cortical myoclonus in angelman syndrome

Cortical Myoclonus in Angelman Syndrome Renzo Guerrini, MD,* Timothy M. De Lorey, PhD,? Paolo Bonanni, MD,* Anne Moncla, MD,f Charlotte Dravet, MD,S Georges Suisse, MD," Marie Odile Livet, MD,S Michelle Bureau, MD,$

Perrine Malzac, PhD,$ Pierre Genton, MD,S Pierre Thomas, MD," Ferdinand0 Sartucci, MD,' Paolo Simi, PhD,' and Josi. M. Serratosa, M D t

Angelman syndrome (AS) results from lack of genetic contribution from maternal chromosome 15qll-13. This region encompasses three GABA,, receptor subunit genes (p3, a 5 , and y3). The characteristic phenotype of AS is severe mental retardation, ataxic gait, tremulousness, and jerky movements. We studied the movement disorder in 11 As patients, aged 3 to 28 years. Two patients had paternal uniparental disomy for chromosome 15, 8 had a >3 Mb deletion, and 1 had a microdeletion involving loci D15S10, D15S113, and GABRB3. All patients exhibited quasicontinuous rhythmic myoclonus mainly involving hands and face, accompanied by rhythmic 5- to 10-Hz electroencephalographic (EEG) activity. Electromyographic bursts lasted 35 f 13 msec and had a frequency of 11 f 2.4 Hz. Burst-locked EEG averaging in 5 patients, generated a premyoclonus transient preceding the burst by 19 +- 5 msec. A cortical spread pattern of myoclonic cortical activity was observed. Seven patients also demonstrated myoclonic seizures. No giant somatosensory evoked potentials or C-reflex were observed. The silent period following motor evoked potentials was shortened by 70%, indicating motor cortex hyperexcitability. Treatment with piracetam in 5 patients significantly improved myoclonus. We conclude that spontaneous, rhythmic, fast-bursting cortical myoclonus is a prominent feature of AS.

Guerrini R, De Lorey TM, Bonanni P, Moncla A, Dravet C, Suisse G, Livet MO, Bureau M, Malzac P, Genton P, Thomas P, Sartucci F, Simi P, Serratosa JM. Cortical myoclonus

in Angelman syndrome. Ann Neurol 1996;40:39-48

Angelman syndrome (AS) [I] is a neurogenetic disorder resulting from lack of genetic contribution from maternal chromosome 15qll-I3 [2, 31. Sixty percent of AS patients demonstrate a chromosome 15qll- 13 cytogenetic or molecular deletion. The remaining patients have either no detectable deletion (-35%) or uniparental disomy (- 5%) where both chromosome 15 alleles are contributed by the father [4]. Affected patients present with severe mental retardation, absent speech or very poor language skills, microbrachyceph- aly, inappropriate laughter, seizures, abnormal electroencephalographic (EEG) activity, and a characteristic "puppetlike" motor pattern consisting of ataxic gait, tremulousness, and jerky limb movements [ 1, 5- lo].

Although the movement disorder is present in almost all patients [b] and represents a major diagnostic criterion, it has not been studied neurophysiologically and, to date, there is no rational treatment.

We present a clinical and neurophysiological study of 11 unrelated AS patients confirmed by genetic analysis. Our findings indicate that the tremulous move-

ment disorder of AS is related to a unique pattern of fast-bursting cortical myoclonus (FBCM) and that antimyoclonic treatment with piracetam can produce marked functional improvement.

Patients and Methods Patients Eleven patients ( 5 male, 6 female), aged 3 to 28 years, were included in the study (see Table I) . Ten patients are new to this study and one has been previously described by Robinson and colleagues [ I 11. To be included in this study, patients were required to be clinically diagnosed with AS and show either a maternal deletion or uniparental disomy on chromosome 15. Clinical diagnosis of AS was based on the presence of the characteristic physical and behavioral phenotype [ l , 6, 91. Follow up varied from 2 to 24 years (mean, 17 years; median, 18 years).

Genetic Analysis HIGH-RESOLUTION BANDING. High-resolution chromosome studies were performed on 10 patients using a synchro-

From the *Institute of Child Neurology and Psychiatry, University of Pisa-IRCCS Stella Maris Foundation, 'Department of Neuro-

Institute of Pediatrics, University of Pisa, Pisa, Italy; ?Department of Pharmacology, UCLA School of Medicine, and California Com- prehensive Epilepsy Program, Los Angeles, CA; and $Department of Medical Genetics, H6pital de la Timone, and Scentre Saint Paul, Marseille, and !'Departments of Neurophysiology and Neurol- ogy, H8pital Pasteur, Nice, France.

Received Sep 27, 1995, and in revised form Dec 20. Accepted for publication Jan 25, 1996.

ogy and Psychiatry, University of Pisa, Via dei Giacinti 2, 56018 Calambrone, Pisa, Italy,

p h y s i o l o ~ ~ Institute Of and Of Generics, Address correspondence to Dr Guerrini, Institute of Child Neural.

Copyright 0 1996 by the American Neurological Association 39

nization method [ 121. RHG banding was obtained by heat- controlled denaturation followed by Giemsa staining.

FLUORESCENT I N SII‘U HYBRIDIZATION (FISH). FISH was performed on chromosomal spreads from 10 patients using the GABRB3 probe and the PML chromosome 15q22 control probe (ONCOR, Inc).

rw7i METHYLATION ANALYSIS. The D15 S63 locus was analyzed for rnethylation using the PW71 probe. Genomic DNA was digested with Hind111 and HpnTI and hybridized with the PW71 probe, as previously described [13].

MICKOSAI‘ELLITE MARKER ANALYSIS. The polymerase chain reaction (PCR) was used to amplify total genomic DNA in 10 patients and their parents. Haplotypes were con- structed using the following microsatellite markers: IR4 3-R (D15Sll), 3-21 (D15S10), LS6-1 (Dl5Sl13), 155 and 85 (Dl5S51 l) , DlSS128, D15S210, D15S122, GABRB3, GABRA5, D15S156, and D15S165 114, 151. These markers cover a 13 cM interval in chromosome 15qll-13.

Clinical and Video-ELectropbysioLogicaL Studies All patients were cvaluated by long-term video-EEG and simultaneous surface electromyographic (EMG) monitoring with bipolar and referential montages using silver-silver chloride surface electrodes. Recordings were carried out in two centers (ICNP-Pisa for Patients 1 to 6 and CSP-Mar- seille for Patients 7 to 11). Scalp electrode placement was performed according to the international 10-20 system. EMG activity was recorded using pairs of electrodes applied 3 cm apart over the masseter, orbicularis oris, deltoids, biceps, and finger flexors and extensors. Back averaging of EEG activity related to the EMG bursts was performed in the 5 patients (1-4 and 6; age range, 7-25 years) for whom artifact-free EEG and EMG could be recorded on computer for later analysis. The EEG signal was filtered using a bandpass of 1 to 100 Hz, and digitalized at the sampling rate of 1,024 Hz. The average of 100 to 120 consecutive 300-msec artifact-free EEG epochs centered at the onset of the EMG burst (burst-locked EEG averages) was computed. At least two averages were generated for each patient to ensure reliability between trials. Averages of 100 to 120 consecutive 300-msec artifact-free EEG epochs related to the onset of the EMG silence (silence-locked EEG averages) were generated from the same EEG data.

Somatosensory evoked potentials (SEPs) were recorded in the 6 patients studied at ICNP-Pisa (1-6; age range, 7-27 years) from central (C3’, C4’) and frontal (F3, F4) regions, from a point at the level of the seventh cervical spine (C7S), and from Erb’s point (EP) using referential montages. The median nerve was electrically stimulated at the wrist using an intensity strong enough to produce a twitch of the thenar muscle and a frequency of 0.5 and 1 Hz. The EEG signal was filtered with a bandpass of 1 to 2,000 Hz. Blocks of 500 consecutive artifact-free responses were averaged. The C-reflex was sought by applying a 0.5-msec electrical stimulus to the median nerve at the wrist at motor threshold intensity and by recording EMG activity from the abductor pol-

licis brevis at rest. Blocks of 50 consecutive stimuli were averaged. Trials were replicated to ensure reproducibility of the responses. Twenty healthy subjects aged 18 to 30 years (mean t SD, 23.4 ? 2.5) were used as control group for Patients 2, 3, and 5. Three groups of 15 healthy subjects (aged 14-18, 12-14, and 6-8 years) were used as control groups for Patients 1, 4, and 6, respectively.

Transcranial Magnetic Stimulation A Novametrix Magstim ME magnetic device was used to obtain motor evoked potentials (MEPs) in the 6 patients studied at ICNP-Pisa (1-6; age range, 7-27 years). A flat, single round coil (inner diameter of 9.5 cm) was placed on the vertex. The EMG surface electrodes were placed in the abductor digiti minimi, at the hypothenar eminence, and at the tibialis anterior. The effects of peripheral nerve, cervical, and transcranial magnetic stimulation (TMS) on the rhythmic EMG bursting pattern of hand myoclonus and on voluntary motor contraction were analyzed in 4 patients (1-3 and 5; age range, 15-27 years). Single TMS were delivered to the contralateral side of the scalp. The stimulus intensity was 100% of the stimulator’s output (1.5 T), approximately 1.2 times the motor threshold for the MEPs. Cervical stimulation was delivered with the coil centered over the C7S. Peripheral nerve stimulation was delivered with the coil centered over the EP. The EMG surface electrodes were posi- tioned over the right wrist extensors and flexors. Trials were replicated to ensure reproducibility of the responses. Normal data for TMS (including central motor conduction time [CMCT], amplitude of responses, and post-MEPs silent period) were obtained from 20 healthy subjects aged 15 to 30 years (mean ? SD, 25.6 2 2.3 years). Although Patient 6 was aged below the age range of controls, we considered CMCT values to be comparable as no significant variations in this pa- rameter are generally observed after the age of 2 [ 161.

Neuroimaging Nine patients underwent brain magnetic resonance imaging using a 0.5- or 1-T instrument. Spin echo, inversion recov- ery, and gradient echo-weighed sequences were obtained in the axial, sagittal, and coronal planes. The remaining 2 patients underwent brain computed tomographic (CT) scan.

Treatment o f Myoclonus with Piracetarn Various drugs, alone or in combinations, had been given chronically to all patients to achieve control of seizures, myoclonus, or both. Piracetam was added to previous drug re- gimes in 5 patients (clobazam [CLB] in Patient 1, CLB + phenobarbital [PB] in Patient 2, CLB + PB + ethosuximide in Patient 3, CLB + valproate in Patient 5, and clonazepam in Patient 6). The initial dose was 2.4 gm/day and was increased until a stable benefit was observed. Clinical benefit was assessed 2 to 4 weeks after a stable dosage was reached, using rating scales for motor impairment, functional disability, and global impression of disability I 17, 181 adapted to AS. Motor impairment was evaluated by obtaining a score that resulted from the addition of the following three sub- scores: spontaneous myoclonus, frequency of action myoclonus, and severity of action rnyoclonus. In the subscore scale

40 Annals of Neurology Vol 40 No 1 July 1996

for spontaneous myoclonus the following 5 body areas were considered: face, right and left arm, and right and left leg. Each body area was scored as follows: 0 for no spontaneous myoclonus, 1 for spontaneous myoclonus occurring only during part of the day, 2 for spontaneous myoclonus occurring less frequently than once every 3 minutes, 3 for spontaneous myoclonus occurring every 1 to 3 minutes, or 4 for spontaneous myoclonus occurring more often than once every minute. The subscore to assess the frequency of action myoclonus was obtained by having the patient grasp an ob- ject with either hand 4 times and rated as follows: 0 for no action-activated jerking, and 1, 2, 3, and 4 for action activated jerking occurring in 1 of 4, 2 of 4, 3 of 4, or in all 4 movements, respectively. The severity of action myoclonus was assessed on the same test on a scale from 0 to 4 with 0, 1, 2, 3, and 4 representing no myoclonus, myoclonus that never, occasionally, frequently, or completely interfered with function, respectively. The latter two scores resulted from the sum of the scores obtained for each hand. The functional disability was scored, based on the simple task of drinking a glass of water, by using the following rating scale: 0 for no myoclonus, 1 for mild myoclonus, 2 for moderate interference, 3 for severe interference, and 4 for complete interference making impossible the task. The global impression of disability was scored as follows: 0 for no myoclonus; 1 for mild myoclonus not annoying the patient; 2 for moderate myoclonus annoying the patient; 3 for severe myoclonus causing distress; and 4 for marked myoclonus causing great distress. To assess the treatment effect, pretreatment scores were compared with those obtained on piracetam, using the Wilcoxon two-sample rank-sum test. Tests were two-tailed with significance being at 5%. Epistat software was used for the analysis.

Results Table 1 summarizes the clinical, neurophysiological, and genetic findings of the 11 patients.

Genetics Eight patients (2-5, 8-1 1) were shown to have a deletion extending more than 3 Mb on maternal chromosome 15ql1-13 as determined by high-resolution banding, FISH, and molecular analyses. High-resolution banding and methylation pattern were normal in Patient 7; but molecular analysis showed a small deletion involving loci D15Sl0, D15S113, and GABRB3 (GABRA5 was noninformative and D 15s 156 was nondeleted). Patient 1 showed paternal uniparental disomy for chromosome 15 as demonstrated by lack of maternal inheritance for GABRB3, GABRA5, LS6-1, 155, and 85 and a normal FISH pattern with probes GABRB3 and PML. Patient 6 also had paternal disomy for chromosome 15 and a 46,XYl47/XY,+inv dup( 15)(pter+q11 :ql1+) karyotype, with a ratio of 40160, as reported by Robinson and colleagues [ l l ] . This patient’s extra chromosome appeared to contain

mostly or only heterochromatic p arm material, which should have no phenotypic effect [ l l ] .

Clinical and Edeo-Electropbysiological Analysis o f Myoclonus Different manifestations of myoclonus were identified. These could coexist in the same patient and often over- lapped to form a continuum.

All 11 patients presented with very rapid jerking of fluctuating amplitude, which caused a coarse distal tremor combined with dystonic limb posturing. Jerks occurred at rest in prolonged runs and were enhanced by voluntary movement. EMG showed synchronous bursting of agonist and antagonist muscles with a mean frequency of 11 2 2.4 Hz (range, 5-24 Hz) and a mean burst duration of 35 2 13 msec. Each burst alternated with a period of EMG silence or near silence. Stable bursting at 10 to 15 Hz was accompanied by dystonic limb posturing that persisted for 20 to 40 seconds, then ceased abruptly and reappeared spontaneously or upon voluntary movement. Jerking at rest usually started in one hand or the face and spread ho- molaterally, or contralaterally, to homologous body segments. Muscle recruitment followed a rostrocaudal sequence passing down the brainstem and spinal cord (Fig 1). Bilateral jerks were asynchronous, with a mean latency of 8 +- 5 msec (Fig 2). Rest EEG activity con- sisted of a 5- to 7-Hz irregular background. Myoclonus was accompanied by contralateral or bilateral asynchronous, rhythmic 5- to 10-Hz sinusoidal or sharp activity, which could be hemispheric or of frontocentral predominance (Fig 3). Although this rhythmic EEG activity was somatotopically related to the opposite part of the body, on visual inspection of EEG traces the individual waves did not appear to be time locked to myoclonic potentials (Fig 4A). This impression was confirmed by the fact that the 5- to 10-Hz activity disappeared on burst-locked EEG averaging, studied in 5 patients (Fig 4B). In contrast, back-averaging generated a reproducible positive-negative biphasic transient in the hemisphere contralateral to the jerking hand (Figs 4C and 5). This reproducible waveform could be identified in all patients and averages analyzed. Since the EEG potential was time locked to EMG activity, it showed exactly the same frequency as the latter and was recognizable in averaged responses as a larger positive-negative wave within a sequence of waves. The premovement positivity had a mean duration of 32.5 2 4.4 msec; peak latency was 19 & 5 msec when EMG bursts were recorded from the belly of the wrist extensors. T o assess whether responses were truly consistent, we used the coefficient of variability (CV), in terms of the ratio between standard deviation of each sample of measurements of peak latencies and relative mean [CV = (SDImean) X 1001. A threshold of 5% was set to

Guerrini et al: Cortical Myoclonus in Angelman Syndrome 41

Table 1. Main Electroclinical and Genetic Characteristics on I I Patients with Angelman Syndrome

Age at Age at Patient Seizure O n w of Age at No.lSex Onser FBCM Fullow-up E t G Ahnoimalitics

-10 yographyl Cmctica Frequency of Myoclonus Assoiiarcd Srizuirr M R I i C T Cyrogenetics and FISH Molecular

l l M

2iF

31M

4iF

5/F

61M

7iF

8iM

9iF

l 0 i M

l l l F

7 yr -

h m o j y r

4 1110 8 Inlo

10 nio 3 yr

3 V I 2 y r

4 yr 2 yr

5 yr 12 yr

17 mo 2 yr

4 mo 2 yr

4 mu 6 ino

1 yr 12 y,

15 yr

25 y r

18 yr

13 yr

27 y r

7 y r

28 y,

12 yr

20 y r

3 yr

20 yi

C3. C4, 8-10 H r rhyrhni

C3, C4. 5-10 H r rhythni; diffuse SWs

C3, (:4, 5-8 H L rhythm; diffuse SWc

M u l r i f o d , 8-15 H,, rhythmic

rhythmic

arrhvthmir

Mulrifocal, 8-15 Hz.

Multifocnl, 5-10 H7,

Fp1, Fp2. 5-8 Hc rhythm; diffuse SWs

rhythm . i r i d SWr C3, C4, 5-8 H z

C3, (74, 5-10 H L ihythm, diffiise SWI

C3, C4, 5-10 Hr rhyrhm and SW.y

( :3 , C4. 5-10 IIZ ihyrhiii and SWs

C3, C4, 5-10 H z rhyrhm .and SWF

C3, C4, 8-10 H z rhythm and SWs

C3, C4, 5-1 0 H, r h y t h m , diffuse 5Ws

Mulrifocal, 7-10 Hz, rhythmic

~hyrhmic, sinusoidal

rhyrhniic

rhythmic, rinusoidal

Moltifncd, 7-10 HL,

MultIfocal, 8-15 H7,

Mulrifocal, 5-10 Hz,

Multifocal, 8-15 Hz, rhythmic, sinusoidrl

rhyrhmic, sinusoidal Mulrifoial, R-15 H L ,

Mulrifocal. 8-15 Hz.

Mulrifocal, 8-15 Hz, rhythmic, iinumidal

rhythmic, cinusaidal

Normal

Myoclonic abscnccs Mild brain atrophy

Myoclonic abscnccs, Mild hrain c h i c , inyoilunii ariophy irarur

Myoclonic Perivenrricular high signal

My"Clo,,K NornA

Myoclonic Mild venrricular

GTC, clan^, Normal

aryninierry

myoclnnic status

GTC, Mild brain ahsence srarus arrophy

myoclonic s t a r u ~ Myoclonic, Normal

C h i c Mild brain dtlophy

Clonic, myoclonic, Mild brain myoclunic ,tatus atruphy

Normal UPD

15ql l -13 dcl mat dcl > 3 M b

15qll-1.3 del mat del > 3 M b

15qll-13 del mat dcl > 3 Mb

15q11-13 dcl

'46,XYi47/XY,+inv dup UPD

Nor& m.it dcl Sl 0,

i n i t del > 3 M b

( l5) (p te r+ql l :q l l+)

S113, GABRB3

mat del > 3 M h 15qll-13 del

15qll-13 dcl

15qll-13 dcl

mar del > 3 M h

mat del > 3 JMh

15qll-13 del mar drl > 3 M b

'Genetic analyais reported by Robinson and collcaguec 11 11

EEG = e1ecrroencephalogr.iphic; FFK:M = fast-bursting cortical myvLlonux M N = nugneiic resonance imaging; CI' = computed tomogiaphy; FISI I = Ruoiescent in siru hyhridlra- tion; Hz = Hertz; UPD = uniparenral disuiny; del = delerion: mat = maternal; Mb = megabase; SWs = ryiki and waver; GTC = generalized tonic clonic, Gen = generalized.

define the measurements as statistically reproducible. Table 2 shows the high level of reproducibility for each patient. Mean interhemispheric latency between peaks of premyoclonus spikes was 8.3 t 2.6 msec (range, 5.5-12.3 msec) (see Fig 2). Silence-locked EEG averages did not generate a potential related to the EMG silence in any of the 5 patients (Fig 6). Polygraphic sleep recordings, obtained in 7 patients, showed atten- uation and disappearance of myoclonus during sleep. The age at onset of this fast-bursting myoclonus was between age 8 months and 12 years. There was no correlation of intensity of jerking with age. There was a strict relationship between severity of myoclonus and that of ataxia. Two patients experienced periods, lasting weeks, during which myoclonus occurred bilaterally in such a continuous and intense way that it could be classified as myoclonic status.

Seven patients developed myoclonic seizures or myoclonic absences between the ages of 4 months and 5 years. These were intractable and often presented as status epilepticus up to the age 10 to 14 years. After- wards they occurred sporadically in 3 patients and ceased in the others. Myoclonias were represented by rhythmic jerking accompanied by 2- to 2.5-Hz-spike waves phase reversing over the frontorolandic regions and often spreading to both hemispheres (see Fig 3). Mean interhemispheric latency between peaks of premyoclonus spikes, studied in 4 patients, was 11.05 2 0.6 msec (range, 9.51-12.56 msec). The leading side

could vary from one discharge to another. EMG burst duration, obtained from the rectified averages of 100 consecutive bursts time locked with the EEG spikes, was 39 k 15 msec. The premyoclonus spikes had a mean duration of 66.2 2 10.1 msec (range, 35-86.2 msec) and preceded the burst by -39 2 15 msec (range, 20.3-57.3 msec). There was a wide within- patient variability in delay (for example, Patient 3 had the widest range, from 28.5 to 57.3 msec and Patient 2 the narrowest, from 30.5 to 43.9) with a coefficient of variability > 10.8%. Bursts were followed by a postmyoclonic silence time locked with a slow wave of equal duration (219 It 21 msec). Myoclonus involved the limbs, more intensely in the proximal areas, and could cause jerky drop attacks or head drops, or simply cause spontaneous movements to become jerky. Since jerks were mild at rest but markedly enhanced by movement, they resembled action myoclonus.

Evoked Potentials SEPs were normal in 1 patient and showed prolonged central conduction times in 5. We did not observe giant SEPs or C-reflex in any patient.

Transcranial Magnetic Stimulation MEPs showed increased CMCTs in 2 patients, low amplitude responses in 5, and no abnormalities in 1 patient. TMS induced a post-MEP silent period (SP) lasting 43 2 10 msec. These values were markedly


Masseter

0. Oris A _I----J\II\*-

Del t

( 1 5 ~ v Flex 20 ms

I NPE- Pi sa

Fig 1. Putient 1. Rectified electromyogmphic activity. Average o f 30 spontaneous jerks o f fast-bursting corticul myoclonus. All muscles recorded from one side ure involved, following u ros- trocuudul pattern of recruitment. This indicutes thut the impulses generating the myoclonus puss down the bruinstem. The masseter @fib cruniul nerve) is activuted before the orbicularis oris (seventh cruniul nerve), which is in turn uctivuted before the more caudal muscles. 0. Oris = orbiculuris oris; Delt = deltoid; Tric = triceps; Bic = biceps; Ext = wrist extensors; Flex = wrist flexors.

shortened with respect to those obtained in controls (135 2 37 msec). The EMG activity following the SP resumed immediately the rhythmic bursting pattern of the prestimulus period.

Neuroimaging Results of neuroimaging are reported in Table 1.

Treatment of Myoclonus with Piracetam Five patients treated with piracetam showed a marked reduction in myoclonus with the drug being well toler- ated. Daily doses ranged from 4.8 to 9.6 gm/day (114-160 mg/kg/day). There was a significant improvement in all scores during piracetam treatment ( p < 0.05). The antimyoclonic effect was stable after 4 to 12 months of treatment. Attempts to reduce CLB comedication in 2 patients resulted in an intolerable exacerbation of myoclonus. There was no exacerbation of seizures during piracetam treatment in the 3 patients with active epilepsy who received this drug.

A

c4

CZ

c3

L. Est

R. Est

100 ms LNPEPisa

Fig 2. Putient 2. Buck-uveruged electroencephalogruphic (EEG) activity (n = 100) preceding the onset of u briefelec- tromyogruphic (EMG) burst. EMG uctivicy in the Left wrist extensor precedes thut o f the contruluterul homologous muscle by about 8 msec. The sume time difference is found between the premyoclonus EEG trunsients recorded fiom the right central (C4) und lefi centrul (C3) ureas.

Discussion The 11 patients presented here showed the abnormal jerky, tremulous, or dystonic motor pattern typical of AS [6]. Since AS patients are severely mentally retarded and frequently hyperkinetic, it may be difficult to rec- ognize the individual components of the abnormal movement. Using long-term video-EEG and polygraphic monitoring we observed that the movement disorder was related to cortical myoclonus.

Most patients exhibited both myocloiiic seizures or myoclonic absences and FBCM. Eight patients had experienced myoclonic seizures or myoclonic absences sometime in their life. These seizure types occurred either as short attacks or as status epilepticus and con- sisted of transitory events during which habitual motor behavior was disrupted and cortical spiking, time locked with bilateral jerking, was demonstrable with standard polygraphic procedures. In addition, all patients presented with almost continuous focal or multifocal fast jerking or twitching, often manifested as dystonic limb posturing. Jerks were either spontaneous or action related and did not appear to be stimulus sensitive. The typical pattern of myoclonus, consisting of brief bursts occurring synchronously in agonist and antagonist muscles at a mean frequency of 11 Hz was observed in the EMG. The jerking involved mainly the hands and face following a pattern consistent with intrahemispheric cortical spread [ 191. Bilateral jerks


Z.S. 25 yrs INPE-Pisa

Fig 3. Patient 2. Surface electroencephalographic-electromyographic (EEG-EMG) polygrphic recording. Rhythmic 12- to 15 -H~ myoclonus (fast-bursting cortical myoclonus [FBCM]) involving all muscles recorded is acconzpanied by difise, rhythmic, 5- to 8-Hz sharp EEG activiry. A discharge of generalized polyspike and wave complexes, lasting 2.5 seconds, is accompanied by rhythmic EMG bursts o f 2 to 4 myoclonic potentials, each time locked with the spikes. This generalized discharge accompanies a short myoclonic absence. AJter the absence, both EEG and EMG resume the rhythmic pattern o f FBCM, which disappears 3 seconds later on the right hemisphere and le j muscles, whereas it persists f i r 3 more seconds contralaterally.

were never synchronous as observed in minipolymyoclonus [2O], but they had a latency consistent with interhemispheric transfer [ 191. Myoclonus was accompanied by rhythmic, somatotopically related 5- to 10- Hz EEG activity well recognizable on conventional recordings, similar to that described by Kelly and associ- ates [21] in action myoclonus. By back averaging EEG recordings related to onset of the EMG burst, in 5 patients, this rhythmic activity disappeared, indicating that it was not time locked to the muscle discharges. On the other hand, back averaging revealed a reproducible EEG potential arising from the contralateral sensorimotor cortex and preceding the EMG burst by a short interval appropriate to conduction through cor- ticomotoneuronal pathways [22] . Negative myoclonus [23] was ruled out because back averaging EEG activiry related to the onset of the silent periods between two bursts did not reveal a cortical potential. The influence of a long-loop was also excluded, since the C-reflex could not be elicited. Therefore, all patients presented with a type of myoclonus resembling cortical tremor

[24, 251, but with some peculiarities that make it unique to AS, which we have designated as FBCM. A transition into a peculiar form of myoclonic status, with bilateral 12- to 15-Hz jerking was seen in 2 patients, which strengthens the evidence for a continuum of manifestations within the spectrum of cortical tnyoc- lonus [26, 271.

We found the time between cortical spiking and subsequent EMG burst during myoclonic seizures or myoclonic absences to be considerably longer than during focal jerking (39 i- 15 vs 19 i- 5 msec). Since in both instances the delay was consistent with conduction in rapidly conducting corticospinal pathways, the difference in latency could be attributed to the time required by myoclonic activity to generalize through- out the motor cortex via corticocortical connections [ 19, 281. Because these patients presented multifocal jerking, the cortical area from which myoclonic activity could arise and spread may have varied from one generalized jerk to another. It follows that the first muscles to be activated during generalized myoclonus might


100 ms

B I 5 v V F4

L. Ext I25 PV

100 ms

125 pv L. Ext

100 ms INPE-Pisa

Fig 4. Patient 2. (A) Su face electroencephalogvaphic-electromyographic (EEG-EMG) recording reproduced after EMG has been rectijed. Rhythmic EEG activity is not time locked to EMG bursts. (B) After 20 averages of EEG activity preceding the onset o f the EMG burst, rhythmic EEG activity disappears and is replaced by more irregular wavefoovms. (C) After 80 averages, a positive-negative EEG transient, time locked to EMG onset, is well recognizable.

vary from one jerk to another, and differ from those recorded. The wide within-patient variability in latencies of generalized myoclonus (CV > 10.8%) seems to confirm this possibility. We demonstrated interhemispheric corticocortical spread of myoclonic activity based upon right to left latencies of both EMG burst and cortical correlates. Unfortunately, we could not record from leg muscles of these hyperkineric patients, and we therefore could not measure variations in latency of activation of widely separated muscle groups, providing timing evidence for intrahemispheric spread (19, 281.

Piracetam has proven to be an effective and safe drug for symptomatic treatment of cortical myoclonus [ 18, 291. Used in association with VPA or benzodiazepines in 5 patients, piracetam produced considerable overall functional improvement. This resulted from a reduc-

F4

P4

c z

c3 -----.&-+d

100 Ins TNPE-Pisa

Fig 5. Patient 3. Back-averaged electroencephalographic activity (n = 100; Oz reference; rectijed electromyograrn) in relation to a spontaneous jerk involving lefi wrist extensor muscles (L. Ext). A positive-negative potential, well recognizable over tbe C4 electrode, precedes the jerk by 20 msec.

tion in myoclonus, as well as from improvement in dystonic limb posturing and ataxic gait. The mechanism of action of piracetam in cortical myoclonus is not known, but it is probably not due to modulation of the effect of other antimyoclonic drugs since it is also effective in monotherapy [18]. However, in 2 of our patients we were unable to switch to piracetam monotherapy because myoclonus worsened during benzodiazepine withdrawal.

The multiple small twitches typical of FBCM may originate from small distinct areas within a hyperexcit- able motor cortex. These areas could generate multiple small spikes leading to tremulous muscle activity [30]. Since we found neither giant SEPs nor C-reflex, it is conceivable that FBCM is produced by discharges orig- inating spontaneously in the motor cortex [31], with- out simultaneous involvement of the parietal cortex. However, we cannot exclude sensitivity to nontested sensory inputs such as muscle stretch, touch, and pres- sure [32]. The short post-MEP-SPs observed in our patients after TMS would indicate that central motor


Table 2. Electrophysiolozic Findings in Fast-Burstin‘? Cortical Myoclonus

Back-Averaged EEG EMG Burst

Latency of Premovement Positivity Frequency Duration Positivity (msec) Duration (msec) (Hz) (msec)

Patient No. Mean SD cv (Yo) Mean SD Mean SD Mean SD

-23.19 0.18 0.78 31.6 1.5 12.0 2.6 25.0 1 .o -22.14 0.21 0.95 30.5 0.5 12.8 0.5 26.0 1 .o -21.21 0.32 1.51 40.4 0.2 10.7 0.2 48.6 1.5 - 18.24 0.1 0 0.55 30.0 0.5 9.1 0.5 47.0 0.9 -13.17 0.15 1.14 30.3 1.5 11.7 1.5 28.0 1 .0

CV = (SD/mean) X 100; threshold at 5%. EEG = electroencephalographic; EMG electromyographic; CV = coefficient of variability.

inhibitory mechanisms are impaired [33] and provide further evidence that the motor cortex is hyperexcit- able.

The only neuropathologic study from an AS patient has revealed marked cerebellar atrophy with loss of Purkinje and granule cells with extensive Bergmann’s gliosis 1341. Neurochemical study of the abnormal cerebellar cortex showed markedly reduced GABA con- tent, possibly related to failure to develop or a loss of Purkinje cells and inhibitory GABAergic interneurons. Although these findings should be considered cau- tiously because that patient had received phenytoin treatment, loss of inhibitory cerebellar influence on motor cortical function is a possible cause of cortical myoclonus [ 3 11.

The majority of AS patients have a large deletion on maternal chromosome 15ql1- 13, which eliminates a cluster of GABA, receptor genes (p3, a5, ~ 3 ) . A similar situation is also observed in the mutant mouse pcp (p locus cleft palate), which exhibits a chromosomal deletion that likewise eliminates the same GABA, receptor cluster [35]. This deleted murine region is considered to be syntenic to the one associated with AS in humans [35] . The mutant mouse pcp dis- plays seizure activity, tremor, and a jerky gait [36]. A significant reduction (6040%) in benzodiazepine binding in most brain regions of this mouse has also been observed [35] . A similar receptor abnormality may be present in AS, resulting in a decrease in the inhibitory control mechanisms exercised by GABAergic nonpyrainidal cells. These cells inhibit intrinsically bursting neurons located in human neocortical layers IV and V, which generate a stereotyped clustering of action potential bursts with a frequency of 5 to 15 Hz, in response to intracellular threshold stimuli [37] . Since this frequency is similar to the spiking accompa- nying FBCM, it is possible that cortical myoclonus in AS results from enhanced firing properties of intrinsically bursting neurons. Studies using the GABA, recep-

c4

L. Ext

L. Flex I 25 $7

I NPE- Pi sa loo Ins

Fig 6 Patient 3. Back-averaged electroencephalographic (EEG) activity (n = 100; Oz reference; rectified electromyo- gram) in relation to the onset o f the EMG silence following a burst. Averages do not generate a potential related to the silence. The premyoclonic potential is still visible, became it is time locked with the burst immediately preceding the EMG silence. Since myoclanic bursts and postmyoclonic silences are temporally related and have a high-frequency rhythmicity, back-averaging EEG activiq related to one of the two does not allow complete elimination of EEG activity related to the other. L. = lefi; Ext = wrist exteyisors; Flex = wi+istJexors.

46 Annals of Neurology Vol 40 No 1 J d y 1996

tor inhibitor penicilline have demonstrated that cortical layers IV and V have the lowest threshold for epileptogenesis [38], Numerous experimental [39-411 and clinical data [42, 431 demonstrate that loss of GABA- ergic inhibition can produce myoclonus, especially of cortical origin.

The observation that the deleted region in AS is al- ways of maternal origin suggests that this region is sub- ject to genetic imprinting [44]. The presence of FBCM in our 2 patients with uniparental disomy, suggests that the gene(s) implicated with FBCM is also an imprinted phenomena. Furthermore, FBCM is fully expressed in a patient with a microdeletion restricted to 3-21 (D15S10), LS6-1 (D15S113), and GABRB3, making it probable that a genic abnormality responsible for AS- associated myoclonus is localized in this small region. GABA f i3 is [he only gene of known funct-ion mapped to this region [45, 461. To demonstrate whether this gene plays a role in FBCM, it will be necessary to perform neurophysiological studies in those rare patients bearing deletions in which the p3 gene is appar- ently intact [47, 481 and in those where the p3 gene is deleted while a5 is not [46, 491. However, one cannot exclude the possibility that nondeleted genes are inacti- vated and that a yet unidentified gene(s) in the AS deletion region may be responsible for AS-associated myoclonus. That we found the same pattern of myoclonus in 5 AS patients with no demonstrable genetic abnormality (not included in this study) indicates thzt myoclonus is similarly expressed in deleted and nondeleted patients [7, 101.

In our experience, the powerful antimyoclonic and antiabsence action of benzodiazepines, which is based on their GABAergic properties, is also confirmed in AS. Based on this rationale, new antiepileptic mole- cules designed €or enhancing GABAergic inhibition, such as Vigabatrin (VGB) (a GABA-T blocker) or Tia- gabine (TGB) (which blocks GABA reuptake), could in theory also be effective in treating AS-associated seizures. However, in experimental models of absence seizures, VGB has shown negative effects [50]. Clinical trials have confirmed such findings and have also shown that myoclonic seizures may worsen with VGB 1511. No experimental or clinical experience on absence or myoclonic seizures has been gathered with TGB as yet [52]. Therefore, a t the current state of‘ knowledge, there is no convincing evidence showing whether these new drugs could be effective in treatment of seizures in AS.

In conclusion, our findings demonstrate that AS patients present with a continuum of manifestations within the spectrum of cortical myoclonus. FBCM- associated jerking causes severe disability and is a major component of the motor pattern observed in AS. Treatment with pitacetam, used as an add-on drug, induced considerable functional improvement and

should be considered in those AS patients in which cortical myoclonus is a prominent manifestation.

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