CAG repeat-binding small molecule improves motor coordination impairment in a mouse model of Dentatorubral-pallidoluysian atrophy.

Dentatorubral-pallidoluysian atrophy (DRPLA) is a devastating genetic disease presenting myoclonus, epilepsy, ataxia, and dementia. DRPLA is caused by the expansion of a CAG repeat in the ATN1 gene. Aggregation of the polyglutamine-expanded ATN1 protein causes neuro-degeneration of the dentatorubral and pallidoluysian systems. The expanded CAG repeats are unstable, and ongoing repeat expansions contribute to disease onset, progression, and severity. Inducing contractions of expanded repeats can be a means to treat DRPLA, for which no disease-modifying or curative therapies exist at present. Previously, we characterized a small molecule, naphthyridine-azaquinolone (NA), which binds to CAG slip-out structures and induces repeat contraction in Huntington's disease mice. Here, we demonstrate that long-term intracerebroventricular infusion of NA leads to repeat contraction, reductions in mutant ATN1 aggregation, and improved motor phenotype in a murine model of DRPLA. Furthermore, NA-induced contraction resulted in the modification of repeat-length-dependent dysregulation of gene expression profiles in DRPLA mice. Our study reveals the therapeutic potential of repeat contracting small molecules for repeat expansion disorders, such as DRPLA.

Progressive Myoclonus Epilepsy Caused by a Homozygous Splicing Variant of SLC7A6OS.

Exome sequencing was performed in 2 unrelated families with progressive myoclonus epilepsy. Affected individuals from both families shared a rare, homozygous c.191A > G variant affecting a splice site in SLC7A6OS. Analysis of cDNA from lymphoblastoid cells demonstrated partial splice site abolition and the creation of an abnormal isoform. Quantitative reverse transcriptase polymerase chain reaction and Western blot showed a marked reduction of protein expression. Haplotype analysis identified a ~0.85cM shared genomic region on chromosome 16q encompassing the c.191A > G variant, consistent with a distant ancestor common to both families. Our results suggest that biallelic loss-of-function variants in SLC7A6OS are a novel genetic cause of progressive myoclonus epilepsy. ANN NEUROL 2021;89:402-407.

Compound heterozygous KCTD7 variants in progressive myoclonus epilepsy.

KCTD7 is a member of the potassium channel tetramerization domain-containing protein family and has been associated with progressive myoclonic epilepsy (PME), characterized by myoclonus, epilepsy, and neurological deterioration. Here we report four affected individuals from two unrelated families in which we identified KCTD7 compound heterozygous single nucleotide variants through exome sequencing. RNAseq was used to detect a non-annotated splicing junction created by a synonymous variant in the second family. Whole-cell patch-clamp analysis of neuroblastoma cells overexpressing the patients' variant alleles demonstrated aberrant potassium regulation. While all four patients experienced many of the common clinical features of PME, they also showed variable phenotypes not previously reported, including dysautonomia, brain pathology findings including a significantly reduced thalamus, and the lack of myoclonic seizures. To gain further insight into the pathogenesis of the disorder, zinc finger nucleases were used to generate kctd7 knockout zebrafish. Kctd7 homozygous mutants showed global dysregulation of gene expression and increased transcription of c-fos, which has previously been correlated with seizure activity in animal models. Together these findings expand the known phenotypic spectrum of KCTD7-associated PME, report a new animal model for future studies, and contribute valuable insights into the disease.

Progressive myoclonus epilepsy KCNC1 variant causes a developmental dendritopathy.

OBJECTIVE: Mutations in KCNC1 can cause severe neurological dysfunction, including intellectual disability, epilepsy, and ataxia. The Arg320His variant, which occurs in the voltage-sensing domain of the channel, causes a highly penetrant and specific form of progressive myoclonus epilepsy with severe ataxia, designated myoclonus epilepsy and ataxia due to potassium channel mutation (MEAK). KCNC1 encodes the voltage-gated potassium channel KV 3.1, a channel that is important for enabling high-frequency firing in interneurons, raising the possibility that MEAK is associated with reduced interneuronal function. METHODS: To determine how this variant triggers MEAK, we expressed KV 3.1bR320H in cortical interneurons in vitro and investigated the effects on neuronal function and morphology. We also performed electrophysiological recordings of oocytes expressing KV 3.1b to determine whether the mutation introduces gating pore currents. RESULTS: Expression of the KV 3.1bR320H variant profoundly reduced excitability of mature cortical interneurons, and cells expressing these channels were unable to support high-frequency firing. The mutant channel also had an unexpected effect on morphology, severely impairing neurite development and interneuron viability, an effect that could not be rescued by blocking KV 3 channels. Oocyte recordings confirmed that in the adult KV 3.1b isoform, R320H confers a dominant negative loss-of-function effect by slowing channel activation, but does not introduce potentially toxic gating pore currents. SIGNIFICANCE: Overall, our data suggest that, in addition to the regulation of high-frequency firing, KV 3.1 channels play a hitherto unrecognized role in neuronal development. MEAK may be described as a developmental dendritopathy.

FBXO28 causes developmental and epileptic encephalopathy with profound intellectual disability.

Chromosome 1q41-q42 deletion syndrome is a rare cause of intellectual disability, seizures, dysmorphology, and multiple anomalies. Two genes in the 1q41-q42 microdeletion, WDR26 and FBXO28, have been implicated in monogenic disease. Patients with WDR26 encephalopathy overlap clinically with those with 1q41-q42 deletion syndrome, whereas only one patient with FBXO28 encephalopathy has been described. Seizures are a prominent feature of 1q41-q42 deletion syndrome; therefore, we hypothesized that pathogenic FBXO28 variants cause developmental and epileptic encephalopathies (DEEs). We describe nine new patients with FBXO28 pathogenic variants (four missense, including one recurrent, three nonsense, and one frameshift) and analyze all 10 known cases to delineate the phenotypic spectrum. All patients had epilepsy and 9 of 10 had DEE, including infantile spasms (3) and a progressive myoclonic epilepsy (1). Median age at seizure onset was 22.5 months (range 8 months to 5 years). Nine of 10 patients had intellectual disability, which was profound in six of nine and severe in three of nine. Movement disorders occurred in eight of 10 patients, six of 10 had hypotonia, four of 10 had acquired microcephaly, and five of 10 had dysmorphic features, albeit different to those typically seen in 1q41-q42 deletion syndrome and WDR26 encephalopathy. We distinguish FBXO28 encephalopathy from both of these disorders with more severe intellectual impairment, drug-resistant epilepsy, and hyperkinetic movement disorders.

Neuroinflammation and progressive myoclonus epilepsies: from basic science to therapeutic opportunities.

Progressive myoclonus epilepsies (PMEs) are a group of genetic neurological disorders characterised by the occurrence of epileptic seizures, myoclonus and progressive neurological deterioration including cerebellar involvement and dementia. The primary cause of PMEs is variable and alterations in the corresponding mutated genes determine the progression and severity of the disease. In most cases, they lead to the death of the patient after a period of prolonged disability. PMEs also share poor information on the pathophysiological bases and the lack of a specific treatment. Recent reports suggest that neuroinflammation is a common trait under all these conditions. Here, we review similarities and differences in neuroinflammatory response in several PMEs and discuss the window of opportunity of using anti-inflammatory drugs in the treatment of several of these conditions.

Dentatorubro-Pallidoluysian Atrophy (DRPLA) among 700 Families with Ataxia in Brazil.

Dentatorubro-pallidoluysian atrophy (DRPLA) is a spinocerebellar ataxia (SCA) very rare in non-Asian populations. To date, DRPLA was undetected in the general Brazilian population. Adult-onset ataxic patients have been recruited from several Brazilian neurology and neurogenetics centers. CAG lengths at SCA1, SCA2, SCA3/MJD, SCA6, SCA7, SCA12, SCA17 and DRPLA associated genes, and ATTCT expansions at SCA10 gene were studied. A single DRPLA case detected is reported. Proband was a 69-year-old Brazilian woman of mixed ancestry, with a late-onset pure ataxia: her alleles at the associated gene, ATN1, presented 14/52 CAG repeats. History of gait ataxia and dementia was observed in two out of six siblings but was absent in her parents. This was the single DRPLA diagnosis obtained from 700 Brazilian unrelated cases with adult-onset ataxia, 487 of them with clear autosomal dominant inheritance. DRPLA accounted for 0.14% of all adult-onset ataxia cases and for 0.2% of families with autosomal dominant inheritance. Normal CAG repeats at ATN1 had a median (range) of 14 (5-20) repeats in other 410 Brazilian chromosomes. DRPLA is quite rare in Brazilian SCA families, which is consistent with the lack of large normal alleles in our population.

SERPINI1 pathogenic variants: An emerging cause of childhood-onset progressive myoclonic epilepsy.

Progressive myoclonic epilepsies are rare neurodegenerative diseases with a wide spectrum of clinical presentations and genetic heterogeneity that render their diagnosis perplexing. Discovering new imputable genes has been an ongoing process in recent years. We present two pediatric cases of progressive myoclonic epilepsy with SERPINI1 pathogenic variants that lead to a severe presentation; we highlight the importance of including this gene, previously known as causing an adult-onset dementia-epilepsy syndrome, in the genetic work-up of childhood-onset progressive myoclonic epilepsies.

'North Sea' progressive myoclonus epilepsy: phenotype of subjects with GOSR2 mutation.

We previously identified a homozygous mutation in the Golgi SNAP receptor complex 2 gene (GOSR2) in six patients with progressive myoclonus epilepsy. To define the syndrome better we analysed the clinical and electrophysiological phenotype in 12 patients with GOSR2 mutations, including six new unrelated subjects. Clinical presentation was remarkably similar with early onset ataxia (average 2 years of age), followed by myoclonic seizures at the average age of 6.5 years. Patients developed multiple seizure types, including generalized tonic clonic seizures, absence seizures and drop attacks. All patients developed scoliosis by adolescence, making this an important diagnostic clue. Additional skeletal deformities were present, including pes cavus in four patients and syndactyly in two patients. All patients had elevated serum creatine kinase levels (median 734 IU) in the context of normal muscle biopsies. Electroencephalography revealed pronounced generalized spike and wave discharges with a posterior predominance and photosensitivity in all patients, with focal EEG features seen in seven patients. The disease course showed a relentless decline; patients uniformly became wheelchair bound (mean age 13 years) and four had died during their third or early fourth decade. All 12 cases had the same variant (c.430G>T, G144W) and haplotype analyses confirmed a founder effect. The cases all came from countries bounding the North Sea, extending to the coastal region of Northern Norway. 'North Sea' progressive myoclonus epilepsy has a homogeneous clinical presentation and relentless disease course allowing ready identification from the other progressive myoclonus epilepsies.

Chronic neuronopathic type of Gaucher's disease with progressive myoclonic epilepsy in the absence of visceromegaly and bone involvement.

INTRODUCTION: Gaucher's disease is a lysosomal storage disorder caused by the deficiency of glucocerebrosidase. Gaucher's disease has three clinical types: non-neuronopathic (Type 1), Acute Neuropathic (Type 2) and chronic neuronopathic (Type 3). The chronic neuronopathic (Type 3) is characterised by a variety of disease variants with onset in childhood with hepatomegaly, skeletal lesions and later slow horizontal saccades, treatment-resistant generalised tonic-clonic and myoclonic seizures, dementia, progressive spasticity, cognitive deterioration, ataxia and death in the second or third decade of life. CASE PRESENTATION: We describe a case of a 17-year-old girl who was born normally but subsequently developed treatment-refractory seizures at the age of nine with myoclonus, oculomotor apraxia, ataxia and cognitive decline. Enzyme activity of beta-glucocerebrosidase was found to be low without visceromegaly or bone involvement. CONCLUSION: Screening for lysosomal enzyme activity should be done in patients exhibiting features suggestive of progressive myoclonic epilepsy.

Retinal vascular pathology in a mouse model of Lafora progressive myoclonus epilepsy.

Neurodegenerative diseases (ND) affect distinct populations of neurons and manifest various clinical and pathological symptoms. A subset of ND prognoses has been linked to vascular risk factors. Consequently, the current study investigated retinal vascular abnormalities in a murine model of Lafora neurodegenerative disease (LD), a fatal and genetic form of progressive myoclonus epilepsy that affects children. Here, arterial rigidity was evaluated by measuring pulse wave velocity and vasculature deformations in the retina. Our findings in the LD mouse model indicate altered pulse wave velocity, retinal vascular thinning, and convoluted retinal arteries.

Identification of COL6A2 mutations in progressive myoclonus epilepsy syndrome.

In this study, a consanguineous family with progressive myoclonus epilepsy (PME) was clinically examined and molecularly investigated to determine the molecular events causing disease. Since exclusion of known genes indicated that novel genes causing PME still remained unidentified, homozygosity mapping, exome sequencing, as well as validation and disease-segregation analyses were subsequently carried out for both loci and gene identification. To further assure our results, a muscle biopsy and gene expression analyses were additionally performed. As a result, a homozygous, disease-segregating COL6A2 mutation, p.Asp215Asn, absent in a large number of control individuals, including control individuals of Iranian ancestry, was identified in both affected siblings. COL6A2 was shown to be expressed in the human cerebral cortex and muscle biopsy revealed no specific histochemical pathology. We conclude that the COL6A2 p.Asp215Asn mutation is likely to be responsible for PME in this family; however, additional studies are warranted to further establish the pathogenic role of both COL6A2 and the extracellular proteolysis system in the pathogenesis of PME.

Severe neurological phenotypes of Q129 DRPLA transgenic mice serendipitously created by en masse expansion of CAG repeats in Q76 DRPLA mice.

We herein provide a thorough description of new transgenic mouse models for dentatorubral-pallidoluysian atrophy (DRPLA) harboring a single copy of the full-length human mutant DRPLA gene with 76 and 129 CAG repeats. The Q129 mouse line was unexpectedly obtained by en masse expansion based on the somatic instability of 76 CAG repeats in vivo. The mRNA expression levels of both Q76 and Q129 transgenes were each 80% of that of the endogenous mouse gene, whereas only the Q129 mice exhibited devastating progressive neurological phenotypes similar to those of juvenile-onset DRPLA patients. Electrophysiological studies of the Q129 mice demonstrated age-dependent and region-specific presynaptic dysfunction in the globus pallidus and cerebellum. Progressive shrinkage of distal dendrites of Purkinje cells and decreased currents through alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and gamma-aminobutyrate type A receptors in CA1 neurons were also observed. Neuropathological studies of the Q129 mice revealed progressive brain atrophy, but no obvious neuronal loss, associated with massive neuronal intranuclear accumulation (NIA) of mutant proteins with expanded polyglutamine stretches starting on postnatal day 4, whereas NIA in the Q76 mice appeared later with regional specificity to the vulnerable regions of DRPLA. Expression profile analyses demonstrated age-dependent down-regulation of genes, including those relevant to synaptic functions and CREB-dependent genes. These results suggest that neuronal dysfunction without neuronal death is the essential pathophysiologic process and that the age-dependent NIA is associated with nuclear dysfunction including transcriptional dysregulations. Thus, our Q129 mice should be highly valuable for investigating the mechanisms of disease pathogenesis and therapeutic interventions.

Novel SCARB2 mutation in action myoclonus-renal failure syndrome and evaluation of SCARB2 mutations in isolated AMRF features.

BACKGROUND: Action myoclonus-renal failure syndrome is a hereditary form of progressive myoclonus epilepsy associated with renal failure. It is considered to be an autosomal-recessive disease related to loss-of-function mutations in SCARB2. We studied a German AMRF family, additionally showing signs of demyelinating polyneuropathy and dilated cardiomyopathy. To test the hypothesis whether isolated appearance of individual AMRF syndrome features could be related to heterozygote SCARB2 mutations, we screened for SCARB2 mutations in unrelated patients showing isolated AMRF features. METHODS: In the AMRF family all exons of SCARB2 were analyzed by Sanger sequencing. The mutation screening of unrelated patients with isolated AMRF features affected by either epilepsy (n = 103, progressive myoclonus epilepsy or generalized epilepsy), demyelinating polyneuropathy (n = 103), renal failure (n = 192) or dilated cardiomyopathy (n = 85) was performed as high resolution melting curve analysis of the SCARB2 exons. RESULTS: A novel homozygous 1 bp deletion (c.111delC) in SCARB2 was found by sequencing three affected homozygous siblings of the affected family. A heterozygous sister showed generalized seizures and reduction of nerve conduction velocity in her legs. No mutations were found in the epilepsy, renal failure or dilated cardiomyopathy samples. In the polyneuropathy sample two individuals with demyelinating disease were found to be carriers of a SCARB2 frameshift mutation (c.666delCCTTA). CONCLUSIONS: Our findings indicate that demyelinating polyneuropathy and dilated cardiomyopathy are part of the action myoclonus-renal failure syndrome. Moreover, they raise the possibility that in rare cases heterozygous SCARB2 mutations may be associated with PNP features.

Highly focal BOLD activation on functional MRI in a patient with progressive myoclonic epilepsy and diffuse giant somatosensory evoked potentials.

We analyzed the effect of afferent input on patterns of brain electrical activation in a 31-year-old man with progressive myoclonic epilepsy (PME) by measuring the somatosensory evoked potential (SSEP) amplitude at the scalp after median nerve stimulation and examining the changes in the functional magnetic resonance imaging blood oxygen level-dependent (fMRI BOLD) signal. High-amplitude SSEPs were elicited at the wrist in association with highly focal BOLD activation of the contralateral sensorimotor areas. By contrast, no diffuse activation of either the frontal or the posterior parietal cortical areas was observed, as seen in previously recorded data on SSEPs from a healthy control group. The highly focal BOLD activation in this patient suggests that cortex hyperexcitability might be limited to the sensorimotor cortex in PME. The combined EEG-fMRI findings highlight a dissociation between BOLD activation and neurophysiological findings.

Adult-onset rapidly worsening progressive myoclonic epilepsy caused by a novel variant in DHDDS.

Progressive myoclonic epilepsy (PME) is a heterogeneous neurogenetic disorder manifesting as progressive myoclonus, seizure, and ataxia. We report a case of PME caused by a novel DHDDS variant. Additionally, by reviewing the literature on DHDDS mutations, we compared the phenotype of our patient with previously reported phenotypes. We identified DHDDS (c.638G>A, p. Ser213Asn) as a likely pathogenic variant. The literature review revealed 15 PME patients with DHDDS mutations from 13 unrelated families. According to previous studies, late-onset patients tend to have a slow-progressive disease course. Although his myoclonus and ataxia were adult onset, our patient experienced rapid disease aggravation.

A novel variant of dehydrodolichol diphosphate synthase (DHDDS) mutation with adult-onset progressive myoclonus ataxia.

We report a novel variant of DHDDS mutation in a patient with progressive adult-onset myoclonus ataxia. The mutation in our patient was different from previous reports of denovo mutations in DHDDS in 6 patients who showed tremor-like myoclonus and generalized epilepsy.

Sympathetic nerve outflow to skin in a case with dentatorubral-pallidoluysian atrophy.

Dentatorubral-pallidoluysian atrophy (DRPLA) is an autosomal dominant neurodegenerative disorder characterized by slowly progressive cerebellar ataxia. Previously, autonomic symptoms or dysfunction have not been reported. To evaluate subclinical autonomic dysfunction regarding thermoregulatory function in SCA, we recorded sympathetic outflow to skin in a DRPLA patient confirmed by genetic analysis. We recorded skin sympathetic nerve activity (SSNA), which was elicited and recorded by using the microneurographical technique. In results, the resting frequency of SSNA bursts was very low (8.2 ± 0.4 bursts/min [institutional normal range: 20.8 ± 2.4 bursts/min]). However, acceleration of SSNA bursts induced by mental arithmetic stress was confirmed. The amplitude of reflex bursts induced by electrical stimuli was slightly low (9.6 ± 1.6 µV [institutional normal range: 10.9 ± 2.2 µV]), and the reflex latency was mildly prolonged (872 ± 23.7 msec [institutional normal range: 761.9 ± 51.7 msec]). These results suggest potentially central autonomic dysfunction in this patient with DRPLA. To our knowledge, this is the first report to record SSNA and confirm subclinical autonomic dysfunction in a case with DRPLA.

Early-onset progressive myoclonic epilepsy with dystonia mapping to 16pter-p13.3.

The authors present three patients from a consanguineous family afflicted with novel recessive myoclonic epilepsy characterized by very early onset and a steadily progressive course. The onset is in early infancy, and death occurs in the first decade. In addition to various types of myoclonic seizures, episodic phenomena such as dystonias, postictal enduring hemipareses, autonomic involvements, and periods of obtundation and lethargy were also observed. Developmental and neurological retardation, coupled with systemic infections, leads to a full deterioration. The authors designated the disease progressive myoclonic epilepsy with dystonia (PMED). A genome scan for the family and subsequent fine mapping localized the gene responsible for the disease to the most telomeric 6.73 mega base pairs at the p-terminus of chromosome 16, with a maximum multipoint logarithm-of-odds score of 7.83 and a maximum two-point score of 4.25. A candidate gene was analyzed for mutations in patients, but no mutation was found.

Can changes in cortical excitability distinguish progressive from juvenile myoclonic epilepsy?

PURPOSE: We used transcranial magnetic stimulation (TMS) to investigate whether there were any characteristic cortical excitability changes in progressive myoclonic epilepsy (PME) compared to juvenile myoclonic epilepsy (JME). METHODS: Six patients with PME were studied. Motor threshold (MT) at rest and recovery curve analysis using paired-pulse stimulation at a number of interstimulus intervals (ISIs) was determined. Results were compared to those of 9 patients with chronic refractory JME and 10 with chronic well-controlled JME. RESULTS: PME showed a marked increase in cortical excitability at all the long ISIs (p < 0.01), compared to refractory JME (effect sizes ranging from 1.4 to 1.9) and well-controlled JME (effect sizes ranging from 2.0 to 2.4). Significant differences at the short ISIs 2-5 ms were seen only on comparison with the well-controlled group (p < 0.05, effect size 0.6, 0.7). There were no significant differences in MTs of PME compared to either JME groups. CONCLUSION: Our findings demonstrate specific differences in cortical excitability using TMS between PME and those with JME, particularly at long latencies in the paired-pulse paradigm, implicating a role for γ-aminobutyric acid (GABA)(B) -mediated networks.