Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0027066 (myoclonus)
 4,275 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1; MIM 254800) is an autosomal recessive disorder that occurs with a low frequency in many populations but is more common in Finland and the Mediterranean region. It is characterized by stimulus-sensitive myoclonus and tonic-clonic seizures with onset at age 6-15 years, typical electroencephalographic abnormalities and a variable rate of progression between and within families. Following the initial mapping of the EPM1 gene to chromosome 21 (ref. 6) and the refinement of the critical region to a small interval, positional cloning identified the gene encoding cystatin B (CST6), a cysteine protease inhibitor, as the gene underlying EPM1 (ref. 10). Levels of messenger RNA encoded by CST6 were dramatically decreased in patients. A 3' splice site and a stop codon mutation were identified in three families, leaving most mutations uncharacterized. In this study, we report a novel type of disease-causing mutation, an unstable 15- to 18-mer minisatellite repeat expansion in the putative promoter region of the CST6 gene. The mutation accounts for the majority of EPM1 patients worldwide. Haplotype data are compatible with a single ancestral founder mutation. The length of the repeat array differs between chromosomes and families, but changes in repeat number seem to be comparatively rare events.
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PMID:Unstable minisatellite expansion causing recessively inherited myoclonus epilepsy, EPM1. 909 Mar 86

Progressive myoclonus epilepsy of the Unverricht-Lundborg type (EPM1; MIM 254800) is an autosomal recessive disorder characterized by seizures, myoclonus and progression to cerebellar ataxia. EPM1 arises due to mutations in the cystatin B (CSTB) gene which encodes a cysteine proteinase inhibitor. Only a minority of EPM1 alleles carry point mutations, while the majority contain large expansions of the dodecamer CCCCGCCCCGCG repeat which is present at two to three copies in normal individuals. The dodecamer repeat is located in the 5' flanking region of the CSTB gene, presumably in its promoter. The pathological repeat expansion results in a reduction in CSTB mRNA, which may be cell specific. To elucidate the mechanism of this reduction of gene expression, we have studied the putative CSTB promoter in vitro. A 3.8 kb fragment, containing the putative promoter with a 600 bp repeat expansion, showed a 2- to 4-fold reduction in luciferase activity compared with an identical fragment with a normal repeat; this reduction was observed only in certain cell types. Introduction of heterologous DNA fragments of 730 and 1000 bp into the normal promoter, instead of the repeat expansion, showed similarly reduced activity. Terminal deletions of the promoter implicate a putative AP-1 binding site, upstream of the repeat, in CSTB transcription activation. We propose that a novel mechanism of pathogenesis, the altering of the spacing of transcription factor binding sites from each other and/or the transcription initiation site due to repeat expansion, is among the causes of reduction in CSTB expression and thus EPM1.
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PMID:Altered spacing of promoter elements due to the dodecamer repeat expansion contributes to reduced expression of the cystatin B gene in EPM1. 1044 45

The progressive myoclonus epilepsy of the Lafora type (LD; MIM 254780) is a rare autosomal recessive disorder characterized by epilepsy, myoclonus, progressive neurological deterioration, and the presence of periodic acid-Schiff-positive polyglucosan inclusions (Lafora bodies). Mutations in the EPM2A gene have recently been found to cause LD and about 30 or more mutations have been reported thus far. LD is relatively common in countries of the Mediterranean Basin, the Middle East, India, and Pakistan. Although a few sporadic cases with the typical LD phenotype have also been reported in the Far East including Korea and Japan, a recent effort to find mutations in Japanese LD families was not successful. In the present study, we report two novel mutations in a Korean girl with LD; a 1-bp insertion mutation (c.223insC; G75fsX107) in exon 1 and a missense mutation (c.559A>G; T187A) in exon 3 of the EPM2A gene. To our knowledge, this is the first report of a genetically confirmed case of LD in Koreans and also in the Far East.
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PMID:Two novel mutations in the EPM2A gene in a Korean patient with Lafora's progressive myoclonus epilepsy. 1256 Aug 77

Progressive myoclonus epilepsy of Lafora type (LD, MIM 254780) is a fatal autosomal recessive disorder characterized by the presence of progressive neurological deterioration, myoclonus, epilepsy and polyglucosan intracellular inclusion bodies, called Lafora bodies. Lafora bodies resemble glycogen with reduced branching, suggesting an alteration in glycogen metabolism. Linkage analysis and homozygosity mapping localized EPM2A, a major gene for LD, to chromosome 6q24. EPM2A encodes a protein of 331 amino acids (named laforin) with two domains, a dual-specificity phosphatase domain and a carbohydrate binding domain. Here we show that, in addition, laforin interacts with itself and with the glycogen targeting regulatory subunit R5 of protein phosphatase 1 (PP1). R5 is the human homolog of the murine Protein Targeting to Glycogen, a protein that also acts as a molecular scaffold assembling PP1 with its substrate, glycogen synthase, at the intracellular glycogen particles. The laforin-R5 interaction was confirmed by pull-down and co-localization experiments. Full-length laforin is required for the interaction. However, a minimal central region of R5 (amino acids 116-238), including the binding sites for glycogen and for glycogen synthase, is sufficient to interact with laforin. Point-mutagenesis of the glycogen synthase-binding site completely blocked the interaction with laforin. The majority of the EPM2A missense mutations found in LD patients result in lack of phosphatase activity, absence of binding to glycogen and lack of interaction with R5. Interestingly, we have found that the LD-associated EPM2A missense mutation G240S has no effect on the phosphatase or glycogen binding activities of laforin but disrupts the interaction with R5, suggesting that binding to R5 is critical for the laforin function. These results place laforin in the context of a multiprotein complex associated with intracellular glycogen particles, reinforcing the concept that laforin is involved in the regulation of glycogen metabolism.
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PMID:Laforin, the dual-phosphatase responsible for Lafora disease, interacts with R5 (PTG), a regulatory subunit of protein phosphatase-1 that enhances glycogen accumulation. 1453 30

Myoclonus-dystonia (M-D) (MIM 159900) is a rare "dystonia plus" syndrome, characterized by rapid myoclonic jerks, predominantly in the neck and upper limbs, in combination with dystonia. Mutations in the gene epsilon-sarcoglycan (SGCE) are known to be responsible for approximately one-third of cases. We screened 21 probands diagnosed with M-D for large deletions who were mutation negative as determined by PCR-direct sequencing. Multiplex PCR and quantification of PCR products was performed using a modified application of denaturing high performance liquid chromatography (dHPLC). We have identified two novel large multiexonic deletions of SGCE, which were confirmed by amplifying and sequencing the deletion breakpoints. Five other families were found to harbor small mutations identified by direct sequencing. Analysis of the region surrounding the deletions demonstrates that both deletions are the result of nonhomologous recombination with homologous end joining. This is only the second report of intragenic deletions with SGCE and it highlights the need to include exonic copy number variation when performing mutational analysis of SGCE.
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PMID:Large deletions account for an increasing number of mutations in SGCE. 1809 80

Hyperekplexia (MIM #149400) is a rare neurological disorder characterized by an exaggerated startle response, infantile hypertonia and hyperreflexia without spasticity, a hesitant gait that usually improves by 3 years of age, and nocturnal myoclonus. Familial hyperekplexia is usually autosomal dominant resulting from mutations in the inhibitory glycine receptor subunit alpha 1 (GLRA1) gene on chromosome 5q. We identified a 3-generation family with progressively severe phenotypes of hyperekplexia. All affected family members were found to be heterozygous for a novel arginine271proline mutation in GLRA1. Long-term follow-up of the affected members of the third generation, now aged 6 and 7 years, reveals enhanced startle responses and persistent hypertonia of the extremities without clonus or a catch, tight heel cords and abnormal toe-walking gait, and plantar flexor reflexes. The 7-year-old child recently reponded well to a benzodiazepine. Future studies are warranted to examine whether this new missense mutation is solely responsible for this atypical phenotype.
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PMID:A novel GLRA1 mutation associated with an atypical hyperekplexia phenotype. 1907 49