Case report: Marked electroclinical improvement by fluoxetine treatment in a patient with KCNT1-related drug-resistant focal epilepsy.

Variants in KCNT1 are associated with a wide spectrum of epileptic phenotypes, including epilepsy of infancy with migrating focal seizures (EIMFS), non-EIMFS developmental and epileptic encephalopathies, autosomal dominant or sporadic sleep-related hypermotor epilepsy, and focal epilepsy. Here, we describe a girl affected by drug-resistant focal seizures, developmental delay and behavior disorders, caused by a novel, de novo heterozygous missense KCNT1 variant (c.2809A > G, p.S937G). Functional characterization in transiently transfected Chinese Hamster Ovary (CHO) cells revealed a strong gain-of-function effect determined by the KCNT1 p.S937G variant compared to wild-type, consisting in an increased maximal current density and a hyperpolarizing shift in current activation threshold. Exposure to the antidepressant drug fluoxetine inhibited currents expressed by both wild-type and mutant KCNT1 channels. Treatment of the proband with fluoxetine led to a prolonged electroclinical amelioration, with disappearance of seizures and better EEG background organization, together with an improvement in behavior and mood. Altogether, these results suggest that, based on the proband's genetic and functional characteristics, the antidepressant drug fluoxetine may be repurposed for the treatment of focal epilepsy caused by gain-of-function variants in KCNT1. Further studies are needed to verify whether this approach could be also applied to other phenotypes of the KCNT1-related epilepsies spectrum.

A novel de novo HCN2 loss-of-function variant causing developmental and epileptic encephalopathy treated with a ketogenic diet.

Missense variants of hyperpolarization-activated, cyclic nucleotide-gated (HCN) ion channels cause variable phenotypes, ranging from mild generalized epilepsy to developmental and epileptic encephalopathy (DEE). Although variants of HCN1 are an established cause of DEE, those of HCN2 have been reported in generalized epilepsies. Here we describe the first case of DEE caused by the novel de novo heterozygous missense variant c.1379G>A (p.G460D) of HCN2. Functional characterization in transfected HEK293 cells and neonatal rat cortical neurons revealed that HCN2 p.G460D currents were strongly reduced compared to wild-type, consistent with a dominant negative loss-of-function effect. Immunofluorescence staining showed that mutant channels are retained within the cell and do not reach the membrane. Moreover, mutant HCN2 also affect HCN1 channels, by reducing the Ih current expressed by the HCN1-HCN2 heteromers. Due to the persistence of frequent seizures despite pharmacological polytherapy, the patient was treated with a ketogenic diet, with a significant and long-lasting reduction of episodes. In vitro experiments conducted in a ketogenic environment demonstrated that the clinical improvement observed with this dietary regimen was not mediated by a direct action on HCN2 activity. These results expand the clinical spectrum related to HCN2 channelopathies, further broadening our understanding of the pathogenesis of DEE.

Adult-onset leukodystrophy with vanishing white matter: a case series of 19 patients.

BACKGROUND: Leukodystrophy with vanishing white matter (LVWM) is an autosomal recessive disease with typical pediatric-onset caused by mutations in one of the five EIF2B genes. Adult-onset (AO) cases are rare. METHODS: In this observational study, we reviewed clinical and laboratory information of the patients with AO-LVWM assessed at two referral centers in Italy and Portugal from Jan-2007 to Dec-2019. RESULTS: We identified 18 patients (13 females) with AO-LVWM caused by EIF2B5 or EIF2B3 mutations. Age of neurological onset ranged from 16 to 60 years, with follow-ups occurring from 2 to 37 years. Crucial symptoms were cognitive and motor decline. In three patients, stroke-like events were the first manifestation; in another, bladder dysfunction remained the main complaint across decades. Brain MRI showed white matter (WM) rarefaction in all cases, except two. Diffusion-weighted imaging documented focal hyperintensity in the acute stage of stroke-like events. 1H-spectroscopy primarily showed N-acetyl-aspartate reduction; 18fluorodeoxyglucose-PET revealed predominant frontoparietal hypometabolism; evoked potential studies demonstrated normal-to-reduced amplitudes; neuro-ophthalmological assessment showed neuroretinal thinning, and b-wave reduction on full-field electroretinogram. Interestingly, we found an additional patient with LVWM-compatible phenotype and monoallelic variants in two distinct eIF2B genes, EIF2B1 and EIF2B2. CONCLUSIONS: AO-LVWM presents varying clinical manifestations at onset, including stroke-like events. WM rarefaction is the most consistent diagnostic clue even in the latest onset cases. Spectroscopy and electrophysiological features are compatible with axon, rather than myelin, damage. Cerebral glucose metabolic abnormalities and retinal alterations can be present. LVWM might also be caused by a digenic inheritance affecting the eIF2B complex.

A novel KCNC1 gain-of-function variant causing developmental and epileptic encephalopathy: "Precision medicine" approach with fluoxetine.

Variable phenotypes, including developmental encephalopathy with (DEE) or without seizures and myoclonic epilepsy and ataxia due to potassium channel mutation, are caused by pathogenetic variants in KCNC1, encoding for Kv3.1 channel subunits. In vitro, channels carrying most KCNC1 pathogenic variants display loss-of-function features. Here, we describe a child affected by DEE with fever-triggered seizures, caused by a novel de novo heterozygous missense KCNC1 variant (c.1273G>A; V425M). Patch-clamp recordings in transiently transfected CHO cells revealed that, compared to wild-type, Kv3.1 V425M currents (1) were larger, with membrane potentials between -40 and +40 mV; (2) displayed a hyperpolarizing shift in activation gating; (3) failed to inactivate; and (4) had slower activation and deactivation kinetics, consistent with a mixed functional pattern with prevalent gain-of-function effects. Exposure to the antidepressant drug fluoxetine inhibited currents expressed by both wild-type and mutant Kv3.1 channels. Treatment of the proband with fluoxetine led to a rapid and prolonged clinical amelioration, with the disappearance of seizures and an improvement in balance, gross motor skills, and oculomotor coordination. These results suggest that drug repurposing based on the specific genetic defect may provide an effective personalized treatment for KCNC1-related DEEs.

MiR-146a in ALS: Contribution to Early Peripheral Nerve Degeneration and Relevance as Disease Biomarker.

Amyotrophic lateral sclerosis (ALS) is characterized by the progressive, irreversible loss of upper and lower motor neurons (UMNs, LMNs). MN axonal dysfunctions are emerging as relevant pathogenic events since the early ALS stages. However, the exact molecular mechanisms leading to MN axon degeneration in ALS still need to be clarified. MicroRNA (miRNA) dysregulation plays a critical role in the pathogenesis of neuromuscular diseases. These molecules represent promising biomarkers for these conditions since their expression in body fluids consistently reflects distinct pathophysiological states. Mir-146a has been reported to modulate the expression of the NFL gene, encoding the light chain of the neurofilament (NFL) protein, a recognized biomarker for ALS. Here, we analyzed miR-146a and Nfl expression in the sciatic nerve of G93A-SOD1 ALS mice during disease progression. The miRNA was also analyzed in the serum of affected mice and human patients, the last stratified relying on the predominant UMN or LMN clinical signs. We revealed a significant miR-146a increase and Nfl expression decrease in G93A-SOD1 peripheral nerve. In the serum of both ALS mice and human patients, the miRNA levels were reduced, discriminating UMN-predominant patients from the LMN ones. Our findings suggest a miR-146a contribution to peripheral axon impairment and its potential role as a diagnostic and prognostic biomarker for ALS.

Complex Ataxia-Dementia Phenotype in Patients with Digenic TBP/STUB1 Spinocerebellar Ataxia.

BACKGROUND AND OBJECTIVES: Spinocerebellar ataxias (SCAs) are autosomal dominant disorders with extensive clinical and genetic heterogeneity. We recently identified a form of SCA transmitted with a digenic pattern of inheritance caused by the concomitant presence of an intermediate-length expansion in TATA-box binding protein gene (TBP40-46 ) and a heterozygous pathogenic variant in the Stip1-homologous and U-Box containing protein 1 gene (STUB1). This SCATBP/STUB1 represents the first example of a cerebellar disorder in which digenic inheritance has been identified. OBJECTIVES: We studied a large cohort of patients with SCATBP/STUB1 with the aim of describing specific clinical and neuroimaging features of this distinctive genotype. METHODS: In this observational study, we recruited 65 affected and unaffected family members from 21 SCATBP/STUB1 families and from eight families with monogenic SCA17. Their characteristics and phenotypes were compared with those of 33 age-matched controls. RESULTS: SCATBP/STUB1 patients had multi-domain dementia with a more severe impairment in respect to patient carrying only fully expanded SCA17 alleles. Cerebellar volume and thickness of cerebellar cortex were reduced in SCATBP/STUB1 compared with SCA17 patients (P = 0.03; P = 0.008). Basal ganglia volumes were reduced in both patient groups, as compared with controls, whereas brainstem volumes were significantly reduced in SCATBP/STUB1 , but not in SCA17 patients. CONCLUSIONS: The identification of the complex SCATBP/STUB1 phenotype may impact on diagnosis and genetic counseling in the families with both hereditary and sporadic ataxia. The independent segregation of TBP and STUB1 alleles needs to be considered for recurrence risk and predictive genetic tests. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Progressive myoclonus epilepsies due to SEMA6B mutations. New variants and appraisal of published phenotypes.

Variants of SEMA6B have been identified in an increasing number of patients, often presenting with progressive myoclonus epilepsy (PME), and to lesser extent developmental encephalopathy, with or without epilepsy. The exon 17 is mainly involved, with truncating mutations causing the production of aberrant proteins with toxic gain of function. Herein, we describe three adjunctive patients carrying de novo truncating SEMA6B variants in this exon (c.1976delC and c.2086C > T novel; c.1978delC previously reported). These subjects presented with PME preceded by developmental delay, motor and cognitive impairment, worsening myoclonus, and epilepsy with polymorphic features, including focal to bilateral seizures in two, and non-convulsive status epilepticus in one. The evidence of developmental delay in these cases suggests their inclusion in the "PME plus developmental delay" nosological group. This work further expands our knowledge of SEMA6B variants causing PMEs. However, the data to date available confirms that phenotypic features do not correlate with the type or location of variants, aspects that need to be further clarified by future studies.

Generation of an iPSC line from a patient with spastic paraplegia type 10 carrying a novel mutation in KIF5A gene.

We generated an iPSC line from a patient with spastic paraplegia type 10 (SPG10) carrying the novel missense variant c.50G > A (p.R17Q) in the N-terminal motor domain of the kinesin family member 5A (KIF5A) gene. This patient-derived in vitro cell model will help to investigate the role of different KIF5A mutations in inducing neurodegeneration in spastic paraplegia and in other KIF5A-related disorders, including Charcot-Marie-Tooth type 2 (CMT2) and amyotrophic lateral sclerosis (ALS).

Analysis of miRNA rare variants in amyotrophic lateral sclerosis and in silico prediction of their biological effects.

Background: Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease affecting upper and/or lower motor neurons and characterized by complex etiology. Familial cases show high genetic heterogeneity and sporadic cases (90%) are associated with several genetic and environmental risk factors. Among the genetic risk factors, the contribution of non-coding elements, such as microRNAs (miRNAs), to ALS disease susceptibility remains largely unexplored. Aim: This work aims to identify rare variants in miRNA genes in sporadic ALS (sALS) patients which may cause a defective miRNA maturation or altered target gene recognition by changing miRNA secondary structure or seed sequence, respectively. Methods: Rare variants located in miRNA loci with a minor allele frequency (MAF) < 0.01 were extracted from whole genome sequencing (WGS) data of 100 sALS patients. The secondary pre-miRNA structures were predicted using MiRVas to evaluate the impact of the variants on RNA folding process. Human TargetScan was used to retrieve all the potential target genes of miRNAs with variants in the seed region. Over Representation Analysis (ORA) was conducted to compare the lists of target genes for the reference and mutated miRNAs in the seed sequence. Results: Our analysis identified 86 rare variants in 77 distinct miRNAs and distributed in different parts of the miRNA precursors. The presence of these variants changed miRNA secondary structures in ∼70% of MiRVas predictions. By focusing on the 6 rare variants mapping within the seed sequence, the predicted target genes increased in number compared to the reference miRNA and included novel targets in a proportion ranging from 30 to 82%. Interestingly, ORA revealed significant changes in gene set enrichment only for mutated miR-509-1 and miR-941-3 for which the Gene Ontology term related to "nervous system development" was absent and present, respectively, compared to target lists of the reference miRNA. Conclusion: We here developed a workflow to study miRNA rare variants from WGS data and to predict their biological effects on miRNA folding, maturation and target gene recognition. Although this in silico approach certainly needs functional validation in vitro and in vivo, it may help define the role of miRNA variability in ALS and complex diseases.

Adults with spinal muscular atrophy: a large-scale natural history study shows gender effect on disease.

BACKGROUND: Natural history of spinal muscular atrophy (SMA) in adult age has not been fully elucidated yet, including factors predicting disease progression and response to treatments. Aim of this retrospective, cross-sectional study, is to investigate motor function across different ages, disease patterns and gender in adult SMA untreated patients. METHODS: Inclusion criteria were as follows: (1) clinical and molecular diagnosis of SMA2, SMA3 or SMA4 and (2) clinical assessments performed in adult age (>18 years). RESULTS: We included 64 (38.8%) females and 101 (61.2%) males (p=0.0025), among which 21 (12.7%) SMA2, 141 (85.5%) SMA3 and 3 (1.8%) SMA4. Ratio of sitters/walkers within the SMA3 subgroup was significantly (p=0.016) higher in males (46/38) than in females (19/38). Median age at onset was significantly (p=0.0071) earlier in females (3 years; range 0-16) than in males (4 years; range 0.3-28), especially in patients carrying 4 SMN2 copies. Median Hammersmith Functional Rating Scale Expanded scores were significantly (p=0.0040) lower in males (16, range 0-64) than in females (40, range 0-62); median revised upper limb module scores were not significantly (p=0.059) different between males (24, 0-38) and females (33, range 0-38), although a trend towards worse performance in males was observed. In SMA3 patients carrying three or four SMN2 copies, an effect of female sex in prolonging ambulation was statistically significant (p=0.034). CONCLUSIONS: Our data showed a relevant gender effect on SMA motor function with higher disease severity in males especially in the young adult age and in SMA3 patients.

Comorbidities in Friedreich ataxia: incidence and manifestations from early to advanced disease stages.

OBJECTIVES: Friedreich's ataxia (FA) is the most common hereditary ataxia, characterized by multisystemic manifestations including neurological, cardiological, and skeletal abnormalities. In this study, we aimed to analyze the incidences of disease-related and unrelated comorbidities occurring in different stages of the disease progression. METHODS: We analyzed longitudinal data from a 10-year prospective observational study in a cohort of 175 FA patients with disease onset < 25 years. We analyzed the time of diagnosis for the most frequently reported medical conditions, with respect to age and disease duration of each patient. RESULTS: In the early stage of the disease, scoliosis (53.3%), hypertrophic cardiomyopathy (46.7%), and pes cavus (33.3%) were the most frequently diagnosed conditions, sometimes occurring even before the onset of ataxia. Diabetes, bone fractures, and depression have the same incidence at all disease stages. In patients with > 20 years of disease duration, the most frequent complications were hearing and visual loss (20% and 26%), arrhythmias (16%), and psychosis (18%). Thirteen patients presented hallucinations/delusions in the absence of neurological acute events or mental illness predisposing to psychotic manifestations. Six of these patients fulfill the diagnostic criteria for Charles Bonnet syndrome. CONCLUSIONS: Incidence of FA-related medical conditions varies according to disease duration. In patients with very long disease duration, we observed an unexpectedly high incidence of visual and auditory pseudo-hallucinations that were not previously reported in FA patients. We hypothesized that these late complications may be possibly related to the severe sensory deafferentation syndrome observed in the advanced stages of FA disease.

Behavioral and Cognitive Phenotypes of Patients With Amyotrophic Lateral Sclerosis Carrying SOD1 Variants.

BACKGROUND AND OBJECTIVES: SOD1 variants in patients with amyotrophic lateral sclerosis (ALS) have been associated to peculiar clinical features and disease progression but rarely to cognitive and behavioural impairment. This study aims at describing the features of frontotemporal syndromes in ALS patients carrying SOD1 variants. METHODS: Italian patients with ALS were consecutively enrolled between 2012 and 2020 at our Motor Neuron Disease center. All underwent clinical assessment, extensive neurophysiological test battery for the evaluation of cognitive functions and behavior, and targeted next generation sequencing of SOD1, FUS, TARDBP, VCP, PFN1, TUBA4A, OPTN, SQSTM1, UBQLN2 and C9orf72 genes. Neuropsychological profiles of SOD1+ patients (SOD1+) were compared to those with no gene variants (SOD1-). To this aim, the occurrence of cognitive and behavioral impairment defined according to current guidelines, the number of pathological test performances based on Italian normative values, and scores of the Frontal Behavioural Inventory were collected. RESULTS: Among 288 patients consecutively examined, we identified 8 known pathogenic SOD1 variants and one variant of uncertain significance (p.Ser26Asn) not previously described in 14 ALS patients belonging to 11 families. The clinical phenotypes were mainly characterized by predominant lower motor neuron involvement with onset at the lower limbs, and one patient had bulbar onset. SOD1+ patients (n=14) were compared to SOD1- patients (N = 274). SOD1+ patients were younger than SOD1-, and both groups had similar functional motor disabilities and disease duration. Based on the overall neuropsychological findings, the percentage of SOD1+ and SOD1- patients with altered profiles were about 60%. However, behavioral impairment defined by the Strong criteria, and most commonly featuring with irritability and mental rigidity, was more frequent in SOD1+ than SOD1- patients, and mainly associated with variants in exon 5. Conversely, cognitive impairment was mainly found in SOD1- patients. DISCUSSION: Our findings from a large cohort of deeply phenotyped ALS patients demonstrated that behavioral involvement is more common than previously thought among patients harboring SOD1 variants, and that it is independent from patients' age and disease stage. These findings could be relevant for the assessment of clinical trial outcomes and disease management.

Identification of a cytokine profile in serum and cerebrospinal fluid of pediatric and adult spinal muscular atrophy patients and its modulation upon nusinersen treatment.

Background and objectives: Multisystem involvement in spinal muscular atrophy (SMA) is gaining prominence since different therapeutic options are emerging, making the way for new SMA phenotypes and consequent challenges in clinical care. Defective immune organs have been found in preclinical models of SMA, suggesting an involvement of the immune system in the disease. However, the immune state in SMA patients has not been investigated so far. Here, we aimed to evaluate the innate and adaptive immunity pattern in SMA type 1 to type 3 patients, before and after nusinersen treatment. Methods: Twenty one pediatric SMA type 1, 2, and 3 patients and 12 adult SMA type 2 and 3 patients were included in this single-center retrospective study. A Bio-Plex Pro-Human Cytokine 13-plex Immunoassay was used to measure cytokines in serum and cerebrospinal fluid (CSF) of the study cohort before and after 6 months of therapy with nusinersen. Results: We detected a significant increase in IL-1ß, IL-4, IL-6, IL-10, IFN-γ, IL-17A, IL-22, IL-23, IL-31, and IL-33, in serum of pediatric and adult SMA patients at baseline, compared to pediatric reference ranges and to adult healthy controls. Pediatric patients showed also a significant increase in TNF-α and IL-17F levels at baseline. IL-4, IFN-γ, Il-22, IL-23, and IL-33 decreased in serum of pediatric SMA patients after 6 months of therapy when compared to baseline. A significant decrease in IL-4, IL-6, INF-γ, and IL-17A was detected in serum of adult SMA patients after treatment. CSF of both pediatric and adult SMA patients displayed detectable levels of all cytokines with no significant differences after 6 months of treatment with nusinersen. Notably, a higher baseline expression of IL-23 in serum correlated with a worse motor function outcome after treatment in pediatric patients. Moreover, after 6 months of treatment, patients presenting a higher IL-10 concentration in serum showed a better Hammersmith Functional Motor Scale Expanded (HFMSE) score. Discussion: Pediatric and adult SMA patients show an inflammatory signature in serum that is reduced upon SMN2 modulating treatment, and the presence of inflammatory mediators in CSF. Our findings enhance SMA knowledge with potential clinical and therapeutic implications.

G507D mutation in FUS gene causes familial amyotrophic lateral sclerosis with a specific genotype-phenotype correlation.

Mutations in FUS gene have been described classically in young ALS patients with aggressive disease course. Here we report a large family carrying a missense mutation c.1520 G>A in FUS gene with a tight association with an atypical FUS-ALS phenotype. A 60-year-old man with unilateral leg involvement at onset showed very slow disease progression with selective posterior legs atrophy, tracing his aunt's disease history. His father and uncle died for ALS after a long disease course. Another patient with a 14 years history of ALS with the same phenotype, was found to belong to the same family. In all cases, genetic analysis of FUS gene revealed a missense mutation c.1520 G>A (p.G507D) inherited with a heterozygous pattern. Co-segregation of p.G507D mutation and a specific disease phenotype within the family, characterised by predominant involvement at the lower limbs, slow progression, late bulbar and respiratory failure, demonstrates pathogenicity of this mutation, establishes a well-defined genotype-phenotype correlation and expands the clinical spectrum of heterogeneity in FUS-ALS.

Missense mutation in ATXN2 gene (c.2860C > T) in an amyotrophic lateral sclerosis patient with aggressive disease phenotype.

BACKGROUND: ALS symptoms have been previously described only in the context of ATXN2 CAG expansions, whereas missense mutations of the gene have never been described in ALS patients. CASE PRESENTATION: We identified a novel missense mutation (c.2860C > T) of ATXN2, for which in silico analysis showed a possible pathogenic effect on protein expression, in a patient presenting an aggressive disease phenotype. DISCUSSION: Our findings raise the possibility for unknown genetic factors interacting with ATXN2 mutations, or for an autonomous pathogenic role for this specific point mutation in ATXN2 gene in driving the clinical phenotype toward ALS. We also found that stress granules in the fibroblasts from the patient entrapped higher amounts of defective ribosomal products compared to fibroblasts from three healthy subjects, suggesting that ATXN2 mutation-related toxicity may have implication in protein quality control.

Functional Characterization of Two Variants at the Intron 6-Exon 7 Boundary of the KCNQ2 Potassium Channel Gene Causing Distinct Epileptic Phenotypes.

Pathogenic variants in KCNQ2 encoding for Kv7.2 potassium channel subunits have been found in patients affected by widely diverging epileptic phenotypes, ranging from Self-Limiting Familial Neonatal Epilepsy (SLFNE) to severe Developmental and Epileptic Encephalopathy (DEE). Thus, understanding the pathogenic molecular mechanisms of KCNQ2 variants and their correlation with clinical phenotypes has a relevant impact on the clinical management of these patients. In the present study, the genetic, biochemical, and functional effects prompted by two variants, each found in a non-familial SLNE or a DEE patient but both affecting nucleotides at the KCNQ2 intron 6-exon 7 boundary, have been investigated to test whether and how they affected the splicing process and to clarify whether such mechanism might play a pathogenetic role in these patients. Analysis of KCNQ2 mRNA splicing in patient-derived lymphoblasts revealed that the SLNE-causing intronic variant (c.928-1G > C) impeded the use of the natural splice site, but lead to a 10-aa Kv7.2 in frame deletion (Kv7.2 p.G310Δ10); by contrast, the DEE-causing exonic variant (c.928G > A) only had subtle effects on the splicing process at this site, thus leading to the synthesis of a full-length subunit carrying the G310S missense variant (Kv7.2 p.G310S). Patch-clamp recordings in transiently-transfected CHO cells and primary neurons revealed that both variants fully impeded Kv7.2 channel function, and exerted strong dominant-negative effects when co-expressed with Kv7.2 and/or Kv7.3 subunits. Notably, Kv7.2 p.G310S, but not Kv7.2 p.G310Δ10, currents were recovered upon overexpression of the PIP2-synthesizing enzyme PIP5K, and/or CaM; moreover, currents from heteromeric Kv7.2/Kv7.3 channels incorporating either Kv7.2 mutant subunits were differentially regulated by changes in PIP2 availability, with Kv7.2/Kv7.2 G310S/Kv7.3 currents showing a greater sensitivity to PIP2 depletion when compared to those from Kv7.2/Kv7.2 G310Δ10/Kv7.3 channels. Altogether, these results suggest that the two variants investigated differentially affected the splicing process at the intron 6-exon 7 boundary, and led to the synthesis of Kv7.2 subunits showing a differential sensitivity to PIP2 and CaM regulation; more studies are needed to clarify how such different functional properties contribute to the widely-divergent clinical phenotypes.

Structural variation analysis of 6,500 whole genome sequences in amyotrophic lateral sclerosis.

There is a strong genetic contribution to Amyotrophic lateral sclerosis (ALS) risk, with heritability estimates of up to 60%. Both Mendelian and small effect variants have been identified, but in common with other conditions, such variants only explain a little of the heritability. Genomic structural variation might account for some of this otherwise unexplained heritability. We therefore investigated association between structural variation in a set of 25 ALS genes, and ALS risk and phenotype. As expected, the repeat expansion in the C9orf72 gene was identified as associated with ALS. Two other ALS-associated structural variants were identified: inversion in the VCP gene and insertion in the ERBB4 gene. All three variants were associated both with increased risk of ALS and specific phenotypic patterns of disease expression. More than 70% of people with respiratory onset ALS harboured ERBB4 insertion compared with 25% of the general population, suggesting respiratory onset ALS may be a distinct genetic subtype.

Duplication of exons 15 and 16 in Matrin-3: a phenotype bridging amyotrophic lateral sclerosis and immune-mediated disorders.

Mutations in Matrin-3 (MATR3) gene have been described in ALS, suggesting a role for this gene in the disease pathogenesis. While most of MATR3 mutations are point mutations, here we report the first case of ALS associated with duplication in exons 15 and 16. The patient presented with limb-onset ALS and a complex past medical history because of Sjögren syndrome, antiphospholipid antibodies positivity, polyallergies, endometriosis, aldosterone-secreting adrenal cortical adenoma, congenital vesicoureteral reflux, and right breast hypoplasia. We discuss MATR3 effect in ALS and the role of this previously undescribed mutation in this peculiar ALS phenotype associated with systemic autoimmunity involvement.

Digenic inheritance of STUB1 variants and TBP polyglutamine expansions explains the incomplete penetrance of SCA17 and SCA48.

PURPOSE: This study aimed to unravel the genetic factors underlying missing heritability in spinocerebellar ataxia type 17 (SCA17) caused by polyglutamine-encoding CAG/CAA repeat expansions in the TBP gene. Alleles with >49 CAG/CAA repeats are fully penetrant. Most patients, however, carry intermediate TBP41-49 alleles that show incomplete penetrance. METHODS: Using next-generation sequencing approaches, we investigated 40 SCA17/TBP41-54 index patients, their affected (n = 55) and unaffected (n = 51) relatives, and a cohort of patients with ataxia (n = 292). RESULTS: All except 1 (30/31) of the index cases with TBP41-46 alleles carried a heterozygous pathogenic variant in the STUB1 gene associated with spinocerebellar ataxias SCAR16 (autosomal recessive) and SCA48 (autosomal dominant). No STUB1 variant was found in patients carrying TBP47-54 alleles. TBP41-46 expansions and STUB1 variants cosegregate in all affected family members, whereas the presence of either TBP41-46 expansions or STUB1 variants individually was never associated with the disease. CONCLUSION: Our data reveal an unexpected genetic interaction between STUB1 and TBP in the pathogenesis of SCA17 and raise questions on the existence of SCA48 as a monogenic disease with crucial implications for diagnosis and counseling. They provide a convincing explanation for the incomplete penetrance of intermediate TBP alleles and demonstrate a dual inheritance pattern for SCA17, which is a monogenic dominant disorder for TBP≥47 alleles and a digenic TBP/STUB1 disease (SCA17-DI) for intermediate expansions.