Familial cortical myoclonic tremor with epilepsy: the third locus (FCMTE3) maps to 5p

Autism Spectrum Disorder- and/or Intellectual Disability-Associated Semaphorin-5A Exploits the Mechanism by Which Dock5 Signalosome Molecules Control Cell Shape

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that includes autism, Asperger's syndrome, and pervasive developmental disorder. Individuals with ASD may exhibit difficulties in social interactions, communication challenges, repetitive behaviors, and restricted interests. While genetic mutations in individuals with ASD can either activate or inactivate the activities of the gene product, impacting neuronal morphogenesis and causing symptoms, the underlying mechanism remains to be fully established. Herein, for the first time, we report that genetically conserved Rac1 guanine-nucleotide exchange factor (GEF) Dock5 signalosome molecules control process elongation in the N1E-115 cell line, a model line capable of achieving neuronal morphological changes. The increased elongation phenotypes observed in ASD and intellectual disability (ID)-associated Semaphorin-5A (Sema5A) Arg676-to-Cys [p.R676C] were also mediated by Dock5 signalosome molecules. Indeed, knockdown of Dock5 using clustered regularly interspaced short palindromic repeat (CRISPR)/CasRx-based guide(g)RNA specifically recovered the mutated Sema5A-induced increase in process elongation in cells. Knockdown of Elmo2, an adaptor molecule of Dock5, also exhibited similar recovery. Comparable results were obtained when transfecting the interaction region of Dock5 with Elmo2. The activation of c-Jun N-terminal kinase (JNK), one of the primary signal transduction molecules underlying process elongation, was ameliorated by either their knockdown or transfection. These results suggest that the Dock5 signalosome comprises abnormal signaling involved in the process elongation induced by ASD- and ID-associated Sema5A. These molecules could be added to the list of potential therapeutic target molecules for abnormal neuronal morphogenesis in ASD at the molecular and cellular levels.

RhoG-Binding Domain of Elmo1 Ameliorates Excessive Process Elongation Induced by Autism Spectrum Disorder-Associated Sema5A

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that includes autism, Asperger's syndrome, and pervasive developmental disorder. ASD is characterized by poor interpersonal relationships and strong attachment. The correlations between activated or inactivated gene products, which occur as a result of genetic mutations affecting neurons in ASD patients, and ASD symptoms are now of critical concern. Here, for the first time, we describe the process in which that the respective ASD-associated mutations (Arg676-to-Cys [R676C] and Ser951-to-Cys [S951C]) of semaphorin-5A (Sema5A) localize Sema5A proteins themselves around the plasma membrane in the N1E-115 cell line, a model line that can achieve neuronal morphological differentiation. The expression of each mutated construct resulted in the promotion of excessive elongation of neurite-like processes with increased differentiation protein markers; R676C was more effective than S951C. The differentiated phenotypes were very partially neutralized by an antibody, against Plexin-B3 as the specific Sema5A receptor, suggesting that the effects of Sema5A act in an autocrine manner. R676C greatly increased the activation of c-Jun N-terminal kinase (JNK), one of the signaling molecules underlying process elongation. In contrast, the blocking of JNK signaling, by a chemical JNK inhibitor or an inhibitory construct of the interaction of RhoG with Elmo1 as JNK upstream signaling molecules, recovered the excessive process elongation. These results suggest that ASD-associated mutations of Sema5A, acting through the JNK signaling cascade, lead to excessive differentiated phenotypes, and the inhibition of JNK signaling recovers them, revealing possible therapeutic targets for recovering the potential molecular and cellular phenotypes underlying certain ASD symptoms.

Nine Hereditary Movement Disorders First Described in Asia: Their History and Evolution

Clinical case studies and reporting are important to the discovery of new disorders and the advancement of medical sciences. Both clinicians and basic scientists play equally important roles leading to treatment discoveries for both cures and symptoms. In the field of movement disorders, exceptional observation of patients from clinicians is imperative, not just for phenomenology but also for the variable occurrences of these disorders, along with other signs and symptoms, throughout the day and the disease course. The Movement Disorders in Asia Task Force (TF) was formed to help enhance and promote collaboration and research on movement disorders within the region. As a start, the TF has reviewed the original studies of the movement disorders that were preliminarily described in the region. These include nine disorders that were first described in Asia: Segawa disease, PARK-Parkin, X-linked dystonia-parkinsonism, dentatorubral-pallidoluysian atrophy, Woodhouse-Sakati syndrome, benign adult familial myoclonic epilepsy, Kufor-Rakeb disease, tremulous dystonia associated with mutation of the calmodulin-binding transcription activator 2 gene, and paroxysmal kinesigenic dyskinesia. We hope that the information provided will honor the original researchers and help us learn and understand how earlier neurologists and basic scientists together discovered new disorders and made advances in the field, which impact us all to this day.

Familial Adult Myoclonus Epilepsy: A Non-Coding Repeat Expansion Disorder of Cerebellar-Thalamic-Cortical Loop

Familial adult myoclonus Epilepsy (FAME) is a non-coding repeat expansion disorder that has been reported under different acronyms and initially linked to four main loci: FAME1 (8q23.3-q24.1), FAME 2 (2p11.1-q12.1), FAME3 (5p15.31-p15.1), and FAME4 (3q26.32-3q28). To date, it is known that the genetic mechanism underlying FAME consists of the expansion of similar non-coding pentanucleotide repeats, TTTCA and TTTTA, in different genes. FAME is characterized by cortical tremor and myoclonus usually manifesting within the second decade of life, and infrequent seizures by the third or fourth decade. Cortical tremor is the core feature of FAME and is considered part of a spectrum of cortical myoclonus. Neurophysiological investigations as jerk-locked back averaging (JLBA) and corticomuscular coherence analysis, giant somatosensory evoked potentials (SEPs), and the presence of long-latency reflex I (or C reflex) at rest support cortical tremor as the result of the sensorimotor cortex hyperexcitability. Furthermore, the application of transcranial magnetic stimulation (TMS) protocols in FAME patients has recently shown that inhibitory circuits are also altered within the primary somatosensory cortex and the concomitant involvement of subcortical networks. Moreover, neuroimaging studies and postmortem autoptic studies indicate cerebellar alterations and abnormal functional connectivity between the cerebellum and cerebrum in FAME. Accordingly, the pathophysiological mechanism underlying FAME has been hypothesized to reside in decreased sensorimotor cortical inhibition through dysfunction of the cerebellar-thalamic-cortical loop, secondary to primary cerebellar pathology. In this context, the non-coding pentameric expansions have been proposed to cause cerebellar damage through an RNA-mediated toxicity mechanism. The elucidation of the underlying pathological mechanisms of FAME paves the way to novel therapeutic possibilities, such as RNA-targeting treatments, possibly applicable to other neurodegenerative non-coding disorders.

History of familial adult myoclonus epilepsy/benign adult familial myoclonic epilepsy around the world

Familial adult myoclonus epilepsy/benign adult familial myoclonic epilepsy (FAME/BAFME) has emerged as a specific and recognizable epilepsy syndrome with autosomal dominant inheritance found around the world. Here, we trace the history of this syndrome. Initially, it was likely conflated with other familial myoclonus epilepsies, especially the progressive myoclonus epilepsies. As the progressive myoclonus epilepsies became better understood clinically and genetically, this group began to stand out and was first recognized as such in Japan. Subsequently, families were recognized around the world and there was debate as to whether they represented one or multiple disorders. Clarification came with the identification of pentanucleotide repeats in Japanese families, and FAME/BAFME was quickly shown to be due to pentanucleotide expansions in at least six genes. These have geographic predilections and appear to have been caused by historically ancient initial mutations. Within and between families, there is some variation in the phenotype, explained in large part by expansion size, but whether there are features specific to individual genes remains uncertain.

Genetics of familial adult myoclonus epilepsy: From linkage studies to noncoding repeat expansions

Familial adult myoclonus epilepsy (FAME) is a genetic epilepsy syndrome that for many years has resisted understanding of its underlying molecular cause. This review covers the history of FAME genetic studies worldwide, starting with linkage and culminating in the discovery of noncoding TTTTA and inserted TTTCA pentanucleotide repeat expansions within six different genes to date (SAMD12, STARD7, MARCHF6, YEATS2, TNRC6A, and RAPGEF2). FAME occurs worldwide; however, repeat expansions in particular genes have regional geographical distributions. FAME repeat expansions are dynamic in nature, changing in length and structure within germline and somatic tissues. This variation poses challenges for molecular diagnosis such that molecular methods used to identify FAME repeat expansions typically require a trade-off between cost and efficiency. A rigorous evaluation of the sensitivity and specificity of each molecular approach remains to be performed. The origin of FAME repeat expansions and the genetic and environmental factors that modulate repeat variability are not well defined. Longer repeats and particular arrangements of the TTTTA and TTTCA motifs within an expansion are correlated with earlier onset and increased severity of disease. Other factors such as maternal or paternal inheritance, parental age, and repeat length alone have been suggested to influence repeat variation; however, further research is required to confirm this. The history of FAME genetics to the present is a chronicle of perseverance and predominantly collaborative efforts that yielded a successful outcome. The discovery of FAME repeats will spark progress toward a deeper understanding of the molecular pathogenesis of FAME, discovery of new loci, and development of cell and animal models.

Molecular Mechanisms in Pentanucleotide Repeat Diseases

The number of neurodegenerative diseases resulting from repeat expansion has increased extraordinarily in recent years. In several of these pathologies, the repeat can be transcribed in RNA from both DNA strands producing, at least, one toxic RNA repeat that causes neurodegeneration by a complex mechanism. Recently, seven diseases have been found caused by a novel intronic pentanucleotide repeat in distinct genes encoding proteins highly expressed in the cerebellum. These disorders are clinically heterogeneous being characterized by impaired motor function, resulting from ataxia or epilepsy. The role that apparently normal proteins from these mutant genes play in these pathologies is not known. However, recent advances in previously known spinocerebellar ataxias originated by abnormal non-coding pentanucleotide repeats point to a gain of a toxic function by the pathogenic repeat-containing RNA that abnormally forms nuclear foci with RNA-binding proteins. In cells, RNA foci have been shown to be formed by phase separation. Moreover, the field of repeat expansions has lately achieved an extraordinary progress with the discovery that RNA repeats, polyglutamine, and polyalanine proteins are crucial for the formation of nuclear membraneless organelles by phase separation, which is perturbed when they are expanded. This review will cover the amazing advances on repeat diseases.

Deciphering Neurodegenerative Diseases Using Long-Read Sequencing

Neurodegenerative diseases exhibit chronic progressive lesions in the central and peripheral nervous systems with unclear causes. The search for pathogenic mutations in human neurodegenerative diseases has benefited from massively parallel short-read sequencers. However, genomic regions, including repetitive elements, especially with high/low GC content, are far beyond the capability of conventional approaches. Recently, long-read single-molecule DNA sequencing technologies have emerged and enabled researchers to study genomes, transcriptomes, and metagenomes at unprecedented resolutions. The identification of novel mutations in unresolved neurodegenerative disorders, the characterization of causative repeat expansions, and the direct detection of epigenetic modifications on naive DNA by virtue of long-read sequencers will further expand our understanding of neurodegenerative diseases. In this article, we review and compare 2 prevailing long-read sequencing technologies, Pacific Biosciences and Oxford Nanopore Technologies, and discuss their applications in neurodegenerative diseases.

Complete sequencing of expanded SAMD12 repeats by long-read sequencing and Cas9-mediated enrichment

A pentanucleotide TTTCA repeat insertion into a polymorphic TTTTA repeat element in SAMD12 causes benign adult familial myoclonic epilepsy. Although the precise determination of the entire SAMD12 repeat sequence is important for molecular diagnosis and research, obtaining this sequence remains challenging when using conventional genomic/genetic methods, and even short-read and long-read next-generation sequencing technologies have been insufficient. Incomplete information regarding expanded repeat sequences may hamper our understanding of the pathogenic roles played by varying numbers of repeat units, genotype-phenotype correlations, and mutational mechanisms. Here, we report a new approach for the precise determination of the entire expanded repeat sequence and present a workflow designed to improve the diagnostic rates in various repeat expansion diseases. We examined 34 clinically diagnosed benign adult familial myoclonic epilepsy patients, from 29 families using repeat-primed PCR, Southern blot, and long-read sequencing with Cas9-mediated enrichment. Two cases with questionable results from repeat-primed PCR and/or Southern blot were confirmed as pathogenic using long-read sequencing with Cas9-mediated enrichment, resulting in the identification of pathogenic SAMD12 repeat expansions in 76% of examined families (22/29). Importantly, long-read sequencing with Cas9-mediated enrichment was able to provide detailed information regarding the sizes, configurations, and compositions of the expanded repeats. The inserted TTTCA repeat size and the proportion of TTTCA sequences among the overall repeat sequences were highly variable, and a novel repeat configuration was identified. A genotype-phenotype correlation study suggested that the insertion of even short (TTTCA)14 repeats contributed to the development of benign adult familial myoclonic epilepsy. However, the sizes of the overall TTTTA and TTTCA repeat units are also likely to be involved in the pathology of benign adult familial myoclonic epilepsy. Seven unsolved SAMD12-negative cases were investigated using whole-genome long-read sequencing, and infrequent, disease-associated, repeat expansions were identified in two cases. The strategic workflow resolved two questionable SAMD12-positive cases and two previously SAMD12-negative cases, increasing the diagnostic yield from 69% (20/29 families) to 83% (24/29 families). This study indicates the significant utility of long-read sequencing technologies to explore the pathogenic contributions made by various repeat units in complex repeat expansions and to improve the overall diagnostic rate.

Comprehensive genetic, clinical and electrophysiological studies of familial cortical myoclonic tremor with epilepsy 1 highlight the role of gene configurations

OBJECTIVES

Two configurations of TTTTA/TTTCA expansion in SAMD12 have been identified in familial cortical myoclonic tremor with epilepsy type 1 (FCMTE1). This study investigated the clinical and neurophysiological features of FCMTE1 and their association with TTTTA/TTTCA expansion patterns.

METHODS

In total, 76 patients from 20 Chinese pedigrees were enrolled. Genetic (TTTTA/TTTCA configuration), clinical (e.g., onset, medication, prognosis, and anticipation) and neurophysiological examination (e.g., electroencephalogram and magnetoencephalography) data were evaluated, and associations between these parameters were analyzed.

RESULTS

All patients carried the TTTTA/TTTCA expansion mutation, 19 displayed the (TTTTA)exp(TTTCA)exp (type I) configuration and 1 displayed the (TTTTA)exp (TTTCA)exp(TTTTA)exp (type II) configuration. All patients manifested as progressive tremor, but symptoms of patients carrying type II expansion were more severe. The onset of tremor but not generalized tonic and clonic seizures displayed clinical anticipation between generations of 7 pedigrees, but the pedigree carrying the type II mutation did not show anticipation. Nanopore sequencing showed that the repeats expanded during maternal/offspring transmission (pedigree #7) but shrank during paternal/offspring transmission (pedigree #9). Magnetoencephalographic dipoles were localized in the right frontal lobe near the central sulcus in 4 patients carrying the type I mutation and on the left side in one patient carrying the type II mutation.

SIGNIFICANCE

We confirmed the causative roles played by TTTTA/TTTCA repeat expansion in the SAMD12 gene in FCTME1. Both the length and the configuration of the repeats contribute to the clinical and neurophysiological characteristics of the disease.

Unravelling the enigma of cortical tremor and other forms of cortical myoclonus

Cortical tremor is a fine rhythmic oscillation involving distal upper limbs, linked to increased sensorimotor cortex excitability, as seen in cortical myoclonus. Cortical tremor is the hallmark feature of autosomal dominant familial cortical myoclonic tremor and epilepsy (FCMTE), a syndrome not yet officially recognized and characterized by clinical and genetic heterogeneity. Non-coding repeat expansions in different genes have been recently recognized to play an essential role in its pathogenesis. Cortical tremor is considered a rhythmic variant of cortical myoclonus and is part of the 'spectrum of cortical myoclonus', i.e. a wide range of clinical motor phenomena, from reflex myoclonus to myoclonic epilepsy, caused by abnormal sensorimotor cortical discharges. The aim of this update is to provide a detailed analysis of the mechanisms defining cortical tremor, as seen in FCMTE. After reviewing the clinical and genetic features of FCMTE, we discuss the possible mechanisms generating the distinct elements of the cortical myoclonus spectrum, and how cortical tremor fits into it. We propose that the spectrum is due to the evolution from a spatially limited focus of excitability to recruitment of more complex mechanisms capable of sustaining repetitive activity, overcoming inhibitory mechanisms that restrict excitatory bursts, and engaging wide areas of cortex. Finally, we provide evidence for a possible common denominator of the elements of the spectrum, i.e. the cerebellum, and discuss its role in FCMTE, according to recent genetic findings.

Genomic analysis of patients in a South Indian Community with autosomal dominant cortical tremor, myoclonus and epilepsy suggests a founder repeat expansion mutation in the SAMD12 gene

Autosomal Dominant Cortical Tremor, Myoclonus and Epilepsy is a non-progressive disorder characterized by distal tremors. Autosomal Dominant Cortical Tremor, Myoclonus and Epilepsy has been reported globally with different genetic predispositions of autosomal dominant inheritance with a high degree of penetrance. In south India, Autosomal Dominant Cortical Tremor, Myoclonus and Epilepsy has been reported in a large cohort of 48 families, in which the genetic defect was not identified. This report pertains to the whole-genome analysis of four individuals followed by repeat-primed PCR for 102 patients from a familial cohort of 325 individuals. All the patients underwent extensive clinical evaluation including neuropsychological examinations. The whole-genome sequencing was done for two affected and two unaffected individuals, belonging to two different families. The whole-genome sequencing analysis revealed the repeat expansion of TTTTA and TTTCA in intron 4 of the SAMD12 gene located on chromosome 8 in the patients affected with Autosomal Dominant Cortical Tremor, Myoclonus and Epilepsy, whereas the unaffected family members were negative for the similar expansion. Further, the repeat-primed PCR analysis of 102 patients showed the expansion of the TTTCA repeats in the intron 4 of SAMD12 gene. All patients registered for this study belong to a single community called “Nadar” whose nativity is confined to the southern districts of India, with reported unique genetic characteristics. This is the largest and most comprehensive single report on clinically and genetically characterized Autosomal Dominant Cortical Tremor, Myoclonus and Epilepsy patients belonging to a unique ethnic group worldwide.

Founder effect of the TTTCA repeat insertions in SAMD12 causing BAFME1

Benign adult familial myoclonic epilepsy type 1 (BAFME1) in several Japanese and Chinese families has recently been found to be caused by pentanucleotide repeat expansions in SAMD12. We identified a Thai family with six members affected with BAFME. Microsatellite studies suggested a linkage to the BAFME1 region on chromosome 8q24. Subsequently, long-read whole-genome sequencing showed the (TTTTA)₄₄₆(TTTCA)₁₄₉ in intron 4 of SAMD12 in an affected member. Repeat-primed PCR and long-range PCR revealed that the pentanucleotide repeat expansions segregated with the disease status. Our Thai family is the first non-Japanese and non-Chinese family with BAFME1. SNP array showed that the aberrant repeats had the same haplotype as those previously determined in Japanese and Chinese patients suggesting a common ancestry. The variant is estimated to arise ~12,000 years ago.

Familial cortical myoclonic tremor with epilepsy: TTTCA/TTTTA repeat expansions and expanding phenotype in two Chinese families

Recently, expanded intronic TTTCA and TTTTA repeat in SAMD12 were identified in families with familial cortical myoclonic tremor with epilepsy (FCMTE). We conducted to this study to clarify the genetic etiology and to describe the clinical, neurophysiologic, and imaging features in two unrelated Chinese families with FCMTE. In this study, we performed the RP-PCR and long-range PCR analysis to examine and verifyTTTCA and TTTTA expansions in five affected members whose severities of cortical tremor, neuropsychology and MRI were also evaluated. Reliable clinical information was collected from another two affected members. Our results revealed that expansions of intronic TTTCA and TTTTA repeats in SAMD12 were both identified in all five affected subjects. All seven affected living patients had cortical tremor with a median age at onset of 16.4 years (range, 10-22 years). Convulsions occurred in 5 of 7 with a median age at onset of 32.4 years (range, 10-42 years). Among five patients evaluated for cortical tremor severity and psychiatric comorbidity, two patients had severe cortical tremor, anxiety and depression. Abnormal brain MRI findings including the possible existence of demyelination, severe atrophy of the cerebral hemisphere and abnormal bilateral symmetrical signals in the globus pallidus were observed in three patients, respectively. These results further expanded the known genotype in two Chinese families affected with FCMTE. Border clinical spectrum needs to be confirmed in future studies from additional FCMTE families genetically diagnosed.

TTTCA repeat insertions in an intron of YEATS2 in benign adult familial myoclonic epilepsy type 4

Epilepsy is a common neurological disorder and identification of its causes is important for a better understanding of its pathogenesis. We previously studied a Thai family with a type of epilepsy, benign adult familial myoclonic epilepsy type 4 (BAFME4), and localized its gene to chromosome 3q26.32-q28. Here, we used single-molecule real-time sequencing and found expansions of TTTTA and insertions of TTTCA repeats in intron 1 of YEATS2 in one affected member of the family. Of all the available members in the family-comprising 13 affected and eight unaffected-repeat-primed PCR and long-range PCR revealed the co-segregation of the TTTCA repeat insertions with the TTTTA repeat expansions and the disease status. For 1116 Thai control subjects, none were found to harbour the TTTCA repeats while four had the TTTTA repeat expansions. Therefore, our findings suggest that BAFME4 is caused by the insertions of the intronic TTTCA repeats in YEATS2. Interestingly, all four types of BAFMEs for which underlying genes have been found (BAFMEs 1, 4, 6 and 7) are caused by the same molecular pathology, suggesting that the insertions of non-coding TTTCA repeats are involved in their pathogenesis.

Familial adult myoclonic epilepsy type 1 SAMD12 TTTCA repeat expansion arose 17,000 years ago and is present in Sri Lankan and Indian families

Familial adult myoclonic epilepsy 1 (FAME1), first recognised in Japanese families, was recently shown to be caused by a TTTCA repeat insertion in intron 4 of SAMD12 on chromosome 8. We performed whole genome sequencing on two families with FAME, one of Sri Lankan origin and the other of Indian origin, and identified a TTTCA repeat insertion in SAMD12 in both families. Haplotype analysis revealed that both families shared the same core ancestral haplotype reported in Japanese and Chinese families with FAME1. Mutation dating, based on the length of shared haplotypes, estimated the age of the ancestral haplotype to be ~670 generations, or 17,000 years old. Our data extend the geographic range of this repeat expansion to Southern Asia and potentially implicate an even broader regional distribution given the age of the variant. This finding suggests patients of Asian ancestry with suspected FAME should be screened for the SAMD12 TTTCA expansion.

Intronic ATTTC repeat expansions in STARD7 in familial adult myoclonic epilepsy linked to chromosome 2

Familial Adult Myoclonic Epilepsy (FAME) is characterised by cortical myoclonic tremor usually from the second decade of life and overt myoclonic or generalised tonic-clonic seizures. Four independent loci have been implicated in FAME on chromosomes (chr) 2, 3, 5 and 8. Using whole genome sequencing and repeat primed PCR, we provide evidence that chr2-linked FAME (FAME2) is caused by an expansion of an ATTTC pentamer within the first intron of STARD7. The ATTTC expansions segregate in 158/158 individuals typically affected by FAME from 22 pedigrees including 16 previously reported families recruited worldwide. RNA sequencing from patient derived fibroblasts shows no accumulation of the AUUUU or AUUUC repeat sequences and STARD7 gene expression is not affected. These data, in combination with other genes bearing similar mutations that have been implicated in FAME, suggest ATTTC expansions may cause this disorder, irrespective of the genomic locus involved.

Unstable TTTTA/TTTCA expansions in MARCH6 are associated with Familial Adult Myoclonic Epilepsy type 3

Familial Adult Myoclonic Epilepsy (FAME) is a genetically heterogeneous disorder characterized by cortical tremor and seizures. Intronic TTTTA/TTTCA repeat expansions in SAMD12 (FAME1) are the main cause of FAME in Asia. Using genome sequencing and repeat-primed PCR, we identify another site of this repeat expansion, in MARCH6 (FAME3) in four European families. Analysis of single DNA molecules with nanopore sequencing and molecular combing show that expansions range from 3.3 to 14 kb on average. However, we observe considerable variability in expansion length and structure, supporting the existence of multiple expansion configurations in blood cells and fibroblasts of the same individual. Moreover, the largest expansions are associated with micro-rearrangements occurring near the expansion in 20% of cells. This study provides further evidence that FAME is caused by intronic TTTTA/TTTCA expansions in distinct genes and reveals that expansions exhibit an unexpectedly high somatic instability that can ultimately result in genomic rearrangements.

Intronic pentanucleotide TTTCA repeat insertion in the SAMD12 gene causes familial cortical myoclonic tremor with epilepsy type 1

Familial cortical myoclonic tremor with epilepsy is an autosomal dominant neurodegenerative disease, characterized by cortical tremor and epileptic seizures. Although four subtypes (types 1-4) mapped on different chromosomes (8q24, 2p11.1-q12.2, 5p15.31-p15.1 and 3q26.32-3q28) have been reported, the causative gene has not yet been identified. Here, we report the genetic study in a cohort of 20 Chinese pedigrees with familial cortical myoclonic tremor with epilepsy. Linkage and haplotype analysis in 11 pedigrees revealed maximum two-point logarithm of the odds (LOD) scores from 1.64 to 3.77 (LOD scores in five pedigrees were >3.0) in chromosomal region 8q24 and narrowed the candidate region to an interval of 4.9 Mb. Using whole-genome sequencing, long-range polymerase chain reaction and repeat-primed polymerase chain reaction, we identified an intronic pentanucleotide (TTTCA)n insertion in the SAMD12 gene as the cause, which co-segregated with the disease among the 11 pedigrees mapped on 8q24 and additional seven unmapped pedigrees. Only two pedigrees did not contain the (TTTCA)n insertion. Repeat-primed polymerase chain reaction revealed that the sizes of (TTTCA)n insertion in all affected members were larger than 105 repeats. The same pentanucleotide insertion (ATTTCATTTC)58 has been reported to form RNA foci resulting in neurotoxicity in spinocerebellar ataxia type 37, which suggests the similar pathogenic process in familial cortical myoclonic tremor with epilepsy type 1.

Familial adult myoclonic epilepsy: A new expansion repeats disorder

Familial adult myoclonic epilepsy (FAME), also described with different acronyms (ADCME, BAFME, FEME, FCTE and others), is a high-penetrant autosomal dominant condition featuring cortical hand tremors, myoclonic jerks, and occasional/rare convulsive seizures. Prevalence is unknown since this condition is often under-recognized, but it is estimated to be less than 1/35,000. The disease usually starts in the second decade of life and has been genetically associated with at least 4 different loci (8q24, 2p11.1-q12.2, 5p15.31-p15 and 3q26.32-3q28). Recently, the expansion of non coding TTTTA and TTTCA repeats has been identified as the causative mutation in Japanese families linked to the 8q24. The diagnosis is supported by clinical features and electrophysiological investigations as jerk-locked back averaging, C-reflex, and somatosensory-evoked potential. Photic stimulation, emotional stress, and sleep deprivation may trigger both tonic-clonic and myoclonic seizures. FAME has a slow but progressive clinical course occurring with intellectual disability and worsening of both tremor and myoclonus although with a less severe decline compared to other progressive myoclonic epilepsies. Valproate, levetiracetam, and benzodiazepines are considered the first-line treatments.

TTTCA repeat expansion causes familial cortical myoclonic tremor with epilepsy

BACKGROUND AND PURPOSE

The aim was to investigate whether abnormal TTTTA and TTTCA repeat expansions in introns of SAMD12, TNRC6A and RAPGEF2 are involved in the pathogenesis of familial cortical myoclonic tremor with epilepsy (FCMTE).

METHODS

Five families diagnosed with FCMTE were included in the current genetic analysis. Whole-exome sequencing was performed in selected patients of each family. TTTTA and TTTCA expansions were examined by repeat-primed polymerase chain reaction. The clinical features of FCMTE were elicited as defined by the common genetic mechanism of 14 patients.

RESULTS

Abnormal TTTCA expansion was identified and co-segregated in all five FCMTE families, four inserted in SAMD12 and one in RAPGEF2. The insertion of expanded TTTCA was not found in 116 control alleles. TTTTA expansion in SAMD12 was detected in 90.9% (10/11) of patients or mutation carriers; TTTTA expansion in RAPGEF2 was not found. The onset age of myoclonic tremor was 27.4 ± 5.9 (19-37) and epilepsy usually presented around age 34. Focal and generalized seizures were witnessed with various origins recorded by electroencephalogram. Cognitive deficits were not common within the first 3 years after epilepsy onset. Emotional instability was reported by most patients. No patients showed any cerebellar deficits. Valproate added with clonazepam is effective in controlling seizures but cannot guarantee a complete remission of tremor. Repeat length showed intergenerational instability and was inversely correlated with age at onset of myoclonic tremor and epilepsy.

CONCLUSIONS

TTTCA expansion insertion is associated with FCMTE in Chinese families. The homogenous genetic mechanism allowed for a higher precision of FCMTE description.

Whole exome sequencing reveals novel NOV and DCAF13 variants in a Chinese pedigree with familial cortical myoclonic tremor with epilepsy

OBJECTIVE

We report a large new family of familial cortical myoclonic tremor with epilepsy(FCMTE) from China and identify the possible causative gene(s) for the family.

METHOD

Whole exome sequencing of blood genomic DNA from 4 patients and 2 unaffected family members were performed. Detected variants and their cosegregation were confirmed by Sanger sequencing.

RESULTS

We identified c.20 G > C variant in the DCAF13 gene and c.983 T > C variant in the NOV gene cosegregating in the family. There was no additional cross-over in the family to narrow to one gene. The two DCAF13 and NOV gene variants are located on 8q23.3 and 8q24.12, which is consistent with the location 8q23.3-q24.13 reported previously for a group of Japanese families. The DCAF13 variant is located in alternative transcription start site(TSS) and the function of alternative TSS is unknown. The missense NOV variant is near the C terminus in a site that is highly conserved across species. It was predicted to be deleterious on protein function.

CONCLUSIONS

In this study, we identify two novel variants in the DCAF13 and NOV genes associated with FCMTE in Asian populations. The interval between two variants is 15.6Mb, which is very close to each other. Future studies of additional families with this phenotype are warranted to confirm whether it is rare bigenic or monogenic inheritance.

Long-read sequencing identified intronic repeat expansions inSAMD12from Chinese pedigrees affected with familial cortical myoclonic tremor with epilepsy

Background

The locus for familial cortical myoclonic tremor with epilepsy (FCMTE) has long been mapped to 8q24 in linkage studies, but the causative mutations remain unclear. Recently, expansions of intronic TTTCA and TTTTA repeat motifs withinSAMD12were found to be involved in the pathogenesis of FCMTE in Japanese pedigrees. We aim to identify the causative mutations of FCMTE in Chinese pedigrees.

Methods

We performed genetic linkage analysis by microsatellite markers in a five-generation Chinese pedigree with 55 members. We also used array-comparative genomic hybridisation (CGH) and next-generation sequencing (NGS) technologies (whole-exome sequencing, capture region deep sequencing and whole-genome sequencing) to identify the causative mutations in the disease locus. Recently, we used low-coverage (~10×) long-read genome sequencing (LRS) on the PacBio Sequel and Oxford Nanopore platforms to identify the causative mutations, and used repeat-primed PCR for validation of the repeat expansions.

Results

Linkage analysis mapped the disease locus to 8q23.3–24.23. Array-CGH and NGS failed to identify causative mutations in this locus. LRS identified the intronic TTTCA and TTTTA repeat expansions inSAMD12as the causative mutations, thus corroborating the recently published results in Japanese pedigrees.

Conclusions

We identified the pentanucleotide repeat expansion inSAMD12as the causative mutation in Chinese FCMTE pedigrees. Our study also suggested that LRS is an effective tool for molecular diagnosis of genetic disorders, especially for neurological diseases that cannot be positively diagnosed by conventional clinical microarray and NGS technologies.

Expansions of intronic TTTCA and TTTTA repeats in benign adult familial myoclonic epilepsy

Epilepsy is a common neurological disorder, and mutations in genes encoding ion channels or neurotransmitter receptors are frequent causes of monogenic forms of epilepsy. Here we show that abnormal expansions of TTTCA and TTTTA repeats in intron 4 of SAMD12 cause benign adult familial myoclonic epilepsy (BAFME). Single-molecule, real-time sequencing of BAC clones and nanopore sequencing of genomic DNA identified two repeat configurations in SAMD12. Intriguingly, in two families with a clinical diagnosis of BAFME in which no repeat expansions in SAMD12 were observed, we identified similar expansions of TTTCA and TTTTA repeats in introns of TNRC6A and RAPGEF2, indicating that expansions of the same repeat motifs are involved in the pathogenesis of BAFME regardless of the genes in which the expanded repeats are located. This discovery that expansions of noncoding repeats lead to neuronal dysfunction responsible for myoclonic tremor and epilepsy extends the understanding of diseases with such repeat expansion.

Familial Cortical Myoclonic Tremor and Epilepsy, an Enigmatic Disorder: From Phenotypes to Pathophysiology and Genetics. A Systematic Review

Background

Autosomal dominant familial cortical myoclonic tremor and epilepsy (FCMTE) is characterized by distal tremulous myoclonus, generalized seizures, and signs of cortical reflex myoclonus. FCMTE has been described in over 100 pedigrees worldwide, under several different names and acronyms. Pathological changes have been located in the cerebellum. This systematic review discusses the clinical spectrum, treatment, pathophysiology, and genetic findings.

Methods

We carried out a PubMed search, using a combination of the following search terms: cortical tremor, myoclonus, epilepsy, benign course, adult onset, familial, and autosomal dominant; this resulted in a total of 77 studies (761 patients; 126 pedigrees) fulfilling the inclusion and exclusion criteria.

Results

Phenotypic differences across pedigrees exist, possibly related to underlying genetic differences. A "benign" phenotype has been described in several Japanese families and pedigrees linked to 8q (FCMTE1). French patients (5p linkage; FCMTE3) exhibit more severe progression, and in Japanese/Chinese pedigrees (with unknown linkage) anticipation has been suggested. Preferred treatment is with valproate (mind teratogenicity), levetiracetam, and/or clonazepam. Several genes have been identified, which differ in potential pathogenicity.

Discussion

Based on the core features (above), the syndrome can be considered a distinct clinical entity. Clinical features may also include proximal myoclonus and mild progression with aging. Valproate or levetiracetam, with or without clonazepam, reduces symptoms. FCMTE is a heterogeneous disorder, and likely to include a variety of different conditions with mutations of different genes. Distinct phenotypic traits might reflect different genetic mutations. Genes involved in Purkinje cell outgrowth or those encoding for ion channels or neurotransmitters seem good candidate genes.

δ-Catenin (CTNND2) missense mutation in familial cortical myoclonic tremor and epilepsy

OBJECTIVE

To identify the causative gene in a large Dutch family with familial cortical myoclonic tremor and epilepsy (FCMTE).

METHODS

We performed exome sequencing for 3 patients of our FCMTE family. Next, we performed knock-down (shRNA) and rescue experiments by overexpressing wild-type and mutant human δ-catenin (CTNND2) proteins in cortical mouse neurons and compared the results with morphologic abnormalities in the postmortem FCMTE brain.

RESULTS

We identified a missense mutation, p.Glu1044Lys, in the CTNND2 gene that cosegregated with the FCMTE phenotype. The knock-down of Ctnnd2 in cultured cortical mouse neurons revealed increased neurite outgrowth that was rescued by overexpression of wild-type, but not mutant, CTNND2 and was reminiscent of the morphologic abnormalities observed in cerebellar Purkinje cells from patients with FCMTE.

CONCLUSIONS

We propose CTNND2 as the causal gene in FCMTE3. Functional testing of the mutant protein revealed abnormal neuronal sprouting, consistent with the abnormal cerebellar Purkinje cell morphology in patients with FCMTE.

Familial cortical myoclonic tremor and epilepsy: Description of a new South African pedigree with 30 year follow up

AIM

The aims of this study were to report the index case of a South African family with cortical myoclonic tremor and epilepsy, to describe the pedigree with the clinical findings and results of additional investigations, and to report the unique follow-up evaluation of affected and unaffected family members after 30 years.

METHODS

The index case led to evaluation of the clinical files of patients from 1978/1979 and clinical assessment and investigation of patients from this cohort as well as newly identified family members. Patients were examined clinically; cortical myoclonic tremor severity was scored by using the Fahn-Tolosa- Marin-Tremor Rating Scale and the Myoclonus Rating Scale. Cortical origin of myoclonus was proven. Statistical analyses were done to assess the impact of cortical myoclonic tremor on quality of life.

CONCLUSION

Clinical data was available for 23 patients. Increase in cortical myoclonic tremor and age showed a statistically significant correlation with worsening of the sub-score for Quality of Life (FTMTRS) and myoclonus rating scale. After 30 years eleven of fourteen patients could be followed up. Progression of cortical myoclonic tremor severity was noted but epilepsy control was adequate with all patients reporting less than two seizures per year. No clinical features of neurodegeneration were found.

DISCUSSION

We describe the initial presentation and 30 year follow-up of a four generation South African family with FCMTE. The unique long term follow up of this pedigree supports previous findings that the condition does not cause additional progressive neurological deterioration and quality of life is mostly influenced by worsening of the cortical myoclonic tremor with age.

Clinical and neurophysiological features of familial cortical myoclonic tremor with epilepsy

OBJECTIVE

Familial cortical myoclonic tremor with epilepsy is a rare epilepsy syndrome. Herein, we report on nine Chinese familial cortical myoclonic tremor with epilepsy pedigrees to delineate its clinical and neurophysiological features.

METHODS

Detailed clinical and neurophysiological data were obtained. Somatosensory evoked potential amplitudes and clinical profile were analyzed using multilevel statistical models. Age-at-onset anticipation was analyzed using Kaplan-Meier survival analysis.

RESULTS

Fifty-five patients were interviewed directly, whose mean age at onset of cortical tremor and generalized tonic-clonic seizures were 31.0 ± 8.3 and 36.0 ± 7.9 years. Giant somatosensory evoked potential was detected in 87.5% (28 of 32) of patients, and long-latency cortical reflex was detected in 93.5% (29 of 31). Cortical tremor severity was significantly higher in patients with longer disease duration of cortical tremor (P = 0.0061). Somatosensory evoked potential amplitudes were significant higher in patients with higher level of cortical tremor severity (P = 0.0003) and those using antiepileptic drugs (P = 0.0150). Age-at-onset anticipation of cortical tremor with paternal transmission was found with statistical significance (P = 0.022).

CONCLUSION

We provided the clinical and neurophysiological features of familial cortical myoclonic tremor with epilepsy patients. This study is reported for the presentation of this rare disease in a Chinese population with the largest single report on familial cortical myoclonic tremor with epilepsy worldwide. Age-at-onset anticipation of cortical tremor with paternal transmission was statistically significant, which further confirmed a possibility of unstable expanding repeat in the genetic mechanism of familial cortical myoclonic tremor with epilepsy. © 2016 International Parkinson and Movement Disorder Society.

Autosomal Dominant Cortical Tremor, Myoclonus, and Epilepsy Syndrome mimicking Juvenile Myoclonic Epilepsy

INTRODUCTION

Autosomal dominant cortical tremor, myoclonus, and epilepsy (ADCME) syndrome is a genetically heterogeneous and under-recognized disease characterized by tremulous movements mimicking essential tremor, myoclonus, and rare generalized tonic-clonic seizures. Here we described the clinical and electrophysiological features of three siblings with ADCME syndrome mimicking juvenile myoclonic epilepsy (JME).

METHODS

Three siblings (two females and one male) diagnosed with ADCME were analyzed by electroencephalogram (EEG), somatosensory evoked potentials, and accelerometric recordings. The results were compared with 14 JME patients without tremor and 14 with essential tremor (ET).

RESULTS

The shared features of the siblings were cortical tremor, myoclonia, epilepsy, migraine, and psychiatric symptoms. In all siblings, tremor had started before myoclonic epilepsy associated with 4-6 Hz generalized spike and wave discharges. The N20-P25 and P25-N35 amplitudes were substantially higher in the three siblings with ADCME. Although tremor frequencies were similar to those of the ET group, the siblings had mild interrupting low-amplitude myoclonus, suggestive of cortical tremor, in the accelerometric analysis.

CONCLUSION

We presented a detailed clinical evaluation with electrophysiological confirmation of ADCME syndrome in a Turkish family. This rare clinical picture might be misdiagnosed as JME and should be kept in mind to ensure correct diagnosis and to provide a homogenous group for genetic studies.

Identification of a novel mutation in PLA2G6 gene in a Chinese pedigree with familial cortical myoclonic tremor with epilepsy

PURPOSE

Familial cortical myoclonic tremor with epilepsy (FCMTE) is an epileptic syndrome with autosomal dominant inheritance, of which four genetic subtypes (FCMTE1-4) have been reported. In the present study, we described the clinical and neurophysiologic features of a newly diagnosed Chinese FCMTE family, and investigated the genetic cause for this disease.

METHODS

Clinical information was obtained from affected and normal individuals of an FCMTE family comprising 41 members. Electroencephalographies were analyzed in five of six affected members (including the proband). Brain magnetic resonance imaging, somatosensory evoked potential with C-reflex analysis and magnetoencephalography was performed in the proband. Genomic DNA of three affected and two unaffected individuals was analyzed to detect the genetic mutations by using whole-exome sequencing.

RESULTS

The inheritance pattern of the pedigree was autosomal dominant. A novel missense mutation c.475C>T (p.Ala159Thr) of PLA2G6 were identified in this family. The mutated locus is highly conserved among other species. The mutation is predicted to have a functional impact, and completely co-segregated with the phenotype.

CONCLUSION

This study identifies a novel PLA2G6 mutation that is the possible genetic cause of FCMTE in this family. This mutation and associated clinical features expand the spectrum and phenotypes of PLA2G6-related disorders including neurodegenerative diseases.

Identity by descent fine mapping of familial adult myoclonus epilepsy (FAME) to 2p11.2-2q11.2

Familial adult myoclonus epilepsy (FAME) is a rare autosomal dominant disorder characterized by adult onset, involuntary muscle jerks, cortical myoclonus and occasional seizures. FAME is genetically heterogeneous with more than 70 families reported worldwide and five potential disease loci. The efforts to identify potential causal variants have been unsuccessful in all but three families. To date, linkage analysis has been the main approach to find and narrow FAME critical regions. We propose an alternative method, pedigree free identity-by-descent (IBD) mapping, that infers regions of the genome between individuals that have been inherited from a common ancestor. IBD mapping provides an alternative to linkage analysis in the presence of allelic and locus heterogeneity by detecting clusters of individuals who share a common allele. Succeeding IBD mapping, gene prioritization based on gene co-expression analysis can be used to identify the most promising candidate genes. We performed an IBD analysis using high-density single nucleotide polymorphism (SNP) array data followed by gene prioritization on a FAME cohort of ten European families and one Australian/New Zealander family; eight of which had known disease loci. By identifying IBD regions common to multiple families, we were able to narrow the FAME2 locus to a 9.78 megabase interval within 2p11.2-q11.2. We provide additional evidence of a founder effect in four Italian families and allelic heterogeneity with at least four distinct founders responsible for FAME at the FAME2 locus. In addition, we suggest candidate disease genes using gene prioritization based on gene co-expression analysis.

Altered cerebellar-cerebral functional connectivity in benign adult familial myoclonic epilepsy

OBJECTIVE

The pathogenesis of benign adult familial myoclonic epilepsy (BAFME) remains unknown, although cerebellar pathologic changes and brain hyperexcitability have been reported. We used resting-state functional magnetic resonance imaging (fMRI) to examine the functional connectivity between the cerebellum and cerebrum in a Chinese family with BAFME for the first time.

METHODS

Eleven adults with BAFME and 15 matched healthy controls underwent resting-state blood oxygen level-dependent (BOLD) fMRI scanning. The cerebellar seeds, including the bilateral crus I, lobule VIII, lobule VIIb, and lobule IV&V, were defined a priori. Next, regional time courses were obtained for each individual by averaging the BOLD time series over all voxels in each seed region. Then, seed-based functional connectivity z-maps were produced by computing Pearson's correlation coefficients (converted to z-scores by Fisher transformation) between each seed signal and the time series from all other voxels within the entire brain. Finally, a second-level random-effect two-sample t-test was performed on the individual z-maps in a voxel-wise manner.

RESULTS

Reduced functional connectivity of the right cerebellar crus I with the left middle frontal gyrus and right cerebellar lobule IX was observed in the default network of BAFME. Enhanced functional connectivity of the left cerebellar lobule VIII with the bilateral middle temporal gyri, right putamen, and left cerebellar crus I was found in the dorsal attention network of BAFME. Enhanced functional connectivity between the left cerebellar lobule VIIb and right frontal pole was found in the control network of BAFME.

SIGNIFICANCE

Altered cerebellar-cerebral functional connectivity may contribute to the understanding of the nosogenesis of BAFME and explain the cognitive dysfunction in this Chinese family with BAFME.

Psychiatric comorbidities in patients from seven families with autosomal dominant cortical tremor, myoclonus, and epilepsy

OBJECTIVE

The objective of this report was to assess the psychiatric comorbidity in a group of patients affected by autosomal dominant cortical tremor, myoclonus, and epilepsy (ADCME).

METHODS

Reliable and validated psychodiagnostic scales including the BDI (Beck Depression Inventory), STAI-Y1 and 2 (State-Trait Anxiety Inventory - Y; 1 and 2), MMPI-2 (Minnesota Multiphasic Personality Inventory - 2), and QoLIE-31 (Quality of Life in Epilepsy Inventory - 31) were administered to 20 patients with ADCME, 20 patients with juvenile myoclonic epilepsy (JME), and 20 healthy controls.

RESULTS

There was a higher prevalence of mood disorders in patients with ADCME compared to patients with JME and healthy controls, particularly depression (p=0.035 and p=0.017, respectively) and state anxiety (p=0.024 and p=0.019, respectively). Trait anxiety was not different from JME (p=0.102) but higher than healthy controls (p=0.017). The myoclonus score positively correlated with both state (rho: 0.58, p=0.042) and trait anxiety (rho: 0.65, p=0.011). These psychiatric features were also often associated with pathological traits of personality: paranoid (OR: 25.7, p=0.003), psychasthenia (OR: 7.0, p=0.023), schizophrenia (OR: 8.5, p=0.011), and hypomania (OR: 5.5, p=0.022). Finally, in patients with ADCME, decreased quality of life correlated with these psychiatric symptoms.

SIGNIFICANCE

Patients with ADCME show a significant psychiatric burden that impairs their quality of life. A comprehensive psychiatric evaluation should be offered at the time of diagnosis to detect these comorbidities and to treat them.

Gray Matter Loss and Related Functional Connectivity Alterations in A Chinese Family With Benign Adult Familial Myoclonic Epilepsy

Benign adult familial myoclonic epilepsy (BAFME) is a non-progressive monogenic epilepsy syndrome. So far, the structural and functional brain reorganizations in BAFME remain uncharacterized. This study aims to investigate gray matter atrophy and related functional connectivity alterations in patients with BAFME using magnetic resonance imaging (MRI).Eleven BAFME patients from a Chinese pedigree and 15 matched healthy controls were enrolled in the study. Optimized voxel-based morphometric and resting-state functional MRI approaches were performed to measure gray matter atrophy and related functional connectivity, respectively. The Trail-Making Test-part A and part B, Digit Symbol Test (DST), and Verbal Fluency Test (VFT) were carried out to evaluate attention and executive functions.The BAFME patients exhibited significant gray matter loss in the right hippocampus, right temporal pole, left orbitofrontal cortex, and left dorsolateral prefrontal cortex. With these regions selected as seeds, the voxel-wise functional connectivity analysis revealed that the right hippocampus showed significantly enhanced connectivity with the right inferior parietal lobule, bilateral middle cingulate cortex, left precuneus, and left precentral gyrus. Moreover, the BAFME patients showed significant lower scores in DST and VFT tests compared with the healthy controls. The gray matter densities of the right hippocampus, right temporal pole, and left orbitofrontal cortex were significantly positively correlated with the DST scores. In addition, the gray matter density of the right temporal pole was significantly positively correlated with the VFT scores, and the gray matter density of the right hippocampus was significantly negatively correlated with the duration of illness in the patients.The current study demonstrates gray matter loss and related functional connectivity alterations in the BAFME patients, perhaps underlying deficits in attention and executive functions in the BAFME.

Fine mapping and whole-exome sequencing of a familial cortical myoclonic tremor with epilepsy family

Familial cortical myoclonic tremor with epilepsy (FCMTE) is an autosomal dominant epilepsy syndrome. Four loci, including 8q24 (FCMTE1), 2p11.1-q12.2 (FCMTE2), 5p15.31-p15.1 (FCMTE3), and 3q26.32-3q28 (FCMTE4) were previously reported. Herein, we report a new FCMTE1 pedigree from Chinese population with its clinical and genetic study results. Whole genome scan was performed to identify the causative gene region and copy number variants. Whole-exome sequencing was used to identify the causative gene. There were twelve affected members alive in this FCMTE1 pedigree. Nine affected members had both cortical myoclonic tremor and epilepsy, while three affected members had only cortical myoclonic tremor. Electrophysiologic examinations manifested giant somatosensory evoked potentials and long-latency cortical reflex in some affected members. Whole genome scan identified a 20.4 Mb causative gene region at 8q22.3-q24.13. No copy number variants were identified as the causative mutation. Whole-exome sequencing identified a co-segregated mutation (c.206A>T; p.Y69F) in the SLC30A8 gene. However, the evidence supporting this gene as the causative gene of FCMTE1 is not enough. We report the first Chinese FCMTE1 pedigree. No copy number variants, point mutation or small insertion/deletion were detected in the identified region that showed an association with FCMTE1. Further studies could focus on other possible genetic mechanisms while the association between the SLC30A8 and FCMTE1 needs further evidence.

A case-control proton magnetic resonance spectroscopy study confirms cerebellar dysfunction in benign adult familial myoclonic epilepsy

BACKGROUND

Benign adult familial myoclonic epilepsy (BAFME) is a rare form of epilepsy syndrome. The pathogenesis of BAFME remains unclear, though it seems to involve dysfunction of the cerebellum.

OBJECTIVES

The purpose of this study was to use proton magnetic resonance spectroscopy ((1)H-MRS) to investigate whether neurochemical changes underlie abnormal brain function in BAFME.

METHODS

Twelve BAFME patients from one family and 12 age- and sex-matched healthy controls were enrolled in this study. The ratios of NAA/Cr, NAA/Cho, Cho/Cr, and NAA/(Cr+Cho) were analyzed.

RESULTS

The BAFME patients exhibited a decreased N-acetylaspartate (NAA)/choline (Cho) ratio in the cerebellar cortex, whereas there were no significant differences in the NAA/creatine (Cr), Cho/Cr, and NAA/(Cr+Cho) ratios compared with healthy controls. There were no significant differences in (1)H-MRS values in the frontal cortex or thalamus between the BAFME patients and controls. No correlation was detected between the NAA/Cho ratio in the cerebellar cortex and disease duration, myoclonus severity, or tremor severity.

CONCLUSION

Our results indicate clear cerebellar dysfunction in BAFME. (1)H-MRS is a useful tool for the diagnosis of BAFME in combination with family history and electrophysiological examination.

The α2B-adrenergic receptor is mutant in cortical myoclonus and epilepsy

OBJECTIVE

Autosomal dominant cortical myoclonus and epilepsy (ADCME) is characterized by distal, fairly rhythmic myoclonus and epilepsy with variable severity. We have previously mapped the disease locus on chromosome 2p11.1-q12.2 by genome-wide linkage analysis. Additional pedigrees affected by similar forms of epilepsy have been associated with chromosomes 8q, 5p, and 3q, but none of the causing genes has been identified. We aim to identify the mutant gene responsible for this form of epilepsy.

METHODS

Genes included in the ADCME critical region were directly sequenced. Coimmunoprecipitation, immunofluorescent, and electrophysiologic approaches to transfected human cells have been utilized for testing the functional significance of the identified mutation.

RESULTS

Here we show that mutation in the α2 -adrenergic receptor subtype B (α2B -AR) is associated with ADCME by identifying a novel in-frame insertion/deletion in 2 Italian families. The mutation alters several conserved residues of the third intracellular loop, hampering neither the α2B -AR plasma membrane localization nor the arrestin-mediated internalization capacity, but altering the binding with the scaffolding protein spinophilin upon neurotransmitter activation. Spinophilin, in turn, regulates interaction of G protein coupled receptors with regulator of G protein signaling proteins. Accordingly, the mutant α2B -AR increases the epinephrine-stimulated calcium signaling.

INTERPRETATION

The identified mutation is responsible for ADCME, as the loss of α2B -AR/spinophilin interaction causes a gain of function effect. This work implicates for the first time the α-adrenergic system in human epilepsy and opens new ways of understanding the molecular pathway of epileptogenesis, widening the spectrum of possible therapeutic targets.

The ACMSD gene, involved in tryptophan metabolism, is mutated in a family with cortical myoclonus, epilepsy, and parkinsonism

Familial cortical myoclonic tremor and epilepsy is a phenotypically and genetically heterogeneous autosomal dominant disorder characterized by the presence of cortical myoclonic tremor and epilepsy that is often accompanied by additional neurological features. Despite the numerous familial studies performed and the number of loci identified, there is no gene associated with this syndrome. It is expected that through the application of novel genomic technologies, such as whole exome sequencing and whole genome sequencing, a substantial number of novel genes will come to light in the coming years. In this study, we describe the identification of two disease-segregating mutations in a large family featuring cortical myoclonic tremor with epilepsy and parkinsonism. Due to the previous association of ACMSD deficiency with the development of epileptic seizures, we concluded that the identified nonsense mutation in the ACMSD gene, which encodes for a critical enzyme of the kynurenine pathway of the tryptophan metabolism, is the disease-segregating mutation most likely to be responsible for the phenotype described in our family. This finding not only reveals the identification of the first gene associated with familial cortical myoclonic tremor and epilepsy but also discloses the kynurenine pathway as a potential therapeutic target for the treatment of this devastating syndrome.

KEY MESSAGE

ACMSD is mutated in a family with cortical myoclonus, epilepsy, and parkinsonism. ACMSD mutation contributes to the development of FCMTE QA accumulation is likely to play an important role in the pathogenesis of FCMTE. The kynurenine pathway as a potential drug target for the treatment of epilepsy.

A novel pedigree with familial cortical myoclonic tremor and epilepsy (FCMTE): clinical characterization, refinement of the FCMTE2 locus, and confirmation of a founder haplotype

PURPOSE

We describe the clinical, neurophysiologic, and genetic features of a new, large family with familial cortical myoclonic tremor and epilepsy (FCMTE).

METHODS

Reliable clinical information was obtained on the 127 members. Thirty-one collaborative individuals were assessed by a detailed clinical interview and a complete neurologic examination. A polygraphic study was conducted in 15 patients, back-averaging analysis and somatosensory evoked potentials with C-reflex study in four. The genetic study investigated 30 subjects with microsatellite markers at three loci on chromosomes 8q (FCMTE1), 2p (FCMTE2), and 5p (FCMTE3).

KEY FINDINGS

The pedigree included 25 affected members (M/F: 9/16). We studied 16 of the 19 living affected members (M/F: 5/11; mean age 47.8 years). Cortical myoclonic tremor (CMT) was associated with generalized seizures in 10 patients (62.5%). The mean age at onset of CMT and seizures was 28.1 and 33.8 years, respectively. Four patients (25%) reported a slow progression of CMT, with severe gait impairment in one. Psychiatric disorders of variable severity recurred in 37.5% of cases. Rhythmic bursts at 7-15 Hz were recorded in all 11 affected members tested. Additional neurophysiologic investigations disclosed a cortical origin of myoclonus in all patients tested. Generalized epileptiform discharges were recorded in 25% of cases, and a photoparoxysmal response in 31%. Genetic analysis established linkage to the FCMTE2 locus on chromosome 2p11.1-2q12.2 (OMIM 607876) and narrowed the critical interval to a 10.4 Mb segment. Haplotype analysis in the present family identified a founder haplotype identical to that previously observed in families from the same geographic area.

SIGNIFICANCE

This study confirms evidence of a founder effect in Italian families and reduces the number of positional candidate genes in the FCMTE2 locus to 59, thereby contributing to future gene identification by Next Generation Sequencing approaches.