GOSR2: a progressive myoclonus epilepsy gene

GOSR2‐associated PME is associated with a homozygous mutation in GOSR2 (c.430G>T, p.Gly144Trp), a Golgi vesicle transport gene. The functional effect of this mutation is a loss of function that results in failure of the GOSR2 protein to localize to the cis‐Golgi. The main clinical features of the GOSR2‐associated PME are early‐onset ataxia, areflexia, action myoclonus and seizures, scoliosis, elevated creatine kinase levels, relative preservation of cognitive function until the late stages of the disease, and relentless disease course. Severe photosensitive myoclonus is a common feature. GOSR2‐associated PME is a rare disease with very few cases reported so far and it can be expected that the identification of further patients will contribute to expanding the phenotype and genotype of this condition.     

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. Ann Neurol 2009;66:532–536     

Clinical stages of progressive myoclonus epilepsy in adult patients

Nineteen hospitalized adult patients with progressive myoclonus epilepsy were studied. According to their clinical status they were divided into three groups of severity. The ages and durations of the disease did not differ significantly between the groups. The groups showed significant differences in ability of daily living, amount of spontaneous myoclonus, IQ and psychomotor reaction time. In EEG the groups differed in respect to the dominant occipital rhythm and amount of myoclonic spikes but not in respect to universal paroxysms. Myoclonic spikes and paroxysms in EEG were only loosely related. The results yield a conclusion that the deterioration caused by the disease is individual and the progression may even cease. In this respect progressive myoclonus epilepsy differs clearly from many hereditary neurometabolic and storage diseases.     

SCARB2/LIMP2 deficiency in action myoclonus‐renal failure syndrome

Action myoclonus–renal failure syndrome (AMRF) is an autosomal recessive progressive myoclonus epilepsy (PME) associated with renal dysfunction that appears in the second or third decade of life and that is caused by loss‐of‐function mutations in the SCARB2 gene encoding lysosomal integral membrane protein type 2 (LIMP2). Recent reports have documented cases with PME associated with SCARB2 mutations without renal compromise. Additional neurological features can be demyelinating peripheral neuropathy, hearing loss and dementia. The course of the disease in relentlessly progressive. In this paper we provide an updated overview of the clinical and genetic features of SCARB2‐related PME and on the functions of the LIMP2 protein.     

Electrophysiological signs of peripheral nerve dysfunction in progressive myoclonus epilepsy

Electrophysiological findings were analysed in a group of 24 patients with progressive myoclonus epilepsy (PME) without Lafora bodies. Denervation activity in needle EMG and diminution of motor and sensory responses pointed out a mild axonal degeneration. We observed a significant slowing of motor and sensory conduction velocities in all the limb nerves examined, but distal motor latencies were not significantly increased. H-reflex latency of the posterior tibial nerve was prolonged. These results yielded the suggestion that there is a systemic peripheral nerve membrane dysfunction in PME.     

Electroneuromyographical and morphological findings in progressive myoclonus epilepsy (PME)

The purpose of this study was to assess the function of peripheral nerves and muscles and to describe morphological changes in muscle biopsies of patients with progressive myoclonus epilepsy. Electroneuromyographic studies were performed on 24 adult patients whose mental and motor skills were either little, moderately or severely impaired by the disease. In 5 patients a specimen of tibial anterior muscle was morphologically and histochemically investigated. The electrophysiological functions of the peripheral nerves and muscles showed gradual increasing abnormalities parallel to the severity of clinical deterioration. The muscle biopsies of 2 patients showed signs compatible with peripheral neuropathy. These findings suggested that progressive myoclonus epilepsy may be related to a systemic membrane disorder.     

Progressive myoclonus epilepsy with nephropathy C1q due to SCARB2/LIMP-2 deficiency: Clinical report of two siblings

Action myoclonus-renal failure syndrome (AMRF) is considered a rare form of progressive myoclonus epilepsy (PME) associated with renal failure. A mutation on the gene encoding the lysosomal integral membrane protein type 2-LIMP-2 (SCARB2), the receptor responsible for targeting glucocerebrosidase to the lysosomes, was recently described, allowing a better understanding of its etiopathogenesis.We describe clinically two sisters with AMRF that resulted from a mutation in the SCARB2 gene. The renal involvement was due to nephropathy C1q. When substrate-reduction therapy, to correct the possible glucocerebroside storage in the cells with glucocerebrosidase deficiency, was administered to one of the siblings, a significant improvement was observed. This report points out a rational for a therapeutical approach to this new lysossomopathy.     

Effects of vagus nerve stimulation on progressive myoclonus epilepsy of Unverricht-Lundborg type

PURPOSE: A 34-year-old woman with progressive myoclonus epilepsy of Unverricht-Lundborg type was considered for vagus nerve stimulation (VNS) therapy. METHODS: After demonstration of intractability to multiple antiepileptic regimens and progressive deterioration in cerebellar function, the patient was implanted with a vagus nerve stimulator and followed for 1 year. Neurological status, seizure frequency, and parameter changes were analyzed. RESULTS: VNS therapy resulted in reduction of seizures (more than 90%) and a significant improvement in cerebellar function demonstrated on neurological examination. The patient reported improved quality of life based in part on her ability to perform activities of daily living. CONCLUSIONS: VNS therapy may be considered a treatment option for progressive myoclonus epilepsy. The effects of VNS on seizure control and cerebellar dysfunction may provide clues to the underlying mechanism(s) of action.     

Leucoencephalopathy with vanishing white matter may cause progressive myoclonus epilepsy

Leucoencephalopathy with vanishing white matter (VWM) is caused by mutations in the genes encoding for one of the five subunits that constitute the eukaryotic initiation factor 2B (eIF2B), and is characterized by a highly suggestive MRI pattern indicating vanishing of the cerebral white matter. Seizures are well known to occur in VWM disease, but usually do not represent a prominent feature. We report a 40-year-old man who was diagnosed with progressive myoclonus epilepsy in his twenties. All major causes of progressive myoclonus epilepsy (PME) were excluded. Brain MRI showed extensive white matter involvement. Mutation analysis of the EIF2B5 gene revealed a homozygous c.338G>A (p.Arg113His) mutation.     

IRF2BPL as a novel causative gene for progressive myoclonus epilepsy

IRF2BPL has recently been described as a novel cause of neurodevelopmental disorders with multisystemic regression, epilepsy, cerebellar symptoms, dysphagia, dystonia, and pyramidal signs. We describe a novel IRF2BPL phenotype consistent with progressive myoclonus epilepsy (PME) in three novel subjects and review the features of the 31 subjects with IRF2BPL-related disorders previously reported. Our three probands, aged 28–40 years, harbored de novo nonsense variants in IRF2BPL (c.370C > T, p.[Gln124*] and c.364C > T; p.[Gln122*], respectively). From late childhood/adolescence, they presented with severe myoclonus epilepsy, stimulus-sensitive myoclonus, and progressive cognitive, speech, and cerebellar impairment, consistent with a typical PME syndrome. The skin biopsy revealed massive intracellular glycogen inclusions in one proband, suggesting a similar pathogenic pathway to other storage disorders. Whereas the two older probands were severely affected, the younger proband had a milder PME phenotype, partially overlapping with some of the previously reported IRF2BPL cases, suggesting that some of them might be unrecognized PME. Interestingly, all three patients harbored protein-truncating variants clustered in a proximal, highly conserved gene region around the “coiled-coil” domain. Our data show that PME can be an additional phenotype within the spectrum of IRF2BPL-related disorders and suggest IRF2BPL as a novel causative gene for PME.     

Altered tryptophan metabolism in the brain of cystatin B-deficient mice: a model system for progressive myoclonus epilepsy

PURPOSE: Progressive myoclonus epilepsy of the Unverricht-Lundborg type (EPM1) is a rare neurologic disorder, associated with mutations in the Cystatin B (Cstb) gene. Mice lacking Cstb, a cysteine protease inhibitor of the cathepsine family of proteases, provide a mammalian model for EPM1 by displaying similarly progressive ataxia, myoclonic seizures, and neurodegeneration. However, the linkage of Cstb deficit on the molecular level to pathologic features like myoclonic jerks or tonic-clonic seizures has remained unclear. We examined the tryptophan (TRP) metabolism, along the serotonin (5HT) and kynurenine (KYN) pathway in the brain of Cstb-deficient mice, in relation to their possible involvement in the seizure phenotype. METHODS: TRP and its metabolites, along the 5HT and KYN pathways, were assayed in brain tissue by high-pressure liquid chromatography (HPLC) with electrochemical detection. The inverted wire grid and mild handling tests were used for evaluation of ataxia and myoclonic activity. RESULTS: The Cstb-deficient mice had constitutively increased TRP, 5HT, and 5-hydroxyindole acetic acid (5HIAA) levels in the cerebral cortex and cerebellum and increased levels of KYN in the cerebellum. These neurochemical changes were accompanied with ataxia and an apparent myoclonic phenotype among the Cstb-deficient mice. CONCLUSIONS: Our findings suggest that secondary processes (i.e., overstimulation of serotoninergic transmission) on the cellular level, initiated by Cstb deficiency in specific brain regions, may be responsible for the myoclonic/seizure phenotype in EPM1.     

Familial cortical myoclonic tremor and epilepsy: Description of a new South African pedigree with 30 year follow up

AimThe aims of this study were to report the index case of a South African family with cortical myoclonic tremor and epilepsy, to describe the pedigree with the clinical findings and results of additional investigations, and to report the unique follow-up evaluation of affected and unaffected family members after 30 years.MethodsThe index case led to evaluation of the clinical files of patients from 1978/1979 and clinical assessment and investigation of patients from this cohort as well as newly identified family members. Patients were examined clinically; cortical myoclonic tremor severity was scored by using the Fahn-Tolosa- Marin-Tremor Rating Scale and the Myoclonus Rating Scale. Cortical origin of myoclonus was proven. Statistical analyses were done to assess the impact of cortical myoclonic tremor on quality of life.ConclusionClinical data was available for 23 patients. Increase in cortical myoclonic tremor and age showed a statistically significant correlation with worsening of the sub-score for Quality of Life (FTMTRS) and myoclonus rating scale.After 30 years eleven of fourteen patients could be followed up. Progression of cortical myoclonic tremor severity was noted but epilepsy control was adequate with all patients reporting less than two seizures per year. No clinical features of neurodegeneration were found.DiscussionWe describe the initial presentation and 30 year follow-up of a four generation South African family with FCMTE. The unique long term follow up of this pedigree supports previous findings that the condition does not cause additional progressive neurological deterioration and quality of life is mostly influenced by worsening of the cortical myoclonic tremor with age.     

Wearable monitoring of positive and negative myoclonus in progressive myoclonic epilepsy type 1

ObjectiveTo develop and test wearable monitoring of surface electromyography and motion for detection and quantification of positive and negative myoclonus in patients with progressive myoclonic epilepsy type 1 (EPM1).MethodsSurface electromyography and three-dimensional acceleration were measured from 23 EPM1 patients from the biceps brachii (BB) of the dominant and the extensor digitorum communis (EDC) of the non-dominant arm for 48 hours. The patients self-reported the degree of myoclonus in a diary once an hour. Severity of myoclonus with action was evaluated by using video-recorded Unified Myoclonus Rating Scale (UMRS). Correlations of monitored parameters were quantified with the UMRS scores and the self-reported degrees of myoclonus.ResultsThe monitoring-based myoclonus index correlated significantly (p < 0.001) with the UMRS scores (ρ = 0.883 for BB and ρ = 0.823 for EDC) and with the self-reported myoclonus degrees (ρ = 0.483 for BB and ρ = 0.443 for EDC). Ten patients were assessed as probably having negative myoclonus in UMRS, while our algorithm detected that in twelve patients.ConclusionsWearable monitoring was able to detect both positive and negative myoclonus in EPM1 patients.SignificanceOur method is suitable for quantifying objective, real-life treatment effects at home and progression of myoclonus.     

Description of a family with a novel progressive myoclonus epilepsy and cognitive impairment

We report a family of Algerian origin presenting an unusual, severe form of progressive myoclonus epilepsy characterized by myoclonus, generalized tonic‐clonic seizures and moderate to severe cognitive impairment, with probable autosomal recessive inheritance. Disease onset was between 6 and 16 years of age. The diagnosis of Unverricht‐Lundborg disease and all other known causes of progressive myoclonus epilepsies were excluded by specific laboratory tests and molecular analysis. © 2009 Movement Disorder Society     

Berardinelli‐Seip syndrome and progressive myoclonus epilepsy

Berardinelli‐Seip syndrome, or congenital generalized lipodystrophy type 2 (CGL2), is characterized by a lack of subcutaneous adipose tissue and precocious metabolic syndrome with insulin resistance, resulting in diabetes, dyslipidaemia, hepatic steatosis, cardiomyopathy, and acanthosis nigricans. Most reported mutations are associated with mild, non‐progressive neurological impairment. We describe the clinical and EEG data of a patient with progressive myoclonus epilepsy (PME), CGL2, and progressive neurological impairment, carrying a homozygous BSCL2 nonsense mutation. The patient had epilepsy onset at the age of two, characterized by monthly generalized tonic‐clonic seizures. By the age of three, he presented with drug‐resistant ongoing myoclonic absence seizures, photosensitivity, progressive neurological degeneration, and moderate cognitive delay. Molecular analysis of the BSCL2 gene yielded a homozygous c.(1076dupC) p.(Glu360*) mutation. Application of a vagus nerve stimulator led to temporary improvement in seizure frequency, general neurological condition, and EEG background activity. Specific BSCL2 mutations may lead to a peculiar CGL2 phenotype characterized by PME and progressive neurodegeneration. Application of a vagus nerve stimulator, rarely used for PMEs, may prove beneficial, if only temporarily, for both seizure frequency and general neurological condition.     

Selective deep brain stimulation in the substantia nigra reduces myoclonus in progressive myoclonic epilepsy: a novel observation and short review of the literature

We report the case of a patient suffering from pharmacotherapy‐resistant bilateral progressive myoclonic epilepsy (PME) showing a beneficial response upon selective deep brain stimulation (DBS) of the substantia nigra pars reticulata. As an individual experimental therapeutic approach, we implanted DBS electrodes in the transitional zone between the subthalamic nucleus (STN) and the substantia nigra pars reticulata (SNr). Electrode placement allowed for a selective stimulation of either the STN, SNr, or both targets. Postoperatively, we observed a moderate subjective and objective improvement in positive and negative myoclonus by high‐frequency DBS of the STN/SNr transitional zone. However, a systematic exploration of different stimulation settings revealed that monopolar stimulation of the substantia nigra alone was more effective than high‐frequency monopolar DBS of either the motor STN (monopolar) or stimulation of both targets (STN/SNr). This observation confirms earlier findings showing that patients with PME benefit from high‐frequency DBS. However, in contrast to previous reports stimulating the STN/SNr transitional zone, our patient showed the most significant effect upon selective stimulation of the SNr. We propose that in patients undergoing DBS for myoclonus, at least one electrode contact should be placed in the SNr allowing for selective monopolar stimulation of this target.     

SCARB2基因突变致动作性肌阵挛―肾衰综合征

背景 动作性肌阵挛―肾衰综合征(AMRF)是进行性肌阵挛性癫痫(PME)的一种类型,是一种常染色体隐性遗传性疾病,与SCARB2基因的突变相关。目的 报道SCARB2基因突变相关性AMRF家系的1个病例,并总结目前所有文献报道的AMRF患者的临床表型和遗传学特征,以提高对该病的认识。方法 回顾AMRF患者的临床资料,采用全外显子组基因靶向二代测序对AMRF家系的1个病例进行基因检测。结合文献报道,对28例（包含本例）AMRF病例资料进行总结分析。结果 AMRF患者主要临床特征为动作性肌阵挛、全身性强直阵挛性癫痫、共济失调、无认知功能障碍、伴或不伴肾功能障碍。先证者携带SCARB2基因纯合移码突变(c.350_351delAT, p.Y117Cfs*3, NM_005506.3)。先证者未患病的母亲及姐姐携带该位点的单杂合突变。国际上目前报道的28例（包括本例）SCARB2基因突变相关性AMRF中共发现22种不同的突变位点,均以常染色体隐性遗传方式发病。结论 该研究在与SCARB2基因突变相关的AMRF患者中发现了1个未见报道过的新的移码突变位点。结合文献复习,可推测当突变位点位于更靠近5端和更重要的功能域时,对蛋白产物功能的影响会更大。 [国际神经病学神经外科学杂志, 2022, 49(3): 51-58.]