The gene for progressive myoclonus epilepsy of the Lafora type maps to chromosome 6q

Gene therapy for Lafora disease in the Epm2a-/- mouse model

Lafora disease is a rare and fatal form of progressive myoclonic epilepsy typically occurring early in adolescence. The disease results from mutations in the EPM2A gene, encoding laforin, or the EPM2B gene, encoding malin. Laforin and malin work together in a complex to control glycogen synthesis and prevent the toxicity produced by misfolded proteins via the ubiquitin-proteasome system. Disruptions in either protein cause alterations in this complex, leading to the formation of Lafora bodies containing abnormal, insoluble, and hyperphosphorylated forms of glycogen. We used the Epm2a-/- knockout mouse model of Lafora disease to apply gene therapy by administering intracerebroventricular injections of a recombinant adeno-associated virus carrying the human EPM2A gene. We evaluated the effects of this treatment through neuropathological studies, behavioral tests, video-electroencephalography, electrophysiological recordings, and proteomic/phosphoproteomic analysis. Gene therapy ameliorated neurological and histopathological alterations, reduced epileptic activity and neuronal hyperexcitability, and decreased the formation of Lafora bodies. Moreover, differential quantitative proteomics and phosphoproteomics revealed beneficial changes in various molecular pathways altered in Lafora disease. Our results represent proof of principle for gene therapy with the coding region of the human EPM2A gene as a treatment for EPM2A-related Lafora disease.

Effect of intracerebroventricular administration of alglucosidase alfa in two mouse models of Lafora disease: Relevance for clinical practice

Lafora disease is a rare and fatal form of progressive myoclonic epilepsy with onset during early adolescence. The disease is caused by mutations in EPM2A, encoding laforin, or EPM2B, encoding malin. Both proteins have functions that affect glycogen metabolism, including glycogen dephosphorylation by laforin and ubiquitination of enzymes involved in glycogen metabolism by malin. Lack of function of laforin or malin results in the accumulation of polyglucosan that forms Lafora bodies in the central nervous system and other tissues. Enzyme replacement therapy through intravenous administration of alglucosidase alfa (Myozyme®) has shown beneficial effects removing polyglucosan aggregates in Pompe disease. We evaluated the effectiveness of intracerebroventricular administration of alglucosidase alfa in the Epm2a-/- knock-out and Epm2aR240X knock-in mouse models of Lafora disease. Seven days after a single intracerebroventricular injection of alglucosidase alfa in 12-month-old Epm2a-/- and Epm2aR240X mice, the number of Lafora bodies was not reduced. Additionally, a prolonged infusion of alglucosidase alfa for 2 or 4 weeks in 6- and 9-month-old Epm2a-/- mice did not result in a reduction in the number of LBs or the amount of glycogen in the brain. These findings hold particular significance in guiding a rational approach to the utilization of novel therapies in Lafora disease.

Gene replacement therapy for Lafora disease in the Epm2a -/- mouse model

Lafora disease is a rare and fatal form of progressive myoclonic epilepsy typically occurring early in adolescence. Common symptoms include seizures, dementia, and a progressive neurological decline leading to death within 5-15 years from onset. The disease results from mutations transmitted with autosomal recessive inheritance in the EPM2A gene, encoding laforin, a dual-specificity phosphatase, or the EPM2B gene, encoding malin, an E3-ubiquitin ligase. Laforin has glucan phosphatase activity, is an adapter of enzymes involved in glycogen metabolism, is involved in endoplasmic reticulum-stress and protein clearance, and acts as a tumor suppressor protein. Laforin and malin work together in a complex to control glycogen synthesis and prevent the toxicity produced by misfolded proteins via the ubiquitin-proteasome system. Disruptions in either protein can lead to alterations in this complex, leading to the formation of Lafora bodies that contain abnormal, insoluble, and hyperphosphorylated forms of glycogen called polyglucosans. We used the Epm2a -/- knock-out mouse model of Lafora disease to apply a gene replacement therapy by administering intracerebroventricular injections of a recombinant adeno-associated virus carrying the human EPM2A gene. We evaluated the effects of this treatment by means of neuropathological studies, behavioral tests, video-electroencephalography recording, and proteomic/phosphoproteomic analysis. Gene therapy with recombinant adeno-associated virus containing the EPM2A gene ameliorated neurological and histopathological alterations, reduced epileptic activity and neuronal hyperexcitability, and decreased the formation of Lafora bodies. Differential quantitative proteomics and phosphoproteomics revealed beneficial changes in various molecular pathways altered in Lafora disease. Improvements were observed for up to nine months following a single intracerebroventricular injection. In conclusion, gene replacement therapy with human EPM2A gene in the Epm2a -/- knock-out mice shows promise as a potential treatment for Lafora disease.

Gys1 Antisense Therapy Prevents Disease-Driving Aggregates and Epileptiform Discharges in a Lafora Disease Mouse Model

Patients with Lafora disease have a mutation in EPM2A or EPM2B, resulting in dysregulation of glycogen metabolism throughout the body and aberrant glycogen molecules that aggregate into Lafora bodies. Lafora bodies are particularly damaging in the brain, where the aggregation drives seizures with increasing severity and frequency, coupled with neurodegeneration. Previous work employed mouse genetic models to reduce glycogen synthesis by approximately 50%, and this strategy significantly reduced Lafora body formation and disease phenotypes. Therefore, an antisense oligonucleotide (ASO) was developed to reduce glycogen synthesis in the brain by targeting glycogen synthase 1 (Gys1). To test the distribution and efficacy of this drug, the Gys1-ASO was administered to Epm2b-/- mice via intracerebroventricular administration at 4, 7, and 10 months. The mice were then sacrificed at 13 months and their brains analyzed for Gys1 expression, glycogen aggregation, and neuronal excitability. The mice treated with Gys1-ASO exhibited decreased Gys1 protein levels, decreased glycogen aggregation, and reduced epileptiform discharges compared to untreated Epm2b-/- mice. This work provides proof of concept that a Gys1-ASO halts disease progression of EPM2B mutations of Lafora disease.

Epm2aR240X knock-in mice present earlier cognitive decline and more epileptic activity than Epm2a-/- mice

Lafora disease is a rare recessive form of progressive myoclonic epilepsy, usually diagnosed during adolescence. Patients present with myoclonus, neurological deterioration, and generalized tonic-clonic, myoclonic, or absence seizures. Symptoms worsen until death, usually within the first ten years of clinical onset. The primary histopathological hallmark is the formation of aberrant polyglucosan aggregates called Lafora bodies in the brain and other tissues. Lafora disease is caused by mutations in either the EPM2A gene, encoding laforin, or the EPM2B gene, coding for malin. The most frequent EPM2A mutation is R241X, which is also the most prevalent in Spain. The Epm2a^-/- and Epm2b^-/- mouse models of Lafora disease show neuropathological and behavioral abnormalities similar to those seen in patients, although with a milder phenotype. To obtain a more accurate animal model, we generated the Epm2a^R240X knock-in mouse line with the R240X mutation in the Epm2a gene, using genetic engineering based on CRISPR-Cas9 technology. Epm2a^R240X mice exhibit most of the alterations reported in patients, including the presence of LBs, neurodegeneration, neuroinflammation, interictal spikes, neuronal hyperexcitability, and cognitive decline, despite the absence of motor impairments. The Epm2a^R240X knock-in mouse displays some symptoms that are more severe that those observed in the Epm2a^-/- knock-out, including earlier and more pronounced memory loss, increased levels of neuroinflammation, more interictal spikes and increased neuronal hyperexcitability, symptoms that more precisely resemble those observed in patients. This new mouse model can therefore be specifically used to evaluate how new therapies affects these features with greater precision.

International League Against Epilepsy classification and definition of epilepsy syndromes with onset at a variable age: position statement by the ILAE Task Force on Nosology and Definitions

The goal of this paper is to provide updated diagnostic criteria for the epilepsy syndromes that have a variable age of onset, based on expert consensus of the International League Against Epilepsy Nosology and Definitions Taskforce (2017-2021). We use language consistent with current accepted epilepsy and seizure classifications and incorporate knowledge from advances in genetics, electroencephalography, and imaging. Our aim in delineating the epilepsy syndromes that present at a variable age is to aid diagnosis and to guide investigations for etiology and treatments for these patients.

Beneficial Effects of Metformin on the Central Nervous System, with a Focus on Epilepsy and Lafora Disease

Metformin is a drug in the family of biguanide compounds that is widely used in the treatment of type 2 diabetes (T2D). Interestingly, the therapeutic potential of metformin expands its prescribed use as an anti-diabetic drug. In this sense, it has been described that metformin administration has beneficial effects on different neurological conditions. In this work, we review the beneficial effects of this drug as a neuroprotective agent in different neurological diseases, with a special focus on epileptic disorders and Lafora disease, a particular type of progressive myoclonus epilepsy. In addition, we review the different proposed mechanisms of action of metformin to understand its function at the neurological level.

Italian cohort of Lafora disease: Clinical features, disease evolution, and genotype-phenotype correlations

BACKGROUND

Lafora disease (LD) is characterized by progressive myoclonus, refractory epilepsy, and cognitive deterioration. This complex neurodegenerative condition is caused by pathogenic variants in EPM2A/EPM2B genes, encoding two essential glycogen metabolism enzymes known as laforin and malin. Long-term follow-up data are lacking. We describe the clinical features and genetic findings of a cohort of 26 Italian patients with a long clinical follow-up.

METHODS

Patients with EPM2A/EPM2B pathogenic variants were identified by direct gene sequencing or gene panels with targeted re-sequencing. Disease progression, motor functions, and mental performance were assessed by a simplified disability scale. Spontaneous/action myoclonus severity was scored by the Magaudda Scale.

RESULTS

Age range was 12.2-46.2 years (mean:25.53 ± 9.14). Age at disease onset ranged from 10 to 22 years (mean:14.04 ± 2.62). The mean follow-up period was 11.48 ± 7.8 years. Twelve out of the 26 (46%) patients preserved walking ability and 13 (50%) maintained speech. A slower disease progression with preserved ambulation and speech after ≥4 years of follow-up was observed in 1 (11%) out of the 9 (35%) EPM2A patients and in 6 (35%) out of the 17 (65%) EPM2B patients. Follow-up was >10 years in 7 (41.2%) EPM2B individuals, including two harbouring the homozygous p.(D146N) pathogenic variant.

CONCLUSIONS

This study supports an overall worse disease outcome with severe deterioration of ambulation and speech in patients carrying EPM2A mutations. However, the delayed onset of disabling symptoms observed in the EPM2B subjects harbouring the p.(D146N) pathogenic variant suggests that the underlying causative variant may still influence LD severity.

The 5th International Lafora Epilepsy Workshop: Basic science elucidating therapeutic options and preparing for therapies in the clinic

Lafora disease (LD) is both a fatal childhood epilepsy and a glycogen storage disease caused by recessive mutations in either the Epilepsy progressive myoclonus 2A (EPM2A) or EPM2B genes. Hallmarks of LD are aberrant, cytoplasmic carbohydrate aggregates called Lafora bodies (LBs) that are a disease driver. The 5th International Lafora Epilepsy Workshop was recently held in Alcala de Henares, Spain. The workshop brought together nearly 100 clinicians, academic and industry scientists, trainees, National Institutes of Health (NIH) representation, and friends and family members of patients with LD. The workshop covered aspects of LD ranging from defining basic scientific mechanisms to elucidating a LD therapy or cure and a recently launched LD natural history study.

A novel EPM2A mutation yields a slow progression form of Lafora disease

Lafora disease (LD, OMIM 254780) is a rare disorder characterized by epilepsy and neurodegeneration leading patients to a vegetative state and death, usually within the first decade from the onset of the first symptoms. In the vast majority of cases LD is related to mutations in either the EPM2A gene (encoding the glucan phosphatase laforin) or the EPM2B gene (encoding the E3-ubiquitin ligase malin). In this work, we characterize the mutations present in the EPM2A gene in a patient displaying a slow progression form of the disease. The patient is compound heterozygous with Y112X and N163D mutations in the corresponding alleles. In primary fibroblasts obtained from the patient, we analyzed the expression of the mutated alleles by quantitative real time PCR and found slightly lower levels of expression of the EPM2A gene respect to control cells. However, by Western blotting we were unable to detect endogenous levels of the protein in crude extracts from patient fibroblasts. The Y112X mutation would render a truncated protein lacking the phosphatase domain and likely degraded. Since minute amounts of laforin-N163D might still play a role in cell physiology, we analyzed the biochemical characteristics of the N163D mutation. We found that recombinant laforin N163D protein was as stable as wild type and exhibited near wild type phosphatase activity towards biologically relevant substrates. On the contrary, it showed a severe impairment in the interaction profile with previously identified laforin binding partners. These results lead us to conclude that the slow progression of the disease present in this patient could be either due to the specific biochemical properties of laforin N163D or to the presence of alternative genetic modifying factors separate from pathogenicity.

Lafora disease offers a unique window into neuronal glycogen metabolism

Lafora disease (LD) is a fatal, autosomal recessive, glycogen-storage disorder that manifests as severe epilepsy. LD results from mutations in the gene encoding either the glycogen phosphatase laforin or the E3 ubiquitin ligase malin. Individuals with LD develop cytoplasmic, aberrant glycogen inclusions in nearly all tissues that more closely resemble plant starch than human glycogen. This Minireview discusses the unique window into glycogen metabolism that LD research offers. It also highlights recent discoveries, including that glycogen contains covalently bound phosphate and that neurons synthesize glycogen and express both glycogen synthase and glycogen phosphorylase.

Oxidative stress, a new hallmark in the pathophysiology of Lafora progressive myoclonus epilepsy

Lafora disease (LD; OMIM 254780, ORPHA501) is a devastating neurodegenerative disorder characterized by the presence of glycogen-like intracellular inclusions called Lafora bodies and caused, in most cases, by mutations in either the EPM2A or the EPM2B gene, encoding respectively laforin, a phosphatase with dual specificity that is involved in the dephosphorylation of glycogen, and malin, an E3-ubiquitin ligase involved in the polyubiquitination of proteins related to glycogen metabolism. Thus, it has been reported that laforin and malin form a functional complex that acts as a key regulator of glycogen metabolism and that also plays a crucial role in protein homeostasis (proteostasis). Regarding this last function, it has been shown that cells are more sensitive to ER stress and show defects in proteasome and autophagy activities in the absence of a functional laforin-malin complex. More recently, we have demonstrated that oxidative stress accompanies these proteostasis defects and that various LD models show an increase in reactive oxygen species and oxidative stress products together with a dysregulated antioxidant enzyme expression and activity. In this review we discuss possible connections between the multiple defects in protein homeostasis present in LD and oxidative stress.

[Lafora disease: histopathological study of axillary cutaneous biopsy]

Lafora body disease is a common and severe form of progressive myoclonic epilepsy. It is an autosomal recessive disorder with a gene locus recently mapped to chromosome 6q23-27. The disease presents between the age of 10 and 18 years with generalised seizures followed by myoclunus. Intellectual deterioration occurs early and progresses to dementia. The diagnosis must be usually confirmed by demonstrating Lafora bodies. The practical procedure is the axillary skin biopsy that shows PAS positive inclusion in the cells of the sweet ducts. We present a case of Lafora disease discovered in a 26-year-old man. Moreover, we emphasize on the diagnosis difficulties of this disease.

Genetics of inherited human epilepsies

Major advances have recently been made in our understanding of the genetic basis of monogenic inherited epilepsies. Progress has been particularly spectacular with respect to idiopathic epilepsies, with the discovery that mutations in ion channel subunits are implicated. However, important advances have also been made in many inherited symptomatic epilepsies, for which direct molecular diagnosis is now possible, simplifying previously complex investigations, it is expected that identification of the genes implicated in familial forms of epilepsies will lead to a better understanding of the underlying pathophysiological mechanisms of these disorders and to the development of experimental models and new therapeutic strategies, in this article, we review the clinical and genetic data concerning most of the inherited human epilepsies.

Lafora disease: epidemiology, pathophysiology and management

Lafora disease is a rare, fatal, autosomal recessive, progressive myoclonic epilepsy. It may also be considered as a disorder of carbohydrate metabolism because of the formation of polyglucosan inclusion bodies in neural and other tissues due to abnormalities of the proteins laforin or malin. The condition is characterized by epilepsy, myoclonus and dementia. Diagnostic findings on MRI and neurophysiological testing are not definitive and biopsy or genetic studies may be required. Therapy in Lafora disease is currently limited to symptomatic management of the epilepsy, myoclonus and intercurrent complications. With a greater understanding of the pathophysiological processes involved, there is justified hope for future therapies.

Novel mutation in the NHLRC1 gene in a Malian family with a severe phenotype of Lafora disease

We studied a Malian family with parental consanguinity and two of eight siblings affected with late-childhood-onset progressive myoclonus epilepsy and cognitive decline, consistent with the diagnosis of Lafora disease. Genetic analysis showed a novel homozygous single-nucleotide variant in the NHLRC1 gene, c.560A>C, producing the missense change H187P. The changed amino acid is highly conserved, and the mutation impairs malin's ability to degrade laforin in vitro. Pathological evaluation showed manifestations of Lafora disease in the entire brain, with particularly severe involvement of the pallidum, thalamus, and cerebellum. Our findings document Lafora disease with severe manifestations in the West African population.

STARCH-EXCESS4 is a laforin-like Phosphoglucan phosphatase required for starch degradation in Arabidopsis thaliana

Starch is the major storage carbohydrate in plants. It is comprised of glucans that form semicrystalline granules. Glucan phosphorylation is a prerequisite for normal starch breakdown, but phosphoglucan metabolism is not understood. A putative protein phosphatase encoded at the Starch Excess 4 (SEX4) locus of Arabidopsis thaliana was recently shown to be required for normal starch breakdown. Here, we show that SEX4 is a phosphoglucan phosphatase in vivo and define its role within the starch degradation pathway. SEX4 dephosphorylates both the starch granule surface and soluble phosphoglucans in vitro, and sex4 null mutants accumulate phosphorylated intermediates of starch breakdown. These compounds are linear alpha-1,4-glucans esterified with one or two phosphate groups. They are released from starch granules by the glucan hydrolases alpha-amylase and isoamylase. In vitro experiments show that the rate of starch granule degradation is increased upon simultaneous phosphorylation and dephosphorylation of starch. We propose that glucan phosphorylating enzymes and phosphoglucan phosphatases work in synergy with glucan hydrolases to mediate efficient starch catabolism.

MR spectroscopy findings in Lafora disease

PURPOSE

Our aim was to investigate the [(1)H] MR spectroscopy (MRS) findings of Lafora Disease (LD), which is a disabling form of progressive myoclonic epilepsy.

METHODS

Twelve patients diagnosed with LD and 12 control subjects underwent MRS studies with single-voxels of 8 cc obtained in the frontal lobe, pons, and cerebellum. The metabolites and NAA/Cr, NAA/Cho, Cho/Cr, mI/Cr ratios were calculated. Subgroup analysis was also done between 5 patients with EPM2B and 6 patients with EPM2A mutations. Two investigators scored neurological symptom severity.

RESULTS

We found a statistically significant difference of NAA/Cho ratio in LD patients compared with normal controls in cerebellum (P= 0.04). In addition, both myoclonus and ataxia scores showed significant correlation with NAA/Cho ratios in the pons (P= 0.03, P= 0.04) and in the cerebellum (P= 0.04, P= 0.01), respectively.

CONCLUSION

We conclude that the cerebellum is the mostly affected structure in LD and there are significant correlations of MRS findings with some clinical parameters. The differences in the group may be related to different genetic mutations besides disease duration and other clinical variables. MRS studies could provide insights about the severity of the involvement of LD.

Advances in lafora progressive myoclonus epilepsy

Abstract Lafora progressive myoclonus epilepsy is an autosomal recessive, fatal, generalized polyglucosan storage disorder that occurs in childhood or adolescence with stimulus sensitive epilepsy (resting and action myoclonias, grand mal, and absence), dementia, ataxia and rapid neurologic deterioration. Mutations in EPM2A/laforin cause 58% of cases and mutations in EPM2B/malin cause 35% of cases. Accumulating evidence points to Lafora disease as primarily a disorder of cell death with impaired clearance of misfolded proteins, as shown by ubiquitin-positive aggresomes in HeLa cells transfected with mutated laforin, ubiquitin-positive polyglucosan inclusion bodies, and malin/E3 ubiquitin ligase polyubiquitination of laforin. How polyglucosan inclusion bodies accumulate is still a mystery. Polyglucosan accumulates hypothetically because of an overactive polyglucosan biosynthetic pathway or a breakdown in polyglucosan degradation. Five separate laboratories are looking for the biochemical pathways that connect laforin and malin to polyglucosan synthesis or degradation. A curative therapy for human Lafora disease with laforin replacement therapy using neutral pegylated immunoliposomes is being investigated.

[Lafora's disease presenting with progressive myoclonus epilepsy]

Lafora's disease is a progressive myoclonus epilepsy and must be evocated if myoclonus, occipital seizures and progressive cognitive impairment are present. We report the case of a 14-year-old boy who suffered from several occipital seizures and two generalised seizures. The diagnosis of Lafora's disease was made six years after these inaugural symptoms because of occurrence of myoclonus, aggravation of the epilepsy with paharmacoresistance and psychic deterioration. Axila sweat gland duct biopsy was performed to conclude to the disease. A mutation was found on the gene EPM2A. Lafora's disease is a genetic autosomal-recessive pathology. Two genes have been recently identified. They code for two proteins, malin and laforin, involved in glycogen metabolism in the cellular endoplasmic reticulum. Mutations of these genes are responsible for intracytoplasmic polyglucosan inclusions called Lafora bodies and pathognomonic of the disease.

[Lafora's disease (EPM2)]

Lafora's disease (LD) is a comparatively frequent and particularly severe type of progressive myoclonus epilepsy. Prevalence varies, LD is seen everywhere but is more common in geographic isolates and areas with high degree of inbreeding. Onset occurs during adolescence, with generalized tonic-clonic, clonic-tonic-clonic seizures, action and resting myoclonus, negative myoclonus, and focal occipital seizures with transient amaurosis. The course is marked by prominent cognitive deterioration, which can precede seizures and myoclonus, and by the progressive, relentless increase of seizures and myoclonus. Transmission is autosomal recessive. LD is genetically heterogeneous. Mutations/deletions of the EPM2A gene, localized in 1995 on 6q24, are found in 80p.cent (product: laforin), the less common EPM2B variant is on 6p22 (product: malin), but these two localizations do not account for all cases of LD. The diagnosis of LD may be suspected on the basis of the family history, age at onset, typical appearance of symptoms, rapid worsening of cognitive function, evaluation of fairly typical EEG aspects, and can easily be confirmed by axillar skin biopsy with proof of Lafora bodies (polyglucosan aggregates) in the sweat duct cells. Other biopsies, like brain biopsy, are generally not necessary. Genetic testing is useful for diagnosis but the genetic heterogeneity cannot rule out LD when none of the known mutations are detected. Genetic counselling and prenatal diagnosis are theoretically possible when the genetic anomaly has been documented in an affected member of the family. The treatment of LD remains purely symptomatic. Drugs that may aggravate myoclonus must be avoided. Psychological and social management is of utmost importance in LD. Death occurs 4 to 10 years after onset in typical forms.

Founder Effect with Variable Age at Onset in Arab Families with Lafora Disease and EPM2A Mutation

PURPOSE

We observed three apparently unrelated and geographically separate Arab families with Lafora disease in Israel and the Palestinian territories.

METHODS

We clinically evaluated the families and analyzed their DNA for EPM2A mutations.

RESULTS

Of seven individuals with Lafora disease, the clinical onset varied from 13 to 20 years. All three families shared the same novel homozygous deletion in EPM2A. Haplotype analysis around the deletion showed that the families shared a common homozygous haplotype. The boundaries of this haplotype varied between families and even within one family.

CONCLUSIONS

We conclude that considerable variability in the age at onset of Lafora disease can occur within families. Identical mutations can be associated with the classic adolescent presentation, as well as late-onset cases. Haplotype analysis suggests that this EPM2A mutation arose many generations previously, so it may be of importance for cases distributed more widely in the Middle East.

Advances in genetics of juvenile myoclonic epilepsies

One by one, mutation-containing mendelian genes that cause monogenic juvenile myoclonic epilepsies (JME) and single nucleotide polymorphisms (SNP)-susceptibility alleles that increase risks for nonmendelian complex JME should fall to the power of molecular genetics. Of 15 chromosome loci, 3 mendelian genes (alpha1-subunit of the GABA(A) receptor [GABRA1], chloride channel 2 gene [CLCN2], and Myoclonin1/EFHC1) and 2 SNP-susceptibility alleles of putative JME genes in epistases (bromodomain-containing protein 2 [BRD2] and connexin [Cx]-36) have been identified, so far. Antiepileptic drugs now can be designed against the specific molecular defects of JME.

Molecular characterization of laforin, a dual-specificity protein phosphatase implicated in Lafora disease

Lafora disease is a progressive myoclonus epilepsy with an early fatal issue. Two genes were identified thus far, the mutations of which cause the disease. The first one, EPM2A, encodes the consensus sequence of a protein tyrosine phosphatase. Its product, laforin, is the object of the present work. We analysed in detail the amino acid sequence of this protein. This suggested, as also observed by others, that it could present two domains, a carbohydrate-binding domain (CBM20, known as a starch-binding domain) and the catalytic domain of a dual-specificity protein phosphatase. We produced the enzyme as two different GST-fused proteins and as an N-terminally His-tagged protein. Differences in solubility were observed between the constructs. Moreover, the N-terminal carbohydrate-binding domain contains a thrombin cleavage site, which is hidden in the simplest GST-fusion protein we produced, but was accessible after introducing a five-residue linker between the engineered cleavage site and the enzyme N-terminus. The two types of constructs hydrolyse pNPP and OMFP with kinetic parameters consistent with those of a dual-specificity phosphatase. We show in addition that the protein not only binds glycogen, but also starch, amylose and cyclodextrin. Neither binding of glycogen nor of beta-cyclodextrin appreciably affects the phosphatase activity. These results suggest that the role of the N-terminal domain is rather that of targeting the protein in the cell, probably to glycogen and the protein complexes attached to it, rather than that of directly modulating the catalytic activity.

Epm2a suppresses tumor growth in an immunocompromised host by inhibiting Wnt signaling

The genetic mechanisms responsible for increased incidence of lymphoma in immunocompromised individuals have not been fully elucidated. We show that, in a line of TCR transgenic TG-B mice, an insertional mutation in one allele of the Epm2a locus and epigenetic silencing of another led to a high rate of lymphoma with early onset. Overexpressing Epm2a suppressed the growth of established tumor cells and the development of lymphoma in the TG-B mice, while specific silencing of the locus increased tumorigenesis in the immune-deficient host. Downregulation of Epm2a expression is widespread among mouse and human lymphoma cell lines. Epm2a-encoded laforin is a phosphatase for GSK-3beta and an important repressor in the Wnt signaling pathway. Inactivation of Epm2a resulted in increased Wnt signaling and tumorigenesis.

MRI volumetry and proton MR spectroscopy of the brain in Lafora disease

PURPOSE

To determine brain involvement in Lafora disease by means of 3-T MRI volumetry and 1H magnetic resonance (MR) spectroscopy.

METHODS

Ten patients with Lafora disease and 10 healthy controls were included in the study. The diagnosis of Lafora disease was proven genetically by the presence of mutations in the EPM2A gene in all patients, and their evolution was staged in three groups according to their functional state. MRI volumetry was performed by means of AX3DT1 images with assessment of the cerebellum and the brainstem, by using the program Stereonauta, and all the brain structures, by using voxel-based morphometry. [1H]MR spectroscopy was performed by using an Eclipse PRESS sequence probe system with 8-cc voxels positioned in the occipital and frontal cortexes, basal ganglia, pons, and cerebellar hemispheres. Spectral peak areas corresponding to NAA (N-acetylaspartate), creatine, and choline were obtained.

RESULTS

MRI volumetry showed no statistically significant differences in patients compared with healthy controls in any of the analyzed structures. Analysis of [1H]MR spectroscopy data showed a statistically significant reduction in the NAA/creatine ratio in patients compared with controls in the frontal (p = 0.001) and occipital cortex (p = 0.043), basal ganglia (p = 0.002), and cerebellar hemispheres (p = 0.007). The NAA/choline and choline/creatine ratios were statistically significantly different in the frontal cortex (p = 0.005). No correlation was observed between the disease-evolution stage and MRI-measured volumes (range, -0.92 to 0.44) or [1H]MR spectroscopy values (range, -0.29 to 0.50).

CONCLUSIONS

In our series of Lafora disease patients, [1H]MR spectroscopy was more sensitive than structural MRI to detect brain involvement. The brain cortex, especially frontal cortex, cerebellum, and basal ganglia, showed the greatest metabolic changes.

Recent advances in the molecular basis of Lafora's progressive myoclonus epilepsy

Lafora's disease (LD) is an autosomal recessive and fatal form of progressive myoclonus epilepsy with onset in late childhood or adolescence. LD is characterised by the presence of intracellular polyglucosan inclusions, called Lafora bodies, in tissues including the brain, liver and skin. Patients have progressive neurologic deterioration, leading to death within 10 years of onset. No preventive or curative treatment is available for LD. At least three genes underlie LD, of which two have been isolated and mutations characterised: EPM2A and NHLRC1. The EPM2A gene product laforin is a protein phosphatase while the NHLRC1 gene product malin is an E3 ubiquitin ligase that ubiquitinates and promotes the degradation of laforin. Analyses of the structure and function of these gene products suggest defects in post-translational modification of proteins as the common mechanism that leads to the formation of Lafora inclusion bodies, neurodegeneration and the epileptic phenotype of LD. In this review, we summarise the available information on the genetic basis of LD, and correlate these advances with the rapidly expanding information about the mechanisms of LD gained from studies on both cell biological and animal models. Finally, we also discuss a possible mechanism to explain the locus heterogeneity observed in LD.

Mutations in the NHLRC1 gene are the common cause for Lafora disease in the Japanese population

Lafora disease (LD) is a rare autosomal recessive genetic disorder characterized by epilepsy, myoclonus, and progressive neurological deterioration. LD is caused by mutations in the EMP2A gene encoding a protein phosphatase. A second gene for LD, termed NHLRC1 and encoding a putative E3 ubiquitin ligase, was recently identified on chromosome 6p22. The LD is relatively common in southern Europe, the Middle East, and Southeast Asia. A few sporadic cases with typical LD phenotype have been reported from Japan; however, our earlier study failed to find EPM2A mutations in four Japanese families with LD. We recruited four new families from Japan and searched for mutations in EPM2A . All eight families were also screened for NHLRC1 mutations. We found five independent families having novel mutations in NHLRC1. Identified mutations include five missense mutations (p.I153M, p.C160R, p.W219R, p.D245N, and p.R253K) and a deletion mutation (c.897insA; p.S299fs13). We also found a family with a ten base pair deletion (c.822-832del10) in the coding region of EPM2A. In two families, no EPM2A or NHLRC1 mutation was found. Our study, in addition to documenting the genetic and molecular heterogeneity observed for LD, suggests that mutations in the NHLRC1 gene may be a common cause of LD in the Japanese population.

The carbohydrate-binding domain of Lafora disease protein targets Lafora polyglucosan bodies

Lafora's disease (LD) is an autosomal recessive and fatal form of epilepsy with onset in late childhood or adolescence. One of the characteristic features of LD pathology is the presence of periodic acid-Schiff (PAS) positive Lafora inclusion bodies. Lafora bodies are present primarily in neurons, but they have also been found in other organs. Histochemical and biochemical studies have indicated that Lafora bodies are composed mainly of polysaccharides. The LD gene, EPM2A, encodes a 331 amino acid long protein named laforin that contains an N-terminal carbohydrate-binding domain (CBD) and a C-terminal dual-specificity phosphatase domain (DSPD). Here we demonstrate that the CBD of laforin targets the protein to Lafora inclusion bodies and this property could be evolutionarily conserved. We also tested in vitro the effects of five LD missense mutations on laforin's affinity to Lafora body. While the missense mutant W32G failed to bind to purified Lafora body, four other mutants (S25P, E28L, F88L, and R108C) did not show any effect on the binding affinity. Based on these observations we propose the existence of a laforin-mediated glycogen metabolic pathway regulating the disposal of pathogenic polyglucosan inclusions. This is the first report demonstrating a direct association between the LD gene product and the disease-defining storage product, the Lafora bodies.

Genetics of epilepsy: current status and perspectives

Epilepsy affects more than 0.5% of the world's population and has a large genetic component. The most common human genetic epilepsies display a complex pattern of inheritance and the susceptibility genes are largely unknown. However, major advances have recently been made in our understanding of the genetic basis of monogenic inherited epilepsies. Progress has been particularly evident in familial idiopathic epilepsies and in many inherited symptomatic epilepsies, with the discovery that mutations in ion channel subunits are implicated, and direct molecular diagnosis of some phenotypes of epilepsy is now possible. This article reviews recent progress made in molecular genetics of epilepsy, focusing mostly on idiopathic epilepsy, and some types of myoclonus epilepsies. Mutations in the neuronal nicotinic acetylcholine receptor alpha4 and beta2 subunit genes have been detected in families with autosomal dominant nocturnal frontal lobe epilepsy, and those of two K(+) channel genes were identified to be responsible for underlying genetic abnormalities of benign familial neonatal convulsions. The voltage-gated Na(+) -channel (alpha1,2 and beta1 subunit), and GABA receptor (gamma2 subunit) may be involved in the pathogenesis of generalized epilepsy with febrile seizure plus and severe myoclonic epilepsy in infancy. Mutations of Ca(2+)-channel can cause some forms of juvenile myoclonic epilepsy and idiopathic generalized epilepsy. Based upon these findings, pathogenesis of epilepsy as a channelopathy and perspectives of molecular study of epilepsy are discussed.

Advances in the genetics of progressive myoclonus epilepsy

The genetic progressive myoclonus epilepsies (PMEs) are clinically characterized by the triad of stimulus sensitive myoclonus (segmental lightning like muscular jerks), epilepsy (grand mal and absences) and progressive neurologic deterioration (dementia, ataxia, and various neurologic signs depending on the cause). Etiologically heterogenous, PMEs are rare and mostly autosomal recessive disorders, with the exception of autosomal dominant dentatorubral-pallidoluysian atrophy and mitochondrial encephalomyopathy with ragged red fibers (MERRF). In the last five years, specific mutations have been defined in Lafora disease (gene for laforin or dual specificity phosphatase in 6q24), Unverricht-Lundborg disease (cystatin B in 21q22.3), Jansky-Bielschowsky ceroid lipofuscinoses (CLN2 gene for tripeptidyl peptidase 1 in 11q15), Finnish variant of late infantile ceroid lipofuscinoses (CLN5 gene in 13q21-32 encodes 407 amino acids with two transmembrane helices of unknown function), juvenile ceroid lipofuscinoses or Batten disease (CLN3 gene in 16p encodes 438 amino acid protein of unknown function), a subtype of Batten disease and infantile ceroid lipofuscinoses of the Haltia-Santavuori type (both are caused by mutations in palmitoyl-protein thiosterase gene at 1p32), dentadorubropallidoluysian atrophy (CAG repeats in a gene in 12p13.31) and the mitochondrial syndrome MERRF (tRNA Lys mutation in mitochondrial DNA). In this review, we cover mainly these rapid advances.

Progressive Myoclonic Epilepsies

The treatment of progressive myoclonus epilepsy (PME) remains a major therapeutic challenge in neurology. Generalized convulsive seizures are often well controlled through classic antiepileptic drugs (AEDs) like valproate and clonazepam, whereas myoclonus, the main symptom that is affecting patients most in their daily life, is usually refractory to standard AEDs. Alternative therapy concepts have been and still are investigated. Among the new drugs, zonisamide and piracetam have shown the most promising results as add-on treatments. Other therapeutic approaches, like the use of antioxidants, 5-hydroxytryptophan (5-HTP), and baclofen should also be taken into consideration for the treatment of intractable cases of PME. Nonpharmacologic treatment options such as diet and physical therapy should always be considered, because they may save costs and side effects. In some instances, the occasional use of alcohol has shown beneficial effects.

Genetics of epilepsy

Understanding the molecular biology of epilepsy is a challenge for modern science. Epilepsy results from alternations in fundamental mechanisms of brain and membrane function. Although an understanding of the mode of inheritance and the etiology of genetic epilepsy syndromes forms the basis for genetic counseling, the development of specific therapies will come from knowing the basic mechanisms of epilepsy. Defining the genes causing epilepsy requires an unambiguous definition of seizure phenotype, along with the stability of that trait, an unremitting clinical course, and an abundance of clinical material. This article reviews the task of defining the genetics of epilepsy and discusses genetic methodology, idiopathic generalized and localization-related partial epilepsies, neuronal migration disorders, progressive myoclonus epilepsies, molecular biology of epileptogenesis, and future research.

Mutation screening for Japanese Lafora's disease patients: identification of novel sequence variants in the coding and upstream regulatory regions of EPM2A gene

The progressive myoclonus epilepsy of Lafora type (LD) is an autosomal recessive disorder caused by mutations in the EPM2A gene. We demonstrated recently that EPM2A encodes a dual-specificity phosphatase that is primarily associated with polyribosomes. In the present study, we screened for mutations in the EPM2A gene in 4 Japanese LD families and identified a novel mis-sense mutation, Ala46Pro (136G-->C), in heterozygous condition in one patient. In addition, sequence analyses in the patient and control DNA samples identified 4 single nucleotide polymorphisms (SNPs) (75G/A, 120G/T, 159C/G, 171C/T) in the coding region and a novel insertion/deletion polymorphic site (-483[T](11/10)[A](2/3)) and a SNP (-547A/G) in the putative regulatory region of the EPM2A gene. None of the sequence variants, however, co-segregated with the LD phenotype. Haplotype analysis for the 6q24 region in the affected families revealed lack of homozygosity at the EPM2A locus. Our studies suggest that EPM2A is not involved in the disease phenotype of the 4 families studied and that locus heterogeneity for LD may exist in Japanese population also. A simple test described for the detection of Ala46Pro mutation present heterozygously in Japanese population (allele frequency 0.026) can be used for screening this novel allele in a larger sample size.

Long-term observations of two siblings with Lafora disease treated with zonisamide

We have reported long-term clinical follow-up for two siblings with Lafora disease, a brother and sister, one of whom autopsied. Both siblings had repeated attacks of severe myoclonus, tonic and tonic-clonic convulsions, and intractable status epilepticus. The addition of orally administered zonisamide brought about striking effective seizure control for about 12-14 years in both patients, relieving not only myoclonus and generalized tonic-clonic seizures but also intractable status epilepticus.

Muscle glycogenoses

There are 11 hereditary disorders of glycogen metabolism affecting muscle alone or together with other tissues, and they cause two main clinical syndromes: episodic, recurrent exercise intolerance with cramps, myalgia, and myoglobinuria; or fixed, often progressive weakness. Great strides have been made in our understanding of the molecular bases of these disorders, all of which show remarkable genetic heterogeneity. In contrast, the pathophysiological mechanisms underlying acute muscle breakdown and chronic weakness remain unclear. Although glycogen storage diseases have been studied for decades, new biochemical defects are still being discovered, especially in the glycolytic pathway. In addition, the pathogenesis of polyglucosan deposition is being clarified both in traditional glycogenoses and in disorders such as Lafora's disease. In some conditions, combined dietary and exercise regimens may be of help, and gene therapy, including recombinant enzyme replacement, is being actively pursued.

Lafora's disease: towards a clinical, pathologic, and molecular synthesis

Lafora's disease is one of five inherited progressive myoclonus epilepsy syndromes. It is an autosomal-recessive disorder with onset in late childhood or adolescence. Characteristic seizures include myoclonic and occipital lobe seizures with visual hallucinations, scotomata, and photoconvulsions. The course of the disease consists of worsening seizures and an inexorable decline in mental and other neurologic functions that result in dementia and death within 10 years of onset. Pathology reveals pathognomonic polyglucosan inclusions that are not seen in any other progressive myoclonus epilepsy. Lafora's disease is one of several neurologic conditions associated with brain polyglucosan bodies. Why Lafora's polyglucosan bodies alone are associated with epilepsy is unknown and is discussed in this article. Up to 80% of patients with Lafora's disease have mutations in the EPM2A gene. Although common mutations are rare, simple genetic tests to identify most mutations have been established. At least one other still-unknown gene causes Lafora's disease. The EPM2A gene codes for the protein laforin, which localizes at the plasma membrane and the rough endoplasmic reticulum and functions as a dual-specificity phosphatase. Work toward establishing the connection between laforin and Lafora's disease polyglucosans is underway, as are attempts to replace it into the central nervous system of patients with Lafora's disease.

Laforin, defective in the progressive myoclonus epilepsy of Lafora type, is a dual-specificity phosphatase associated with polyribosomes

The progressive myoclonus epilepsy of Lafora type is an autosomal recessive disorder caused by mutations in the EPM2A gene. EPM2A is predicted to encode a putative tyrosine phosphatase protein, named laforin, whose full sequence has not yet been reported. In order to understand the function of the EPM2A gene, we isolated a full-length cDNA, raised an antibody and characterized its protein product. The full-length clone predicts a 38 kDa laforin that was very close to the size detected in transfected cells. Recombinant laforin was able to hydrolyze phosphotyrosine as well as phosphoserine/threonine substrates, demonstrating that laforin is an active dual-specificity phosphatase. Biochemical, immunofluorescence and electron microscopic studies on the full-length laforin expressed in HeLa cells revealed that laforin is a cytoplasmic protein associated with polyribosomes, possibly through a conformation-dependent protein-protein interaction. We analyzed the intracellular targeting of two laforin mutants with missense mutations. Expression of both mutants resulted in ubiquitin-positive perinuclear aggregates suggesting that they were misfolded proteins targeted for degradation. Our results suggest that laforin is involved in translational regulation and that protein misfolding may be one of the molecular bases of the Lafora disease phenotype caused by missense mutations in the EPM2A gene.

Superoxide dismutase and glutathione peroxidase function in progressive myoclonus epilepsies

Progressive myoclonic epilepsies (EPM) are difficult to treat and refractory to most antiepileptic drugs. Besides epilepsy, EPMs also involve continuous neurological deterioration. Oxidative stress is thought to be an important factor in this process. We therefore analyzed a series of antioxidant enzymes in the blood of patients and compared with healthy age matched controls. In addition patients were given high doses of N-acetylcysteine (NAC), a glutathione percursor to determine if symptoms of EPM would improve. Five patients, four with EPM 1 (Unverricht-Lundborg disease) and one patient with EPM2 (Lafora body disease) were treated with 6 g/day of NAC. Before treatment, plasma samples were analyzed for glutathione peroxidase activity, catalase activity, extracellular superoxide dismutase (SOD) and CuZn-SOD and compared with the controls. Erythrocyte CuZn-SOD was significantly lower in the EPM patients compared to controls. NAC improved markedly and stabilized the neurological symptoms in patients with EPM 1 but had a doubtful effect in the patient with EPM 2.

Biology of chromosome 6

The major histocompatibility (HLA) complex on the short arm of human chromosome 6 has attracted many scientists over the last three decades. It is the purpose of this brief review to point out that the remaining large regions of chromosome 6 contain genes involved in several interesting biological phenomena as well. Focus will be particularly on genes affecting behavioural features and sensory perception. The likely involvement of HLA and closely linked olfactory receptor loci in mate selection and their possible role in favouring heterozygosity among the offspring will also be discussed.