Véronique V. Belzil

Mutations in FUS cause FALS and SALS in French and French Canadian populations

Background: The identification of mutations in the TARDBP and more recently the identification of mutations in the FUS gene as the cause of amyotrophic lateral sclerosis (ALS) is providing the field with new insight about the mechanisms involved in this severe neurodegenerative disease. Methods: To extend these recent genetic reports, we screened the entire gene in a cohort of 200 patients with ALS. An additional 285 patients with sporadic ALS were screened for variants in exon 15 for which mutations were previously reported. Results: In total, 3 different mutations were identified in 4 different patients, including 1 3-bp deletion in exon 3 of a patient with sporadic ALS and 2 missense mutations in exon 15 of 1 patient with familial ALS and 2 patients with sporadic ALS. Conclusions: Our study identified sporadic patients with mutations in the FUS gene. The accumulation and description of different genes and mutations helps to develop a more comprehensive picture of the genetic events underlying amyotrophic lateral sclerosis.

Exome Sequencing Identifies FUS Mutations as a Cause of Essential Tremor

Essential tremor (ET) is a common neurodegenerative disorder that is characterized by a postural or motion tremor. Despite a strong genetic basis, a gene with rare pathogenic mutations that cause ET has not yet been reported. We used exome sequencing to implement a simple approach to control for misdiagnosis of ET, as well as phenocopies involving sporadic and senile ET cases. We studied a large ET-affected family and identified a FUS p.Gln290(∗) mutation as the cause of ET in this family. Further screening of 270 ET cases identified two additional rare missense FUS variants. Functional considerations suggest that the pathogenic effects of ET-specific FUS mutations are different from the effects observed when FUS is mutated in amyotrophic lateral sclerosis cases; we have shown that the ET FUS nonsense mutation is degraded by the nonsense-mediated-decay pathway, whereas amyotrophic lateral sclerosis FUS mutant transcripts are not.

Association of Long ATXN2 CAG Repeat Sizes With Increased Risk of Amyotrophic Lateral Sclerosis

OBJECTIVE To analyze the ataxin 2 (ATXN2) CAG repeat size in a cohort of patients with amyotrophic lateral sclerosis (ALS) and healthy controls. Large (CAG)(n) alleles of the ATXN2 gene (27-33 repeats) were recently reported to be associated with an increased risk of ALS. DESIGN Case-control study. SETTING France and Quebec, Canada. PARTICIPANTS A total of 556 case patients with ALS and 471 healthy controls; both groups of participants are of French or French-Canadian origin. RESULTS We observed a significant association between ATXN2 high-length alleles (≥29 CAG repeats) and ALS in French and French-Canadian ALS populations. Furthermore, we identified spinocerebellar ataxia type 2-pathogenic polyglutamine expansions (≥32 CAG repeats) in both familial and sporadic ALS cases. CONCLUSIONS Altogether, our findings support ATXN2 high-length repeats as a risk factor for ALS and further indicate a genetic link between spinocerebellar ataxia type 2 and ALS.

Deleterious mutations in the essential mRNA metabolism factor, hGle1, in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by the selective death of motor neurons. Causative mutations in the global RNA-processing proteins TDP-43 and FUS among others, as well as their aggregation in ALS patients, have identified defects in RNA metabolism as an important feature in this disease. Lethal congenital contracture syndrome 1 and lethal arthrogryposis with anterior horn cell disease are autosomal recessive fetal motor neuron diseases that are caused by mutations in another global RNA-processing protein, hGle1. In this study, we carried out the first screening of GLE1 in ALS patients (173 familial and 760 sporadic) and identified 2 deleterious mutations (1 splice site and 1 nonsense mutation) and 1 missense mutation. Functional analysis of the deleterious mutants revealed them to be unable to rescue motor neuron pathology in zebrafish morphants lacking Gle1. Furthermore, in HeLa cells, both mutations caused a depletion of hGle1 at the nuclear pore where it carries out an essential role in nuclear export of mRNA. These results suggest a haploinsufficiency mechanism and point to a causative role for GLE1 mutations in ALS patients. This further supports the involvement of global defects in RNA metabolism in ALS.

Exome sequencing reveals SPG11 mutations causing juvenile ALS.

We report here the description of a nonconsanguineous family with 2 affected individuals with a recessively inherited juvenile motor neuron disease. Exome sequencing of these 2 affected individuals led us to identify 2 compound heterozygous deletions leading to a frameshift and a premature stop codon in the SPG11 gene. One of these deletions, c.5199delA in exon 30, has not been previously reported. Interestingly, these deletions are associated with an intrafamilial phenotypic heterogeneity as one affected has atypical juvenile amyotrophic lateral sclerosis (ALS) and the other has classical hereditary spastic paraplegia with thin corpus callosum. Our findings confirm SPG11 as a genetic cause of juvenile amyotrophic lateral sclerosis and indicate that SPG11 mutations could be associated with 2 different clinical phenotypes within the same family.

Analysis of OPTN as a causative gene for amyotrophic lateral sclerosis

Mutations in the OPTN gene are well known to be associated with the development of glaucoma. Recently, unique variations in the same gene have been reported in familial and sporadic Japanese cases of amyotrophic lateral sclerosis (ALS). We set out to evaluate the frequency of OPTN mutations in a sample of our familial and sporadic ALS cohorts. All coding exons of the OPTN gene were amplified and sequenced in 95 unrelated familial ALS (FALS) and 95 sporadic ALS (SALS) cases of European descent. Two variants were newly identified in 2 individual FALS cases. Unique variations in the OPTN gene are rare in FALS cases and were not identified in any SALS patients, all of European descent.

Identification of novel FUS mutations in sporadic cases of amyotrophic lateral sclerosis

Abstract Mutations in the FUS gene have been recently associated with amyotrophic lateral sclerosis (ALS). While most of the variants have been identified in patients with a family history of the disease, a few mutations were also found in sporadic patients. Considering this, we wanted to evaluate the frequency of mutations in the coding region of the FUS gene in a sporadic ALS (SALS) cohort compared to a control population. We tested 475 SALS cases of European origin and 475 matched controls for coding variations in the 15 exons of the FUS gene. Rare novel variants were identified in a total of five SALS patients: one missense, one deletion, one frameshift, and one nonsense substitution. Two of the four variants are located in the carboxy terminal of the protein where the previously reported variants were mostly clustered. In conclusion, FUS gene mutations are rare in SALS, with four new FUS variants identified in five different SALS cases. These findings will help evaluate the proportion of FUS variations in the SALS population, and to better understand its contributing role to ALS pathology.

Genetic analysis of SIGMAR1 as a cause of familial ALS with dementia

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron diseases (MND), while frontotemporal lobar degeneration (FTLD) is the second most common cause of early-onset dementia. Many ALS families segregating FTLD have been reported, particularly over the last decade. Recently, mutations in TARDBP, FUS/TLS, and C9ORF72 have been identified in both ALS and FTLD patients, while mutations in VCP, a FTLD associated gene, have been found in ALS families. Distinct variants located in the 3′-untranslated region (UTR) of the SIGMAR1 gene were previously reported in three unrelated FTLD or FTLD–MND families. We directly sequenced the coding and UTR regions of the SIGMAR1 gene in a targeted cohort of 25 individual familial ALS cases of Caucasian origin with a history of cognitive impairments. This screening identified one variant in the 3′-UTR of the SIGMAR1 gene in one ALS patient, but the same variant was also observed in 1 out of 380 control chromosomes. Subsequently, we screened the same samples for a C9ORF72 repeat expansion: 52% of this cohort was found expanded, including the sample with the SIGMAR1 3′-UTR variant. Consequently, coding and noncoding variants located in the 3′-UTR region of the SIGMAR1 gene are not the cause of FTLD–MND in our cohort, and more than half of this targeted cohort is genetically explained by C9ORF72 repeat expansions.

Resequencing of 29 Candidate Genes in Patients With Familial and Sporadic Amyotrophic Lateral Sclerosis

OBJECTIVE To identify novel disease-causing genes for amyotrophic lateral sclerosis (ALS). DESIGN, SETTING, AND PATIENTS We carried out a systematic mutation screening of the entire coding regions of 29 candidate genes encoding critically important proteins for proper differentiation and development of corticospinal motor neurons in 190 patients with familial and sporadic ALS. MAIN OUTCOME MEASURES We focused our analysis on coding variants and evaluated the distribution of nonsynonymous and synonymous variants in our cohort of patients with ALS. RESULTS We identified 40 novel nonsynonymous variants and showed a significant excess of unique nonsynonymous variants in our cohort of patients with ALS, which suggests the presence of ALS-predisposing mutations. CONCLUSIONS Using a multifaceted approach based on the functional prediction of missense variants, the conservation of the altered amino acid, and the cosegregation of the variants identified in familial cases, we identified several promising novel genes for ALS such as LUM and CRYM. We have also highlighted the analytical challenges of large-scale sequencing screens to detect disease-causing variants.

Analysis of the UNC13A gene as a risk factor for sporadic amyotrophic lateral sclerosis.

A myotrophic lateral sclerosis (ALS) is an adultonset neurodegenerative disease characterized by progressive loss of motor neurons from the spinal cord, brainstem, and cerebral cortex that typically results in death 2 to 5 years following onset. Approximately 10% of patients with ALS have a family history, of which 15% to 20% are linked to mutations in the SOD1 gene; these patients most frequently inherit the disease in an autosomal dominant manner. Mutations in other genes including ALS2, ANG, DCTN1, SETX, VAPB, TARDBP, and FUS have also been reported in familial cases. The remaining 90% of cases have no obvious family history and are referred to as sporadic ALS (SALS). The etiology of these sporadic cases is considered multifactorial, with environmental and genetic factors contributing to disease susceptibility. Although candidate gene studies have identified potential risk factors for SALS, replication of these associations in different populations have often failed. Similarly, several genome-wide association studies for SALS have identified novel candidate susceptibility genes including ITPR2, FGGY, and DPP6; however, these associations have not been consistently replicated. Recently, a large-scale genome-wide association study that included 19 838 subjects showed that the variant rs12608932 located in the unc-13 homologue A gene (UNC13A) is strongly associated with SALS. The aim of this study is to investigate the variant as a possible risk factor for developing ALS in a French population.