Clinical and genetic features of dominant Essential Tremor in Tuscany, Italy: FUS, CAMTA1, ATXN1 and beyond

OBJECTIVE

Essential Tremor (ET) is one of the most common neurological disorders. In most instances ET is inherited as an autosomal dominant trait with age-related penetrance (virtually complete in advanced age); however, ET genetics remains elusive. The current study aims to identify possibly pathogenic genetic variants in a group of well-characterized ET families.

METHODS

34 individuals from 14 families with dominant ET were clinically evaluated and studied by whole exome sequencing studies (after excluding trinucleotide expansion disorders).

RESULTS

Most patients had pure ET. In 4 families, exome studies could identify a genetic variant potentially able to significantly alter the protein structure (CADD >20, REVEL score > 0.25), shared by all the affected individuals (in CAMTA1, FUS, MYH14, SGCE genes). In another family there were two variants in dominant genes (PCDH9 and SQSTM1). Moreover, an interrupted "intermediate" trinucleotide expansion in ATXN1 ("SCA1") was identified in a further family with pure ET.

CONCLUSION

Combining our observations together with earlier reports, we can conclude that ET genes confirmed in at least two families to date include CAMTA1 and FUS (reported here), as well as CACNA1G, NOTCH2NLC and TENM4. Most cases of familial ET, inherited with an autosomal dominant inheritance, may result from "mild" variants of many different genes that, when affected by more harmful genetic variants, lead to more severe neurological syndromes (still autosomal dominant). Thus, ET phenotype may be the "mild", incomplete manifestation of many other dominant neurogenetic diseases. These findings further support evidence of genetic heterogeneity for such disease(s). Author's keywords: cerebellar ataxias, movement disorders, neurogenetics, rare neurological disorders, tremor.

Large-Scale Screening: Phenotypic and Mutational Spectrum in Isolated and Combined Dystonia Genes

BACKGROUND

Pathogenic variants in several genes have been linked to genetic forms of isolated or combined dystonia. The phenotypic and genetic spectrum and the frequency of pathogenic variants in these genes have not yet been fully elucidated, neither in patients with dystonia nor with other, sometimes co-occurring movement disorders such as Parkinson's disease (PD).

OBJECTIVES

To screen >2000 patients with dystonia or PD for rare variants in known dystonia-causing genes.

METHODS

We screened 1207 dystonia patients from Germany (DysTract consortium), Spain, and South Korea, and 1036 PD patients from Germany for pathogenic variants using a next-generation sequencing gene panel. The impact on DNA methylation of KMT2B variants was evaluated by analyzing the gene's characteristic episignature.

RESULTS

We identified 171 carriers (109 with dystonia [9.0%]; 62 with PD [6.0%]) of 131 rare variants (minor allele frequency <0.005). A total of 52 patients (48 dystonia [4.0%]; four PD [0.4%, all with GCH1 variants]) carried 33 different (likely) pathogenic variants, of which 17 were not previously reported. Pathogenic biallelic variants in PRKRA were not found. Episignature analysis of 48 KMT2B variants revealed that only two of these should be considered (likely) pathogenic.

CONCLUSION

This study confirms pathogenic variants in GCH1, GNAL, KMT2B, SGCE, THAP1, and TOR1A as relevant causes in dystonia and expands the mutational spectrum. Of note, likely pathogenic variants only in GCH1 were also found among PD patients. For DYT-KMT2B, the recently described episignature served as a reliable readout to determine the functional effect of newly identified variants. © 2024 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Loss-of-function mutations in SGCE found in Japanese patients with myoclonus-dystonia

SGCE myoclonus-dystonia is a monogenic form of dystonia with an autosomal dominant mode of inheritance that co-occurs with a myoclonic jerk. In this study, we present 12 Japanese patients from nine families with this disease. Targeted next-generation sequencing covering major causative genes for monogenic dystonias identified nine distinct SGCE mutations from each of the families: three nonsense, two frameshift, two missense, one in-frame 15 bp deletion, and one splice donor site mutations, of which four were previously unreported. One missense mutation (c.662G>T, p.Gly221Val) was located at the 3' end of exon 5 (NM_001099400), which was predicted to cause aberrant splicing according to in silico predictions. Minigene assays performed together with the c.825+1G>C mutation demonstrated complete skipping of exon 5 and 6, respectively, in their transcripts. The other missense (c.1345A>G, p.Met449Val) and 15 bp deletion (c.168_182del, p.Phe58_Leu62del) mutations showed a significant reduction in cell membrane expression via HiBiT bioluminescence assay. Therefore, we concluded that all the detected mutations were disease-causing. Unlike the other detected mutations, p.Met449Val affects only isoform 3 (NP_001092870 encoded by NM_001099400) among the variously known isoforms of SGCE. This isoform is brain-specific and is mostly expressed in the cerebellum, which supports recent studies showing that cerebellar dysfunction is a key element in the pathophysiology of SGCE myoclonus-dystonia.

Clinical features and genetic analysis of SGCE myoclonus-dystonia: A case report

Myoclonus-dystonia caused by mutations in the SGCE gene is clinically characterized by early onset, myoclonus, and dystonia. Here we describe a family in which several members exhibit varying degrees of myoclonus and dystonia, caused by a novel heterozygous mutation in the SGCE gene.

Mutation in ε-Sarcoglycan Induces a Myoclonus-Dystonia Syndrome-Like Movement Disorder in Mice

Myoclonus dystonia syndrome (MDS) is an inherited movement disorder, and most MDS-related mutations have so far been found in the ε-sarcoglycan (SGCE) coding gene. By generating SGCE-knockout (KO) and human 237 C > T mutation knock-in (KI) mice, we showed here that both KO and KI mice exerted typical movement defects similar to those of MDS patients. SGCE promoted filopodia development in vitro and inhibited excitatory synapse formation both in vivo and in vitro. Loss of function of SGCE leading to excessive excitatory synapses that may ultimately contribute to MDS pathology. Indeed, using a zebrafish MDS model, we found that among 1700 screened chemical compounds, Vigabatrin was the most potent in readily reversing MDS symptoms of mouse disease models. Our study strengthens the notion that mutations of SGCE lead to MDS and most likely, SGCE functions to brake synaptogenesis in the CNS.

The Landscape of Genomic Imprinting at the Porcine SGCE/PEG10 Locus from Methylome and Transcriptome of Parthenogenetic Embryos

In mammals, imprinted genes often exist in the form of clusters in specific chromosome regions. However, in pigs, genomic imprinting of a relatively few genes and clusters has been identified, and genes within or adjacent to putative imprinted clusters need to be investigated including those at the SGCE/PEG10 locus. The objective of this study was to, using porcine parthenogenetic embryos, investigate imprinting status of genes within the genomic region spans between the COL1A2 and ASB4 genes in chromosome 9. Whole-genome bisulfite sequencing (WGBS) and RNA sequencing (RNA-seq) were conducted with normal and parthenogenetic embryos, and methylome and transcriptome were analyzed. As a result, differentially methylated regions (DMRs) between the embryos were identified, and parental allele-specific expressions of the SGCE and PEG10 genes were verified. The pig imprinted interval was limited between SGCE and PEG10, since both the COL1A2 and CASD1 genes at the centromere-proximal region and the genes between PPP1R9A and ASB4 toward the telomere were non-imprinted and biallelically expressed. Consequently, our combining analyses of methylome, transcriptome, and informative polymorphisms revealed the boundary of imprinting cluster at the SGCE/PEG10 locus in pig chromosome 9 and consolidated the landscape of genomic imprinting in pigs.

Population Prevalence of Deleterious SGCE Variants

Background:

Myoclonus-Dystonia (M-D) is a pleiotropic neuropsychiatric disorder of variable penetrance. Pathogenic variants in SGCE, a maternally imprinted gene, are the most frequent known genetic cause of M-D. The population prevalence of SGCE-linked M-D is unknown, the pathogenicity of SGCE variants identified in patients with M-D may be indeterminant, and SGCE variants predicted to be deleterious by in silico analysis may appear in patients undergoing whole-exome or whole-genome sequencing for seemingly unrelated disorders. The Genome Aggregation Database (gnomAD) v2 provides variant data on 125,748 exomes and 15,708 genomes from unrelated individuals sequenced as part of various disease-specific and population genetic studies.

Methods:

SGCE variants included in the gnomAD v2 dataset were analyzed with Combined Annotation Dependent Depletion (CADD), and database for nonsynonymous single nucleotide polymorphisms’ functional predictions (dbNSFP). We determined the frequency of annotated SGCE variants, ranked by scores of deleteriousness, within the gnomAD v2 dataset. Deleteriousness scores were compared to a subset of published disease associated SGCE pathogenic variants.

Results:

Within gnomAD v2, there were 56, 408, and 1250 alleles harboring SGCE variants with CADD scores greater than 30, 25, and 20, respectively. We estimate that approximately 1/348 individuals in the United States population harbors an SGCE variant with a CADD score ≥ 25.

Discussion:

SGCE M-D may be underdiagnosed due to pleiotropy, mild phenotypes, variable penetrance, and impaired access to genetic testing. Due to the high population prevalence of deleterious SGCE variants, caution should be used when asserting pathogenicity without co-segregation analyses and expert neurological examination of phenotypes within pedigrees.

Highlights

In silico analyses of a large population database of genetic variants revealed that over 0.2% of individuals in the United States harbor a highly deleterious SGCE variant. This finding suggests that M-D and minor phenotypic variants such as mild isolated myoclonus may be underdiagnosed.

A novel SGCE variant is associated with myoclonus-dystonia with phenotypic variability

Myoclonus-dystonia associated with epsilon-sarcoglycan gene (SGCE) is a rare disorder characterized by myoclonus involving the upper body (neck, trunk, upper limbs) and proximal muscles associated with dystonia in more than half of the patients. When the clinical picture is clearly identified, more than half of the cases are associated with mutations in the SGCE gene. We herein describe a family with myoclonus-dystonia associated with a novel mutation in exon 7 of SGCE, c.904A>T (p.Lys302Ter) [Chr7:(GRCh38):g.94600779 T>A], which was absent in a non-affected member. A video recording of two of the affected members is provided. While the index case presents a severe cervical dystonia even affecting back posture, his sibling shows a much milder phenotype with mild myoclonic jerks. None of them had alcohol responsiveness or psychiatric comorbidity.

Delayed Diagnoses of SGCE Myoclonus-Dystonia

Background:

Myoclonus-dystonia due to SGCE mutations (OMIM: 159900) most commonly presents during childhood with mainly upper body myoclonus, and mild dystonia affecting the neck and arms.

Case reports:

Herein, we report patients misdiagnosed during childhood with Tourette syndrome and dyskinetic cerebral palsy, and, during adulthood, found to harbor SGCE frameshift mutations.

Discussion:

Myoclonus-dystonia may be underdiagnosed due to phenotypic misclassification during childhood. SGCE mutations should be included in the differential diagnosis of childhood movement disorders that ostensibly manifest with tics, myoclonus, or abnormal posturing secondary to dystonia and/or spasticity.

Highlights:

Due to pleiotropy, variable penetrance, broad differential, and hereditary effects of imprinting, the diagnosis of a disorder of childhood onset, myoclonus-dystonia due to SGCE mutations, may be delayed until adulthood, often compromising appropriate clinical management and genetic counseling.

SGCE Promotes Breast Cancer Stem Cells by Stabilizing EGFR

Breast cancer stem cells (BCSCs) are responsible for resistance to chemotherapy, high degree of metastasis, and poor prognosis, especially in triple-negative breast cancer (TNBC). The CD24lowCD44high and high aldehyde dehydrogenase 1 (ALDH1) cell subpopulation (CD24lowCD44high ALDH1+) exhibit very high tumor initiating capacity. In the current study, the upregulated genes are analyzed in both CD24lowCD44high and ALDH1+ cell populations at single-cell resolution, and a highly expressed membrane protein, SGCE, is identified in both BCSC populations. Further results show that SGCE depletion reduces BCSC self-renewal, chemoresistance, and metastasis both in vitro and in vivo, partially through affecting the accumulation of extracellular matrix (ECM). For the underlying mechanism, SGCE functions as a sponge molecule for the interaction between epidermal growth factor receptor (EGFR) and its E3 ubiquitination ligase (c-Cbl), and thus inhibits EGFR lysosomal degradation to stabilize the EGFR protein. SGCE knockdown promotes sensitivity to EGFR tyrosine kinase inhibitors (TKIs), providing new clues for deciphering the current failure of targeting EGFR in clinical trials and highlighting a novel candidate for BCSC stemness regulation.

Clinical phenotype heterogeneity in a family with ε-sarcoglycan gene mutation

AIM OF THE STUDY

This paper describes six cases of patients with myoclonus-dystonia syndrome who are members of a family in which an SGCE gene mutation has been confirmed.

CLINICAL RATIONALE FOR THE STUDY

Myoclonus-dystonia syndrome is a very rare disease, with an incidence in Europe of about 2 in every million. Due to the fact that only a few case reports of this illness are accessible in the literature, the material we collected seems to be valuable for clinical practice.

MATERIALS AND METHODS

A history was taken, and physical and genetic examinations of the patients were performed. Furthermore, the clinical examination of three patients was video-recorded.

RESULTS

The clinical picture of the disease varied significantly between the described individuals, from a healthy carrier of the SGCE mutation to patients presenting mild to moderate symptoms. The differences concerned the age at onset of the disease, the initial symptoms, the intensity of involuntary movements, and the predominant symptoms. In addition to the typical movement disorders which are myoclonus and dystonia, in the described family there was also the coexistence of epilepsy, obsessive-compulsive behaviour, dyslexia, dysgraphia, non-harmonious development of cognitive processes, as well as mild phenotypic features of muscular dystrophy. The mutation (NM_001099401.2:c.806-809delACTG) found in the presented family has not been described elsewhere.

CONCLUSIONS AND CLINICAL IMPLICATIONS

Our description of six cases of patients demonstrates the heterogeneity of the natural course of the disease, even in patients with the same mutation. It seems reasonable to regularly examine relatives of patients with myoclonus-dystonia syndrome, who should be observed for involuntary movements as well as non-motor symptoms.

A Novel SGCE Nonsense Variant Associated With Marked Intrafamilial Variability in a Turkish Family With Myoclonus-Dystonia

Background

Myoclonus-Dystonia syndrome (M-D) is an autosomal-dominant movement disorder related to SGCE gene pathogenic variants. Although there can be observed variability in clinical findings, here we describe intrafamilial variability in a Turkish family with a novel nonsense SGCE pathogenic variant.

Methods

A family with variable clinical symptoms resembling M-D were referred to our clinic. After preliminary diagnosis, patients were tested for mutations in the SGCE gene by Sanger sequencing.

Results

Novel pathogenic heterozygous nonsense mutation in exon 3, c.272T>G; p.Leu91* (NM_003919.2) were observed in affected family members.

Conclusion

Intrafamilial clinical variability, despite the same pathogenic variant described in this work, suggests that there are regulatory factors, epigenetic or environmental modifiers, which are the subject of a matter for future studies.

Hereditary Myoclonus Dystonia: A Novel SGCE Variant and Phenotype Including Intellectual Disability

Background

Hereditary myoclonus dystonia is often due to changes in the SGCE gene. Dystonia (DYT)-SGCE has a variable phenotype that can involve focal or generalized myoclonus and various forms of task-specific, segmental, or generalized dystonia. Psychiatric comorbidities are common.

Case Report

We report a case of a young woman with generalized myoclonus, dystonia, and intellectual disability. She was found to have a novel SGCE splice site variant.

Discussion

This novel variant is very likely pathogenic by in silico analysis and has not been previously reported. Additionally, her intellectual disability may constitute a novel phenotype for patients with SGCE variants.

Report of progressive myoclonus ataxia (PMA) in two Chinese pedigrees

OBJECTIVE

To describe the clinical characteristics of patients diagnosed with progressive myoclonus ataxia (PMA) from two Chinese pedigrees.

METHODS

An analysis of clinical data is presented and inferences drawn.

RESULTS

The propositus from pedigree-I (9-year-old female) could not walk stably and had a history of frequent falls. The symptoms aggravated over time until she lost the ability to take care of herself. Her physical and mental development (including cognitive ability) was normal. She had an ataxic gait, ataxic dysarthria, bilateral horizontal nystagmus and visible limb myoclonus. She failed the bilateral finger-to-nose and heel-knee-tibia tests and could not walk in a straight line. Babinski signs were not observed. EEG tracing during sleep showed low-amplitude spikes and spike-and-slow waves in the bilateral frontal and mid-frontal areas. Her magnetic resonance imaging scan was normal. In pedigree-II, the propositus (a 54-year-old male) could not walk stably and had a history of occasional falls for the past 34 years. The symptoms aggravated gradually until he lost the ability to perform routine daily activities. There was no history of convulsions. His physical and mental faculties, as well as the neurological findings were similar to those of the pedigree-I. Both proposituses did not respond well to symptomatic treatment. A novel mutation has been identified in SGCE gene (NM_003919:exon3:c.360delT:p.A120fs) using exome sequencing.

CONCLUSION

PMA patients from the two pedigrees had autosomal dominant mode of inheritance, with variability in the age of onset and disease severity. The cardinal symptoms were myoclonic seizures and ataxia without mental retardation.

A novel description of a syndrome consisting of 7q21.3 deletion including DYNC1I1 with preserved DLX5/6 without ectrodactyly: a case report

BACKGROUND

Chromosomal region 7q21.3 comprises approximately 5.2 mega base pairs that include genes DLX5/6, SHFM1, and DYNC1I1 associated with split hand/split foot malformation 1. So far, there are reports of eight families with deletion of DYNC1I1 and preserved DLX5/6 associated with ectrodactyly. From these families, only three patients did not present ectrodactyly and, unlike our patient, no other cases have been described as having craniofacial dysmorphology, mitral valve prolapse, kyphoscoliosis, inguinal herniae, or personality disorder. There is no designation described in the literature for patients with syndromic manifestations without ectrodactyly, which hinders diagnosis.

CASE PRESENTATION

We report the case of a 44-year-old mestizo (combined European and Amerindian descent) man with a 3191 kilo base pairs deletion and International System for Human Cytogenetic Nomenclature array 7q21.3 (93,389,222-96,579,845)x1. Clinical manifestations included micrognathia, retrognathia, wormian bones, auditory canal stenosis, depressed nasal bridge, epicanthal fold, fullness of upper eyelid, long philtrum, low-set ears, sensorineural hearing loss, kyphoscoliosis, bilateral inguinal herniae, mild mitral valve prolapse, and paranoid personality disorder. His isolated DNA was analyzed using a CytoScan HD Microarray system. Chromosome Analysis Suite software was utilized for the microarray analysis. All copy number changes were determined using the human genome build 19 (hg19/NCBI build 37).

CONCLUSIONS

Cases of deletions within chromosome 7q21.3 that include the split hand/split foot malformation 1 region represent a diagnostic challenge when not presenting ectrodactyly despite being syndromic. Due to the heterogeneity of the region, a better method to group and classify these patients is needed to facilitate their clinical diagnosis. For this purpose, we suggest that patients with 7q21.3 deletion including DYNC1I1 and preserved DLX5/6 without ectrodactyly, accompanied by craniofacial dysmorphology, personality disorder, hearing loss, musculoskeletal disorder, inguinal herniae and/or mitral valve prolapse be referred to by the eponym Ramos-Martínez syndrome.

Progression of neuropsychiatric and cognitive features due to exons 2 to 5 deletion in the epsilon-sarcoglycan gene: a case report

Physical symptoms of myoclonus dystonia due to epsilon-sarcoglycan mutations are well documented; however, the progression of neuropsychiatric and cognitive symptoms remains unclear. We present a case of a 34-year-old woman with early childhood onset of myoclonic jerks, dystonic posture and developmental delay due to exons 2 to 5 deletion in the epsilon-sarcoglycan gene. Over time, she developed neuropsychiatric symptoms. She underwent bilateral deep brain stimulation of the ventral intermediate nucleus of the thalamus for her motor symptoms, which greatly improved but she exhibited slow deterioration of her neuropsychiatric and cognitive symptoms, particularly apathy, aggression and severe executive dysfunction.

Japanese familial case of myoclonus-dystonia syndrome with a splicing mutation in SGCE

Myoclonus-dystonia syndrome (MDS) is a rare autosomal-dominant movement disorder characterized by brief, frequently alcohol-responsive myoclonic jerks that begin in childhood or early adolescence, caused by mutations in the ε-sarcoglycan gene (SGCE). The patient was a 6-year-old boy. At 2 years 8 months, he had abnormal movement when he ran due to dystonia of his left leg. At 3 years 5 months, he exhibited dystonia and myoclonic movement of his arms when eating. Myoclonus was likely to develop when he felt anxiety or exhaustion. Genomic DNA showed a heterozygous mutation in SGCE (c.109 + 1 G > T). His father and uncle with the same mutation also experienced milder dystonia or myoclonic movements. SGCE mutation can cause a broad range of clinical symptoms between and within families. We should consider MDS as a differential diagnosis for patients with paroxysmal walking abnormalities and/or myoclonic movements.

Incomplete nonsense-mediated decay facilitates detection of a multi-exonic deletion mutation in SGCE

Mutations in SGCE represent the major cause of the myoclonus-dystonia syndrome (DYT11), an autosomal dominant disorder of reduced penetrance. Virtually all affected individuals have myoclonus, which is concentrated in the upper extremities, neck and trunk. Over half of patients have dystonia, usually affecting the neck or arms. SGCE is maternally imprinted. Of the more than 70 SGCE mutations reported in the literature, 18 are large deletions disrupting at least one exon. Therefore, testing for exonic deletions should be considered in individuals with a classic phenotype in whom Sanger sequencing is unrevealing. However, standard methodologies for detection of exonic deletion mutations are expensive, labor intensive and can produce false negatives. Herein, we report the use of cDNA derived from leukocyte RNA to identify a deletion mutation (exons 4 and 5) of SGCE in a family with DYT11. Residual RNA from incomplete nonsense-mediated decay permitted reverse transcription to cDNA. Breakpoints of the 8939 bp heterozygous deletion were then defined with long-range polymerase chain reaction and Sanger sequencing. Use of cDNA generated by reverse transcription of leukocyte RNA can reduce the costs associated with diagnostic genetic testing and can facilitate detection of deletion mutations.