Friedrich Asmus

Mutations in LRRK2 Cause Autosomal-Dominant Parkinsonism with Pleomorphic Pathology

We have previously linked families with autosomal-dominant, late-onset parkinsonism to chromosome 12p11.2-q13.1 (PARK8). By high-resolution recombination mapping and candidate gene sequencing in 46 families, we have found six disease-segregating mutations (five missense and one putative splice site mutation) in a gene encoding a large, multifunctional protein, LRRK2 (leucine-rich repeat kinase 2). It belongs to the ROCO protein family and includes a protein kinase domain of the MAPKKK class and several other major functional domains. Within affected carriers of families A and D, six post mortem diagnoses reveal brainstem dopaminergic degeneration accompanied by strikingly diverse pathologies. These include abnormalities consistent with Lewy body Parkinsons disease, diffuse Lewy body disease, nigral degeneration without distinctive histopathology, and progressive supranuclear palsy-like pathology. Clinical diagnoses of Parkinsonism with dementia or amyotrophy or both, with their associated pathologies, are also noted. Hence, LRRK2 may be central to the pathogenesis of several major neurodegenerative disorders associated with parkinsonism.

Mutations in the gene encoding ε-sarcoglycan cause myoclonus-dystonia syndrome

The dystonias are a common clinically and genetically heterogeneous group of movement disorders. More than ten loci for inherited forms of dystonia have been mapped, but only three mutated genes have been identified so far. These are DYT1, encoding torsin A and mutant in the early-onset generalized form, GCH1 (formerly known as DYT5), encoding GTP–cyclohydrolase I and mutant in dominant dopa-responsive dystonia, and TH, encoding tyrosine hydroxylase and mutant in the recessive form of the disease. Myoclonus–dystonia syndrome (MDS; DYT11) is an autosomal dominant disorder characterized by bilateral, alcohol-sensitive myoclonic jerks involving mainly the arms and axial muscles. Dystonia, usually torticollis and/or writers cramp, occurs in most but not all affected patients and may occasionally be the only symptom of the disease. In addition, patients often show prominent psychiatric abnormalities, including panic attacks and obsessive–compulsive behavior. In most MDS families, the disease is linked to a locus on chromosome 7q21 (refs. 11–13). Using a positional cloning approach, we have identified five different heterozygous loss-of-function mutations in the gene for ɛ-sarcoglycan (SGCE), which we mapped to a refined critical region of about 3.2 Mb. SGCE is expressed in all brain regions examined. Pedigree analysis shows a marked difference in penetrance depending on the parental origin of the disease allele. This is indicative of a maternal imprinting mechanism, which has been demonstrated in the mouse ɛ-sarcoglycan gene.

The PARK8 locus in autosomal dominant parkinsonism: confirmation of linkage and further delineation of the disease-containing interval.

Recently, a new locus (PARK8) for autosomal dominant parkinsonism has been identified in one large Japanese family. Linkage has been shown to a 16-cM centromeric region of chromosome 12, between markers D12S1631 and D12S339. We tested 21 white families with Parkinson disease and an inheritance pattern compatible with autosomal dominant transmission for linkage in this region. Criteria for inclusion were at least three affected individuals in more than one generation. A total of 29 markers were used to saturate the candidate region. One hundred sixty-seven family members were tested (84 affected and 83 unaffected). Under the assumption of heterogeneity and through use of an affecteds-only model, a maximum multipoint LOD score of 2.01 was achieved in the total sample, with an estimated proportion of families with linkage of 0.32. This LOD score is significant for linkage in a replication study and corresponds to a P value of.0047. Two families (family A [German Canadian] and family D [from western Nebraska]) reached significant linkage on their own, with a combined maximum multipoint LOD score of 3.33, calculated with an affecteds-only model (family A: LOD score 1.67, P=.0028; family D: LOD score 1.67, P=.0028). When a penetrance-dependent model was calculated, the combined multipoint LOD score achieved was 3.92 (family A: LOD score 1.68, P=.0027; family D: LOD score 2.24, P=.0007). On the basis of the multipoint analysis for the combined families A and D, the 1-LOD support interval suggests that the most likely disease location is between a CA repeat polymorphism on genomic clone AC025253 (44.5 Mb) and marker D12S1701 (47.7 Mb). Our data provide evidence that the PARK8 locus is responsible for the disease in a subset of families of white ancestry with autosomal dominant parkinsonism, suggesting that it could be a more common locus.

Variant in the sequence of the LINGO1 gene confers risk of essential tremor

We identified a marker in LINGO1 showing genome-wide significant association (P = 1.2 x 10(-9), odds ratio = 1.55) with essential tremor. LINGO1 has potent, negative regulatory influences on neuronal survival and is also important in regulating both central-nervous-system axon regeneration and oligodendrocyte maturation. Increased axon integrity observed in Lingo1 mouse [corrected] knockout models highlights the potential role of LINGO1 in the pathophysiology of ET [corrected]We identified a marker in LINGO1 showing genome-wide significant association (P = 1.2 × 10−9, odds ratio = 1.55) with essential tremor. LINGO1 has potent, negative regulatory influences on neuronal survival and is also important in regulating both central-nervous-system axon regeneration and oligodendrocyte maturation. Increased axon integrity observed in Lingo1 mouse knockout models highlights the potential role of LINGO1 in the pathophysiology of essential tremor.

Myoclonus-dystonia syndrome : epsilon-sarcoglycan mutations and phenotype

Mutations in the gene for ε‐sarcoglycan (SGCE) have been found to cause myoclonus‐dystonia syndrome. We now report clinical and genetic findings in nine additional European families with myoclonus‐dystonia syndrome. The clinical presentation in 24 affecteds was homogeneous with myoclonus predominantly of neck and upper limbs in 23 of them and dystonia, presenting as cervical dystonia and/or writers cramp, in 13 cases. Six novel and one previously known heterozygous SGCE mutations were identified. SGCE deficiency seems to be the common pathogenetic mechanism in myoclonus‐dystonia syndrome.

The epsilon-sarcoglycan gene ( SGCE ), mutated in myoclonus-dystonia syndrome, is maternally imprinted

Myoclonus-dystonia syndrome (MDS) is a non-degenerative neurological disorder that has been described to be inherited in an autosomal dominant mode with incomplete penetrance. MDS is caused by loss of function mutations in the epsilon-sarcoglycan gene. Reinvestigation of MDS pedigrees provided evidence for a maternal imprinting mechanism. As differential methylated regions (DMRs) are a characteristic feature of imprinted genes, we studied the methylation pattern of CpG dinucleotides within the CpG island containing the promoter region and the first exon of the SGCE gene by bisulphite genomic sequencing. Our findings revealed that in peripheral blood leukocytes the maternal allele is methylated, while the paternal allele is unmethylated. We also showed that most likely the maternal allele is completely methylated in brain tissue. Furthermore, CpG dinucleotides in maternal and paternal uniparental disomy 7 (UPD7) lymphoblastoid cell lines show a corresponding parent-of-origin specific methylation pattern. The effect of differential methylation on the expression of the SGCE gene was tested in UPD7 cell lines with only a weak RT–PCR signal observed in matUPD7 and a strong signal in patUPD7. These results provide strong evidence for a maternal imprinting of the SGCE gene. The inheritance pattern in MDS families is in agreement with such an imprinting mechanism with the exception of a few cases. We investigated one affected female that inherited the mutated allele from her mother. Surprisingly, we found the paternal wild type allele expressed whereas the mutated maternal allele was not detectable in peripheral blood cDNA.

Pallidal and thalamic deep brain stimulation in myoclonus-dystonia.

Deep brain stimulation (DBS) of the internal globus pallidus (GPi) and ventral intermediate thalamic nucleus (VIM) are established treatment options in primary dystonia and tremor syndromes and have been reported anecdotally to be efficacious in myoclonus‐dystonia (MD). We investigated short‐ and long‐term effects on motor function, cognition, affective state, and quality of life (QoL) of GPi‐ and VIM‐DBS in MD. Ten MD‐patients (nine ε‐sarcoglycan‐mutation‐positive) were evaluated pre‐ and post‐surgically following continuous bilateral GPi‐ and VIM‐DBS at four time points: presurgical, 6, 12, and as a last follow‐up at a mean of 62.3 months postsurgically, and in OFF‐, GPi‐, VIM‐, and GPi‐VIM‐DBS conditions by validated motor [unified myoclonus rating scale (UMRS), TSUI Score, Burke‐Fahn‐Marsden dystonia rating scale (BFMDRS)], cognitive, affective, and QoL‐scores. MD‐symptoms significantly improved at 6 months post‐surgery (UMRS: 61.5%, TSUI Score: 36.5%, BFMDRS: 47.3%). Beneficial effects were sustained at long‐term evaluation post‐surgery (UMRS: 65.5%, TSUI Score: 35.1%, BFMDRS: 48.2%). QoL was significantly ameliorated; affective status and cognition remained unchanged postsurgically irrespective of the stimulation conditions. No serious long‐lasting stimulation‐related adverse events (AEs) were observed. Both GPi‐ and VIM‐DBS offer equally effective and safe treatment options for MD. With respect to fewer adverse, stimulation‐induced events of GPi‐DBS in comparison with VIM‐DBS, GPi‐DBS seems to be preferable. Combined GPi‐VIM‐DBS can be useful in cases of incapaciting myoclonus, refractory to GPi‐DBS alone.

Polymorphisms in the glial glutamate transporter SLC1A2 are associated with essential tremor

Objective: Sporadic, genetically complex essential tremor (ET) is one of the most common movement disorders and may lead to severe impairment of the quality of life. Despite high heritability, the genetic determinants of ET are largely unknown. We performed the second genome-wide association study (GWAS) for ET to elucidate genetic risk factors of ET. Methods: Using the Affymetrix Genome-Wide SNP Array 6.0 (1000K) we conducted a two-stage GWAS in a total of 990 subjects and 1,537 control subjects from Europe to identify genetic variants associated with ET. Results: We discovered association of an intronic variant of the main glial glutamate transporter (SLC1A2) gene with ET in the first-stage sample (rs3794087, p = 6.95 × 10−5, odds ratio [OR] = 1.46). We verified the association of rs3794087 with ET in a second-stage sample (p = 1.25 × 10−3, OR = 1.38). In the subgroup analysis of patients classified as definite ET, rs3794087 obtained genome-wide significance (p = 3.44 × 10−10, OR = 1.59) in the combined first- and second-stage sample. Genetic fine mapping using nonsynonymous single nucleotide polymorphisms (SNPs) and SNPs in high linkage disequilibrium with rs3794087 did not reveal any SNP with a stronger association with ET than rs3794087. Conclusions: We identified SLC1A2 encoding the major glial high-affinity glutamate reuptake transporter in the brain as a potential ET susceptibility gene. Acute and chronic glutamatergic overexcitation is implied in the pathogenesis of ET. SLC1A2 is therefore a good functional candidate gene for ET.

Myoclonus-dystonia due to genomic deletions in the epsilon-sarcoglycan gene

Direct genomic DNA sequencing fails to detect epsilon‐sarcoglycan (SGCE) mutations in up to 30% of familial myoclonus‐dystonia (M‐D) cases. We identified novel large heterozygous deletions of SGCE exon 5 or exon 6 in two M‐D pedigrees. Like nonsense mutations, exon rearrangements result in the generation of premature stop codons downstream of the deleted exon. SGCE exon dosage assays may identify additional families with SGCE mutation and thus reduce “genetic heterogeneity.” Ann Neurol 2005;58:792–797

Inherited myoclonus-dystonia syndrome : Narrowing the 7q21-q31 locus in German families

Genetic studies were performed in four German families with autosomal dominant myoclonus‐dystonia syndrome. Mutations in the D2 dopamine receptor gene, which have been implicated in this disorder, were excluded in all four families by linkage analysis and direct sequencing. All four families supported linkage to the second reported locus on chromosome 7q21 with a combined maximum multipoint lod score of 5.99. The observation of key recombinations in one family refined the disease locus to a 7.2 cM region flanked by the markers D7S652 and D7S2480. Ann Neurol 2001;49:121–124