Screening for OPTN mutations in a cohort of British amyotrophic lateral sclerosis patients

Familial normal tension glaucoma genetics

Glaucoma is defined by characteristic optic nerve damage and corresponding visual field defects and is the leading cause of irreversible blindness in the world. Elevated intraocular pressure (IOP) is a strong risk factor for developing glaucoma. However, glaucoma can occur at any IOP. Normal tension glaucoma (NTG) arises with IOPs that are within what has been defined as a normal range, i.e., 21 mm Hg or less, which may present challenges in its diagnosis and management. Identifying inheritance patterns and genetic mutations in families with NTG has helped elucidate mechanisms of NTG, however the pathophysiology is complex and not fully understood. Approximately 2% of NTG cases are caused primarily by mutations in single genes, optineurin (OPTN), TANK binding kinase 1 (TKB1), or myocilin (MYOC). Herein, we review pedigree studies of NTG and autosomal dominant NTG caused by OPTN, TBK1, and MYOC mutations. We review identified mutations and resulting clinical features of OPTN-associated and TBK1-associated NTG, including long-term follow up of these patients with NTG. In addition, we report a new four-generation pedigree of NTG caused by a Glu50Lys OPTN mutation, including six family members with a mean follow up of 17 years. Common features of OPTN -associated NTG due to Glu50Lys mutation included early onset of disease with an IOP <21 mm Hg, marked optic disc cupping, and progressive visual field loss which appeared to stabilize once an IOP of less than 10 mm Hg was achieved. Lastly, we review risk factor genes which have been identified to contribute to the complex inheritance of NTG.

Four novel optineurin mutations in patients with sporadic amyotrophic lateral sclerosis in Mainland China

This study was to investigate the genetic contribution of optineurin (OPTN), a gene associated with primary open-angle glaucoma and amyotrophic lateral sclerosis (ALS), in Chinese patients with ALS. To gain additional insight into the spectrum and pathogenic relevance of this gene for ALS, we sequenced all the coding exons of OPTN and intron-exon boundaries in 398 patients with ALS [33 familial ALS (FALS), 365 unrelated sporadic ALS (SALS)] using next-generation sequencing. Six nonsynonymous variants were identified in 6 unrelated patients with SALS, in which one patient harbored 2 different OPTN variants and another carried an SETX mutation at the same time. Among those 6 variants, 4 were novel missense mutations: c.247C>T (p.R83C), c.676T>C (p.F226L), c.1699A>G (p.Y567A), and c.1713C>G (p.H571Q) (all heterozygous). The remaining 2 were already reported in previous studies. All 6 patients were spinal onset but showed differences in ALS subtypes as well as age of onset and disease progression. Taken together, we detected 4 novel missense OPTN mutations and 2 previously described mutations that might be causal for ALS, accounting for a mutant frequency of 1.10% (4/365) in patients with SALS after excluding 2 benign variants, and confirmed that OPTN mutations are common in Asian populations. In addition, our data suggested that variability in phenotype of the same mutation might partly be due to the oligogenic basis of ALS.

Alternative Splicing of ALS Genes: Misregulation and Potential Therapies

Neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), Parkinson's, Alzheimer's, and Huntington's disease affect a rapidly increasing population worldwide. Although common pathogenic mechanisms have been identified (e.g., protein aggregation or dysfunction, immune response alteration and axonal degeneration), the molecular events underlying timing, dosage, expression, and location of RNA molecules are still not fully elucidated. In particular, the alternative splicing (AS) mechanism is a crucial player in RNA processing and represents a fundamental determinant for brain development, as well as for the physiological functions of neuronal circuits. Although in recent years our knowledge of AS events has increased substantially, deciphering the molecular interconnections between splicing and ALS remains a complex task and still requires considerable efforts. In the present review, we will summarize the current scientific evidence outlining the involvement of AS in the pathogenic processes of ALS. We will also focus on recent insights concerning the tuning of splicing mechanisms by epigenomic and epi-transcriptomic regulation, providing an overview of the available genomic technologies to investigate AS drivers on a genome-wide scale, even at a single-cell level resolution. In the future, gene therapy strategies and RNA-based technologies may be utilized to intercept or modulate the splicing mechanism and produce beneficial effects against ALS.

Genetic epidemiology of motor neuron disease-associated variants in the Scottish population

Genetic understanding of motor neuron disease (MND) has evolved greatly in the past 10 years, including the recent identification of association between MND and variants in TBK1 and NEK1. Our aim was to determine the frequency of pathogenic variants in known MND genes and to assess whether variants in TBK1 and NEK1 contribute to the burden of MND in the Scottish population. SOD1, TARDBP, OPTN, TBK1, and NEK1 were sequenced in 441 cases and 400 controls. In addition to 44 cases known to carry a C9orf72 hexanucleotide repeat expansion, we identified 31 cases and 2 controls that carried a loss-of-function or pathogenic variant. Loss-of-function variants were found in TBK1 in 3 cases and no controls and, separately, in NEK1 in 3 cases and no controls. This study provides an accurate description of the genetic epidemiology of MND in Scotland and provides support for the contribution of both TBK1 and NEK1 to MND susceptibility in the Scottish population.

It's all about talking: two-way communication between proteasomal and lysosomal degradation pathways via ubiquitin

Selective degradation of proteins requires a fine-tuned coordination of the two major proteolytic pathways, the ubiquitin-proteasome system (UPS) and autophagy. Substrate selection and proteolytic activity are defined by a plethora of regulatory cofactors influencing each other. Both proteolytic pathways are initiated by ubiquitylation to mark substrate proteins for degradation, although the size and/or topology of the modification are different. In this context E3 ubiquitin ligases, ensuring the covalent attachment of activated ubiquitin to the substrate, are of special importance. The regulation of E3 ligase activity, competition between different E3 ligases for binding E2 conjugation enzymes and substrates, as well as their interplay with deubiquitylating enzymes (DUBs) represent key events in the cross talk between the UPS and autophagy. The coordination between both degradation routes is further influenced by heat shock factors and ubiquitin-binding proteins (UBPs) such as p97, p62, or optineurin. Mutations in enzymes and ubiquitin-binding proteins or a general decline of both proteolytic systems during aging result in accumulation of damaged and aggregated proteins. Thus further mechanistic understanding of how UPS and autophagy communicate might allow therapeutic intervention especially against age-related diseases.

Genotype-phenotype correlations of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease characterized by progressive neuronal loss and degeneration of upper motor neuron (UMN) and lower motor neuron (LMN). The clinical presentations of ALS are heterogeneous and there is no single test or procedure to establish the diagnosis of ALS. Most cases are diagnosed based on symptoms, physical signs, progression, EMG, and tests to exclude the overlapping conditions. Familial ALS represents about 5 ~ 10 % of ALS cases, whereas the vast majority of patients are sporadic. To date, more than 20 causative genes have been identified in hereditary ALS. Detecting the pathogenic mutations or risk variants for each ALS individual is challenging. However, ALS patients carrying some specific mutations or variant may exhibit subtly distinct clinical features. Unraveling the respective genotype-phenotype correlation has important implications for the genetic explanations. In this review, we will delineate the clinical features of ALS, outline the major ALS-related genes, and summarize the possible genotype-phenotype correlations of ALS.

Replication analysis of genetic variants on 17q11.2 and 9p21.2 with sporadic amyotrophic lateral sclerosis and Parkinson's disease in a Chinese population

We performed a replication study of the 2 genetic variants, rs34517613 on 17q11.2 and rs3849942 on 9p21.2 in patients with sporadic amyotrophic lateral sclerosis (ALS) and Parkinson's disease in a Chinese population. These 2 variants are identified to be associated with increased risk of ALS in European-descended populations by genome-wide association studies. Both rs34517613 and rs3849942 showed no evidence of association in Chinese. These loci are not risk factors for sporadic ALS and Parkinson's disease in the western Han Chinese population.

Oligogenic inheritance of optineurin (OPTN) and C9ORF72 mutations in ALS highlights localisation of OPTN in the TDP-43-negative inclusions of C9ORF72-ALS

Amyotrophic lateral sclerosis (ALS) is characterized by motor neurone loss resulting in muscle weakness, spasticity and ultimately death. 5-10% are caused by inherited mutations, most commonly C9ORF72, SOD1, TARDBP and FUS. Rarer genetic causes of ALS include mutation of optineurin (mt OPTN). Furthermore, optineurin protein has been localized to the ubiquitylated aggregates in several neurodegenerative diseases, including ALS. This study: (i) investigated the frequency of mt OPTN in ALS patients in England; (ii) characterized the clinical and neuropathological features of ALS associated with a mt OPTN; and (iii) investigated optineurin neuropathology in C9ORF72-related ALS (C9ORF72-ALS). We identified a heterozygous p.E322K missense mutation in exon 10 of OPTN in one familial ALS patient who additionally had a C9ORF72 mutation. This patient had bulbar, limb and respiratory disease without cognitive problems. Neuropathology revealed motor neurone loss, trans-activation response DNA protein 43 (TDP-43)-positive neuronal and glial cytoplasmic inclusions together with TDP-43-negative neuronal cytoplasmic inclusions in extra motor regions that are characteristic of C9ORF72-ALS. We have demonstrated that both TDP-43-positive and negative inclusion types had positive staining for optineurin by immunohistochemistry. We went on to show that optineurin was present in TDP-43-negative cytoplasmic extra motor inclusions in C9ORF72-ALS cases that do not carry mt OPTN. We conclude that: (i) OPTN mutations are associated with ALS; (ii) optineurin protein is present in a subset of the extramotor inclusions of C9ORF72-ALS; (iii) It is not uncommon for multiple ALS-causing mutations to occur in the same patient; and (iv) studies of optineurin are likely to provide useful dataregarding the pathophysiology of ALS and neurodegeneration.

Genome-wide analysis of the heritability of amyotrophic lateral sclerosis

IMPORTANCE

Considerable advances have been made in our understanding of the genetics underlying amyotrophic lateral sclerosis (ALS). Nevertheless, for the majority of patients who receive a diagnosis of ALS, the role played by genetics is unclear. Further elucidation of the genetic architecture of this disease will help clarify the role of genetic variation in ALS populations.

OBJECTIVE

To estimate the relative importance of genetic factors in a complex disease such as ALS by accurately quantifying heritability using genome-wide data derived from genome-wide association studies.

DESIGN, SETTING, AND PARTICIPANTS

We applied the genome-wide complex trait analysis algorithm to 3 genome-wide association study data sets that were generated from ALS case-control cohorts of European ancestry to estimate the heritability of ALS. Cumulatively, these data sets contained genotype data from 1223 cases and 1591 controls that had been previously generated and are publically available on the National Center for Biotechnology Information database of genotypes and phenotypes website (http://www.ncbi.nlm.nih.gov/gap). The cohorts genotyped as part of these genome-wide association study efforts include the InCHIANTI (aging in the Chianti area) Study, the Piemonte and Valle d'Aosta Register for Amyotrophic Lateral Sclerosis, the National Institute of Neurological Disorders and Stroke Repository, and an ALS specialty clinic in Helsinki, Finland.

MAIN OUTCOMES AND MEASURES

A linear mixed model was used to account for all known single-nucleotide polymorphisms simultaneously and to quantify the phenotypic variance present in ostensibly outbred individuals. Variance measures were used to estimate heritability.

RESULTS

With our meta-analysis, which is based on genome-wide genotyping data, we estimated the overall heritability of ALS to be approximately 21.0% (95% CI, 17.1-24.9) (SE = 2.0%), indicating that additional genetic variation influencing risk of ALS loci remains to be identified. Furthermore, we identified 17 regions of the genome that display significantly high heritability estimates. Eleven of these regions represent novel candidate regions for ALS risk.

CONCLUSIONS AND RELEVANCE

We found the heritability of ALS to be significantly higher than previously reported. We also identified multiple, novel genomic regions that we hypothesize may contain causative risk variants that influence susceptibility to ALS.

Targeted exon capture and sequencing in sporadic amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease that results in progressive degeneration of motor neurons, ultimately leading to paralysis and death. Approximately 10% of ALS cases are familial, with the remaining 90% of cases being sporadic. Genetic studies in familial cases of ALS have been extremely informative in determining the causative mutations behind ALS, especially as the same mutations identified in familial ALS can also cause sporadic disease. However, the cause of ALS in approximately 30% of familial cases and in the majority of sporadic cases remains unknown. Sporadic ALS cases represent an underutilized resource for genetic information about ALS; therefore, we undertook a targeted sequencing approach of 169 known and candidate ALS disease genes in 242 sporadic ALS cases and 129 matched controls to try to identify novel variants linked to ALS. We found a significant enrichment in novel and rare variants in cases versus controls, indicating that we are likely identifying disease associated mutations. This study highlights the utility of next generation sequencing techniques combined with functional studies and rare variant analysis tools to provide insight into the genetic etiology of a heterogeneous sporadic disease.

Amyotrophic lateral sclerosis (ALS), also known as Charcot disease or Lou Gehrig's disease, is one of the most common neuromuscular diseases worldwide. This disease is characterized by a progressive degeneration of motor neurons, leading to patient death within a few years after onset. Despite the fact that most ALS cases are sporadic, most of the ALS genetic studies have focused on familial forms, leading to the genetic determination of cause for 70% of cases of familial ALS but for only 10% of sporadic ALS cases. This, coupled with the dearth of families available for study, suggests that researchers should begin tapping into the relatively untouched reservoir of available sporadic samples to identify novel genetic causes of sporadic ALS. Here we take advantage of high-throughput target sequencing techniques to test four different hypotheses about the genetic causes of ALS in sporadic ALS and uncover new candidate genes and pathways implicated in ALS.

Extensive molecular genetic survey of Taiwanese patients with amyotrophic lateral sclerosis

Identification of genetic mutations has been of burgeoning importance in amyotrophic lateral sclerosis (ALS) in recent years. The aim of this study was to determine the frequency and spectrum of mutations in major ALS-causing genes in a Taiwanese ALS cohort of Han Chinese origin. Mutational analyses of the SOD1, TARDBP, FUS, OPTN, VCP, UBQLN2, SQSTM1, PFN1, HNRNPA1, and HNRNPA2B1 genes were carried out by direct sequencing in 161 unrelated patients with ALS, including 30 with familial ALS (FALS) and 131 with sporadic ALS (SALS). The CAG repeat size in ATXN2 and the GGGGCC repeat expansion in C9ORF72 of the patients were also investigated. Mutations were identified in 33 patients (20.5%, 33/161), including 22 with FALS and 11 with SALS. Mutations were identified most frequently in SOD1 (7.5%). Three mutations are novel, including SOD1 p.G10A, SOD1 p.D83N, and OPTN p.L494W. These findings broaden the spectrum of ALS-causing mutations and are indispensable for designing optimal strategies of mutational analysis and genetic counseling of ALS for patients of Chinese origin.

PFN1 mutations are rare in Han Chinese populations with amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease with unknown pathophysiological mechanisms. Profilin 1 gene (PFN1) has been identified as a causative gene, which accounts for 1% to 2% of familial ALS. In this study, we investigated the mutation spectrum of PFN1 in Chinese patients with ALS. A total of 550 ALS patients (including 540 sporadic ALS [SALS] and 10 familial ALS) from the Department of Neurology, West China Hospital of Sichuan University, were recruited for the study. From the same region, 545 healthy control individuals (HC) were recruited as a control group. The encoding regions of the PFN1 gene were screened by direct sequencing. Novel candidate mutations or variations were confirmed by polymerase chain reaction-restriction fragment length polymorphism. A novel nonsynonymous p.R136W mutation was identified in an early-onset SALS female patient. A novel synonymous mutation p.L88L detected in a late-onset SALS female patient was considered nonpathogenic, as it was also detected in a control subject. No mutations were found in 10 familial ALS patients. Moreover, we found a significant difference in the genotype distribution of reported rs13204 (p.L112L) between SALS patients and HC (p = 0.0030). The frequency of minor allele 'T' of rs13204 in the SALS group was significantly lower than that in HC (p = 0.0040, OR = 0.7270, 95% CI = 0.5848-0.9039). Our results suggest that PFN1 mutation is an uncommon cause of ALS in the Han Chinese population. The SNP rs13204 of the PFN1 gene may have an important function in ALS development. The phenotype of ALS patients with mutantPFN1 gene varies among different genetic backgrounds.