title: Clinical and neurophysiologic features of progressive myoclonus epilepsy without renal failure caused by SCARB2 mutations.
abstract: OBJECTIVE
  Mutations of the SCARB2 gene cause action myoclonus renal failure syndrome (AMRF), a rare condition that combines progressive myoclonus epilepsy (PME) with severe renal dysfunction. We describe the clinical and neurophysiologic features of PME associated with SCARB2 mutations without renal impairment.
  
  
  METHODS
  Clinical and neurophysiologic investigations, including wakefulness and sleep electroencephalography (EEG), polygraphic recording (with jerk-locked back-averaging and analysis of the EEG-EMG (electromyography) relationship by coherence spectra and phase calculation), multimodal evoked potentials, and electromyography were performed on five Italian patients with SCARB2 mutations.
  
  
  RESULTS
  The main clinical features were adolescent-young adulthood onset, progressive action myoclonus, ataxia, absence of cognitive deterioration and, in most cases, epilepsy. The severity of the epilepsy could vary from uncontrolled seizures and status epilepticus in patients with adolescent onset to absent or rare seizures in patients with adult onset. Relevant neurophysiologic findings were a pronounced photosensitivity and massive action myoclonus associated with rhythmic myoclonic jerks at a frequency of 12-20 Hz, clinically resembling a postural tremor. The cortical origin of rhythmic myoclonus was demonstrated mainly by coherence and phase analysis of EEG-EMG signals indicating a significant EEG-EMG coupling and a direct corticospinal transfer.
  
  
  CONCLUSIONS
  Our patients with SCARB2 mutations showed the clinical and neurophysiologic phenotype of PME, in which epilepsy could be extremely severe, extending the spectrum reported in the typical AMRF syndrome. Patients with PME of unknown origin of adolescent or young adult onset, with these neurophysiologic features, should be tested for SCARB2 mutations, even in the absence of renal impairment.
authors: Neurology Unit, IRCCS Institute of Neurological Sciences, Bologna, Italy. guido.rubboli@ausl.bo.it
authors: Guido
authors: G
authors: Rubboli
authors: Silvana
authors: S
authors: Franceschetti
authors: Samuel F
authors: SF
authors: Berkovic
authors: Laura
authors: L
authors: Canafoglia
authors: Antonio
authors: A
authors: Gambardella
authors: Leanne M
authors: LM
authors: Dibbens
authors: Patrizia
authors: P
authors: Riguzzi
authors: Claudio
authors: C
authors: Campieri
authors: Adriana
authors: A
authors: Magaudda
authors: Carlo Alberto
authors: CA
authors: Tassinari
authors: Roberto
authors: R
authors: Michelucci
mesh_terms: D000328:Adult; D001921:Brain / Q000473:pathology / Q000503:physiopathology*; D004569:Electroencephalography; D004576:Electromyography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005074:Evoked Potentials, Visual / Q000502:physiology*; D005260:Female; D006801:Humans; D051907:Lysosomal Membrane Proteins / Q000235:genetics*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D009154:Mutation / Q000235:genetics*; D020191:Myoclonic Epilepsies, Progressive / Q000150:complications / Q000235:genetics* / Q000473:pathology; D010775:Photic Stimulation; D051116:Receptors, Scavenger / Q000235:genetics*; D012018:Reflex / Q000502:physiology; D051437:Renal Insufficiency / Q000150:complications / Q000235:genetics; D013997:Time Factors; D055815:Young Adult
chemical_list: D051907:Lysosomal Membrane Proteins; D051116:Receptors, Scavenger; C074299:SCARB2 protein, human