Correspondence *Division of Neurology, The Hospital for Sick Children, 555 University Avenue, Toronto, ON M5G 1X8, Canada

Email bminass@sickkids.ca

The case

A 20-year-old woman presented to a specialist epilepsy center with seizures, myoclonus, ataxia, and impaired executive functions. She was born to unrelated parents, had febrile seizures in infancy, but developed normally, completing secondary school. From the age of 17 years, she had experienced monthly tonic–clonic seizures and visual hallucinations, but electroencephalography (EEG) findings at that time were unremarkable (Figure 1A). In the following months, the patient's parents noted erratic jerks of her arms and legs and a decline in her school performance. At the age of 19 years, MRI scans were unremarkable but EEG showed spikes over the occipital regions and generalized spike–wave discharges (Figure 1B), enhanced by photic stimulation. Juvenile myoclonic epilepsy was diagnosed and treatment with valproic acid initiated, which alleviated the myoclonus and decreased the frequency of the seizures.

Figure 1 Progression of electroencephalography (EEG) changes in a patient with Lafora disease.

(A) At the time of disease onset (age 17 years) there is normal to slightly slowed background activity. (B) Two years later (age 19 years), EEG demonstrates asymmetric generalized spikes and polyspikes, with maximum discharges over the anterior regions on a slowed background. (C) At age 20 years, the occurrence of fast (four to six cycles per second) spike–waves was concomitant with head drops. (D,E) During the final stages of the disease, EEG recordings show long bursts of diffuse spike–waves and fast polyspikes associated with major volleys or massive myoclonic jerks (D) dramatically enhanced by photic stimulation at low frequency (E).

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Several months later, the patient was hospitalized with multiple seizures; diffuse fragmentary myoclonus was present at rest and exaggerated by action and excitement. At the specialist epilepsy center, examination of the patient demonstrated that she had impaired cognition, emotional lability, dysarthria, ataxia, and a broad-based gait. Her muscle tone was increased, but reflexes were barely detectable. Sensory examination was normal. Sudden, brief head drops were evident. Routine hematological and biochemical investigations and basal and postexercise blood lactate curves were normal. EEG revealed slow background activity, irregular generalized spike–waves and polyspike–waves asynchronous with myoclonic jerks, and fast (four to six cycles per second) spike–waves concomitant with head drops (Figure 1C). Photosensitivity with increased paroxysmal activity and myoclonus was also present. The paroxysmal abnormalities were reduced on sleep EEG. Jerk-locked averaging disclosed a premyoclonic spike on the contralateral cerebral areas 15–20 ms before the electromyographic burst. Visual evoked potentials showed increased latency (N1 105 ms; P1 145 ms; N2 184 ms), and somatosensory evoked potentials showed increased amplitudes (P25–N30 120 V). Nerve conduction velocities were normal. Neuropsychological testing showed that the patient had a full-scale IQ of 74 (a verbal score of 87 and a performance score of 65 on the Wechsler Adult Intelligence Scale) and deficits in executive function (Stroop color–word test) accompanied by deficits in inhibition. Lafora disease (LD) was suspected on the basis of the electroclinical picture; a skin biopsy revealed periodic-acid–Schiff-positive pathognomonic Lafora bodies (LBs; Figure 2A,B), confirming the diagnosis. Genetic analysis showed a previously reported homozygous mutation (c205C>G; Pro69Ala) in the EPM2B (NHLRC1) gene (Figure 3). Clonazepam (2 mg/day) and levetiracetam (3,000 mg/day) were added to the valproic acid; these agents improved the patient's myoclonus and the frequency of her status epilepticus, but the tonic–clonic seizures and head drops persisted.

Figure 2 Skin biopsy specimen of a patient with Lafora disease.

(A) Periodic acid–Schiff diastase stained section of an eccrine duct. Note the numerous LBs in the ductile cells (arrows). (B) Low-power electron micrograph of the myoepithelial cells surrounding an apocrine sweat gland. LBs are seen in the cytoplasm. Bar equals 2 m. Abbreviation: LB, Lafora body.

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Figure 3 Genetic analysis of Lafora disease.

The patient's EPM2A and EPM2B (NHLRC1) genes were sequenced. A homozygous missense mutation (c205C>G; Pro69Ala) was found in the EPM2B gene. This is the most common EPM2B mutation.

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In the following months, the patient's mental decline continued, with the development of agitation and psychosis. At the age of 23 years, examination revealed that she had severe dementia (a score of 9 out of 30 on the Mini Mental State Examination), marked rigidity, hypokinesia, and hypertonia. She also had trains of massive myoclonias, with relative preservation of consciousness, mimicking generalized seizures. EEG showed slowed background activity, loss of sleep features, and generalized high-voltage spikes, polyspikes, sharp–waves and spike–waves (Figure 1D). Photic stimulation evoked a massive myoclonus and photoparoxysmal response (Figure 1E). MRI scans revealed cerebral and cerebellar atrophy. Organ systems other than the brain remained clinically unaffected. Over the next months, the patient became akinetic, wheelchair-dependent, mute, and unable to feed. She died following contraction of aspiration pneumonia, at the age of 25 years.

At autopsy, the patient's brain was replete with LBs, with varying numbers in different regions. The LBs were most abundant in the thalamus, brainstem and cerebellum, and present in lesser numbers in the frontal and occipital cortices. LBs were not present in subcortical white matter. They were abundant in the spinal cord gray matter and absent from spinal cord white matter tracts. LBs were of both types previously described in the literature: type I, punctate structures present in neuronal processes; and type II, large structures found in neuronal cell bodies, usually apposed to the nucleus and often so large as to occupy the entire soma, displacing the nucleus and organelles to the sides of the cell (Figure 4A,B). LBs in this patient were ubiquitin-negative. Electron microscopy showed that the LBs consisted of accumulations of a fibrillar material (Figure 4B,C). LBs were also present in clinically unaffected organs, especially skeletal and cardiac muscle, the liver, and skin.

Figure 4 Brain at autopsy.

(A) Light micrograph of the neuropil stained with periodic acid–Schiff reagent following diastase digestion. Both type I (thin arrows) and type II (thick arrow) LBs are present. (B) Electron micrograph of a type I LB. A postsynaptic density (arrow) demonstrates the location of the LB in the dendrite. Bar equals 1 m. (C) Electron micrograph of a type II LB. Note that the LB occupies the majority of the cytoplasm. The nucleus (N) is pressed to the periphery of the cell. Bar equals 2 m. Abbreviations: LB, Lafora body; N, nucleus.

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Discussion of diagnosis

First described in 1911, LD (Online Mendelian Inheritance in Man^® [OMIM^®] 254780 [Johns Hopkins University, Baltimore, MD]) is an autosomal-recessive progressive myoclonus epilepsy (PME), with onset in teenage years in previously normal adolescents.¹ The first symptoms are myoclonus and tonic–clonic, absence, atonic, and visual seizures. Headaches, decline in school performance, depression, and apathy are also present early in the disease course. Commonly, as in this case, in the earliest phases a diagnosis of juvenile myoclonic epilepsy is briefly considered because of similarities in age at onset and the presence of myoclonus and photosensitive seizures in both LD and this common benign epilepsy. However, slow EEG background activity, a poor response to medication, the presence of other seizure types (visual, complex partial, or absence), cognitive decline, and the rapid progression of symptoms soon raise doubts of a PME, and in adolescents these symptoms specifically suggest LD. In the years following onset, symptoms of LD progress towards intractable action-sensitive and stimulus-sensitive myoclonus, refractory seizures, psychosis, ataxia, dysarthria, and dementia. Death usually occurs within 10 years, often in status epilepticus with aspiration pneumonia.²

EEG abnormalities precede clinical symptoms of LD and initially consist of slowed background activity and generalized and focal (occipital) paroxysmal activity typically not accentuated by sleep. Positive or negative myoclonus and marked photosensitivity are prominent features. Electrophysiological investigations (jerk-locked averaging, somatosensory evoked potentials, C-reflex, and visual evoked potentials) can reveal aberrant integration of somatosensory stimuli and cortical hyperexcitability. In later stages of the disease, EEG background activity deteriorates, sleep features are lost, and generalized and multifocal epileptiform discharges abound (Figure 1).^{3, 4, 5}

LD is characterized by the presence of LBs, which are periodic-acid–Schiff-positive intracellular inclusions consisting of an abnormal form of glycogen—termed 'polyglucosan'—that accumulates in neurons and other tissues, such as heart, liver, muscle, and skin. Neuronal LBs localize in perikarya and dendrites but not in axons,^{2, 6} possibly explaining the cortical hyperexcitability reported in LD. LBs can be identified by use of skin biopsy, whereby they are found in sweat glands. This diagnostic approach has limited invasiveness and high sensitivity.^{2, 7} Interpretation of the biopsy, however, requires expertise in distinguishing LBs from normal polysaccharide contents of apocrine sweat glands; without such expertise, false-positive diagnosis is common.⁷

LD is caused by mutations in the EPM2A or EPM2B genes, encoding laforin dual-specificity phosphatase and malin ubiquitin E3 ligase, respectively.^{8, 9} Laforin binds malin and, through a carbohydrate-binding domain in its N-terminus, also binds glycogen and other polysaccharides.^{10, 11} The number of EPM2A and EPM2B mutations known so far each exceeds 40. Genotype–phenotype correlations do not reveal substantial differences between patients carrying EPM2A mutations and those carrying EPM2B mutations, but a few specific EPM2B mutations seem to correlate to a late-onset and slowly progressing LD.^{12, 13}

LBs are accumulations of polyglucosans. Normal glycogen is a polysaccharide of glucose with a spherical shape, which is a result of the polysaccharide being regularly branched instead of linear and is necessary for solubility. The regular branching of glycogen is a result of balanced activities between glycogen synthase (GS), the enzyme that elongates glycogen strands linearly, and glycogen branching enzyme, which cleaves strand extensions made by GS and places them at branch points to keep the growth of the molecule spherical. If the activity of GS overtakes that of glycogen branching enzyme, poorly branched glycogen (polyglucosan) forms.^{2, 14} Polyglucosans are insoluble and precipitate in the cytoplasm to form LBs. The pathogenesis of polyglucosans has received intense attention recently. Data to date suggest two different hypotheses. In the first, the laforin–malin complex is thought to recognize polyglucosans and function to decrease the activity of GS through phosphoregulation or polyubiquitination of the enzyme (Figure 5A).² The second hypothesis stems from two recent, unexpected observations, these being that laforin was shown to dephosphorylate polysaccharides,^{15, 16} and that malin was shown to polyubiquitinate laforin and decrease its concentration by proteosomal degradation.¹⁰ In this second hypothesis, digestion of polyglucosans requires that they must first be dephosphorylated, and this does not occur in the absence of laforin. After dephosphorylation, laforin, which binds polysaccharides tightly,^{17, 18} would need to be removed by malin before polyglucosan-digesting enzymes could associate and function. As a result, laforin or malin deficiency would prevent digestion of polyglucosans and result in their accumulation (Figure 5B).¹⁶

Figure 5 Two recent theories of the pathogenesis of Lafora bodies.

(A) GS (light blue) extends the growing glycogen chain in a linear manner. GBE1 (green) branches the linear glycogen, giving the molecule its spherical shape. If the balance between extension and branching is disrupted, poorly branched glycogen, or polyglucosans, form instead of normal glycogen. Laforin, malin, and, possibly, other proteins involved in Lafora disease regulate the balance of the two enzymes, preventing polyglucosan formation. (B) Glycogen is normally phosphorylated, and this hinders its degradation. Laforin (yellow) dephosphorylates glycogen. Laforin must then be removed to enable degradation to start, and this is accomplished by malin (red circle). If laforin or malin is not present, glycogen cannot be degraded and, over time, it loses its spherical structure, accumulating as polyglucosans to form Lafora bodies. Abbreviations: GBE1, glycogen branching enzyme; GS, glycogen synthase; P, phosphate.

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Differential diagnosis

PMEs are a group of inherited neurodegenerative disorders characterized by progressively worsening myoclonus and epilepsy, early dementia, and death (Table 1). LD is the principal teenage-onset PME. Unverricht–Lundborg disease (EPM1), caused by mutations of the cystatin B (CSTB, or PME) gene, is the closest differential diagnosis. Although EPM1 has an earlier onset overall, it has a much milder and slower course than LD. Myoclonus can be prominent, but the seizures are comparatively easy to treat. There is no specific pathology. In the case discussed here, the rapid disease course and presence of LBs ruled out EPM1. Of the other PMEs, neuronal ceroid lipofuscinoses (NCLs) are the largest group, with nine known causative genes, most encoding lysosomal proteins. All NCLs exhibit accumulations of ceroid lipofuscin, not LBs, in various organs, including the skin. Most NCLs present in early childhood. A juvenile form of NCL (Batten disease; CLN3 gene) can have an onset late enough to overlap with that of LD, but this form has a prolonged initial period of visual loss—resulting from retinal degeneration—and mild seizures, which this patient did not have. Some cases of the infantile form (Santavuori–Haltia disease; CLN1 [PPT1] gene) present late as a result of particular mutations and there is an exceedingly rare form of adult-onset NCL (Kuf disease; causative gene unknown), but these diseases were all ruled out in this patient by the presence of LBs. Myoclonic epilepsy with ragged red fibers is a mitochondriopathy that exhibits elevated lactate levels in the blood, in the cerebrospinal fluid, and on magnetic resonance spectroscopy, and ragged red fibers on muscle biopsy. Sialidosis is an extremely rare lysosomal disease associated with cherry red spot maculopathy and elevated levels of oligosaccharides in the urine. Sialidosis and myoclonic epilepsy with ragged red fibers were not further considered in this patient after the pathognomonic LBs were revealed by skin biopsy.

Table 1 Main differentiating features of some of the more common inherited progressive myoclonic epilepsies.

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Treatment and management

There is no specific treatment for LD; however, commonly used antiepileptic therapy for the management of myoclonus might improve symptoms in the early stages of the disease. Combinations that include valproate, phenobarbital, benzodiazepines, piracetam, levetiracetam, and zonisamide are useful for symptomatic treatment. To prevent worsening of myoclonus, vigabatrin, carbamazepine, phenytoin, gabapentin, pregabalin, and probably lamotrigine, must be avoided. Future therapies could include replacement of the missing genes. Currently, experiments to replace EPM2A through use of immunoliposome vectors are in progress.¹⁹

Conclusions

This report illustrates in detail the typical course of LD, from its earliest phases through its progression to eventual death. It is important for clinicians to distinguish LD from the much more common juvenile myoclonic epilepsy, in addition to other PMEs. The prognosis of LD is presently dismal, and treatment remains palliative. However, much more has been learned about LD in the past 10 years, since its first genetic cause was discovered, than in the preceding 87 years, from when the disease was first described. It is hoped that a more complete pathogenetic understanding of the disease will, in parallel with therapies developed through gene-replacement experiments, enable the clinician to offer patients who have LD a better prognosis.

References

1. Lafora GR and Glueck B (1911) Contribution to the histopathology of the myoclonic epilepsies [German]. Z Gesamte Neurol Psychiatr 6: 1–14
2. Lohi H et al. (2006) On the road to tractability: the current biochemical understanding of progressive myoclonus epilepsies. Adv Neurol 97: 399–415 | PubMed |
3. Boccella P et al. (2003) Bioptically demonstrated Lafora disease without EPM2A mutation: a clinical and neurophysiological study of two sisters. Clin Neurol Neurosurg 106: 55–59 | Article | PubMed | ChemPort |
4. Canafoglia L et al. (2004) Sensorimotor cortex excitability in Unverricht–Lundborg disease and Lafora body disease. Neurology 63: 2309–2315 | PubMed | ChemPort |
5. Panzica F et al. (2003) Movement-activated myoclonus in genetically defined progressive myoclonic epilepsies: EEG–EMG relationship estimated using autoregressive models. Clin Neurophysiol 114: 1041–1052 | Article | PubMed | ChemPort |
6. Cavanagh JB (1999) Corpora-amylacea and the family of polyglucosan diseases. Brain Res Brain Res Rev 29: 265–295 | Article | PubMed | ChemPort |
7. Andrade DM et al. (2003) Skin biopsy in Lafora disease: genotype–phenotype correlations and diagnostic pitfalls. Neurology 61: 1611–1614 | PubMed | ChemPort |
8. Minassian BA et al. (1998) Mutations in a gene encoding a novel protein tyrosine phosphatase cause progressive myoclonus epilepsy. Nat Genet 20: 171–174 | Article | PubMed | ISI | ChemPort |
9. Chan EM et al. (2003) Mutations in NHLRC1 cause progressive myoclonus epilepsy. Nat Genet 35: 125–127 | Article | PubMed | ISI | ChemPort |
10. Gentry MS et al. (2005) Insights into Lafora disease: malin is an E3 ubiquitin ligase that ubiquitinates and promotes the degradation of laforin. Proc Natl Acad Sci USA 102: 8501–8506 | Article | PubMed | ChemPort |
11. Lohi H et al. (2005) Novel glycogen synthase kinase 3 and ubiquitination pathways in progressive myoclonus epilepsy. Hum Mol Genet 14: 2727–2736 | Article | PubMed | ChemPort |
12. Gomez-Abad C et al. (2005) Lafora disease due to EPM2B mutations: a clinical and genetic study. Neurology 64: 982–986 | PubMed | ChemPort |
13. Lohi H et al. (2007) Genetic diagnosis in Lafora disease: genotype–phenotype correlations and diagnostic pitfalls. Neurology 68: 996–1001 | Article | PubMed | ChemPort |
14. Roach PJ (2002) Glycogen and its metabolism. Curr Mol Med 2: 101–120 | Article | PubMed | ChemPort |
15. Worby CA et al. (2006) Laforin, a dual specificity phosphatase that dephosphorylates complex carbohydrates. J Biol Chem 281: 30412–30418 | Article | PubMed | ChemPort |
16. Gentry MS et al. (2007) The phosphatase laforin crosses evolutionary boundaries and links carbohydrate metabolism to neuronal disease. J Cell Biol 178: 477–488 | Article | PubMed | ChemPort |
17. Wang W et al. (2006) Relationship between glycogen accumulation and the laforin dual specificity phosphatase. Biochem Biophys Res Commun 350: 588–592 | Article | PubMed | ChemPort |
18. Girard JM et al. (2006) Molecular characterization of laforin, a dual-specificity protein phosphatase implicated in Lafora disease. Biochimie 88: 1961–1971 | Article | PubMed | ChemPort |
19. Delgado-Escueta AV (2007) Advances in Lafora progressive myoclonus epilepsy. Curr Neurol Neurosci Rep 7: 428–433 | Article | PubMed | ChemPort |

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Subject areas under which this article appears: Epilepsy