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Genetics of Parkinson disease and essential tremor.

ABSTRACT: Elucidating the genetic background of Parkinson disease and essential tremor is crucial to understand the pathogenesis and improve diagnostic and therapeutic strategies.A number of approaches have been applied including familial and association studies, and studies of gene expression profiles to identify genes involved in susceptibility to Parkinson disease. These studies have nominated a number of candidate Parkinson disease genes and novel loci including Omi/HtrA2, GIGYF2, FGF20, PDXK, EIF4G1 and PARK16. A recent notable finding has been the confirmation for the role of heterozygous mutations in glucocerebrosidase (GBA) as risk factors for Parkinson disease. Finally, association studies have nominated genetic variation in the leucine-rich repeat and Ig containing 1 gene (LINGO1) as a risk for both Parkinson disease and essential tremor, providing the first genetic evidence of a link between the two conditions.Although undoubtedly genes remain to be identified, considerable progress has been achieved in the understanding of the genetic basis of Parkinson disease. This same effort is now required for essential tremor. The use of next-generation high-throughput sequencing and genotyping technologies will help pave the way for future insight leading to advances in diagnosis, prevention and cure.

SUBMITTER: Wider C

PROVIDER: S-EPMC3930090 | biostudies-literature | 2010 Aug

REPOSITORIES: biostudies-literature

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Genetics of Parkinson disease and essential tremor.

Wider Christian C Ross Owen A OA Wszolek Zbigniew K ZK

Current opinion in neurology 20100801 4

<h4>Purpose of review</h4>Elucidating the genetic background of Parkinson disease and essential tremor is crucial to understand the pathogenesis and improve diagnostic and therapeutic strategies.<h4>Recent findings</h4>A number of approaches have been applied including familial and association studies, and studies of gene expression profiles to identify genes involved in susceptibility to Parkinson disease. These studies have nominated a number of candidate Parkinson disease genes and novel loci ...[more]

PMID: 20489616

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Project description:The field of essential tremor (ET) genetics remains extremely challenging. The relative lack of progress in understanding the genetic etiology of ET, however, does not reflect the lack of a genetic contribution, but rather, the presence of substantial phenotypic and genotypic heterogeneity. A meticulous approach to phenotyping is important for genetic research in ET. The only tool for phenotyping is the clinical history and examination. There is currently no ET-specific serum or imaging biomarker or defining neuropathological feature (e.g., a protein aggregate specific to ET) that can be used for phenotyping, and there is considerable clinical overlap with other disorders such as Parkinson's disease (PD) and dystonia. These issues greatly complicate phenotyping; thus, in some studies, as many as 30-50% of cases labeled as "ET" have later been found to carry other diagnoses (e.g., dystonia, PD) rather than ET. A cursory approach to phenotyping (e.g., merely defining ET as an "action tremor") is likely a major issue in some family studies of ET, and this as well as lack of standardized phenotyping across studies and patient centers is likely to be a major contributor to the relative lack of success of genome wide association studies (GWAS). To dissect the genetic architecture of ET, whole genome sequencing (WGS) in carefully characterized and well-phenotyped discovery and replication datasets of large case-control and familial cohorts will likely be of value. This will allow specific hypotheses about the mode of inheritance and genetic architecture to be tested. There are a number of approaches that still remain unexplored in ET genetics, including the contribution of copy number variants (CNVs), 'uncommon' moderate effect alleles, 'rare' variant large effect alleles (including Mendelian and complex/polygenic modes of inheritance), de novo and gonadal mosaicism, epigenetic changes and non-coding variation. Using these approaches is likely to yield new ET genes.

Project description:ObjectiveCurrent pharmacological agents used to treat Parkinson disease (PD) tremor and essential tremor (ET) provide suboptimal benefit and are commonly associated with significant adverse effects. Botulinum toxin type A (BoNT-A) has been shown to be effective for wrist tremor though functionally bothersome muscle weakness frequently occurs. This is the longest study to date demonstrating that BoNT-A therapy coupled with kinematic guidance can provide efficacious outcomes for upper limb tremor with minimized unwanted weakness.MethodsA total of 28 PD and 24 ET participants with bothersome, disabling tremor, received six serial BoNT-A treatments every 16 weeks starting at week 0 with a follow-up visit 6 weeks following a treatment, totaling 96 weeks. Clinical scales, including Fahn-Tolosa-Marin tremor rating scale (FTM), and sensor-based tremor assessments were conducted at each visit. Kinematics was utilized to identify which arm muscles contributed to the tremulous movements and the experienced injector used clinical expertise in determining BoNT-A dosages.ResultsFollowing BoNT-A treatment, clinical ratings of tremor severity and functional ability (FTM) showed significant improvements following the first treatment which was maintained up to week 96 in PD and ET. Kinematics detected a significant reduction in PD and ET tremor amplitudes by 70% and 76% over the treatment course, respectively. By objectively distinguishing tremulous muscles and tremor severity, adverse effects were limited to mild perceived weakness by participants in injected muscles during follow-ups. Following the fourth treatment, BoNT-A dosages in flexor and extensor wrist muscles and biceps were reduced for those experiencing residual weakness which ultimately did not interfere with tremor relief or arm function.ConclusionsKinematics is an objective method that can aid clinicians in assessing and determining optimal BoNT-A parameters to alleviate both PD and ET tremor. BoNT-A injections are tolerable and effective when focal therapy regimens are determined and optimized kinematically over a long-term.

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Genetics of Parkinson disease and essential tremor.

Publications

Genetics of Parkinson disease and essential tremor.

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