Familial aggregation of Parkinson's disease: The Mayo Clinic family study

Applications of Machine Learning to Diagnosis of Parkinson's Disease

BACKGROUND

Accurate diagnosis of Parkinson's disease (PD) is challenging due to its diverse manifestations. Machine learning (ML) algorithms can improve diagnostic precision, but their generalizability across medical centers in China is underexplored.

OBJECTIVE

To assess the accuracy of an ML algorithm for PD diagnosis, trained and tested on data from different medical centers in China.

METHODS

A total of 1656 participants were included, with 1028 from Beijing (training set) and 628 from Fuzhou (external validation set). Models were trained using the least absolute shrinkage and selection operator-logistic regression (LASSO-LR), decision tree (DT), random forest (RF), eXtreme gradient boosting (XGboost), support vector machine (SVM), and k-nearest neighbor (KNN) techniques. Hyperparameters were optimized using five-fold cross-validation and grid search techniques. Model performance was evaluated using the area under the curve (AUC) of the receiver operating characteristic (ROC) curve, accuracy, sensitivity (recall), specificity, precision, and F1 score. Variable importance was assessed for all models.

RESULTS

SVM demonstrated the best differentiation between healthy controls (HCs) and PD patients (AUC: 0.928, 95% CI: 0.908-0.947; accuracy: 0.844, 95% CI: 0.814-0.871; sensitivity: 0.826, 95% CI: 0.786-0.866; specificity: 0.861, 95% CI: 0.820-0.898; precision: 0.849, 95% CI: 0.807-0.891; F1 score: 0.837, 95% CI: 0.803-0.868) in the validation set. Constipation, olfactory decline, and daytime somnolence significantly influenced predictability.

CONCLUSION

We identified multiple pivotal variables and SVM as a precise and clinician-friendly ML algorithm for prediction of PD in Chinese patients.

Clinical and Non-Clinical Cardiovascular Disease Associated Pathologies in Parkinson's Disease

Despite considerable breakthroughs in Parkinson's disease (PD) research, understanding of non-motor symptoms (NMS) in PD remains limited. The lack of basic level models that can properly recapitulate PD NMS either in vivo or in vitro complicates matters. Even so, recent research advances have identified cardiovascular NMS as being underestimated in PD. Considering that a cardiovascular phenotype reflects sympathetic autonomic dysregulation, cardiovascular symptoms of PD can play a pivotal role in understanding the pathogenesis of PD. In this study, we have reviewed clinical and non-clinical published papers with four key parameters: cardiovascular disease risks, electrocardiograms (ECG), neurocardiac lesions in PD, and fundamental electrophysiological studies that can be linked to the heart. We have highlighted the points and limitations that the reviewed articles have in common. ECG and pathological reports suggested that PD patients may undergo alterations in neurocardiac regulation. The pathological evidence also suggested that the hearts of PD patients were involved in alpha-synucleinopathy. Finally, there is to date little research available that addresses the electrophysiology of in vitro Parkinson's disease models. For future reference, research that can integrate cardiac electrophysiology and pathological alterations is required.

What have we learned from genome-wide association studies (GWAS) in Parkinson's disease?

After fifteen years of genome-wide association studies (GWAS) in Parkinson's disease (PD), what have we learned? Addressing this question will help catalogue the progress made towards elucidating disease mechanisms, improving the clinical utility of the identified loci, and envisioning how we can harness the strides to develop translational GWAS strategies. Here we review the advances of PD GWAS made to date while critically addressing the challenges and opportunities for next-generation GWAS. Thus, deciphering the missing heritability in underrepresented populations is currently at the reach of hand for a truly comprehensive understanding of the genetics of PD across the different ethnicities. Moreover, state-of-the-art GWAS designs hold a true potential for enhancing the clinical applicability of genetic findings, for instance, by improving disease prediction (PD risk and progression). Lastly, advanced PD GWAS findings, alone or in combination with clinical and environmental parameters, are expected to have the capacity for defining patient enriched cohorts stratified by genetic risk profiles and readily available for neuroprotective clinical trials. Overall, envisioning future strategies for advanced GWAS is currently timely and can be instrumental in providing novel genetic readouts essential for a true clinical translatability of PD genetic findings.

Somatic Mutations Detected in Parkinson Disease Could Affect Genes With a Role in Synaptic and Neuronal Processes

The role of somatic mutations in complex diseases, including neurodevelopmental and neurodegenerative disorders, is becoming increasingly clear. However, to date, no study has shown their relation to Parkinson disease’s phenotype. To explore the relevance of embryonic somatic mutations in sporadic Parkinson disease, we performed whole-exome sequencing in blood and four brain regions of ten patients. We identified 59 candidate somatic single nucleotide variants (sSNVs) through sensitive calling and a careful filtering strategy (COSMOS). We validated 27 of them with amplicon-based ultra-deep sequencing, with a 70% validation rate for the highest-confidence variants. The identified sSNVs are in genes with synaptic functions that are co-expressed with genes previously associated with Parkinson disease. Most of the sSNVs were only called in blood but were also found in the brain tissues with ultra-deep amplicon sequencing, demonstrating the strength of multi-tissue sampling designs.

Heterogeneity of prodromal Parkinson symptoms in siblings of Parkinson disease patients

A prodromal phase of Parkinson's disease (PD) may precede motor manifestations by decades. PD patients' siblings are at higher risk for PD, but the prevalence and distribution of prodromal symptoms are unknown. The study objectives were (1) to assess motor and non-motor features estimating prodromal PD probability in PD siblings recruited within the European PROPAG-AGEING project; (2) to compare motor and non-motor symptoms to the well-established DeNoPa cohort. 340 PD siblings from three sites (Bologna, Seville, Kassel/Goettingen) underwent clinical and neurological evaluations of PD markers. The German part of the cohort was compared with German de novo PD patients (dnPDs) and healthy controls (CTRs) from DeNoPa. Fifteen (4.4%) siblings presented with subtle signs of motor impairment, with MDS-UPDRS-III scores not clinically different from CTRs. Symptoms of orthostatic hypotension were present in 47 siblings (13.8%), no different to CTRs (p = 0.072). No differences were found for olfaction and overall cognition; German-siblings performed worse than CTRs in visuospatial-executive and language tasks. 3/147 siblings had video-polysomnography-confirmed REM sleep behavior disorder (RBD), none was positive on the RBD Screening Questionnaire. 173/300 siblings had <1% probability of having prodromal PD; 100 between 1 and 10%, 26 siblings between 10 and 80%, one fulfilled the criteria for prodromal PD. According to the current analysis, we cannot confirm the increased risk of PD siblings for prodromal PD. Siblings showed a heterogeneous distribution of prodromal PD markers and probability. Additional parameters, including strong disease markers, should be investigated to verify if these results depend on validity and sensitivity of prodromal PD criteria, or if siblings' risk is not elevated.

The development of inhibitors of leucine-rich repeat kinase 2 (LRRK2) as a therapeutic strategy for Parkinson's disease: the current state of play

Current therapeutic approaches for Parkinson's disease (PD) are based around treatments that alleviate symptoms but do not slow or prevent disease progression. As such, alternative strategies are needed. A promising approach is the use of molecules that reduce the function of leucine-rich repeat kinase (LRRK2). Gain-of-function mutations in LRRK2 account for a notable proportion of familial Parkinson's disease cases, and significantly, elevated LRRK2 kinase activity is reported in idiopathic Parkinson's disease. Here, we describe progress in finding therapeutically effective LRRK2 inhibitors, summarising studies that range from in vitro experiments to clinical trials. LRRK2 is a complex protein with two enzymatic activities and a myriad of functions. This creates opportunities for a rich variety of strategies and also increases the risk of unintended consequences. We comment on the strength and limitations of the different approaches and conclude that with two molecules under clinical trial and a diversity of alternative options in the pipeline, there is cause for optimism.

Role of Genes and Treatments for Parkinson’s Disease

Parkinson’s Disease (PD) is a complex neurodegenerative disorder that mainly results due to the loss of dopaminergic neurons in the substantia nigra of the midbrain. It is well known that dopamine is synthesized in substantia nigra and is transported to the striatumvianigrostriatal tract. Besides the sporadic forms of PD, there are also familial cases of PD and number of genes (both autosomal dominant as well as recessive) are responsible for PD. There is no permanent cure for PD and to date, L-dopa therapy is considered to be the best option besides having dopamine agonists. In the present review, we have described the genes responsible for PD, the role of dopamine, and treatment strategies adopted for controlling the progression of PD in humans.

Drug-Induced Movement Disorders and Its Associated Factors Among Patients Attending Treatment at Public Hospitals in Eastern Ethiopia

BACKGROUND

Antipsychotic medications have both beneficial and undesired effects at a dose used for treatment purposes. Among undesired effects caused by antipsychotics, movement disorders are prevalent. However, there is no study done to determine the prevalence of movement disorders that occurred due to antipsychotics and their determinants in eastern Ethiopia.

OBJECTIVE

This study aimed to find out the prevalence of drug-induced movement disorders and its determinants among patients who had been on follow-up at public hospitals in eastern Ethiopia.

METHODS

A cross-sectional study was conducted from May to June 2018 at HFSUH and Jugal hospital. Extrapyramidal symptom rating scale (ESRS) was used to identify patients with drug-induced movement disorders in a sample of 411 outpatients. A systematic random sampling method was used to select the sample. Logistic regression was done to identify factors associated.

RESULTS

A drug-induced movement disorder was found in 44% of the participants: Of this, 27.3% had drug-induced pseudo-Parkinsonism, 21.2% had drug-induced akathisia, 9.5% had drug-induced tardive dyskinesia, and 3.4% had drug-induced tardive dystonia. Being female was associated with pseudo-Parkinsonism (AOR=3.6, 95% CI: 2.03, 6.35), akathisia (AOR=4.9, 95% CI: 2.73, 8.78), and tardive dyskinesia (AOR=2.51, 95% CI: 1.08, 5.86) and being male with tardive dystonia (AOR=4.6, 95% CI: 1.8, 18.5). Alcohol use was associated with tardive dyskinesia (AOR= 5.89, 95% CI: 2.20, 15.69).

CONCLUSION

Drug-induced movement disorder in this study was high and nearly half of patients on antipsychotic treatment were experiencing it. Age, sex, and doses of antipsychotics were factors associated with all of the types of drug-induced movement disorders.

Variants in saposin D domain of prosaposin gene linked to Parkinson's disease

Recently, the genetic variability in lysosomal storage disorders has been implicated in the pathogenesis of Parkinson's disease. Here, we found that variants in prosaposin (PSAP), a rare causative gene of various types of lysosomal storage disorders, are linked to Parkinson's disease. Genetic mutation screening revealed three pathogenic mutations in the saposin D domain of PSAP from three families with autosomal dominant Parkinson's disease. Whole-exome sequencing revealed no other variants in previously identified Parkinson's disease-causing or lysosomal storage disorder-causing genes. A case-control association study found two variants in the intronic regions of the PSAP saposin D domain (rs4747203 and rs885828) in sporadic Parkinson's disease had significantly higher allele frequencies in a combined cohort of Japan and Taiwan. We found the abnormal accumulation of autophagic vacuoles, impaired autophagic flux, altered intracellular localization of prosaposin, and an aggregation of α-synuclein in patient-derived skin fibroblasts or induced pluripotent stem cell-derived dopaminergic neurons. In mice, a Psap saposin D mutation caused progressive motor decline and dopaminergic neurodegeneration. Our data provide novel genetic evidence for the involvement of the PSAP saposin D domain in Parkinson's disease.

A Meta-Analysis of α-Synuclein Multiplication in Familial Parkinsonism

Chronic alpha-synuclein (SNCA) overexpression is a relatively homogenous and well-defined cause of parkinsonism and dementia. Parkinson's disease (PD), PD with dementia, dementia with Lewy bodies and multiple system atrophy all manifest in SNCA multiplication families. Herein we summarize genealogic, clinical and genetic data from 59 families (25 not previously published) with parkinsonism caused by SNCA multiplications. Longitudinal clinical assessments and genealogic relationships were documented for all family members. All probands were genotyped with an Illumina MEGA high-density genotyping array to identify copy number variants (CNV) and enable SNCA multiplication breakpoints to be defined. Three SNCA short tandem repeat (STR) markers were genotyped in all available samples to validate genomic dosage and inheritance. A web-application was built as a forum for future data sharing. CNV analysis identified 49 subjects with heterozygous SNCA duplication (CNV3), 2 with homozygous duplication (CNV4) and 7 with a triplication mutation (CNV4). Clinical presentations varied greatly throughout the cohort. SNCA dosage correlates with disease onset (mean age of onset CNV3: 46.9 ± 10.5 years vs. 34.5 ± 7.4 CNV4, p = 0.003). Atypical or more severe clinical courses were described in several patients and dementia was noted in 50.9% of the probands. Neither the multiplication size (average 2.05 ± 2.45 Mb) nor the number of genes included (range 1-50) was associated with motor symptom onset or dementia. Families with SNCA multiplication are rare and globally-distributed. Nevertheless, they may both inform and benefit from the development of SNCA targeted therapeutic strategies relevant to the treatment of all alpha-synucleinopathies.

Cognitive changes in prodromal Parkinson's disease: A review

Although other nonmotor phenomena representing possible prodromal symptoms of Parkinson's disease have been described in some detail, the occurrence and characteristics of cognitive decline in this early phase of the disease are less well understood. The aim of this review is to summarize the current state of research on cognitive changes in prodromal PD. Only a small number of longitudinal studies have been conducted that examined cognitive function in individuals with a subsequent PD diagnosis. However, when we consider data from at-risk groups, the evidence suggests that cognitive decline may occur in a substantial number of individuals who have the potential for developing PD. In terms of specific cognitive domains, executive function in particular and, less frequently, memory scores are reduced. Prospective longitudinal studies are thus needed to clarify whether cognitive, and specifically executive, decline might be added to the prodromal nonmotor symptom complex that may precede motor manifestations of PD by years and may help to update the risk scores used for early identification of PD. © 2017 International Parkinson and Movement Disorder Society.

Familial aggregation of Parkinson's disease may affect progression of motor symptoms and dementia

BACKGROUND

Familial aggregation has been described in PD of both early and late onset, but has not been studied in a true population-based sample. Moreover, little is known about its association with disease progression and endophenotypes.

OBJECTIVES

The objectives of this work were to determine familial aggregation of idiopathic PD in a population-based cohort and study the association with clinical endophenotypes and disease progression.

METHODS

We examined family history data from the Norwegian ParkWest study, a well-characterized, population-based cohort of incident PD patients and age-matched healthy controls. Family data were collected at baseline with a simplified questionnaire (192 cases and 193 controls) and after 3 years of longitudinal follow-up using an extended questionnaire (172 cases and 171 controls).

RESULTS

Compared to the controls, the PD patients had an increased relative risk of having a first-degree relative with PD when using the extended questionnaire (relative risk = 1.988; P = 0.036), but not when using the simplified questionnaire (relative risk = 1.453; P = 0.224). There was no significant difference in age of onset or motor subtype (P = 0.801). However, cases with a family history of PD had reduced progression over 7 years as measured by UPDRS II (P = 0.008) and smaller rate of decrease of MMSE (P = 0.046).

CONCLUSIONS

Our findings confirm familial aggregation in a population-based cohort of idiopathic PD. Moreover, we show that positive family history of PD in patients is associated with a slower progression of PD symptoms and cognitive decline. © 2016 International Parkinson and Movement Disorder Society.

Disease-Toxicant Interactions in Parkinson's Disease Neuropathology

Human disease commonly manifests as a result of complex genetic and environmental interactions. In the case of neurodegenerative diseases, such as Parkinson's disease (PD), understanding how environmental exposures collude with genetic polymorphisms in the central nervous system to cause dysfunction is critical in order to develop better treatment strategies, therapies, and a more cohesive paradigm for future research. The intersection of genetics and the environment in disease etiology is particularly relevant in the context of their shared pathophysiological mechanisms. This review offers an integrated view of disease-toxicant interactions in PD. Particular attention is dedicated to how mutations in the genes SNCA, parkin, leucine-rich repeat kinase 2 (LRRK2) and DJ-1, as well as dysfunction of the ubiquitin proteasome system, may contribute to PD and how exposure to heavy metals, pesticides and illicit drugs may further the consequences of these mutations to exacerbate PD and PD-like disorders. Although the toxic effects induced by exposure to these environmental factors may not be the primary causes of PD, their mechanisms of action are critical for our current understanding of the neuropathologies driving PD. Elucidating how environment and genetics collude to cause pathogenesis of PD will facilitate the development of more effective treatments for the disease. Additionally, we discuss the neuroprotection exerted by estrogen and other compounds that may prevent PD and provide an overview of current treatment strategies and therapies.

MDS research criteria for prodromal Parkinson's disease

This article describes research criteria and probability methodology for the diagnosis of prodromal PD. Prodromal disease refers to the stage wherein early symptoms or signs of PD neurodegeneration are present, but classic clinical diagnosis based on fully evolved motor parkinsonism is not yet possible. Given the lack of clear neuroprotective/disease-modifying therapy for prodromal PD, these criteria were developed for research purposes only. The criteria are based upon the likelihood of prodromal disease being present with probable prodromal PD defined as ≥80% certainty. Certainty estimates rely upon calculation of an individual's risk of having prodromal PD, using a Bayesian naïve classifier. In this methodology, a previous probability of prodromal disease is delineated based upon age. Then, the probability of prodromal PD is calculated by adding diagnostic information, expressed as likelihood ratios. This diagnostic information combines estimates of background risk (from environmental risk factors and genetic findings) and results of diagnostic marker testing. In order to be included, diagnostic markers had to have prospective evidence documenting ability to predict clinical PD. They include motor and nonmotor clinical symptoms, clinical signs, and ancillary diagnostic tests. These criteria represent a first step in the formal delineation of early stages of PD and will require constant updating as more information becomes available.

Benign tremulous Parkinsonism: a unique entity or another facet of Parkinson's disease?

Benign tremulous parkinsonism (BTP) is characterized by a prominent tremor that occurs both at rest and with action in conjunction with other mild features of parkinsonism. The progression of symptoms is typically slow and there is often a positive family history. Although BTP is included within the phenotypic spectrum of Parkinsonism its exact relationship with idiopathic Parkinson’s disease remains unclear. Treatment of BTP is challenging especially considering the poor response to levodopa, therefore surgical therapies such as deep brain stimulation surgery are sought for treatment of these tremors. In this review, we will summarize the clinical features, diagnosis, neuropathology and treatment for BTP.

Familial aggregation of Parkinson disease in Utah: A population-based analysis using death certificates

Objective:

To describe clustering of death from Parkinson disease (PD) in relatives in a large US study.

Methods:

We analyzed the Utah Population Database resource, which includes genealogy data of more than 2.7 million individuals linked to 519,061 individuals with a Utah death certificate (DC). We identified individuals whose DC included PD as a cause of death using ICD coding. In those individuals whose Utah DC listed PD as a cause of death, the relative risk (RR) of death with PD was determined among close and distant relatives using sex-, birth year–, and birthplace-specific rates.

Results:

We identified 4,031 individuals whose DC indicated PD. Among 18,127 first-degree relatives of probands with a Utah DC, the RR of death with PD was significantly increased (RR = 1.82, 95% confidence interval [CI] 1.61–2.04). The RR of death with PD was also significantly increased among 40,546 second-degree relatives with a Utah DC (RR = 1.44, 95% CI 1.29–1.60) and among 93,398 third-degree relatives with a Utah DC (RR = 1.10, 95% CI 1.03–1.18).

Conclusions:

Significant evidence for excess familial clustering was observed for PD deaths. The excess familial clustering and the significantly elevated RRs for PD among close and distant relatives strongly support a genetic contribution to PD mortality. These results confirm and expand the results of previous studies of PD by quantifying the risk of PD death among more distant relatives.

Epidemiology of early-onset Parkinson's disease in Finland

OBJECTIVE

The contribution of genetic causes to Parkinson's disease (PD) is strongest in early-onset cases. We ascertained a nationwide cohort of patients in order to study the genetic epidemiology of early-onset PD (EOPD) in Finland.

METHODS

By means of a search in a national database we ascertained all patients with EOPD. These patients had become eligible for reimbursement of PD drugs between the years 1995-2006 and were <55 years of age at the time of PD diagnosis. A total of 441 patients consented and provided clinical and genealogical information.

RESULTS

The incidence of EOPD increased 1.7-fold between the years 1995-2006, the mean annual incidence being 3.3/100,000. Fifty-two patients (11.8%) reported an affected first-degree relative. The birthplaces of patients with PD among first-degree relatives were clustered in certain regions in the southwestern and western coastal provinces of Finland and in the eastern province of Savo. Furthermore, the distance between the birthplaces of the patients' parents was smaller for patients, who had first-degree relatives with PD than for patients with no family history of PD.

CONCLUSIONS

Our data suggest that the incidence of EOPD is increasing. The birthplaces of patients with PD among first-degree relatives were clustered in certain provinces of Finland suggesting that monogenic forms of PD or genetic susceptibility of PD are present in the population.

Models of α-synuclein aggregation in Parkinson's disease

Parkinson's disease (PD) is not only characterized by motor disturbances but also, by cognitive, sensory, psychiatric and autonomic dysfunction. It has been proposed that some of these symptoms might be related to the widespread pathology of α-synuclein (α-syn) aggregation in different nuclei of the central and peripheral nervous system. However, the pathogenic formation of α-syn aggregates in different brain areas of PD patients is poorly understood. Most experimental models of PD are valuable to assess specific aspects of its pathogenesis, such as toxin-induced dopaminergic neurodegeneration. However, new models are required that reflect the widespread and progressive formation of α-syn aggregates in different brain areas. Such α-syn aggregation is induced in only a few animal models, for example perikaryon inclusions are found in rats administered rotenone, aggregates with a neuritic morphology develop in mice overexpressing either mutated or wild-type α-syn, and in Smad3 deficient mice, aggregates form extensively in the perikaryon and neurites of specific brain nuclei. In this review we focus on α-syn aggregation in the human disorder, its genetics and the availability of experimental models. Indeed, evidences show that dopamine (DA) metabolism may be related to α-syn and its conformational plasticity, suggesting an interesting link between the two pathological hallmarks of PD: dopaminergic neurodegeneration and Lewy body (LB) formation.

Environmental toxins and Parkinson's disease

Parkinson's disease (PD) is a chronic, progressive, disabling neurodegenerative disorder that begins in mid to late life and is characterized by motor impairment, autonomic dysfunction, and, in many, psychological and cognitive changes. Recent advances have helped delineate pathogenetic mechanisms, yet the cause of PD in most individuals is unknown. Although at least 15 genes and genetic loci have been associated with PD, identified genetic causes are responsible for only a few percent of cases. Epidemiologic studies have found increased risk of PD associated with exposure to environmental toxicants such as pesticides, solvents, metals, and other pollutants, and many of these compounds recapitulate PD pathology in animal models. This review summarizes the environmental toxicology of PD, highlighting the consistency of observations across cellular, animal, and human studies of PD pathogenesis.

Risk factors for Parkinson's disease may differ in men and women: an exploratory study

Although several environmental and genetic risk or protective factors have been associated with Parkinson's disease (PD), their interactions overall and in men and women separately remain unknown. We used the medical records-linkage system of the Rochester Epidemiology Project to identify 196 subjects who developed PD in Olmsted County, MN, from 1976 through 1995. Each incident case was matched by age (±1 year) and sex to a general population control. We considered the following 12 risk or protective factors: personal history of head trauma, pesticide use, immunologic diseases, anemia, hysterectomy (in women only), cigarette smoking, coffee consumption, and education; and family history of parkinsonism, essential tremor, dementia, or psychiatric disorders. We used recursive partitioning analyses to explore interactions overall and in men and women separately and used logistic regression analyses to test for interactions. In the overall group, we observed the independent effects of anemia, lack of coffee consumption (never vs. ever), and head trauma; however, the findings were different in men and women. In men, we observed the independent effects of lack of coffee consumption (never vs. ever), head trauma, and pesticide use, and a suggestive synergistic interaction between immunologic diseases and family history of dementia. By contrast, in women, anemia was the most important factor and we observed a suggestive synergistic interaction between anemia and higher education. Risk factors for PD and their interactions may differ in men and women.

Female cluster headache in the United States of America: what are the gender differences? Results from the United States Cluster Headache Survey

OBJECTIVE

To present results from the United States Cluster Headache Survey regarding gender differences in cluster headache demographics, clinical characteristics, diagnostic delay, triggers, treatment response and personal burden.

BACKGROUND

Very few studies have looked at the gender differences in cluster headache presentation. The United States Cluster Headache Survey is the largest study of cluster headache sufferers ever completed in the United States and it is also the largest study of female cluster headache patients ever presented.

METHODS

The total survey consisted of 187 multiple choice questions which dealt with various issues related to cluster headache including: demographics, clinical characteristics, concomitant medical conditions, family history, triggers, smoking history, diagnosis, treatment response and personal burden. A group of questions were specifically targeted to female cluster headache patients. The survey was placed on a website from October to December 2008. For all survey responders the diagnosis of cluster headache needed to be made by a neurologist but there was no validation of the headache diagnosis by the authors.

RESULTS

1134 individuals completed the survey (816 male, 318 female). Key Points that define the differences between female and male cluster headache include: a. Age of onset: women develop cluster headache at an earlier age than men and are more likely to develop a second peak of cluster headache onset after 50 years of age. b. Family history: woman cluster headache sufferers are more likely to have a family history of both cluster headache and migraine and have an increased familial risk of Parkinson's disease. c. Comorbid conditions: female cluster headaches sufferers are significantly more likely to experience depression and have asthma than males. d. Aura issues: aura with cluster headache is equally common in both sexes, but aura duration is shorter in women. Women are much more likely to experience sensory, language and brainstem auras. e. Pain location: cluster headache pain is typically retro-orbital in location in both sexes but women are significantly more likely to experience cluster headache pain in the jaw, cheek and ear than men. f. Associated symptoms: women with cluster headache develop more “migrainous” associated symptoms than men, especially nausea and they are also more likely to have self-injurious behavior than men. g. Triggers: women with cluster headache are much less likely to have alcohol trigger a headache, but are significantly more likely to have “migrainous” triggers for their cluster headaches than men. h. Smoking issues: women are much less likely to have a smoking history than male cluster headache sufferers, more likely to have never smoked prior to cluster headache onset. i. Cycle issues: spring and fall are the most common time to start a cluster headache cycle in both sexes. Women are statistically significantly less likely to start a cluster headache cycle in the months of October–December than men. Women have more attacks per day and higher pain intensity nighttime attacks than men. j.

TREATMENT

in regard to acute treatment women statistically were less response to sumatriptan injectable and nasal spray than men, but statistically more likely to respond to inhaled lidocaine. There was equal efficacy in the sexes to inhaled oxygen but slower response in women. For preventive treatment no significant gender differences were noted, but overall women were less responsive to almost all preventives than men. k. Diagnostic delay: there remains a significant diagnostic delay for cluster headache patients in both sexes but women were more likely to be diagnosed after 10 years of symptom onset than males and significantly fewer women were diagnosed correctly at an initial physician visit than men. l. Female specific issues: cluster headache does not appear to be influenced by menses or menopause but 50% of the survey responders stated their headaches improved with pregnancy. Cluster headache does not appear to alter fertility rates in female cluster headache sufferers. m. Personal burden: cluster headache causes significantly more personal burden in women than men with more loss of employment and/or need of disability, as well as more homebound days.

CONCLUSION

Overall women and men with cluster headache have a similar presentation but there are some distinct differences that have been suggested in smaller studies of female cluster headache that we have now verified, while some of our study conclusions have not been shown previously. One major limitation to the study is a lack of validation of diagnosis. A substantial false positive cluster headache diagnosis rate, especially in females, cannot be excluded by the study methods utilized.

Cluster headache in the United States of America: demographics, clinical characteristics, triggers, suicidality, and personal burden

OBJECTIVE

To present results from the United States (US) Cluster Headache Survey including data on cluster headache demographics, clinical characteristics, suicidality, diagnostic delay, triggers, and personal burden.

BACKGROUND

There are few large-scale studies looking at cluster headache patients and none from the USA. This manuscript will present data from The US Cluster Headache Survey, the largest survey ever completed of cluster headache patients living in the USA.

METHODS

The total survey was composed of 187 multiple-choice questions that dealt with issues related to cluster headache including demographics, clinical characteristics, comorbid medical conditions, family history, triggers, smoking history, and personal burden. The survey was placed on a Web site from October through December 2008.

RESULTS

A total of 1134 individuals completed the survey (816 male, 318 female). Some key highlights from the survey include the following: (1) diagnostic delay: there remains a significant diagnostic delay for cluster headache patients on average 5+ years with only 21% receiving a correct diagnosis at time of initial presentation. (2) Suicidality: suicidal ideations are substantial, occurring in 55%. (3) Eye color: the predominant eye color in cluster headache patients is brown and blue, not hazel as suggested in previous descriptions. (4) Laterality: cluster headache has a right-sided predominance. (5) Attack profile: in US cluster headache sufferers, most attacks occur between early evening and early morning hours with peak time of headache onset between midnight and 3 am; the circadian periodicity for cluster headache is present but is not as predominant in the population as previously thought. (6) Triggers: beer is the most common type of alcohol trigger in US cluster headache patients; noted migraine triggers such as weather changes and smells are also very common cluster headache triggers. (7) Medical comorbidities: peptic ulcer disease does not have a high prevalence in US cluster headache patients as suggested by previous literature; cluster headache is associated with a low prevalence of cardiac disease as well as cerebrovascular disease even though the majority of patients are chronic heavy smokers. In US cluster headache sufferers, there appears to be comorbidity with restless leg syndrome, and this has not been demonstrated in non-US cluster headache populations. (8) Personal burden: cluster headache is disabling to the individual as almost 20% of cluster headache patients have lost a job secondary to cluster headache, while another 8% are out of work or on disability secondary to their headaches.

CONCLUSION

Some findings from the US Cluster Headache Survey expound on what is currently known about cluster headache, while some of the results contradict what has been previously written, while other information is completely new about this fascinating headache disorder.

Gene-environment interactions: key to unraveling the mystery of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disease. The gradual, irreversible loss of dopamine neurons in the substantia nigra is the signature lesion of PD. Clinical symptoms of PD become apparent when 50-60% of nigral dopamine neurons are lost. PD progresses insidiously for 5-7 years (preclinical period) and then continues to worsen even under the symptomatic treatment. To determine what triggers the disease onset and what drives the chronic, self-propelling neurodegenerative process becomes critical and urgent, since lack of such knowledge impedes the discovery of effective treatments to retard PD progression. At present, available therapeutics only temporarily relieve PD symptoms. While the identification of causative gene defects in familial PD uncovers important genetic influences in this disease, the majority of PD cases are sporadic and idiopathic. The current consensus suggests that PD develops from multiple risk factors including aging, genetic predisposition, and environmental exposure. Here, we briefly review research on the genetic and environmental causes of PD. We also summarize very recent genome-wide association studies on risk gene polymorphisms in the emergence of PD. We highlight the new converging evidence on gene-environment interplay in the development of PD with an emphasis on newly developed multiple-hit PD models involving both genetic lesions and environmental triggers.

Epidemiology and etiology of Parkinson's disease: a review of the evidence

The etiology of Parkinson's disease (PD) is not well understood but likely to involve both genetic and environmental factors. Incidence and prevalence estimates vary to a large extent-at least partly due to methodological differences between studies-but are consistently higher in men than in women. Several genes that cause familial as well as sporadic PD have been identified and familial aggregation studies support a genetic component. Despite a vast literature on lifestyle and environmental possible risk or protection factors, consistent findings are few. There is compelling evidence for protective effects of smoking and coffee, but the biologic mechanisms for these possibly causal relations are poorly understood. Uric acid also seems to be associated with lower PD risk. Evidence that one or several pesticides increase PD risk is suggestive but further research is needed to identify specific compounds that may play a causal role. Evidence is limited on the role of metals, other chemicals and magnetic fields. Important methodological limitations include crude classification of exposure, low frequency and intensity of exposure, inadequate sample size, potential for confounding, retrospective study designs and lack of consistent diagnostic criteria for PD. Studies that assessed possible shared etiological components between PD and other diseases show that REM sleep behavior disorder and mental illness increase PD risk and that PD patients have lower cancer risk, but methodological concerns exist. Future epidemiologic studies of PD should be large, include detailed quantifications of exposure, and collect information on environmental exposures as well as genetic polymorphisms.

Familial aggregation of Parkinson's disease in a multiethnic community-based case-control study

To assess the familial aggregation of Parkinson's disease (PD), we compared the cumulative incidence of PD among first-degree relatives of PD cases and controls. We identified newly diagnosed patients with PD (n = 573) during 1994 to 1995 within Kaiser Permanente Medical Care Program of Northern California and recruited 496 cases (87%) for the case-control study. Of 720 eligible controls matched by birth year and sex to cases, 541 (75%) agreed to participate. Information on family history of PD and other neurodegenerative diseases was obtained by in-person structured interview. We used the reconstructed cohort approach that provides a better estimate of the risk. The cumulative incidence of PD was significantly higher among relatives of PD patients compared with relatives of controls (2.0 vs. 0.7%; relative risk (RR) = 3.4, 95% confidence interval (CI) 1.9-5.9; P = 0.0001). The degree of familial aggregation was higher among first-degree relatives of Hispanic PD cases compared with Hispanic controls (3.7% vs. 0.4%; RR = 8.5, 95% CI 1.0-68.9) than it was among non-Hispanic Caucasian cases and controls (2.0% vs. 0.8%; RR = 2.7, 95% CI 1.5-5.1; P = 0.02). The familial aggregation of PD was stronger among the siblings of PD cases (RR = 5.4, 95% CI 1.8-16.0) than among parents (RR = 2.7, 95% CI 1.3-5.2). The incidence and familial aggregation of PD is highest among Hispanics, warranting further studies of genetic and environmental risk factors in the Hispanic population.

Distinguishing SWEDDs patients with asymmetric resting tremor from Parkinson's disease: a clinical and electrophysiological study

Approximately 10% of patients diagnosed clinically with early Parkinson's disease (PD) have normal dopaminergic functional imaging (Scans Without Evidence of Dopaminergic Deficit [SWEDDs]). An important subgroup of SWEDDs are those with asymmetric rest tremor resembling parkinsonian tremor. Clinical and pathophysiological features which could help to distinguish SWEDDs from PD have not been explored. We therefore studied clinical details including non-motor symptoms in 25 tremulous SWEDDs patients in comparison to 25 tremor-dominant PD patients. Blinded video rating was used to compare examination findings. Electrophysiological tremor parameters and also response to a cortical plasticity protocol using paired associative stimulation (PAS) was studied in 9 patients with SWEDDs, 9 with tremor-dominant PD (with abnormal dopamine transporter single photon emission computed tomography findings), 8 with segmental dystonia, and 8 with essential tremor (ET). Despite clinical overlap, lack of true bradykinesia, presence of dystonia, and head tremor favored a diagnosis of SWEDDs, whereas re-emergent tremor, true fatiguing or decrement, good response to dopaminergic drugs, and presence of non-motor symptoms favored PD. A single tremor parameter could not differentiate between groups, but the combination of re-emergent tremor and highest tremor amplitude at rest was characteristic of PD tremor. SWEDDs and segmental dystonia patients exhibited an abnormal exaggerated response to the PAS protocol, in contrast to a subnormal response in PD and a normal response in ET. We conclude that despite clinical overlap, there are features that can help to distinguish between PD and SWEDDs which may be useful in clinical practice. The underlying pathophysiology of SWEDDs differs from PD but has similarities with primary dystonia.

The RET51/FKBP52 complex and its involvement in Parkinson disease

The tyrosine kinase receptor RET51 is expressed in distinct families of neurons where it promotes different functions. FKBP52 is an immunophilin with neuroprotective effects on different kinds of neurons. In this paper, we demonstrate that RET51 activation by both glial cell line-derived neurotrophic factor (GDNF) and NGF triggers the formation of RET51/FKBP52 complex. The substitution of the tyrosine 905 of RET51, a key residue phosphorylated by both GDNF and NGF, disrupts the RET51/FKBP52 complex. NGF and GDNF have a functional role in dopaminergic (DA) neurons where RET51 and FKBP52 are expressed with a yet undefined function. To clarify if RET51/FKBP52 complex should exert its function in DA neurons, we used an indirect approach by screening the genes encoding for RET51 and FKBP52 in a group of 30 Parkinson's disease patients. The degeneration of DA neurons is the main feature of PD, which is associated to a complex multifactorial aetiology combining environmental, age-related and genetic factors. We found a compound heterozygous carrying two mutations in RET and FKBP52 that are sufficient to disrupt the RET51/FKBP52 complex, indicating its potential role in PD.

The Gly2019Ser mutation in LRRK2 is not fully penetrant in familial Parkinson's disease: the GenePD study

BACKGROUND

We report age-dependent penetrance estimates for leucine-rich repeat kinase 2 (LRRK2)-related Parkinson's disease (PD) in a large sample of familial PD. The most frequently seen LRRK2 mutation, Gly2019Ser (G2019S), is associated with approximately 5 to 6% of familial PD cases and 1 to 2% of idiopathic cases, making it the most common known genetic cause of PD. Studies of the penetrance of LRRK2 mutations have produced a wide range of estimates, possibly due to differences in study design and recruitment, including in particular differences between samples of familial PD versus sporadic PD.

METHODS

A sample, including 903 affected and 58 unaffected members from 509 families ascertained for having two or more PD-affected members, 126 randomly ascertained PD patients and 197 controls, was screened for five different LRRK2 mutations. Penetrance was estimated in families of LRRK2 carriers with consideration of the inherent bias towards increased penetrance in a familial sample.

RESULTS

Thirty-one out of 509 families with multiple cases of PD (6.1%) were found to have 58 LRRK2 mutation carriers (6.4%). Twenty-nine of the 31 families had G2019S mutations while two had R1441C mutations. No mutations were identified among controls or unaffected relatives of PD cases. Nine PD-affected relatives of G2019S carriers did not carry the LRRK2 mutation themselves. At the maximum observed age range of 90 to 94 years, the unbiased estimated penetrance was 67% for G2019S families, compared with a baseline PD risk of 17% seen in the non-LRRK2-related PD families.

CONCLUSION

Lifetime penetrance of LRRK2 estimated in the unascertained relatives of multiplex PD families is greater than that reported in studies of sporadically ascertained LRRK2 cases, suggesting that inherited susceptibility factors may modify the penetrance of LRRK2 mutations. In addition, the presence of nine PD phenocopies in the LRRK2 families suggests that these susceptibility factors may also increase the risk of non-LRRK2-related PD. No differences in penetrance were found between men and women, suggesting that the factors that influence penetrance for LRRK2 carriers are independent of the factors which increase PD prevalence in men.

Familial aggregation of Parkinson's disease: a meta-analysis

We sought to determine the relative risk (RR) of Parkinson's disease (PD) for having a first-degree relative with PD versus having no first-degree relative with PD. Studies of familial aggregation of PD were identified by searching Medline and other sources. From each study, RRs were extracted or calculated based on the published data. Studies were categorized according to methodological characteristics, as well as by first-degree relationship type and age at PD onset restrictions. Meta-analyses and meta-regressions were based on random effect models. Twenty-nine studies of familial aggregation of PD were identified with results for first-degree relatives. The best estimate of the RR of PD for having a first-degree relative with PD was 2.9 (95% CI: 2.2, 3.8; P = 2.2 E-14), based on the studies with the most rigorous methods. The RR for sibling pairs was 4.4 (95% CI: 3.1, 6.1; P < 1.0 E-30), while for child-parent pairs it was 2.7 (95% CI: 2.0, 3.7; P = 3.6 E-10). The RR for early onset PD was 4.7 (95% CI: 3.2, 6.8; P = 6.7 E-16), while for late onset PD it was 2.7 (95% CI: 1.9, 3.9; P = 1.8 E-8). Inclusion of methodologically less rigorous investigations tended to increase the RR estimates. Summary RRs were clearly elevated above one for all study methods, all first-degree relationship types, and all age at onset categories. Familial aggregation of PD is strong and unlikely to be due to chance or to deficiencies in study methodology.

Advances in the genetics of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder affecting a significant proportion of the ageing population. The etiology is unknown and it is likely due to a multifactorial interaction of genes and the environment on the background of ageing. Findings in the last decade suggest that the contribution of genetics to familial forms of PD is much greater than previously appreciated. Twelve loci are now associated with highly penetrant autosomal dominant or recessive PD, and causative mutations have been identified in eight genes with mutation carriers often characterized by a phenotype indistinguishable from idiopathic disease. To date, PD pharmacotherapy is symptomatic only and does not slow disease progression. Understanding how genetic mutations cause familial PD is likely to clarify molecular mechanisms underlying PD in general and will provide a guide for the development of novel therapies, both preventative and palliative, applicable to all forms of parkinsonism. This review outlines the advances in the study of the genetic background of PD and their possible clinical implications.

A genomic pathway approach to a complex disease: axon guidance and Parkinson disease

While major inroads have been made in identifying the genetic causes of rare Mendelian disorders, little progress has been made in the discovery of common gene variations that predispose to complex diseases. The single gene variants that have been shown to associate reproducibly with complex diseases typically have small effect sizes or attributable risks. However, the joint actions of common gene variants within pathways may play a major role in predisposing to complex diseases (the paradigm of complex genetics). The goal of this study was to determine whether polymorphism in a candidate pathway (axon guidance) predisposed to a complex disease (Parkinson disease [PD]). We mined a whole-genome association dataset and identified single nucleotide polymorphisms (SNPs) that were within axon-guidance pathway genes. We then constructed models of axon-guidance pathway SNPs that predicted three outcomes: PD susceptibility (odds ratio = 90.8, p = 4.64 × 10⁻³⁸), survival free of PD (hazards ratio = 19.0, p = 5.43 × 10⁻⁴⁸), and PD age at onset (R² = 0.68, p = 1.68 × 10⁻⁵¹). By contrast, models constructed from thousands of random selections of genomic SNPs predicted the three PD outcomes poorly. Mining of a second whole-genome association dataset and mining of an expression profiling dataset also supported a role for many axon-guidance pathway genes in PD. These findings could have important implications regarding the pathogenesis of PD. This genomic pathway approach may also offer insights into other complex diseases such as Alzheimer disease, diabetes mellitus, nicotine and alcohol dependence, and several cancers.

Complex diseases are common disorders that are believed to have many causes. Examples include Alzheimer disease, diabetes mellitus, nicotine and alcohol dependence, and several cancers. This study represents a paradigm shift from single gene to pathway studies of complex diseases. We present the example of Parkinson disease (PD) and a complex array of chemical signals that wires the brain during fetal development (the axon guidance pathway). We mined a dataset that studied hundreds of thousands of DNA variations (single nucleotide polymorphisms [SNPs]) in persons with and without PD and identified SNPs that were assigned to axon-guidance pathway genes. We then identified sets of SNPs that were highly predictive of PD susceptibility, survival free of PD, and age at onset of PD. The effect sizes and the statistical significance observed for the pathway were far greater than for any single gene. We validated our findings for the pathway using a second SNP dataset for PD and also a dataset for PD that studied RNA variations. There is prior evidence that the axon guidance pathway might play a role in other brain disorders (e.g., Alzheimer disease, Tourette syndrome, dyslexia, epilepsy, and schizophrenia). A genomic pathway approach may lead to important breakthroughs for many complex diseases.

Comparative features of the epidemiology of multiple sclerosis and Parkinson's disease: Environmental factors of potential etiological importance

Multiple sclerosis (MS) and Parkinson's disease (PD) are diseases of unknown cause. The etiology of MS is usually considered to be due to a number of potential biological agents while the etiology of PD is usually associated with toxic agents. Despite these differences, both pathologies have strong epidemiological similarities. A comparative analysis is performed of the epidemiology of MS and PD. Potential causal factors for PD may include dopamine-like pharmacological agents. It is proposed that potential causal agents such as certain drugs plus certain vaccines could explain rationally the epidemiology of MS. Ecology and genetics could not be the appropriate lines of research in the etiology of MS/PD because they are supported only in part by the epidemiology.

A prospective study of familial versus sporadic Parkinson's disease

BACKGROUND

Parkinson's disease (PD) is one of the most common neurodegenerative disorders. Most cases are sporadic but about 10-15% of patients have a positive family history of PD.

OBJECTIVE

To compare clinical phenotypes between familial (fPD) and sporadic (sPD) PD patients.

METHODS

Fifty-nine consecutive patients with at least one first-degree relative with PD were prospectively studied. After exclusion of 9 PD patients with positive family carrying known disease causing mutations, the remaining 50 were compared with 50 age- and sex-matched sPD patients.

RESULTS

Despite our methodological approach (strict diagnostic criteria, validated scales, structured interviews, multi- and two-member group formation and exclusion of patients with identifiable mutations) no major differences in the clinical phenotype between fPD and sPD were found.

CONCLUSION

Similar phenotypic characteristics of motor signs and symptoms suggest that at least the topography of the neurodegenerative insult leading to the parkinsonian clinical syndrome in fPD and sPD is similar. Similar etiologies are also suggested.

Genetics of Parkinson's disease and parkinsonism

The past 10 years has seen a shift in our etiological concepts of Parkinson's disease, moving from a nearly exclusively environmentally mediated disease towards a complex disorder with important genetic contributors. The identification of responsible mutations in certain genes, particularly alpha-synuclein, Parkin, PINK1, DJ-1 and LRRK2, has increased our understanding of the clinical and pathological changes underlying Parkinson's disease, with implications for patient diagnosis, management and future research. This review will outline the specific genetic advances, discuss their implications for clinical practice and hint at future directions for research into this common and disabling disease.

Complete ascertainment of Parkinson disease in the Swedish Twin Registry

This report describes the ascertainment of Parkinson disease (PD) in all individuals aged 50 years or older (49,814 individuals) from the Swedish Twin Registry. In phase one of the study, all twins were screened for PD using telephone interviews, with a response rate of 72.7%. In phase two, twins with suspected PD were re-contacted to exclude anyone from follow-up who reported parkinsonian symptoms due to diseases other than PD. In the third phase, in-person clinical evaluations were completed for twins who were still considered PD suspects after phase two and for a sample of co-twins. During the clinical evaluations, we also collected blood samples and information about a variety of environmental exposures. Overall prevalence rate for PD was 496 per 100,000 individuals. Among the 132 PD cases identified, there were only three concordant twin pairs. In total 7.2% of PD cases reported a first degree relative with PD.

Cross-sectional study discloses a positive family history for Parkinson’s disease and male gender as epidemiological risk factors for substantia nigra hyperechogenicity

Hyperechogenicity of the substantia nigra (SN) has been proposed to be a typical finding in Parkinson's disease (PD) and a marker of vulnerability to nigrostriatal dysfunction in healthy subjects. This large cross-sectional study including 1120 subjects older than 50 years without any signs of PD was performed to evaluate the association of SN hyperechogenicity and other proposed epidemiological risk factors for PD. Among all variables assessed only family history of PD and male gender proved to be significantly associated with SN hyperechogenicity, indicating a genetic predisposition for the ultrasound marker.

Interaction between genes and environment in neurodegenerative diseases

Alzheimer's disease (AD) and Parkinson's disease (PD) are highly prevalent disorders that account for a large part of the global burden of neurodegenerative diseases. Most AD and PD cases occur sporadically and it is generally agreed that they could arise through interactions among genetic and environmental factors. Candidate genes involved in the metabolism of xenobiotics, neurodegeneration and functioning of dopaminergic neurons were found to be associated with PD. Some of these genes interact with environmental factors that could modify PD risk. Thus, we found that the inverse association between smoking and the risk of PD depended on a polymorphism of the iNOS (inducible NO synthase) gene. We also found that the cytochrome P450 2D6 gene could have a modifying effect on the risk of PD among persons exposed to pesticides. Both interactions have biological plausibility supported by laboratory studies and could contribute to better understand the aetiology of PD. A single susceptibility gene has been identified in sporadic AD. The epsilon4 allele of epsilon polymorphism of the apolipoprotein E gene (APOE) is strongly associated with AD, the risk of AD being multiplied by 5 in persons carrying two epsilon4 alleles. The mechanism of the association between APOE and AD is poorly understood. A few interactions between the epsilon polymorphism and possible risk factors for AD have been described. However, these interactions had no biological plausibility and were likely due to chance.

Increased risk of essential tremor in first-degree relatives of patients with Parkinson's disease

We conducted a historical cohort study of 981 first-degree relatives of 162 patients with Parkinson's disease (PD) and of 838 first-degree relatives of 147 controls representative of the population of Olmsted County, Minnesota. In addition, we studied 2,684 first-degree relatives of 411 patients with PD referred to the Mayo Clinic. Relatives were interviewed and screened for tremor either directly or through a proxy, and those who screened positive were examined or copies of their medical records were obtained to confirm the diagnosis of essential tremor (ET). We also obtained ET information from a medical records-linkage system (family study method). In the population-based sample, the risk of ET was significantly increased for relatives of patients with onset of PD<or=66 years (first tertile; hazard ratio [HR]=2.24; 95% confidence interval [95% CI]=1.26-3.98; P=0.006). In the referral-based sample, the risk of ET among relatives increased with younger onset of PD in patients (linear trend; P=0.001), and was higher in relatives of PD patients with the tremor-predominant or mixed form when compared with relatives of patients with the akinetic-rigid form, and in men compared with women. These findings suggest that PD and ET may share familial susceptibility factors.

Parkinson's disease and family history

The study of family history in Parkinson's disease (PD) has resulted in considerable debate over the role of genetic factors in the development of PD. Despite this, family history is consistently identified as an independent risk factor for PD. A multifactorial disease process in which genetic, environmental and lifestyle factors culminate in overall risk seems most likely. This article reviews existing studies of familial aggregation in PD. Recent insights into rare genetic causes of PD have affirmed the importance of ongoing family history research. Future efforts should emphasise well-designed family studies with extensive, non-exclusive phenotyping and ideally long-term follow-up.

Parkinson's disease: the genetics of a heterogeneous disorder

Since the first description of Parkinson's disease (PD) in 1817 attempts have been made to resolve the etiology of this common neurodegenerative disorder. In the last century the influence of heredity in PD was controversial. The identification of mutations in six genes responsible for Mendelian forms of PD; alpha-synuclein (SNCA), parkin (PRKN), ubiquitin C-terminal hydrolase L1 (UCH-L1), oncogene DJ-1, PTEN-induced putative kinase 1 (PINK1), and most recently leucine-rich repeat kinase 2 (LRRK2), has confirmed the role of genetics in familial forms of the disease. The exact relationship of these familial disorders and related genes to the more common sporadic form is currently uncertain. The identification of LRRK2 mutations and the association of common variants in SNCA and UCH-L1 in apparently sporadic late-onset disease indicate these genes may be of greater importance than previously believed. The protein products of the six genes are involved in different pathways of neurodegeneration and have opened new avenues of research. This focused research will lead to the development of novel targeted therapies, which may revolutionize the treatment of PD for a substantial proportion of patients.

Familial risks of hospitalization for Parkinson’s disease in first-degree relatives: a nationwide follow-up study from Sweden

The aim of this study was to estimate familial risks of Parkinson's disease (PD) in first-degree relatives of probands with PD compared with first-degree relatives of control probands. Standardized incidence ratios (SIRs) of PD were estimated in the total Swedish population for the period January 1, 1987 to December 31, 2001. SIRs were calculated by age, sex, occupation, geographic region, family size, and type of related proband on the basis of first hospital diagnoses of PD during the study period. Results showed that during the study period, there were 65 cases of first-degree relatives who were hospitalized for PD out of the total 13,276 events (first hospital diagnoses of PD) between 1987 and 2001. Age-specific analyses of familial PD revealed that there was no apparent difference in SIRs by age category. Overall, significant SIRs for PD in first-degree relatives were 3.1 (95% CI 2.1-4.3) for men and 4.0 (95% CI 2.8-5.7) for women. When the related PD proband was a sibling, the SIR was significantly higher (8.7) than when the related proband was a parent (SIR=2.9, p=0.01) or a child (SIR=3.6, p=0.04). For spouses, no increased risks were found. In conclusion, the findings of the present study suggest that genetic factors are important in early- (age < or =50 years) and later (age >50 years) onset PD, and that shared environmental factors during childhood or recessive effects may partly be important for familial aggregation of the disease.

Complex segregation analysis of Parkinson's disease: The Mayo Clinic Family Study

OBJECTIVE

To conduct complex segregation analyses of Parkinson's disease (PD).

METHODS

Data on the familial aggregation of PD remain conflicting. We conducted a historical cohort study of 1,234 relatives of 162 patients with PD representative of people of Olmsted County, MN, and of 3,009 relatives of 411 patients with PD referred to the Mayo Clinic. Relatives were interviewed and screened for parkinsonism either directly or through a proxy, those who screened positive were examined, or a copy of their medical record was obtained to confirm the diagnosis. For subjects who resided in Olmsted County, additional information was obtained from the archives of the Olmsted County Historical Society and from a records-linkage system.

RESULTS

Thirty-two relatives of population-based probands and 69 relatives of referral patients developed PD (101 in total). Combining population-based and referral samples, the model that best explained the familial clustering of PD overall was a major gene with additive effect on the penetrance. This model predicted an average decrease in age at onset of PD of approximately 18 years for each copy of the putative high-risk allele. The best fitting model for younger onset PD (age <or= 59 years) was an autosomal recessive model. The best fitting models for older onset PD (age > 59 years) were a recessive or an additive model.

INTERPRETATION

The familial aggregation of PD may be explained in part by a major gene with additive effect on the penetrance.

Genetics of Parkinson disease: paradigm shifts and future prospects

Parkinson disease is a complex, multifactorial neurodegenerative disease. Although a heritable basis was originally thought unlikely, recent studies have implicated several genes in its pathogenesis, and molecular findings now allow accurate diagnosis and challenge past criteria for defining Parkinson disease. Most importantly, genetic insights provide the rationale for new strategies for prevention or therapy, and have led to animal models of disease in which these strategies can be tested. Neuroprotective therapies can now be designed to slow or halt disease progression in affected subjects and asymptomatic carriers.

Prevalence of movement disorders in men and women aged 50-89 years (Bruneck Study cohort): a population-based study

BACKGROUND

There is emerging awareness that movement disorders rank among the most common neurological diseases. However, the overall burden of these disorders in the general community is not well defined. We sought to assess the prevalence of all common categories of movement disorders in a population, accounting for sex differences and age trends.

METHODS

As part of an ongoing prospective population-based study of carotid atherosclerosis and stroke risk (the Bruneck Study), a total of 706 men and women aged 50-89 years underwent a thorough neurological assessment. The diagnosis of movement disorders and ratings for disease severity were based on standard criteria and scales. Prevalences were estimated from logistic regression models (regression-smoothed rates) and standardised to the age and sex structure of the general community.

FINDINGS

The prevalence of all common categories of movement disorders was 28.0% (95% CI 25.9-30.1). Proportions in men (27.6% [95% CI 24.5-30.7]) and women (28.3% [25.5-31.2]) were closely similar and sharply increased with age (from 18.5% [15.0-22.0] in 50-59-year olds to 51.3% [44.9-57.7] in 80-89-year olds). Almost half of all patients (90/214) had moderate-to-severe disease expression, but only 7.0% (15/214) received standard drug treatment. Prevalence of tremor was 14.5%, followed by restless legs syndrome (10.8%), parkinsonism (7%), primary dystonia and secondary dystonia (1.8%), and chorea and tics (<1% each). A fifth of all movement disorders were diagnosed to be probably drug-induced.

INTERPRETATION

There is a high prevalence of and substantial under-recognition and under-treatment of movement disorders in the general community.