Efhc1 deficiency causes spontaneous myoclonus and increased seizure susceptibility

Mutations in EFHC1 gene have been previously reported in patients with epilepsies, including those with juvenile myoclonic epilepsy. Myoclonin1, also known as mRib72-1, is encoded by the mouse Efhc1 gene. Myoclonin1 is dominantly expressed in embryonic choroid plexus, post-natal ependymal cilia, tracheal cilia and sperm flagella. In this study, we generated viable Efhc1-deficient mice. Most of the mice were normal in outward appearance, and both sexes were found to be fertile. However, the ventricles of the brains were significantly enlarged in the null mutants, but not in the heterozygotes. Although the ciliary structure was found intact, the ciliary beating frequency was significantly reduced in null mutants. In adult stages, both the heterozygous and null mutants developed frequent spontaneous myoclonus. Furthermore, the threshold of seizures induced by pentylenetetrazol was significantly reduced in both heterozygous and null mutants. These observations seem to further suggest that decrease or loss of function of myoclonin1 may be the molecular basis for epilepsies caused by EFHC1 mutations.

Novel mutations in Myoclonin1/EFHC1 in sporadic and familial juvenile myoclonic epilepsy

BACKGROUND

Juvenile myoclonic epilepsy (JME) accounts for 3 to 12% of all epilepsies. In 2004, the GENESS Consortium demonstrated four missense mutations in Myoclonin1/EFHC1 of chromosome 6p12.1 segregating in 20% of Hispanic families with JME.

OBJECTIVE

To examine what percentage of consecutive JME clinic cases have mutations in Myoclonin1/EFHC1.

METHODS

We screened 44 consecutive patients from Mexico and Honduras and 67 patients from Japan using heteroduplex analysis and direct sequencing.

RESULTS

We found five novel mutations in transcripts A and B of Myoclonin1/EFHC1. Two novel heterozygous missense mutations (c.755C>A and c.1523C>G) in transcript A occurred in both a singleton from Mexico and another singleton from Japan. A deletion/frameshift (C.789del.AV264fsx280) in transcript B was present in a mother and daughter from Mexico. A nonsense mutation (c.829C>T) in transcript B segregated in four clinically and seven epileptiform-EEG affected members of a large Honduran family. The same nonsense mutation (c.829C>T) occurred as a de novo mutation in a sporadic case. Finally, we found a three-base deletion (-364--362del.GAT) in the promoter region in a family from Japan.

CONCLUSION

Nine percent of consecutive juvenile myoclonic epilepsy cases from Mexico and Honduras clinics and 3% of clinic patients from Japan carry mutations in Myoclonin1/EFCH1. These results represent the highest number and percentage of mutations found for a juvenile myoclonic epilepsy causing gene of any population group.

Hyperglycosylation and reduced GABA currents of mutated GABRB3 polypeptide in remitting childhood absence epilepsy

Childhood absence epilepsy (CAE) accounts for 10% to 12% of epilepsy in children under 16 years of age. We screened for mutations in the GABA(A) receptor (GABAR) beta 3 subunit gene (GABRB3) in 48 probands and families with remitting CAE. We found that four out of 48 families (8%) had mutations in GABRB3. One heterozygous missense mutation (P11S) in exon 1a segregated with four CAE-affected persons in one multiplex, two-generation Mexican family. P11S was also found in a singleton from Mexico. Another heterozygous missense mutation (S15F) was present in a singleton from Honduras. An exon 2 heterozygous missense mutation (G32R) was present in two CAE-affected persons and two persons affected with EEG-recorded spike and/or sharp wave in a two-generation Honduran family. All mutations were absent in 630 controls. We studied functions and possible pathogenicity by expressing mutations in HeLa cells with the use of Western blots and an in vitro translation and translocation system. Expression levels did not differ from those of controls, but all mutations showed hyperglycosylation in the in vitro translation and translocation system with canine microsomes. Functional analysis of human GABA(A) receptors (alpha 1 beta 3-v2 gamma 2S, alpha 1 beta 3-v2[P11S]gamma 2S, alpha 1 beta 3-v2[S15F]gamma 2S, and alpha 1 beta 3-v2[G32R]gamma 2S) transiently expressed in HEK293T cells with the use of rapid agonist application showed that each amino acid transversion in the beta 3-v2 subunit (P11S, S15F, and G32R) reduced GABA-evoked current density from whole cells. Mutated beta 3 subunit protein could thus cause absence seizures through a gain in glycosylation of mutated exon 1a and exon 2, affecting maturation and trafficking of GABAR from endoplasmic reticulum to cell surface and resulting in reduced GABA-evoked currents.

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.

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.

Mutational analysis ofCACNA1Gin idiopathic generalized epilepsy

Recent studies have strongly implicated low voltage-activated/T-type calcium channels (T-channels) in the etiology of epilepsy. Here, we report the results of a mutational analysis of the CACNA1G gene, encoding the T-channel Ca(V)3.1/(1G) subunit, using a cohort of 123 mostly Japanese and Hispanic patients with idiopathic generalized epilepsies (IGE) and 360 healthy control individuals. We found 13 variants, including five which involved amino acid substitutions. One variant, c.1709C>T (Ala570Val), is present in a sporadic case of juvenile myoclonic epilepsy (JME) with early childhood absence and astatic seizures, but was not found in control samples. Another variant, c.3265G>T (Ala1089Ser), was observed in three family members affected with JME, and also in one control individual. Two JME patients and three control individuals harbored a third variant, c.2968G>A (Asp980Asn). Although not statistically significant, slightly faster inactivation decay rates were observed in some mutant channels. Our collective findings flag CACNA1G as a potential susceptibility locus for IGE subsyndromes that warrants closer investigation.

Novel NHLRC1 mutations and genotype-phenotype correlations in patients with Lafora's progressive myoclonic epilepsy

BACKGROUND

Lafora's progressive myoclonic epilepsy (Lafora's disease) is an autosomal recessive neurodegenerative disorder characterised by the presence of polyglucosan intracellular inclusions called Lafora bodies. Mutations in two genes, EPM2A and NHLRC1, have been shown to cause the disease. A previous study showed mutations in the EPM2A gene in 14 Lafora's disease families and excluded the involvement of this gene in five other families who were biopsy proven to have the disease.

OBJECTIVE

To relate the genetic findings to the clinical course of the disease.

METHODS

As part of an ongoing mutational study of the Lafora's disease genes, five new families with the disease were recruited and the genetic analysis was extended to screen the entire coding region of the NHLRC1 gene. Genotype-phenotype correlations were carried out.

RESULTS

Seven NHLRC1 mutations were identified, including five novel mutations (E91K, D195N, P218S, F216_D233del, and V359fs32), in eight families with Lafora's disease. On relating the genetic findings to the clinical course of the disease it was shown that patients with NHLRC1 mutations had a slower rate of disease progression (p<0.0001) and thus appeared to live longer than those with EPM2A mutations. A simple DNA based test is described to detect the missense mutation C26S (c.76T-->A) in the NHLRC1 gene, which is prevalent among French Canadians.

CONCLUSIONS

Patients with NHLRC1 mutations have a slower rate of disease progression than those with EPM2A mutations.

Mutation analyses of genes on 6p12-p11 in patients with juvenile myoclonic epilepsy

Juvenile myoclonic epilepsy (JME) is a distinct form of idiopathic generalized epilepsy (IGE). One of the candidate regions for human JME has been mapped on chromosome band 6p11-p12 by linkage analyses and is termed EJM1 (MIM 254770). Recently, we reported the reduction of the EJM1 region to 3.5cM that contains 18 genes, the exclusion of three genes (LRRC1, GCLC, KIAA0057) by mutation analyses, and the identification of Myoclonin1/EFHC1 as the EJM1 gene. Here, we describe detailed physical and transcriptome maps of the 3.5cM EJM1 region, and detailed results of mutation analyses for the remained 14 genes (HELO1, GCMA, KIAA0936, FBXO9, GSTA3, GSTA4, PTD011, KIAA0576, LMPB1, IL17F, MCM3, PKHD1, KIAA0105, TFAP2B) in patients with JME. We identified 49 single nucleotide changes in eight genes. Twelve amino acid substitutions occurred in two genes, 11 silent mutations in seven genes, and 26 in the non-coding or intronic regions of seven genes. Twelve amino acid substitutions in the two genes (IL17F, PKHD1) were also observed in healthy control individuals or did not co-segregate with the disease phenotypes in other family members. Thus, the absence of significant and potentially functional mutations in the remaining 14 genes further supports the concept that Myoclonin1/EFHC1 is the EJM1 gene in chromosome 6p12.

EFHC1, a protein mutated in juvenile myoclonic epilepsy, associates with the mitotic spindle through its N-terminus

A novel gene, EFHC1, mutated in juvenile myoclonic epilepsy (JME) encodes a protein with three DM10 domains of unknown function and one putative EF-hand motif. To study the properties of EFHC1, we expressed EGFP-tagged protein in various cell lines. In interphase cells, the fusion protein was present in the cytoplasm and in the nucleus with specific accumulation at the centrosome. During mitosis EGFP-EFHC1 colocalized with the mitotic spindle, especially at spindle poles and with the midbody during cytokinesis. Using a specific antibody, we demonstrated the same distribution of the endogenous protein. Deletion analyses revealed that the N-terminal region of EFHC1 is crucial for the association with the mitotic spindle and the midbody. Our results suggest that EFHC1 could play an important role during cell division.

Juvenile myoclonic epilepsy subsyndromes: family studies and long-term follow-up

The 2001 classification subcommittee of the International League Against Epilepsy (ILAE) proposed to 'group JME, juvenile absence epilepsy, and epilepsy with tonic clonic seizures only under the sole heading of idiopathic generalized epilepsies (IGE) with variable phenotype'. The implication is that juvenile myoclonic epilepsy (JME) does not exist as the sole phenotype of family members and that it should no longer be classified by itself or considered a distinct disease entity. Although recognized as a common form of epilepsy and presumed to be a lifelong trait, a long-term follow-up of JME has not been performed. To address these two issues, we studied 257 prospectively ascertained JME patients and encountered four groups: (i) classic JME (72%), (ii) CAE (childhood absence epilepsy) evolving to JME (18%), (iii) JME with adolescent absence (7%), and (iv) JME with astatic seizures (3%). We examined clinical and EEG phenotypes of family members and assessed clinical course over a mean of 11 +/- 6 years and as long as 52 years. Forty per cent of JME families had JME as their sole clinical phenotype. Amongst relatives of classic JME families, JME was most common (40%) followed by grand mal (GM) only (35%). In contrast, 66% of families with CAE evolving to JME expressed the various phenotypes of IGE in family members. Absence seizures were more common in family members of CAE evolving to JME than in those of classic JME families (P < 0.001). Female preponderance, maternal transmission and poor response to treatment further characterized CAE evolving to JME. Only 7% of those with CAE evolving to JME were seizure-free compared with 58% of those with classic JME (P < 0.001), 56% with JME plus adolescent pyknoleptic absence and 62% with JME plus astatic seizures. Long-term follow-up (1-40 years for classic JME; 5-52 years for CAE evolving to JME, 5-26 years for JME with adolescent absence and 3-18 years for JME with astatic seizures) indicates that all subsyndromes are chronic and perhaps lifelong. Seven chromosome loci, three epilepsy-causing mutations and two genes with single nucleotide polymorphisms (SNPs) associating with JME reported in literature provide further evidence for JME as a distinct group of diseases.

Seizures of idiopathic generalized epilepsies

Idiopathic generalized epilepsies (IGEs) comprise at least 40% of epilepsies in the United States, 20% in Mexico, and 8% in Central America. Here, we review seizure phenotypes across IGE syndromes, their response to treatment and advances in molecular genetics that influence nosology. Our review included the Medline database from 1945 to 2005 and our prospectively collected Genetic Epilepsy Studies (GENESS) Consortium database. Generalized seizures occur with different and similar semiologies, frequencies, and patterns, ages at onset, and outcomes in different IGEs, suggesting common neuroanatomical pathways for seizure phenotypes. However, the same seizure phenotypes respond differently to the same treatments in different IGEs, suggesting different molecular defects across syndromes. De novo mutations in SCN1A in sporadic Dravet syndrome and germline mutations in SCN1A, SCN1B, and SCN2A in generalized epilepsies with febrile seizures plus have unraveled the heterogenous myoclonic epilepsies of infancy and early childhood. Mutations in GABRA1, GABRG2, and GABRB3 are associated with absence seizures, while mutations in CLCN2 and myoclonin/EFHC1 substantiate juvenile myoclonic epilepsy as a clinical entity. Refined understanding of seizure phenotypes, their semiology, frequencies, and patterns together with the identification of molecular lesions in IGEs continue to accelerate the development of molecular epileptology.

Sacred disease secrets revealed: the genetics of human epilepsy

Neurons throughout the brain suddenly discharging synchronously and recurrently cause primarily generalized seizures. Discharges localized awhile in one part of the brain cause focal-onset seizures. A genetically determined generalized hyperexcitability had been predicted in primarily generalized seizures, but surprisingly the first epilepsy gene discovered, CHRNA4, was in a focal (frontal lobe)-onset syndrome. Another surprise with CHRNA4 was its encoding of an ion channel present throughout the brain. The reason why CHRNA4 causes focal-onset seizures is unknown. Recently, the second focal (temporal lobe)-onset epilepsy gene, LGI1 (unknown function), was discovered. CHRNA4 led the way to mutation identifications in 15 ion channel genes, most causing primarily generalized epilepsies. Potassium channel mutations cause benign familial neonatal convulsions. Sodium channel mutations cause generalized epilepsy with febrile seizures plus or, if more severe, severe myoclonic epilepsy of infancy. Chloride and calcium channel mutations are found in rare families with the common syndromes childhood absence epilepsy and juvenile myoclonic epilepsy (JME). Mutations in the EFHC1 gene (unknown function) occur in other rare JME families, and yet in other families, associations are present between JME (or other generalized epilepsies) and single nucleotide polymorphisms in the BRD2 gene (unknown function) and the malic enzyme 2 (ME2) gene. Hippocrates predicted the genetic nature of the 'sacred' disease. Genes underlying the 'malevolent' forces seizing 1% of humans have now been revealed. These, however, still account for a mere fraction of the genetic contribution to epilepsy. Exciting years are ahead, in which the genetics of this extremely common, and debilitating, neurological disorder will be solved.

Transcriptional profiling of a mouse model for Lafora disease reveals dysregulation of genes involved in the expression and modification of proteins

Lafora's progressive myoclonus epilepsy (Lafora disease: LD) is caused by mutations in the EPM2A or NHLRC1 gene, but cellular mechanisms of the pathogenesis remain unclear. In an attempt to understand and elucidate the disease pathway, we have investigated the global gene expression profile in a mouse model for LD that developed a phenotype similar to that observed in human patients, including presence of Lafora bodies, neurodegeneration and profound neurological disturbances. We found 62 differentially expressed genes in the Epm2a knockout mice brains. These genes encode factors involved in protein catabolism, phosphatase, transcription factors, and molecules involved in protein translation, and homeostasis. The two largest functional groups of mRNAs that showed altered expression were predicted to be involved in post-translational modification of proteins and transcriptional regulation, suggesting that defects in protein activity and/or turnover may be the key trigger in the pathophysiology of LD. Furthermore we show that changes in gene expression are not limited to brain and are seen in other organs that develop Lafora bodies. Our study may provide valuable insights into the pathophysiology of LD and may aid in developing potential therapeutic targets.

Sacred disease secrets revealed: the genetics of human epilepsy

Neurons throughout the brain suddenly discharging synchronously and recurrently cause primarily generalized seizures. Discharges localized awhile in one part of the brain cause focal-onset seizures. A genetically determined generalized hyperexcitability had been predicted in primarily generalized seizures, but surprisingly the first epilepsy gene discovered, CHRNA4, was in a focal (frontal lobe)-onset syndrome. Another surprise with CHRNA4 was its encoding of an ion channel present throughout the brain. The reason why CHRNA4 causes focal-onset seizures is unknown. Recently, the second focal (temporal lobe)-onset epilepsy gene, LGI1 (unknown function), was discovered. CHRNA4 led the way to mutation identifications in 15 ion channel genes, most causing primarily generalized epilepsies. Potassium channel mutations cause benign familial neonatal convulsions. Sodium channel mutations cause generalized epilepsy with febrile seizures plus or, if more severe, severe myoclonic epilepsy of infancy. Chloride and calcium channel mutations are found in rare families with the common syndromes childhood absence epilepsy and juvenile myoclonic epilepsy (JME). Mutations in the EFHC1 gene (unknown function) occur in other rare JME families, and yet in other families, associations are present between JME (or other generalized epilepsies) and single nucleotide polymorphisms in the BRD2 gene (unknown function) and the malic enzyme 2 (ME2) gene. Hippocrates predicted the genetic nature of the 'sacred' disease. Genes underlying the 'malevolent' forces seizing 1% of humans have now been revealed. These, however, still account for a mere fraction of the genetic contribution to epilepsy. Exciting years are ahead, in which the genetics of this extremely common, and debilitating, neurological disorder will be solved.

Mutations in EFHC1 cause juvenile myoclonic epilepsy

Juvenile myoclonic epilepsy (JME) is the most frequent cause of hereditary grand mal seizures. We previously mapped and narrowed a region associated with JME on chromosome 6p12-p11 (EJM1). Here, we describe a new gene in this region, EFHC1, which encodes a protein with an EF-hand motif. Mutation analyses identified five missense mutations in EFHC1 that cosegregated with epilepsy or EEG polyspike wave in affected members of six unrelated families with JME and did not occur in 382 control individuals. Overexpression of EFHC1 in mouse hippocampal primary culture neurons induced apoptosis that was significantly lowered by the mutations. Apoptosis was specifically suppressed by SNX-482, an antagonist of R-type voltage-dependent Ca(2+) channel (Ca(v)2.3). EFHC1 and Ca(v)2.3 immunomaterials overlapped in mouse brain, and EFHC1 coimmunoprecipitated with the Ca(v)2.3 C terminus. In patch-clamp analysis, EFHC1 specifically increased R-type Ca(2+) currents that were reversed by the mutations associated with JME.

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.

Body part asymmetry in partial seizure

Clinically differentiating between localisation related and generalised epilepsy is important because it carries significant implications for planning diagnostic management strategy. Asymmetry of body parts such as toes, popliteal crease levels, thumbs, cubital crease levels, and forehead and facial structures, are common in patients with localisation related epilepsy syndromes. We retrospectively studied 337 patients with seizure disorders. Body part asymmetry was routinely documented. Fifty-six were excluded because of non-epileptic seizures, pure psychiatric disorders, non-epileptic neurological disorders, brain tumours and strokes. The relationship between clinically detectable body asymmetry (BA) and the electro-anatomic characteristics of their epilepsy was explored. Body asymmetry was found in 88 out of 282 cases, in which 64 (73.5%) suffered from localisation related epilepsy. Among localisation related epilepsy, BA were found in 41.5% (n=64/154) of patients. In contrast, only 18.75% (n=24/128) of patients with generalised seizure disorders showed similar findings (P<0.0001). Among patients with partial onset seizures, lateralisation of BA was concordant with their seizure origin in 75.9% (n=41/54) and discordant in 24.1% (n=13/54). Investigation results of 10 partial epilepsy cases were non-lateralising at the time of study. Peak age of onset of concordant case was 0-5 years old while discordant group was 6-15 years old. We conclude that BA in patients with seizure disorder is a useful clue to diagnosis of localisation related seizure and may provide clues for lateralising seizure origin in partial onset seizures.

Recent Developments in the Quest for Myoclonic Epilepsy Genes

Understanding the latest advances in the molecular genetics of the epilepsies is important, as it provides a basis for comprehending the new practice of epileptology. Epilepsies have traditionally been classified and subtyped on the basis of clinical and neurophysiologic concepts. However, the complexity and variability of phenotypes and overlapping clinical features limit the resolution of phenotype-based classification and confound epilepsy nosology. Identification of tightly linked epilepsy DNA markers and discovery of epilepsy-causing mutations provide a basis for refining the classification of epilepsies. Recent discoveries regarding the genetics surrounding certain epilepsy types (including Lafora's progressive myoclonic epilepsy, the severe myoclonic epilepsy of infancy of Dravet, and idiopathic generalized epilepsies) may be the beginning of a better understanding of how rare Mendelian epilepsy genes and their genetic architecture can explain some complexities of the common epilepsies.

Mutations in NHLRC1 cause progressive myoclonus epilepsy

Lafora progressive myoclonus epilepsy is characterized by pathognomonic endoplasmic reticulum (ER)-associated polyglucosan accumulations. We previously discovered that mutations in EPM2A cause Lafora disease. Here, we identify a second gene associated with this disease, NHLRC1 (also called EPM2B), which encodes malin, a putative E3 ubiquitin ligase with a RING finger domain and six NHL motifs. Laforin and malin colocalize to the ER, suggesting they operate in a related pathway protecting against polyglucosan accumulation and epilepsy.