrying the C/C rs12608932 genotype and those carrying the A/A + A/C genotype were assessed. A subset of patients underwent ¹⁸F-FDG-PET.

Results

The C/C genotype was associated with an increased risk of ALS (odds ratio: 1.54, 95% confidence interval 1.18–2.01, p = 0.001). Patients with the C/C genotype were older, had more frequent bulbar onset, and manifested a higher rate of weight loss. In addition, they showed significantly reduced performance in the letter fluency test, fluency domain of Edinburgh Cognitive and Behavioural ALS Screen (ECAS) and story-based empathy task (reflecting social cognition). Patients with the C/C genotype had a shorter survival (median survival time, C/C 2.25 years, interquartile range [IQR] 1.33–3.92; A/A + C/C: 2.90 years, IQR 1.74–5.41; p = 0.0001). In Cox multivariable analysis, C/C genotype resulted to be an independent prognostic factor. Finally, patients with a C/C genotype had a specific pattern of hypometabolism on brain ¹⁸F-FDG-PET extending to frontal and precentral areas of the right hemisphere.

Discussion

C/C rs12608932 genotype of UNC13A is associated with a specific motor and cognitive/behavioral phenotype, which reflects on ¹⁸F-FDG-PET findings. Our observations highlight the importance of adding the rs12608932 variant in UNC13A to the ALS genetic panel to refine the individual prognostic prediction and reduce heterogeneity in clinical trials.

Genetic factors for survival in amyotrophic lateral sclerosis: an integrated approach combining a systematic review, pairwise and network meta-analysis

BACKGROUND

The time of survival in patients with amyotrophic lateral sclerosis (ALS) varies greatly, and the genetic factors that contribute to the survival of ALS are not well studied. There is a lack of a comprehensive study to elucidate the role of genetic factors in the survival of ALS.

METHODS

The published studies were systematically searched and obtained from PubMed, EMBASE, and the Cochrane Library without any language restrictions from inception to Oct 27, 2021. A network meta-analysis for ALS causative/risk genes and a systematic review and pairwise meta-analysis for other genetic modifiers were conducted. The PROSPERO registration number: CRD42022311646.

RESULTS

A total of 29,764 potentially relevant references were identified, and 71 papers were eligible for analysis based on pre-decided criteria, including 35 articles in network meta-analysis for 9 ALS causative/risk genes, 17 articles in pairwise meta-analysis for four genetic modifiers, and 19 articles described in the systematic review. Variants in three genes, including ATXN2 (HR: 3.6), C9orf72 (HR: 1.6), and FUS (HR:1.8), were associated with short survival of ALS, but such association was not identified in SOD1, TARDBP, TBK1, NEK1, UBQLN2, and CCNF. In addition, UNC13A rs12608932 CC genotype and ZNF521B rs2275294 C allele also caused a shorter survival of ALS; however, APOE ε4 allele and KIFAP3 rs1541160 did not be found to have any effect on the survival of ALS.

CONCLUSIONS

Our study summarized and contrasted evidence for prognostic genetic factors in ALS and would help to understand ALS pathogenesis and guide clinical trials and drug development.

TDP-43 represses cryptic exon inclusion in the FTD-ALS gene UNC13A

A hallmark pathological feature of the neurodegenerative diseases amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) is the depletion of RNA-binding protein TDP-43 from the nucleus of neurons in the brain and spinal cord1. A major function of TDP-43 is as a repressor of cryptic exon inclusion during RNA splicing2-4. Single nucleotide polymorphisms in UNC13A are among the strongest hits associated with FTD and ALS in human genome-wide association studies5,6, but how those variants increase risk for disease is unknown. Here we show that TDP-43 represses a cryptic exon-splicing event in UNC13A. Loss of TDP-43 from the nucleus in human brain, neuronal cell lines and motor neurons derived from induced pluripotent stem cells resulted in the inclusion of a cryptic exon in UNC13A mRNA and reduced UNC13A protein expression. The top variants associated with FTD or ALS risk in humans are located in the intron harbouring the cryptic exon, and we show that they increase UNC13A cryptic exon splicing in the face of TDP-43 dysfunction. Together, our data provide a direct functional link between one of the strongest genetic risk factors for FTD and ALS (UNC13A genetic variants), and loss of TDP-43 function.

Advances in the genetic classification of amyotrophic lateral sclerosis

PURPOSE OF REVIEW

Amyotrophic lateral sclerosis (ALS) is an archetypal complex disease wherein disease risk and severity are, for the majority of patients, the product of interaction between multiple genetic and environmental factors. We are in a period of unprecedented discovery with new large-scale genome-wide association study (GWAS) and accelerating discovery of risk genes. However, much of the observed heritability of ALS is undiscovered and we are not yet approaching elucidation of the total genetic architecture, which will be necessary for comprehensive disease subclassification.

RECENT FINDINGS

We summarize recent developments and discuss the future. New machine learning models will help to address nonlinear genetic interactions. Statistical power for genetic discovery may be boosted by reducing the search-space using cell-specific epigenetic profiles and expanding our scope to include genetically correlated phenotypes. Structural variation, somatic heterogeneity and consideration of environmental modifiers represent significant challenges which will require integration of multiple technologies and a multidisciplinary approach, including clinicians, geneticists and pathologists.

SUMMARY

The move away from fully penetrant Mendelian risk genes necessitates new experimental designs and new standards for validation. The challenges are significant, but the potential reward for successful disease subclassification is large-scale and effective personalized medicine.

Different gene expression profiles in iPSC-derived motor neurons from ALS8 patients with variable clinical courses suggest mitigating pathways for neurodegeneration

Amyotrophic lateral sclerosis type 8 (ALS8) is an autosomal dominant form of ALS, which is caused by pathogenic variants in the VAPB gene. Here we investigated five ALS8 patients, classified as 'severe' and 'mild' from a gigantic Brazilian kindred, carrying the same VAPB mutation but displaying different clinical courses. Copy number variation and whole exome sequencing analyses in such individuals ruled out previously described genetic modifiers of pathogenicity. After deriving induced pluripotent stem cells (iPSCs) for each patient (N = 5) and controls (N = 3), motor neurons were differentiated, and high-throughput RNA-Seq gene expression measurements were performed. Functional cell death and oxidative metabolism assays were also carried out in patients' iPSC-derived motor neurons. The degree of cell death and mitochondrial oxidative metabolism were similar in iPSC-derived motor neurons from mild patients and controls and were distinct from those of severe patients. Similar findings were obtained when RNA-Seq from such cells was performed. Overall, 43 genes were upregulated and 66 downregulated in the two mild ALS8 patients when compared with severe ALS8 individuals and controls. Interestingly, significantly enriched pathways found among differentially expressed genes, such as protein translation and protein targeting to the endoplasmic reticulum (ER), are known to be associated with neurodegenerative processes. Taken together, the mitigating mechanisms here presented appear to maintain motor neuron survival by keeping translational activity and protein targeting to the ER in such cells. As ALS8 physiopathology has been associated with proteostasis mechanisms in ER-mitochondria contact sites, such differentially expressed genes appear to relate to the bypass of VAPB deficiency.

Genetic and Transcriptomic Biomarkers in Neurodegenerative Diseases: Current Situation and the Road Ahead

Neurodegenerative diseases are etiologically and clinically heterogeneous conditions, often reflecting a spectrum of disease rather than well-defined disorders. The underlying molecular complexity of these diseases has made the discovery and validation of useful biomarkers challenging. The search of characteristic genetic and transcriptomic indicators for preclinical disease diagnosis, prognosis, or subtyping is an area of ongoing effort and interest. The next generation of biomarker studies holds promise by implementing meaningful longitudinal and multi-modal approaches in large scale biobank and healthcare system scale datasets. This work will only be possible in an open science framework. This review summarizes the current state of genetic and transcriptomic biomarkers in Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis, providing a comprehensive landscape of recent literature and future directions.

The Distinct Traits of the UNC13A Polymorphism in Amyotrophic Lateral Sclerosis

Objective

The rs12608932 single nucleotide polymorphism in UNC13A is associated with amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) susceptibility, and may underlie differences in treatment response. We aimed to characterize the clinical, cognitive, behavioral, and neuroimaging phenotype of UNC13A in patients with ALS.

Methods

We included 2,216 patients with ALS without a C9orf72 mutation to identify clinical characteristics associated with the UNC13A polymorphism. A subcohort of 428 patients with ALS was used to study cognitive and behavioral profiles, and 375 patients to study neuroimaging characteristics. Associations were analyzed under an additive genetic model.

Results

Genotyping rs12608932 resulted in 854 A/A, 988 A/C, and 374 C/C genotypes. The C allele was associated with a higher age at symptom onset (median years A/A 63.5, A/C 65.6, and C/C 65.5; p < 0.001), more frequent bulbar onset (A/A 29.6%, A/C 31.8%, and C/C 43.1%; p < 0.001), higher incidences of ALS‐FTD (A/A 4.3%, A/C 5.2%, and C/C 9.5%; p = 0.003), lower forced vital capacity at diagnosis (median percentage A/A 92.0, A/C 90.0, and C/C 86.5; p < 0.001), and a shorter survival (median in months A/A 33.3, A.C 30.7, and C/C 26.6; p < 0.001). UNC13A was associated with lower scores on ALS‐specific cognition tests (means A/A 79.5, A/C 78.1, and C/C 76.6; p = 0.037), and more frequent behavioral disturbances (A/A 16.7%, A/C 24.4%, and C/C 27.7%; p = 0.045). Thinner left inferior temporal and right fusiform cortex were associated with the UNC13A single nucleotide polymorphism (SNP; p = 0.045 and p = 0.036).

Interpretation

Phenotypical distinctions associated with UNC13A make it an important factor to take into account in clinical trial design, studies on cognition and behavior, and prognostic counseling. ANN NEUROL 2020;88:796–806

Progression and survival of patients with motor neuron disease relative to their fecal microbiota

Gut microbiota studies have been well-investigated for neurodegenerative diseases such as Alzheimer's and Parkinson's disease, however, fewer studies have comprehensively examined the gut microbiome in Motor Neuron Disease (MND), with none examining its impact on disease prognosis. Here, we investigate MND prognosis and the fecal microbiota, using 16S rRNA case-control data from 100 individuals with extensive medical histories and metabolic measurements. We contrast the composition and diversity of fecal microbiome signatures from 49 MND and 51 healthy controls by combining current gold-standard 16S microbiome pipelines. Using stringent quality control thresholds, we conducted qualitative assessment approaches including; direct comparison of taxa, PICRUSt2 predicted metagenomics, Shannon and Chao1-index and Firmicutes/Bacteroidetes ratio. We show that the fecal microbiome of patients with MND is not significantly different from that of healthy controls that were matched by age, sex, and BMI, however there are distinct differences in Beta-diversity in some patients with MND. Weight, BMI, and metabolic and clinical features of disease in patients with MND were not related to the composition of their fecal microbiome, however, we observe a greater risk for earlier death in patients with MND with increased richness and diversity of the microbiome, and in those with greater Firmicutes to Bacteroidetes ratio. This was independent of anthropometric, metabolic, or clinical features of disease, and warrants support for further gut microbiota studies in MND. Given the disease heterogeneity in MND, and complexity of the gut microbiota, large studies are necessary to determine the detailed role of the gut microbiota and MND prognosis.

Amyotrophic Lateral Sclerosis: Current Status in Diagnostic Biomarkers

Amyotrophic lateral sclerosis (ALS) is a rare, neurodegenerative disease that affects the human motor system. ALS is a highly heterogeneous disease, depending on several causative factors. The heterogeneity of the disease is also reflected in the variation of the symptoms in ALS patients. The worldwide annual incidence of ALS is about 2.08 per 100,000 with uniform rates in Caucasian populations and lower rates in African, Asian, and Hispanic populations, while the number of individuals with ALS is expected to grow significantly between 2015 and 2040 with an estimated increase of 69% (Chio et al. 2013a; Arthur et al. 2016).

UNC13A variant rs12608932 is associated with increased risk of amyotrophic lateral sclerosis and reduced patient survival: a meta-analysis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease associated with both genetic and environmental risk factors. Previous studies trying to find an association between ALS and unc-13 homolog A (UNC13A) gene variants have shown inconsistent results. This study aimed to conduct a meta-analysis of the association between the C allele of rs12608932, a single-nucleotide polymorphism located in an intron of UNC13A, and risk of ALS and patient survival.

METHODS

PubMed, Web of Science, Embase, Chinese National Knowledge Infrastructure, Wanfang, and SinoMed databases were systematically searched for genome-wide association studies or case-control studies published up to January 2019 on the association between this variant in UNC13A and risk and/or prognosis of ALS. Data from eligible studies were extracted and analyzed.

RESULTS

The pooled data (28,072 patients with sporadic ALS and 56,545 controls) showed that rs12608932(C) was associated with an increased risk of ALS (OR = 1.13, 95%CI 1.07-1.20). Subgroup analysis revealed that rs12608932(C) increased the risk of sporadic ALS in non-Asian individuals, including those from the USA and Europe (OR 1.17, 95%CI 1.10-1.25, P < 0.000), but not in Japanese or Chinese subjects (OR 1.01, 95%CI 0.92-1.10, P = 0.85). The available data demonstrated that the CC genotype decreased the survival time of patients with ALS (OR 1.33, 95%CI 1.19-1.49, P < 0.001).

CONCLUSION

The present meta-analysis suggests that rs12608932(C) is associated with increased ALS susceptibility, especially in Caucasian and European subjects, and that the CC genotype of rs12608932 is associated with reduced ALS patient survival.

Combined Tissue-Fluid Proteomics to Unravel Phenotypic Variability in Amyotrophic Lateral Sclerosis

The lack of biomarkers for early diagnosis, clinical stratification and to monitor treatment response has hampered the development of new therapies for amyotrophic lateral sclerosis (ALS), a clinically heterogeneous neurodegenerative disorder with a variable site of disease initiation and rate of progression. To identify new biomarkers and therapeutic targets, two separate proteomic workflows were applied to study the immunological response and the plasma/brain proteome in phenotypic variants of ALS. Conventional multiplex (TMT) proteomic analysis of peripheral blood mononuclear cells (PBMCs) was performed alongside a recently introduced method to profile neuronal-derived proteins in plasma using brain tissue-enhanced isobaric tagging (TMTcalibrator). The combined proteomic analysis allowed the detection of regulated proteins linked to ALS pathogenesis (RNA-binding protein FUS, superoxide dismutase Cu-Zn and neurofilaments light polypeptide) alongside newly identified candidate biomarkers (myosin-9, fructose-bisphosphate aldolase and plectin). In line with the proteomic results, orthogonal immunodetection showed changes in neurofilaments and ApoE in bulbar versus limb onset fast progressing ALS. Functional analysis of significantly regulated features showed enrichment of pathways involved in regulation of the immune response, Rho family GTPases, semaphorin and integrin signalling. Our cross-phenotype investigation of PBMCs and plasma/brain proteins provides a more sensitive biomarker exploratory platform than conventional case-control studies in a single matrix. The reported regulated proteins may represent novel biomarker candidates and potentially druggable targets.

UNC13A polymorphism contributes to frontotemporal disease in sporadic amyotrophic lateral sclerosis

The majority (90%-95%) of amyotrophic lateral sclerosis (ALS) is sporadic, and ∼50% of patients develop symptoms of frontotemporal degeneration (FTD) associated with shorter survival. The genetic polymorphism rs12608932 in UNC13A confers increased risk of sporadic ALS and sporadic FTD and modifies survival in ALS. Here, we evaluate whether rs12608932 is also associated with frontotemporal disease in sporadic ALS. We identified reduced cortical thickness in sporadic ALS with T1-weighted magnetic resonance imaging (N = 109) relative to controls (N = 113), and observed that minor allele (C) carriers exhibited greater reduction of cortical thickness in the dorsal prefrontal, ventromedial prefrontal, anterior temporal, and middle temporal cortices and worse performance on a frontal lobe-mediated cognitive test (reverse digit span). In sporadic ALS with autopsy data (N = 102), minor allele homozygotes exhibited greater burden of phosphorylated tar DNA-binding protein-43 kda (TDP-43) pathology in the middle frontal, middle temporal, and motor cortices. Our findings demonstrate converging evidence that rs12608932 may modify frontotemporal disease in sporadic ALS and suggest that rs12608932 may function as a prognostic indicator and could be used to define patient endophenotypes in clinical trials.

The clinical assessment of amyotrophic lateral sclerosis patients' prognosis by ZNF512B gene, neck flexor muscle power score and body mass index (BMI)

BACKGROUND

Assessment on the prognosis of amyotrophic lateral sclerosis (ALS) is becoming a focus of research in recent years since there is no effective treatment. The aim of the research is to explore the major factors involving in prognosis of ALS patients through long-term follow-up.

METHODS

ALS patients' DNA extracted from peripheral blood white cells were detected for the risk allele by single nucleotide polymorphism (SNP) analysis. Neck flexor muscle score and body mass index (BMI) were recorded during Medical Research Council follow-up using manual muscle testing method.

RESULTS

ALS patients with risk alleles (C) deteriorated rapidly with poor clinical outcome. It seemed that the higher neck flexor muscle strength score in ALS patients with the longer survival time but without significant correlation (p > 0.05). The lower the basal body mass index, the shorter the survival time and the faster deterioration (p < 0.05). The patients with body mass index less than 22.04 seemed to have short survival time than those with BMI more than 22.04 (p < 0.05), however, the speed of deterioration in two groups of patients had no significant difference (p > 0.05).

CONCLUSION

The risk (C) allele of the SNP (rs2275294) in the ZNF512B gene, cervical flexor muscle power and body weight index might have clinical potential for ALS prognostication, since these indicators is so simple to perform that they might be very suitable for primary clinics and even community medical institutions to carry out.

Genetics of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating, uniformly lethal degenerative disorder of motor neurons that overlaps clinically with frontotemporal dementia (FTD). Investigations of the 10% of ALS cases that are transmitted as dominant traits have revealed numerous gene mutations and variants that either cause these disorders or influence their clinical phenotype. The evolving understanding of the genetic architecture of ALS has illuminated broad themes in the molecular pathophysiology of both familial and sporadic ALS and FTD. These central themes encompass disturbances of protein homeostasis, alterations in the biology of RNA binding proteins, and defects in cytoskeletal dynamics, as well as numerous downstream pathophysiological events. Together, these findings from ALS genetics provide new insight into therapies that target genetically distinct subsets of ALS and FTD.

Meta-analysis of pharmacogenetic interactions in amyotrophic lateral sclerosis clinical trials

OBJECTIVE

To assess whether genetic subgroups in recent amyotrophic lateral sclerosis (ALS) trials responded to treatment with lithium carbonate, but that the treatment effect was lost in a large cohort of nonresponders.

METHODS

Individual participant data were obtained from 3 randomized trials investigating the efficacy of lithium carbonate. We matched clinical data with data regarding the UNC13A and C9orf72 genotype. Our primary outcome was survival at 12 months. On an exploratory basis, we assessed whether the effect of lithium depended on the genotype.

RESULTS

Clinical data were available for 518 of the 606 participants. Overall, treatment with lithium carbonate did not improve 12-month survival (hazard ratio [HR] 1.0, 95% confidence interval [CI] 0.7-1.4; p = 0.96). Both the UNC13A and C9orf72 genotype were independent predictors of survival (HR 2.4, 95% CI 1.3-4.3; p = 0.006 and HR 2.5, 95% CI 1.1-5.2; p = 0.032, respectively). The effect of lithium was different for UNC13A carriers (p = 0.027), but not for C9orf72 carriers (p = 0.22). The 12-month survival probability for UNC13A carriers treated with lithium carbonate improved from 40.1% (95% CI 23.2-69.1) to 69.7% (95% CI 50.4-96.3).

CONCLUSIONS

This study incorporated genetic data into past ALS trials to determine treatment effects in a genetic post hoc analysis. Our results suggest that we should reorient our strategies toward finding treatments for ALS, start focusing on genotype-targeted treatments, and standardize genotyping in order to optimize randomization and analysis for future clinical trials.

Lack of association between the P413L variant of chromogranin B and ALS risk or age at onset: a meta-analysis

BACKGROUND

Amyotrophic lateral sclerosis (ALS), the most common motor neuron disease, is thought to result from interaction of genetic and environmental risk factors. Whether the potentially functional exonic P413L variant in the chromogranin B gene influences ALS risk and age at onset is controversial.

METHOD

We meta-analysed or other studies assessing the association between the P413L variant and ALS risk or age at ALS onset indexed in Web of Science, PubMed, Embase, Chinese National Knowledge Infrastructure, Wanfang, and SinoMed databases.

RESULTS

Five case-control studies were analysed, involving 2639 patients with sporadic ALS, 201 with familial ALS and 3381 controls. No association was detected between risk of either ALS type and the CT + TT genotype or T-allele of the P413L variant. Age at ALS onset was similar between carriers and non-carriers of the T-allele.

CONCLUSION

The available evidence suggests that the P413L variant of chromogranin B is not associated with ALS risk or age at ALS onset. These results should be validated in large, well-designed studies.

Common polymorphisms of chemokine (C-X3-C motif) receptor 1 gene modify amyotrophic lateral sclerosis outcome: A population-based study

INTRODUCTION

In the brain, the chemokine (C-X3-C motif) receptor 1 (1CX3CR1) gene is expressed only by microglia, where it acts as a key mediator of the neuron-microglia interactions. We assessed whether the 2 common polymorphisms of the CX3CR1 gene (V249I and T280M) modify amyotrophic lateral sclerosis (ALS) phenotype.

METHODS

The study included 755 ALS patients diagnosed in Piemonte between 2007 and 2012 and 369 age-matched and sex-matched controls, all genotyped with the same chips.

RESULTS

Neither of the variants was associated with an increased risk of ALS. Patients with the V249I V/V genotype had a 6-month-shorter survival than those with I/I or V/I genotypes (dominant model, P = 0.018). The T280M genotype showed a significant difference among the 3 genotypes (additive model, P = 0.036). Cox multivariable analysis confirmed these findings.

DISCUSSION

We found that common variants of the CX3CR1 gene influence ALS survival. Our data provide further evidence for the role of neuroinflammation in ALS. Muscle Nerve 57: 212-216, 2018.

Rare genetic variation in UNC13A may modify survival in amyotrophic lateral sclerosis

Our objective was to identify whether rare genetic variation in amyotrophic lateral sclerosis (ALS) candidate survival genes modifies ALS survival. Candidate genes were selected based on evidence for modifying ALS survival. Each tail of the extreme 1.5% of survival was selected from the UK MND DNA Bank and all samples available underwent whole genome sequencing. A replication set from the Netherlands was used for validation. Sequences of candidate survival genes were extracted and variants passing quality control with a minor allele frequency ≤0.05 were selected for association testing. Analysis was by burden testing using SKAT. Candidate survival genes UNC13A, KIFAP3, and EPHA4 were tested for association in a UK sample comprising 25 short survivors and 25 long survivors. Results showed that only SNVs in UNC13A were associated with survival (p = 6.57 × 10-3). SNV rs10419420:G > A was found exclusively in long survivors (3/25) and rs4808092:G > A exclusively in short survivors (4/25). These findings were not replicated in a Dutch sample. In conclusion, population specific rare variants of UNC13A may modulate survival in ALS.

Further development of biomarkers in amyotrophic lateral sclerosis

INTRODUCTION

Amyotrophic lateral sclerosis (ALS) is an idiopathic neurodegenerative disease usually fatal in less than three years. Even if standard guidelines are available to diagnose ALS, the mean diagnosis delay is more than one year. In this context, biomarker discovery is a priority. Research has to focus on new diagnostic tools, based on combined explorations.

AREAS COVERED

In this review, we specifically focus on biology and imaging markers. We detail the innovative field of 'omics' approach and imaging and explain their limits to be useful in routine practice. We describe the most relevant biomarkers and suggest some perspectives for biomarker research. Expert commentary: The successive failures of clinical trials in ALS underline the need for new strategy based on innovative tools to stratify patients and to evaluate their responses to treatment. Biomarker data may be useful to improve the designs of clinical trials. Biomarkers are also needed to better investigate disease pathophysiology, to identify new therapeutic targets, and to improve the performance of clinical assessments for diagnosis and prognosis in the clinical setting. A consensus on the best management of neuroimaging and 'omics' methods is necessary and a systematic independent validation of findings may add robustness to future studies.

Recent advances in amyotrophic lateral sclerosis

ALS is a relentlessly progressive and fatal disease, with no curative therapies available to date. Symptomatic and palliative care, provided in a multidisciplinary context, still remains the cornerstone of ALS management. However, our understanding of the molecular mechanisms underlying the disease has advanced greatly over the past years, giving new hope for the development of novel diagnostic and therapeutic approaches. Here, we have reviewed the most recent studies that have contributed to improving both clinical management and our understanding of ALS pathogenesis.

Toward precision medicine in amyotrophic lateral sclerosis

Precision medicine is an innovative approach that uses emerging biomedical technologies to deliver optimally targeted and timed interventions, customized to the molecular drivers of an individual's disease. This approach is only just beginning to be considered for treating amyotrophic lateral sclerosis (ALS). The clinical and biological complexities of ALS have hindered development of effective therapeutic strategies. In this review we consider applying the key elements of precision medicine to ALS: phenotypic classification, comprehensive risk assessment, presymptomatic period detection, potential molecular pathways, disease model development, biomarker discovery and molecularly tailored interventions. Together, these would embody a precision medicine approach, which may provide strategies for optimal targeting and timing of efforts to prevent, stop or slow progression of ALS.

Large-scale screening in sporadic amyotrophic lateral sclerosis identifies genetic modifiers in C9orf72 repeat carriers

Sporadic amyotrophic lateral sclerosis (ALS) is considered to be a complex disease with multiple genetic risk factors contributing to the pathogenesis. Identification of genetic risk factors that co-occur frequently could provide relevant insight into underlying mechanisms of motor neuron degeneration. To dissect the genetic architecture of sporadic ALS, we undertook a large sequencing study in 755 apparently sporadic ALS cases and 959 controls, analyzing 10 ALS genes: SOD1, C9orf72, TARDBP, FUS, ANG, CHMP2B, ATXN2, NIPA1, SMN1, and UNC13A. We observed sporadic cases with multiple genetic risk variants in 4.1% compared with 1.3% in controls. The overall difference was not in excess of what is to be expected by chance (binomial test, p = 0.59). We did, however, observe a higher frequency than expected of C9orf72 repeat carriers with co-occurring susceptibility variants (ATXN2, NIPA1, and SMN1; p = 0.001), which is mainly because of the co-occurrence of NIPA1 repeats in 15% of C9orf72 repeat carriers (p = 0.006).

Familial Amyotrophic Lateral Sclerosis

Genes linked to amyotrophic lateral sclerosis (ALS) susceptibility are being identified at an increasing rate owing to advances in molecular genetic technology. Genetic mechanisms in ALS pathogenesis seem to exert major effects in about 10% of patients, but genetic factors at some level may be important components of disease risk in most patients with ALS. Identification of gene variants associated with ALS has informed concepts of the pathogenesis of ALS, aided the identification of therapeutic targets, facilitated research to develop new ALS biomarkers, and supported the establishment of clinical diagnostic tests for ALS-linked genes.

UNC13A confers risk for sporadic ALS and influences survival in a Spanish cohort

To investigate the association of functional variants of the human UNC13A gene with the risk of ALS, survival and the disease progression rate in a Spanish ALS cohort. 136 sporadic ALS (sALS) patients and 487 healthy controls were genotyped for the UNC13A rs12608932 variant. Clinical characterization of ALS patients included gender, age at first symptom, initial topography, disease progression rate, and survival. Genetic association was analyzed under five inheritance models. The sALS patients with the rs12608932(CC) genotype had an increased risk of ALS under a recessive genetic model [OR 2.16; 95 % CI (1.23, 3.8), p = 0.009; corrected p = 0.028]. Genotypes with a C allele are also associated with increased risk [OR 1.47; 95 % CI (1.11, 1.95); p = 0.008; corrected p = 0.023] under an additive model. sALS patients with a C/C genotype had a shorter survival than patients with A/A and A/C genotypes [HR 1.44; 95 % CI (1.11, 1.873); p = 0.007] under a recessive model. In an overdominant model, heterozygous patients had a longer survival than homozygous patients [HR 0.36; 95 % CI (0.22, 0.59); p = 0.001]. The rs12608932 genotypes modify the progression of symptoms measured using the ALSFRS-R. No association with age of onset, initial topography or rate of decline in FVC was found. Our results show that rs12608932 is a risk factor for ALS in the Spanish population and replicate the findings described in other populations. The rs12608932 is a modifying factor for survival and disease progression rate in our series. Our results also corroborated that it did not influence the age of onset.

HFE p.H63D polymorphism does not influence ALS phenotype and survival

It has been recently reported that the p.His63Asp polymorphism of the HFE gene accelerates disease progression both in the SOD1 transgenic mouse and in amyotrophic lateral sclerosis (ALS) patients. We have evaluated the effect of HFE p.His63Asp polymorphism on the phenotype in 1351 Italian ALS patients (232 of Sardinian ancestry). Patients were genotyped for the HFE p.His63Asp polymorphism (CC, GC, and GG). All patients were also assessed for C9ORF72, TARDBP, SOD1, and FUS mutations. Of the 1351 ALS patients, 363 (29.2%) were heterozygous (GC) for the p.His63Asp polymorphism and 30 (2.2%) were homozygous for the minor allele (GG). Patients with CC, GC, and GG polymorphisms did not significantly differ by age at onset, site of onset of symptoms, and survival; however, in SOD1 patients with CG or GG polymorphism had a significantly longer survival than those with a CC polymorphism. Differently from what observed in the mouse model of ALS, the HFE p.His63Asp polymorphism has no effect on ALS phenotype in this large series of Italian ALS patients.

Genetic causes of amyotrophic lateral sclerosis: new genetic analysis methodologies entailing new opportunities and challenges

The genetic architecture of amyotrophic lateral sclerosis (ALS) is being increasingly understood. In this far-reaching review, we examine what is currently known about ALS genetics and how these genes were initially identified. We also discuss the various types of mutations that might underlie this fatal neurodegenerative condition and outline some of the strategies that might be useful in untangling them. These include expansions of short repeat sequences, common and low-frequency genetic variations, de novo mutations, epigenetic changes, somatic mutations, epistasis, oligogenic and polygenic hypotheses. This article is part of a Special Issue entitled ALS complex pathogenesis.

Use of biomarkers in ALS drug development and clinical trials

The past decade has seen a dramatic increase in the discovery of candidate biomarkers for ALS. These biomarkers typically can either differentiate ALS from control subjects or predict disease course (slow versus fast progression). At the same time, late-stage clinical trials for ALS have failed to generate improved drug treatments for ALS patients. Incorporation of biomarkers into the ALS drug development pipeline and the use of biologic and/or imaging biomarkers in early- and late-stage ALS clinical trials have been absent and only recently pursued in early-phase clinical trials. Further clinical research studies are needed to validate biomarkers for disease progression and develop biomarkers that can help determine that a drug has reached its target within the central nervous system. In this review we summarize recent progress in biomarkers across ALS model systems and patient population, and highlight continued research directions for biomarkers that stratify the patient population to enrich for patients that may best respond to a drug candidate, monitor disease progression and track drug responses in clinical trials. It is crucial that we further develop and validate ALS biomarkers and incorporate these biomarkers into the ALS drug development process. This article is part of a Special Issue entitled ALS complex pathogenesis.

Genome-wide association studies in neurology

Genome-wide association studies (GWAS) are a powerful tool for understanding the genetic underpinnings of human disease. In this article, we briefly review the role and findings of GWAS in common neurological diseases, including Stroke, Alzheimer's disease, Parkinson's disease, epilepsy, multiple sclerosis, migraine, amyotrophic lateral sclerosis, frontotemporal lobar degeneration, restless legs syndrome, intracranial aneurysm, human prion diseases and moyamoya disease. We then discuss the present and future implications of these findings with regards to disease prediction, uncovering basic biology, and the development of potential therapeutic agents.

C9orf72 and UNC13A are shared risk loci for amyotrophic lateral sclerosis and frontotemporal dementia: a genome-wide meta-analysis

OBJECTIVE

Substantial clinical, pathological, and genetic overlap exists between amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). TDP-43 inclusions have been found in both ALS and FTD cases (FTD-TDP). Recently, a repeat expansion in C9orf72 was identified as the causal variant in a proportion of ALS and FTD cases. We sought to identify additional evidence for a common genetic basis for the spectrum of ALS-FTD.

METHODS

We used published genome-wide association studies data for 4,377 ALS patients and 13,017 controls, and 435 pathology-proven FTD-TDP cases and 1,414 controls for genotype imputation. Data were analyzed in a joint meta-analysis, by replicating topmost associated hits of one disease in the other, and by using a conservative rank products analysis, allocating equal weight to ALS and FTD-TDP sample sizes.

RESULTS

Meta-analysis identified 19 genome-wide significant single nucleotide polymorphisms (SNPs) in C9orf72 on chromosome 9p21.2 (lowest p = 2.6 × 10(-12) ) and 1 SNP in UNC13A on chromosome 19p13.11 (p = 1.0 × 10(-11) ) as shared susceptibility loci for ALS and FTD-TDP. Conditioning on the 9p21.2 genotype increased statistical significance at UNC13A. A third signal, on chromosome 8q24.13 at the SPG8 locus coding for strumpellin (p = 3.91 × 10(-7) ) was replicated in an independent cohort of 4,056 ALS patients and 3,958 controls (p = 0.026; combined analysis p = 1.01 × 10(-7) ).

INTERPRETATION

We identified common genetic variants in C9orf72, but in addition in UNC13A that are shared between ALS and FTD. UNC13A provides a novel link between ALS and FTD-TDP, and identifies changes in neurotransmitter release and synaptic function as a converging mechanism in the pathogenesis of ALS and FTD-TDP.

Clinical neurogenetics: amyotrophic lateral sclerosis

Our understanding of amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease, is expanding rapidly as its genetic causes are uncovered. The pace of new gene discovery over the last 5 years has accelerated, providing new insights into the pathogenesis of disease and highlighting biological pathways as targets for therapeutic development. This article reviews our current understanding of the heritability of ALS and provides an overview of each of the major ALS genes, highlighting their phenotypic characteristics and frequencies as a guide for clinicians evaluating patients with ALS.