The Ramsay Hunt syndrome revisited: Mediterranean myoclonus versus mitochondrial encephalomyopathy with ragged-red fibers and Baltic myoclonus

Clinical and molecular characterization of Unverricht-Lundborg disease among Egyptian patients

BACKGROUND AND PURPOSE

Unverricht-Lundborg disease (ULD) is a common type of progressive myoclonic epilepsy (PME). It is caused mostly by biallelic dodecamer repeat expansions in the promoter region of CSTB gene. Despite highly prevalent in the Mediterranean countries, no studies have been reported from Egypt. This article study the presence of CSTB gene mutations among Egyptian patients clinically suspected with ULD, and describes the clinical and genetic characteristics of those with confirmed gene mutation.

METHODS

Medical records of patients following up in two specialized epilepsy clinics in Cairo, Egypt were retrospectively reviewed. Twenty patients who belonged to 13 unrelated families were provisionally diagnosed with ULD based on the clinical presentation. Genetic testing was done. Clinical characteristics, demographic data and EEG findings were documented.

RESULTS

Genetic studies confirmed the presence of the CSTB dodecamer repeat expansion in 14 patients from 8 families (frequency 70 %). The mean duration of the follow-up was 5 years. Male to female distribution was 1:1 with a mean age of onset 9.7 years. Consanguinity was noted in 4 families. Eight patients had their first seizure between the age of 10 and 20 years. Myoclonic jerks ranged in severity from mild in three unrelated patients to severe in one. Only 3 had cognitive impairment.

CONCLUSION

Our study confirms the presence of CSTB mutation among Egyptian patients suspected with ULD. There was no clear phenotype-genotype correlation among the studied group of patients. In addition, we noticed variable inter and intra familial severity among patients from the same family.

Myoclonus epilepsy and ataxia due to KCNC1 mutation: Analysis of 20 cases and K+ channel properties

OBJECTIVE

To comprehensively describe the new syndrome of myoclonus epilepsy and ataxia due to potassium channel mutation (MEAK), including cellular electrophysiological characterization of observed clinical improvement with fever.

METHODS

We analyzed clinical, electroclinical, and neuroimaging data for 20 patients with MEAK due to recurrent KCNC1 p.R320H mutation. In vitro electrophysiological studies were conducted using whole cell patch-clamp to explore biophysical properties of wild-type and mutant K_V 3.1 channels.

RESULTS

Symptoms began at between 3 and 15 years of age (median = 9.5), with progressively severe myoclonus and rare tonic-clonic seizures. Ataxia was present early, but quickly became overshadowed by myoclonus; 10 patients were wheelchair-bound by their late teenage years. Mild cognitive decline occurred in half. Early death was not observed. Electroencephalogram (EEG) showed generalized spike and polyspike wave discharges, with documented photosensitivity in most. Polygraphic EEG-electromyographic studies demonstrated a cortical origin for myoclonus and striking coactivation of agonist and antagonist muscles. Magnetic resonance imaging revealed symmetrical cerebellar atrophy, which appeared progressive, and a prominent corpus callosum. Unexpectedly, transient clinical improvement with fever was noted in 6 patients. To explore this, we performed high-temperature in vitro recordings. At elevated temperatures, there was a robust leftward shift in activation of wild-type K_V 3.1, increasing channel availability.

INTERPRETATION

MEAK has a relatively homogeneous presentation, resembling Unverricht-Lundborg disease, despite the genetic and biological basis being quite different. A remarkable improvement with fever may be explained by the temperature-dependent leftward shift in activation of wild-type K_V 3.1 subunit-containing channels, which would counter the loss of function observed for mutant channels, highlighting KCNC1 as a potential target for precision therapeutics. Ann Neurol 2017;81:677-689.

The history of progressive myoclonus epilepsies

The history of the progressive myoclonus epilepsies (PMEs) spans more than a century. However, the recent history of PMEs begins with a consensus statement published in the wake of the Marseille PME workshop in 1989 (Marseille Consensus Group, 1990). This consensus helped define the various types of PME known at the time and set the agenda for a new era of genetic research which soon lead to the discovery of many PME genes. Prior to the Marseille meeting, and before the molecular era, there had been much confusion and controversy. Because investigators had but limited and biased experience with these rare disorders due to the uneven, skewed distribution of PMEs around the world, opinions and nosologies were based on local expertise which did not match well with the experiences of other researchers and clinicians. The three major areas of focus included: (1) the nature and limits of the concept of PME in varying scopes, which was greatly debated; (2) the description of discrete clinical entities by clinicians; and (3) the description of markers (pathological, biological, neurophysiological, etc.) which could lead to a precise diagnosis of a given PME type, with, in the best cases, a reliable correlation with clinical findings. In this article, we shall also examine the breakthroughs achieved in the wake of the 1989 Marseille meeting and recent history in the field, following the identification of several PME genes. As in other domains, the molecular and genetic approach has challenged some established concepts and has led to the description of new PME types. However, as may already be noted, this approach has also confirmed the existence of the major, established types of PME, which can now be considered as true diseases.

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.

Progressive myoclonus epilepsies: clinical and genetic aspects

The progressive myoclonus epilepsies (PMEs) are a group of rare genetic disorders previously shrouded in nosological confusion. Recent advances have clarified the features of these disorders and provided a rational approach to diagnosis. The major causes of PME are now known to be Unverricht-Lundborg disease, myoclonus epilepsy ragged-red fiber (MERRF) syndrome, Lafora disease, neuronal ceroid lipofuscinoses, and sialidoses. Over the past 3 years, a series of molecular genetic findings have further refined the understanding of the PMEs. The specific mutation responsible for many cases of MERRF has been identified, and the genes for Unverricht-Lundborg disease and for juvenile neuronal ceroid lipofuscinosis have been linked to chromosomes 21 and 16, respectively. Although the PMEs are among the rarest of the inherited epilepsies, because of molecular genetic discoveries they may soon be the best understood at the neurobiologic level.

SCARB2 mutations in progressive myoclonus epilepsy (PME) without renal failure

OBJECTIVE

Mutations in SCARB2 were recently described as causing action myoclonus renal failure syndrome (AMRF). We hypothesized that mutations in SCARB2 might account for unsolved cases of progressive myoclonus epilepsy (PME) without renal impairment, especially those resembling Unverricht-Lundborg disease (ULD). Additionally, we searched for mutations in the PRICKLE1 gene, newly recognized as a cause of PME mimicking ULD.

METHODS

We reviewed cases of PME referred for diagnosis over two decades in which a molecular diagnosis had not been reached. Patients were classified according to age of onset, clinical pattern, and associated neurological signs into "ULD-like" and "not ULD-like." After exclusion of mutations in cystatin B (CSTB), DNA was examined for sequence variation in SCARB2 and PRICKLE1.

RESULTS

Of 71 cases evaluated, 41 were "ULD-like" and five had SCARB2 mutations. None of 30 "not ULD-like" cases were positive. The five patients with SCARB2 mutations had onset between 14 and 26 years of age, with no evidence of renal failure during 5.5 to 15 years of follow-up; four were followed until death. One living patient had slight proteinuria. A subset of 25 cases were sequenced for PRICKLE1 and no mutations were found.

INTERPRETATION

Mutations in SCARB2 are an important cause of hitherto unsolved cases of PME resembling ULD at onset. SCARB2 should be evaluated even in the absence of renal involvement. Onset is in teenage or young adult life. Molecular diagnosis is important for counseling the patient and family, particularly as the prognosis is worse than classical ULD.

A longitudinal study of Taiwanese sialidosis type 1: an insight into the concept of cherry-red spot myoclonus syndrome

BACKGROUND AND PURPOSE

Sialidosis type 1 (ST-1) is a neurodegenerative disorder with limited long-term follow-up report. This study is to document the chronological profile of ST-1.

METHODS

We perform serial analysis of 17 Taiwanese patients with ST-1 focusing on evolution of clinical features, electrophysiological findings, genetic studies, and neuroimage examinations.

RESULTS

All patients had a mutation at 554A-->G in exon 3 of the NEU1 gene causing Ser182Gly substitution. Fifteen patients were homozygous. Two patients were heterozygous with novel mutations, 956C-->T causing Ala319Val in one and 163C-->T causing Gln55stop codon in the other. The neuraminidase activity was markedly decreased in all 11 available patients. Only three patients (17.6%) manifested the macular cherry-red spot. The majority of patients (82.3%) developed full-blown manifestation of myoclonus, ataxia, and seizures within 5 years. Abnormal somatosensory evoked potentials with giant cortical waves were found in all patients. Prolonged P100 peak latency of the visual evoked potentials (VEPs) were found in 16 patients (94.1%) in the early stage even without visual symptoms.

CONCLUSION

ST-1 in Taiwanese population illustrates distinct characteristics of phenotype with infrequent cherry-red spot. We suggest to screen the NEU1 mutations in patients presenting action myoclonus with abnormal VEPs, even without macular cherry-red spots.

Clinical picture of EPM1-Unverricht-Lundborg disease

Unverricht-Lundborg disease (ULD), progressive myoclonic epilepsy type 1 (EPM1, OMIM254800), is an autosomal recessively inherited neurodegenerative disorder characterized by age of onset from 6 to 16 years, stimulus-sensitive myoclonus, and tonic-clonic epileptic seizures. Some years after the onset ataxia, incoordination, intentional tremor, and dysarthria develop. Individuals with EPM1 are mentally alert but show emotional lability, depression, and mild decline in intellectual performance over time. The diagnosis of EPM1 can be confirmed by identifying disease-causing mutations in a cysteine protease inhibitor cystatin B (CSTB) gene. Symptomatic pharmacologic and rehabilitative management, including psychosocial support, are the mainstay of EPM1 patients' care. Valproic acid, the first drug of choice, diminishes myoclonus and the frequency of generalized seizures. Clonazepam and high-dose piracetam are used to treat myoclonus, whereas levetiracetam seems to be effective for both myoclonus and generalized seizures. There are a number of agents that aggravate clinical course of EPM1 such as phenytoin aggravating the associated neurologic symptoms or even accelerating cerebellar degeneration. Sodium channel blockers (carbamazepine, oxcarbazepine) and GABAergic drugs (tiagabine, vigabatrin) as well as gabapentin and pregabalin may aggravate myoclonus and myoclonic seizures. EPM1 patients need lifelong clinical follow-up, including evaluation of the drug-treatment and comprehensive rehabilitation.

Substantial thalamostriatal dopaminergic defect in Unverricht-Lundborg disease

PURPOSE

Unverricht-Lundborg disease (ULD) is currently classified as progressive myoclonus epilepsy. Myoclonus, the characteristic symptom in ULD, suggests that dopamine neurotransmission may be involved in the pathophysiology of ULD. Our purpose was to examine brain dopaminergic function in ULD patients.

METHODS

Four genetically and clinically diagnosed ULD patients and eight healthy controls were scanned with [(11)C]raclopride-PET. PET images were coregistered to individual 1.5 T MR images and region-of-interest analysis was performed for the striatum and thalamus. Standardized uptake values and individual voxel-wise binding potential maps of the patients and controls were also analyzed.

RESULTS

ULD patients had markedly higher (31-54%) dopamine D2-like receptor availabilities than healthy controls in both the striatum and the thalamus. The proportionally highest binding potentials were detected in the thalamus. There were no significant differences in the cerebellar uptake of [(11)C]raclopride in ULD patients versus healthy controls. Voxel-based results were in accordance with the region-of-interest analysis.

CONCLUSIONS

These results suggest that dopaminergic modulation at the level of the striatum and thalamus could be a crucial factor contributing to the symptoms of ULD. In the light of our data, we propose that ULD with dopamine dysfunction and dyskinetic symptoms shares certain pathophysiological mechanisms with classical movement disorders. Future studies are therefore warranted to study the effect of dopaminergic pharmacotherapy in ULD.

La maladie d’Unverricht-Lundborg (EPM1)

Unverricht-Lundborg disease (ULD) is the purest and least severe type of progressive myoclonus epilepsy (PME), and is not associated with progressive cognitive deficit. Symptoms stabilize in adulthood, with a varying degree of permanent, often severe handicap that is mostly due to myoclonus. The disorder follows an autosomal recessive transmission pattern, with onset between 8 and 15 years years of age of generalized tonic-clonic or clonic-tonic-clonic seizures, action myoclonus (massive or segmental), photosensitivity, and often ataxia. Prevalence varies, it is highest in certain isolates (Finland, La Réunion Island) and in region with higher levels of inbreeding (Maghreb). ULD is due to a deficit in cystatin B (stefin B), but the mechanisms leading to the clinical symptoms are not well understood. The causative gene, PME1, was identified in 1991 and localized to chromosome 21q22.3. The mutations are mainly expansions of the CCCCGCCCCGCG dodecamer, but less common point mutations were also found. A variant has been recently reported in a Palestinian family, with localization on chromosome 12. The diagnosis of ULD is made on the basis of family history, age at onset, geographical and ethnic context, and on the typical features of myoclonus and epilepsy, in the absence of cognitive and sensory deficits. Neurophysiological evaluation yields interesting, but unspecific results. There are no biological or pathological markers for ULD. Molecular analysis confirms the diagnosis in most patients. Genetic testing for heterozygotes and even prenatal diagnosis are possible, although seldom performed, if the mutation has been identified. In spite of intensive research, ULD has yet to reveal all of its secrets. It remains a quasi "idiopathic" type of PME, with limited progression. Clinicians and patients are still waiting for an etiologically oriented treatment, which should, ideally, be admnistered early in the course of the disease, if possible before the onset of invalidating symptoms.

Unverricht-Lundborg Disease, a Condition with Self-limited Progression: Long-term Follow-up of 20 Patients

PURPOSE

To assess the long-term evolution of Unverricht-Lundborg disease (ULD), especially concerning myoclonus, seizures, and EEG characteristics.

METHODS

We retrospectively evaluated 20 patients (six women, 14 men; mean age, 37.9 years; range, 26-53 years) with ULD who had been closely followed up since the onset of the disease (mean age, 12.3 years; range, 6-17 years) for an average of 25.6 years (range, 13-41 years). ULD was confirmed by genetic tests in all. We used simplified myoclonus and seizure rating scales.

RESULTS

The geographic origin of the patients was Northern Africa in nine, France in two, Italy in six, and mixed European in three. Three patients were severely handicapped, six led fully autonomous lives, and 11 required various degrees of social support. Myoclonus progressed only during the first 5 years of disease. Major seizures occurred in 19. Three patients had a single seizure, and eight became seizure free, whereas six had rare seizures, and two had frequent attacks. Overall, seizures became much less frequent after 10 years of evolution. EEG changes abated during follow-up: background activity remained stable or improved, spontaneous discharges disappeared, and photoparoxysmal responses were abolished in all patients but two.

CONCLUSIONS

This study shows that ULD progresses only over a limited period and stabilizes thereafter. This self-limited progression may be the consequence of age-related apoptosis of selected neuronal populations.

Progressive myoclonic epilepsies: a review of genetic and therapeutic aspects

The progressive myoclonic epilepsies (PMEs) are a group of symptomatic generalised epilepsies caused by rare disorders, most of which have a genetic component, a debilitating course, and a poor outcome. Challenges with PME arise from difficulty with diagnosis, especially in the early stages of the illness, and further problems of management and drug treatment. Recent advances in molecular genetics have helped achieve better understanding of the different disorders that cause PME. We review the PMEs with emphasis on updated genetics, diagnosis, and therapeutic options.

Univerricht-Lundborg Disease: Underdiagnosed in the Netherlands

PURPOSE

Univerricht-Lundborg disease (ULD), with its major symptom of action myoclonus, is supposed to be very rare in the Netherlands and western Europe. We hypothesized that the syndrome may be underdiagnosed in patients with myoclonus epilepsy.

METHODS

Mutation analysis of the cystatin B gene was performed in 21 cases with uncontrolled myoclonus.

RESULTS

Seven of the 21 evaluated cases carried mutations in the cystatin B gene. Diagnosis of ULD was made with a mean delay of 20 years from symptom onset.

CONCLUSIONS

This study from a country without previous reports of ULD suggests that underdiagnosis of the syndrome is likely. These findings also indicate that persons with juvenile-onset myoclonus epilepsy with action myoclonus should be analyzed for ULD.

Cystatin-B is expressed by neural stem cells and by differentiated neurons and astrocytes

Mutation in the gene encoding cystatin-B (CSTB) has been shown to cause progressive myoclonus epilepsy. Mice with a gene deletion of CSTB exhibit increased apoptosis of specific neurons but the physiological role of CSTB in brain cells is not fully understood. In the present study, we have examined the expression of CSTB in neural stem cells (NSC) and in differentiating mature brain cells. The results show that CSTB is present in embryonic and adult NSC and in the neuroepithelium. CSTB was expressed by both neurons and glial cells differentiated from NSC and in hippocampal cultures. CSTB localized mainly to the nucleus in NSC and in neurons, whilst in astrocytes CSTB was also in the cytoplasm. Double labeling showed that CSTB was present in the lysosomes in glial cells. The results demonstrate a nuclear expression of CSTB in NSC and in neurons, suggesting novel function for this molecule.

Progressive myoclonus epilepsy of Unverricht-Lundborg type

Progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1) is characterized by onset at age 6-15 years, stimulus-sensitive myoclonus, tonic-clonic seizures, and typical EEG findings, with marked sensitivity to photic stimulation. Previously the course of the disease was progressive throughout the life, and no biochemical or pathologic marker existed for the diagnosis of EPM1. With modern anticonvulsive therapy, the prognosis has improved significantly, the symptoms are nowadays relatively well controlled, and the disease may not always progress. Moreover, the molecular genetic findings have now made possible an etiologic diagnosis of EPM1. The positional cloning strategy was applied to identify the gene whose defects are responsible for EPM1. The underlying gene encodes cystatin B, a cysteine protease inhibitor. The major mutation worldwide is an unstable expansion of a dodecamer minisatellite repeat unit in the promoter region of the cystatin B gene. In addition, five "minor" mutations have been described. Cystatin B mutations are now known to account for both Mediterranean myoclonus and for "Baltic" myoclonus, described mainly from Finland, thus solving a long-term controversy and proving that these two disorders are one single disease entity. The pathogenetic mechanisms in EPM1 are yet unknown, but in the majority of patients, a reduced level of the cystatin B gene product seems to be the primary mechanism in the pathology. Understanding the molecular pathogenesis of EPM1 may lead to the development of specific therapies for the disease.

Clinical features and genetics of progressive myoclonus epilepsy of the Univerricht-Lundborg type

Progressive myoclonus epilepsy of the Unverricht-Lundborg type is the most common cause of progressive myoclonus epilepsy worldwide. Typical features include onset at the age of 6-15 years, stimulus-sensitive myoclonus, tonic-clonic seizures, a progressive course and characteristic electroencephalographic findings with an exceptionally high sensitivity to photic stimulation. With modern anticonvulsive therapy the symptoms are relatively well controlled, and the disease may not always progress. Previously, no biochemical or pathological marker existed for the diagnosis of Unverricht-Lundborg disease. The positional cloning strategy was applied to identify the genetic defects that are responsible for this disease. The underlying gene encodes cystatin B, a cysteine protease inhibitor. The major mutation worldwide is an unstable expansion of a dodecamer minisatellite repeat unit in the promoter region of the cystatin B gene. In addition, five 'minor' mutations have been described. In the majority of patients, a reduced level of the cystatin B gene product seems to be the primary mechanism in the pathology, but the pathogenetic mechanisms are yet unknown. The molecular genetic findings have made a specific diagnosis possible and are the basis for understanding the molecular pathogenesis of the disease. This understanding may lead to the development of specific therapies for Unverricht-Lundborg disease.

Myoclonus and epilepsies

The possible associations of myoclonic phenomenae, progressive or non-progressive encephalopathies and epileptic features are reviewed, with special emphasis on pediatric age. This leads to recognize the following five groups of conditions: (1) Myoclonus without encephalopathy and without epilepsy; (2) Encephalopathies with non-epileptic myoclonus; (3) Progressive encephalopathies presenting myoclonus seizures of epileptic syndromes (Progressive myoclonus epilepsies); (4) Epileptic encephalopathies with myoclonic seizures; (5) Myoclonic epilepsies. Within the first group, which also includes physiologic myoclonus, a more thorough description of "Benign sleep myoclonus of newborn" and "Benign myoclonus of early infancy" is given. Characteristics of group 2 are "Kinsbourne Syndrome" and certain types of "Hyperekplexia" which pose interesting differential diagnosis with stimulus-sensitive epilepsies. In group 3, the concept of progressive encephalopathies is stressed. The fourth group refers to severe epilepsies, mainly on infancy and childhood, which lead to mental retardation irrespective of their aetiology. Group 5 comprises the true myoclonic epilepsies, differentiating syndromes recognized as idiopathic--such as "Benign myoclonic epilepsy of infancy" and "Juvenile myoclonic epilepsy"--from those which are cryptogenic and carry a more cautious prognosis--as "Cryptogenic myoclonic and myoclonoastatic epilepsies" and "Severe myoclonic epilepsy of infancy". Other epileptic syndromes not usually considered as myoclonic epilepsies, but presenting sometimes as myoclonic seizures, are finally referred.

Allelic heterogeneity of Mediterranean myoclonus and the cystatin B gene

Mediterranean myoclonus is a progressive myoclonus epilepsy with autosomal recessive inheritance. Another form has been described in Finland, the so-called Baltic myoclonus. Mediterranean myoclonus and Baltic myoclonus are also known as Unverricht-Lundborg disease. Linkage analyses have shown that the genes for both these forms of myoclonus are closely linked to 21q22.3 DNA markers, suggesting that they are caused by mutations at the same locus (EPM1). Recently, two heterozygous mutations were found in the cystatin B gene in patients with Unverricht-Lundborg disease. We report recombinational and linkage disequilibrium mapping of EPM1, and cystatin B gene sequencing, in 14 consanguineous pedigrees with Mediterranean myoclonus. Linkage to 21q22.3 DNA markers was observed in all these families. Haplotype analysis suggests that a common mutation segregates within these pedigrees, and that this mutation is different from the common one responsible for the Finnish form of Unverricht-Lundborg disease. No mutation was found in the exons or splice junctions of the cystatin B gene in the 14 pedigrees.

Dodecamer repeat expansion in cystatin B gene in progressive myoclonus epilepsy

Progressive myoclonus epilepsy of the Unverricht-Lundborg type (EPM1; MIM 254800) is an autosomal recessive disorder with onset between 6 and 13 years followed by variable progression to mental deterioration and cerebellar ataxia. It is a rare disorder but more common in Finland (1 in 20,000) and the western Mediterranean. Two point mutations in the cysteine proteinase inhibitor gene cystatin B (CSTB), proved that this gene is responsible for EPM1 (ref. 3). An extensive search in the CSTB gene revealed mutations accounting only for 14% of the 58 unrelated EPM1 alleles studied. Here we report that the majority of EPM1 alleles contain expansions of a dodecamer (12-mer) repeat located about 70 nucleotides upstream of the transcription start site nearest to the 5' end of the CSTB gene. Normal alleles contain 2 or 3 copies of this repeat whereas mutant alleles contain more than 60 such repeats and have reduced levels of CSTB messenger RNA in blood but not in cell lines. 'Premutation' CSTB alleles with 12-17 repeats show marked instability when transmitted to offspring.

Unstable insertion in the 5' flanking region of the cystatin B gene is the most common mutation in progressive myoclonus epilepsy type 1, EPM1

Progressive myoclonus epilepsy type 1 (EPM1, also known as Unverricht-Lundborg disease) is an autosomal recessive disorder characterized by progressively worsening myoclonic jerks, frequent generalized tonic-clonic seizures, and a slowly progressive decline in cognition. Recently, two mutations in the cystatin B gene (also known as stefin B, STFB) mapping to 21q22.3 have been implicated in the EPM1 phenotype: a G-->C substitution in the last nucleotide of intron 1 that was predicted to cause a splicing defect in one family, and a C-->T substitution that would change an Arg codon (CGA) to a stop codon (TGA) at amino acid position 68, resulting in a truncated cystatin B protein in two other families. A fourth family showed undetectable amounts of STFB mRNA by northern blot analysis in an affected individual. We present haplotype and mutational analyses of our collection of 20 unrelated EPM1 patients and families from different ethnic groups. We identify four different mutations, the most common of which consists of an unstable approximately 600-900 bp insertion which is resistant to PCR amplification. This insertion maps to a 12-bp polymorphic tandem repeat located in the 5' flanking region of the STFB gene, in the region of the promoter. The size of the insertion varies between different EPM1 chromosomes sharing a common haplotype and a common origin, suggesting some level of meiotic instability over the course of many generations. This dynamic mutation, which appears distinct from conventional trinucleotide repeat expansions, may arise via a novel mechanism related to the instability of tandemly repeated sequences.

Acetazolamide therapy improves action myoclonus in Ramsay Hunt Syndrome

Acetazolamide treatment significantly improves action myoclonus in Ramsay Hunt Syndrome. A family with two brothers and a sister, and a sporadic case with Ramsay Hunt Syndrome and uncontrollable action myoclonus, are described where addition of oral acetazolamide lead to marked improvement in their action myoclonus.

Arylsulfatase A pseudodeficiency and Lafora bodies in a patient with progressive myoclonic epilepsy

Since age 12 years, a 25-year-old woman had a syndrome with myoclonic epilepsy, cerebellar signs, and spontaneous myoclonus. Skin biopsy showed typical Lafora bodies (LB), but she lacked a progressive course and mental impairment, hallmarks of Lafora disease. Lysosomal enzyme assays showed low level arylsulfatase A (ASA) activity. DNA study disclosed a homozygous ASA Pd genotype. Both parents carried one Pd allele. The still-unknown relationship between the pathologic level of ASA activity and myoclonic epilepsies suggests introduction of ASA assays in patients with PME.

Unverricht-Lundborg disease: absence of nonallelic genetic heterogeneity

Unverricht-Lundborg disease is a clinically recognizable form of progressive myoclonus epilepsy. Recently, in several families of both Finnish and Mediterranean extraction segregating Unverricht-Lundborg disease, the gene for this disease was linked to the same region of the long arm of chromosome 21. We performed linkage analysis in eight families, including four of neither Baltic nor Mediterranean origin, using a polymorphic (CA)n repeat marker for the human liver-type 6 phosphofructokinase (PFKL) gene, previously mapped to 21q22.3. No recombinations were observed between the disease phenotype and the PFKL marker and a maximum lod score of 5.63 was obtained. These findings confirm tight linkage between PFKL and the gene for Unverricht-Lundborg disease and strongly suggest a lack of nonallelic genetic heterogeneity of the disease.

Searching for human epilepsy genes: a progress report

Application of new genetic techniques has brought remarkable discoveries in the study of genetic diseases. The potential benefits from applying such technology to idiopathic epilepsies include improved understanding of cellular mechanisms and potential new methods of prevention and treatment. The complex problems involved in studying the hereditary epilepsies include: defining of specific phenotypes; detecting genetic and non-genetic heterogeneity; and specifying the appropriate mode of inheritance and penetrance. The gene loci for three primary epilepsies have been localized to specific chromosomal regions, and serve to demonstrate the process used in generalized linkage studies of hereditary epilepsy syndromes. Benign familial neonatal convulsions (BFNC) and Unverricht-Lundborg progressive myoclonus epilepsy are rare single-gene disorders that are sufficiently localized to chromosomal regions that positional cloning studies are likely to succeed. Juvenile myoclonic epilepsy (JME), a common hereditary syndrome with an uncertain mode of inheritance, has been reported to be linked to chromosome 6p. JME presents a challenge for generalized linkage methodology that may be overcome by attending to potential problems reviewed here. The candidate-gene method, combined with studies using animal models, holds promise for understanding these as well as other hereditary epilepsies.

Progressive myoclonus epilepsies: an electroclinical, biochemical, morphological and molecular genetic study of 17 cases

Electroclinical, morphological, biochemical and molecular genetic data from 17 patients affected by progressive myoclonus epilepsies (PME) are reported. Twelve patients were characterized by prominent action myoclonus, sporadic seizures, mild ataxia, lack of dementia and persistence of normal EEG background activity; three patients showed a more rapid worsening of symptomatology, characterized by early mental impairment, massive and action myoclonus, cerebellar signs and tonic clonic seizures; in these patients EEG background activity was slow, even in early stages of the disease. In two patients, previously classified as cryptogenetic PME, a mitochondrial aetiology was recognized by the presence of ragged red fibers in muscle biopsy and by a reduction of the respiratory chains enzymes. Molecular genetical investigation of mtDNA demonstrated the reported heteroplasmic point mutation at nt 8344 of mtDNA in the two MERRF patients, while it was negative in all of the others.

Progressive myoclonic ataxia without ragged red fibres: Unverricht-Lundborg disease vs Ramsay Hunt syndrome

We describe eight patients from three families presenting with myoclonus, ataxia, infrequent seizures and minimal intellectual impairment. All were Arabs from different parts of the Arabian peninsula. The new consensus on terminology, genetic and clinical definition of Baltic myoclonus, Ramsay Hunt syndrome and Unverricht-Lundborg disease suggests that our group are best categorised under the term of progressive myoclonic ataxia of the Unverricht-Lundborg type. Moreover, this report reinforces the existence of this syndrome outside Scandinavia.

Identical genetic locus for Baltic and Mediterranean myoclonus

Genetic linkage analysis shows that Baltic and Mediterranean myoclonus, two forms of progressive myoclonus epilepsy, are closely linked to marker D21S113 on the long arm of chromosome 21. Baltic and Mediterranean myoclonus are most probably due to mutations of the same gene.

Clinical and neurophysiological development of Unverricht-Lundborg disease in four Swedish siblings

Four siblings aged 12-18 years with progressive myoclonus epilepsy demonstrated a subclinical stage at the age of 9-11 years, with visual blackouts and polyspike electroencephalographic (EEG) activity on photic stimulation, an early myoclonic stage at the age of 12-15 years, with increasing segmental, stimulus-sensitive myoclonus, occasional nocturnal buildup myoclonic "cascade" seizures, slowing of EEG alpha-activity, episodic 4-6 Hz bilateral sharp waves and polyspikes with myoclonias on photic stimulation, and a disabling myoclonic stage at the age of 16-18 years, with periodic generalized myoclonias, nocturnal myoclonic "cascade" seizures, ataxia, dysarthria, mental changes, intermittent wheelchair dependency, and continuous EEG slow waves with polyspikes and intense myoclonias on photic stimulation. One of the siblings died at the age of 18 years with no apparent cause of death. Treatment with antiepileptic drugs other than valproate may have contributed but none of the siblings were ever treated with phenytoin. Extensive clinical and laboratory investigations revealed no abnormalities and excluded other known possible causes of progressive myoclonus epilepsy. The diagnosis was consistent with Unverricht-Lundborg disease and rested on typical age of onset, clinical signs, EEG, and evoked response abnormalities. Buildup myoclonic seizures are typical in advanced stages of Unverricht-Lundborg disease. We have labeled these myoclonic "cascade" seizures. A typical seizure was studied with video-EEG and cardiorespiratory monitoring. Characteristics revealed were onset with continuous arrhythmic myoclonic jerks followed by intense rhythmic myoclonus with increasing muscle tone that successively reduced the amplitude of the jerks. The EEG during the whole seizure showed intense polyspike activity. Obstructive apnea was seen at the peak of the seizure. There were no cardiac dysrhythmias. Consciousness was normal or only slightly impaired. Postictal drowsiness was not observed. Myoclonic "cascade" seizures are easily confused with generalized tonic-clonic seizures.

Genetic biochemical and pathophysiological characterization of a familial mitochondrial encephalomyopathy (MERRF)

Myoclonic epilepsy with ragged-red fibers (MERRF) syndrome is a neuromuscular disorder characterized by mitochondrial myopathy and progressive myoclonus epilepsy. A heteroplasmic A to G transition mutation in the mitochondrial encoded tRNA(Lys) gene at nucleotide pair 8344 has been suggested to be linked to the MERRF-syndrome. We have investigated biochemically and histochemically muscle biopsies and studied the mitochondrial genomes of hair, blood and muscle tissue of a family including three cases of MERRF-syndrome as well as unaffected relatives within the maternal lineage. Sequence analysis of the mtDNAs, performed after amplification by the polymerase chain reaction (PCR), confirmed the A to G transition mutation in the tRNA(Lys) gene at position 8344. The additional point mutation at nucleotide pair 750 in the 12 S rRNA gene, which was also found by Shoffner et al. (1990), however, was absent in all investigated tissues. Quantitative analysis of the percentage of mutated mtDNA by mispairing PCR (Seibel et al., 1990) revealed variable contents in different tissues and individuals, including unaffected family members. Mitochondrial protein synthesis in cultured fibroblasts from MERRF patients revealed diminished incorporation of 35S-methionine into lysine-containing peptides.