Familial aggregation of early- and late-onset Parkinson's disease

Emerging perspectives on precision therapy for Parkinson's disease: multidimensional evidence leading to a new breakthrough in personalized medicine

PD is a prevalent and progressive neurodegenerative disorder characterized by both motor and non-motor symptoms. Genes play a significant role in the onset and progression of the disease. While the complexity and pleiotropy of gene expression networks have posed challenges for gene-targeted therapies, numerous pathways of gene variant expression show promise as therapeutic targets in preclinical studies, with some already in clinical trials. With the recognition of the numerous genes and complex pathways that can influence PD, it may be possible to take a novel approach to choose a treatment for the condition. This approach would be based on the symptoms, genomics, and underlying mechanisms of the disease. We discuss the utilization of emerging genetic and pathological knowledge of PD patients to categorize the disease into subgroups. Our long-term objective is to generate new insights for the therapeutic approach to the disease, aiming to delay and treat it more effectively, and ultimately reduce the burden on individuals and society.

Re-evaluation of Genetic Variants in Parkinson's Disease Using Targeted Panel and Next-Generation Sequencing

Parkinson's disease (PD) is a complex disorder with a significant genetic component. Genetic variations associated with PD play a crucial role in the disease's inheritance and prognosis. Currently, 31 genes have been linked to PD in the OMIM database, and the number of genes and genetic variations identified is steadily increasing. To establish a robust correlation between phenotype and genotype, it is essential to compare research findings with existing literature. In this study, we aimed to identify genetic variants associated with PD using a targeted gene panel with next-generation sequencing (NGS) technology. Our objective was also to explore the idea of re-analyzing genetic variants of unknown significance (VUS). We screened 18 genes known to be related to PD using NGS in 43 patients who visited our outpatient clinic between 2018-2019. After 12-24 months, we re-evaluated the detected variants. We found 14 different heterozygous variants classified as pathogenic, likely pathogenic, or VUS in 14 individuals from nonconsanguineous families. We re-evaluated 15 variants and found changes in their interpretation. Targeted gene panel analysis with NGS can help identify genetic variants associated with PD with confidence. Re-analyzing certain variants at specific time intervals can be especially beneficial in selected situations. Our study aims to expand the clinical and genetic understanding of PD and emphasizes the importance of re-analysis.

Genetic Study of Early Onset Parkinson's Disease in Cyprus

Parkinson's Disease (PD) is a multifactorial neurodegenerative disease characterized by motor and non-motor symptoms. The etiology of PD remains unclear. However, several studies have demonstrated the interplay of genetic, epigenetic, and environmental factors in PD. Early-onset PD (EOPD) is a subgroup of PD diagnosed between the ages of 21 and 50. Population genetic studies have demonstrated great genetic variability amongst EOPD patients. Hence, this study aimed to obtain a genetic landscape of EOPD in the Cypriot population. Greek-Cypriot EOPD patients (n = 48) were screened for variants in the six most common EOPD-associated genes (PINK1, PRKN, FBXO7, SNCA, PLA2G6, and DJ-1). This included DNA sequencing and Multiplex ligation-dependent probe amplification (MLPA). One previously described frameshift variant in PINK1 (NM_032409.3:c.889del) was detected in five patients (10.4%)-the largest number to be detected to date. Copy number variations in the PRKN gene were identified in one homozygous and 3 compound heterozygous patients (8.3%). To date, the pathogenic variants identified in this study have explained the PD phenotype for 18.8% of the EOPD cases. The results of this study may contribute to the genetic screening of EOPD in Cyprus.

Differential seeding and propagating efficiency of α-synuclein strains generated in different conditions

Background

Accumulation of alpha-synuclein (α-syn) is a main pathological hallmark of Parkinson’s and related diseases, which are collectively known as synucleinopathies. Growing evidence has supported that the same protein can induce remarkably distinct pathological progresses and disease phenotypes, suggesting the existence of strain difference among α-syn fibrils. Previous studies have shown that α-syn pathology can propagate from the peripheral nervous system (PNS) to the central nervous system (CNS) in a “prion-like” manner. However, the difference of the propagation potency from the periphery to CNS among different α-syn strains remains unknown and the effect of different generation processes of these strains on the potency of seeding and propagation remains to be revealed in more detail.

Methods

Three strains of preformed α-syn fibrils (PFFs) were generated in different buffer conditions which varied in pH and ionic concentrations. The α-syn PFFs were intramuscularly (IM) injected into a novel bacterial artificial chromosome (BAC) transgenic mouse line that expresses wild-type human α-syn, and the efficiency of seeding and propagation of these PFFs from the PNS to the CNS was evaluated.

Results

The three strains of α-syn PFFs triggered distinct propagation patterns. The fibrils generated in mildly acidic buffer led to the most severe α-syn pathology, degeneration of motor neurons and microgliosis in the spinal cord.

Conclusions

The different α-syn conformers generated in different conditions exhibited strain-specific pathology and propagation patterns from the periphery to the CNS, which further supports the view that α-syn strains may be responsible for the heterogeneity of pathological features and disease progresses among synucleinopathies.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40035-021-00242-5.

Is Attention-Deficit/Hyperactivity Disorder a Risk Syndrome for Parkinson's Disease?

Recent epidemiological evidence indicates that diagnosis of attention-deficit/hyperactivity disorder (ADHD) is associated with increased risk for diseases of the basal ganglia and cerebellum, including Parkinson's disease (PD). The evidence reviewed here indicates that deficits in striatal dopamine are a shared component of the causal chains that produce these disorders. Neuropsychological studies of adult ADHD, prodromal PD, and early-stage PD reveal similar deficits in executive functions, memory, attention, and inhibition that are mediated by similar neural substrates. These and other findings are consistent with the possibility that ADHD may be part of the PD prodrome. The mechanisms that may mediate the association between PD and ADHD include neurotoxic effects of stimulants, other environmental exposures, and Lewy pathology. Understanding the nature of the association between PD and ADHD may provide insight into the etiology and pathogenesis of both disorders. The possible contribution of stimulants to this association may have important clinical and public health implications.

Societal Burden and Persisting Unmet Needs of Parkinson’s Disease

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Familial aggregation of Parkinson's disease and coaggregation with neuropsychiatric diseases: a population-based cohort study

Background

Individuals with a family history of Parkinson's disease (PD) appear to have a higher risk of developing PD and other neuropsychiatric diseases. However, estimates of the relative risks (RRs) of PD and the roles of genetic and environmental factors in PD susceptibility are unclear. The aim of this study was to examine familial aggregation and genetic contributions to PD and the RRs of other neuropsychiatric diseases in relatives of PD patients.

Methods

In this population-based family cohort study, the records of all individuals actively registered in the Taiwan National Health Insurance Research Database in 2015 were queried (N=24,349,599). In total, 149,187 individuals with a PD-affected parent, 3,698 with an affected offspring, 3,495 with an affected sibling, and 15 with an affected twin were identified. Diagnoses of PD were ascertained between January 1, 1999, and December 31, 2015. The prevalence and RRs of PD and other neuropsychiatric diseases in individuals with first-degree relatives with PD, as well as the contributions of heritability and environmental factors to PD susceptibility were investigated.

Results

The prevalence of PD was 0.46% in the general population and 0.52% in individuals with first-degree relatives with PD. The RR (95% CI) for PD was 2.20 (1.41-3.45) for siblings, 1.59 (1.47-1.73) for parents, 1.86 (1.63-2.11) for offspring, 63.12 (16.45-242.16) for twins, and 1.46 (1.41-1.52) for spouses. The RR (95% CI) in individuals with first-degree relatives with PD was 1.66 (1.57-1.76) for essential tremor, 1.68 (1.61-1.75) for schizophrenia, and 1.20 (1.12-1.28) for Alzheimer's disease. The estimated contribution to the phenotypic variance of PD was 11.0% for heritability, 9.1% for shared environmental factors, and 79.9% for non-shared environmental factors.

Conclusion

First-degree relatives of PD patients are more likely to develop PD and other neuropsychiatric diseases. Environmental factors account for a high proportion of the phenotypic variance of PD.

Investigation of non-motor symptoms in first-degree relatives of patients with Parkinson's disease

OBJECTIVE

Non-motor symptoms (NMS) are important prodromal characteristics of Parkinson's disease (PD). However, the incidence of NMS in first-degree relatives, such as siblings of PD patients, is still unknown.

METHODS

A total of 98 PD patients of the Affiliated Hospital of Yangzhou University were recruited; 210 siblings of these patients were included in a first-degree relatives (FDR) group and 250 healthy individuals were included in a control group. Various scales were used to assess NMS, including depression, anxiety, cognitive function, sleep status, constipation, daytime sleepiness, Rapid-Eye-Movement Sleep Behavior Disorder (RBD), and Restless Legs Syndrome (RLS).

RESULTS

NMS were more common in the PD group than the control group. The incidence of anxiety (OR = 3.434, 95%CI: 2.058-5.731, P < 0.001), depression (OR = 2.438, 95%CI: 1.289-4.609, P = 0.005), and RBD (OR = 4.120, 95%CI: 1.897-8.945, P < 0.001) was higher in the FDR group than the control group. There were non-significant differences in constipation, cognitive impairment, sleep disorder, daytime sleepiness, and RLS between the two groups. The incidence of RLS in FDR of PD with an age of onset <60 years was higher than in the controls (OR = 2.273, 95%CI: 1.107-4.667, P = 0.023).

CONCLUSIONS

Siblings of PD are more likely to suffer from anxiety, depression and RBD than the general population. RLS is more common in siblings of PD with onset age<60 than in the general population. It is speculated that PD patients and their siblings have common pathogenic genetic factors and early living environment for neurodegeneration.

Genetics of Parkinson's disease and related disorders

Parkinson's disease (PD) is a complex and heterogeneous neurological condition characterised mainly by bradykinesia, resting tremor, rigidity and postural instability, symptoms that together comprise the parkinsonian syndrome. Non-motor symptoms preceding and following clinical onset are also helpful diagnostic markers revealing a widespread and progressive pathology. Many other neurological conditions also include parkinsonism as primary or secondary symptom, confounding their diagnosis and treatment. Although overall disease course and end-stage pathological examination single out these conditions, the significant overlaps suggest that they are part of a continuous disease spectrum. Recent genetic discoveries support this idea because mutations in a few genes (α-synuclein, LRRK2, tau) can cause partially overlapping pathologies. Additionally, mutations in causative genes and environmental toxins identify protein homeostasis and the mitochondria as key mediators of degeneration of dopaminergic circuits in the basal ganglia. The evolving mechanistic insight into the pathophysiology of PD and related conditions will contribute to the development of targeted and effective symptomatic treatments into disease-modifying therapies that will reduce the burden of these dreadful conditions.

Genetics of Tinnitus: Still in its Infancy

Tinnitus is the perception of a phantom sound that affects between 10 and 15% of the general population. Despite this considerable prevalence, treatments for tinnitus are presently lacking. Tinnitus exhibits a diverse array of recognized risk factors and extreme clinical heterogeneity. Furthermore, it can involve an unknown number of auditory and non-auditory networks and molecular pathways. This complex combination has hampered advancements in the field. The identification of specific genetic factors has been at the forefront of several research investigations in the past decade. Nine studies have examined genes in a case-control association approach. Recently, a genome-wide association study has highlighted several potentially significant pathways that are implicated in tinnitus. Two twin studies have calculated a moderate heritability for tinnitus and disclosed a greater concordance rate in monozygotic twins compared to dizygotic twins. Despite the more recent data alluding to genetic factors in tinnitus, a strong association with any specific genetic locus is lacking and a genetic study with sufficient statistical power has yet to be designed. Future research endeavors must overcome the many inherent limitations in previous study designs. This review summarizes the previously embarked upon tinnitus genetic investigations and summarizes the hurdles that have been encountered. The identification of candidate genes responsible for tinnitus may afford gene based diagnostic approaches, effective therapy development, and personalized therapeutic intervention.

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.

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.

Motor fluctuations due to interaction between dietary protein and levodopa in Parkinson's disease

Background

The modulation of levodopa transport across the blood brain barrier by large neutral amino acids is well documented. Protein limitation and protein redistribution diets may improve motor fluctuations in patients with Parkinson’s disease but the pharmacokinetics and pharmacodynamics of levodopa and amino acids are highly variable.

Methods

Clinical records of 1037 Parkinson’s disease patients were analyzed to determine the proportion of patients with motor fluctuations related to protein interaction with levodopa. Motor fluctuations due to protein interaction with levodopa were defined as dietary protein being associated with (i) longer time to levodopa effectiveness, (ii) reduced benefit or duration of benefit, (iii) dose failures or (iv) earlier wearing off from a previously effective dose. Dose failures, sudden, painful or behavioral wearing-off periods, gait freezing, nausea, hallucinations, orthostasis, and dyskinesias were taken as markers of motor fluctuations, disease severity, and levodopa side effects potentially influenced by protein.

Results

5.9 % of Parkinson’s disease patients on levodopa, and 12.4 % with motor fluctuations on levodopa correlated their fluctuations with the relative timing of levodopa and protein intake. These patients were younger at disease onset, had worse motor fluctuations and had a higher incidence of family members with Parkinson’s disease. Early wearing off or decreased dose efficacy were most commonly associated with protein interaction. 60 % of patients who modified their diets had weight loss.

Conclusions

This study suggests that clinically significant protein interaction with levodopa may occur mostly in a subset of Parkinson’s disease patients with earlier disease onset and those with familial disease.

Familial Aggregation and Co-Aggregation of Essential Tremor and Parkinson's Disease

BACKGROUND

Current data suggest that the 2 common tremor disorders, essential tremor (ET) and Parkinson's disease (PD), may be associated with one another. Familial aggregation studies allow one to further explore their relatedness.

METHODS

Probands with ET (n = 110), PD (n = 130) or both ET and PD (n = 27) and control probands (n = 177) reported whether they had relatives with these diseases or with non-specific tremor.

RESULTS

A greater proportion of ET probands than control probands reported relatives with ET (30.0 vs. 2.8%, p < 0.001), non-specific tremor (38.2 vs. 13.6%, p < 0.001) and both ET and PD in different relatives (6.4 vs. 0.6%, p = 0.004). A greater proportion of PD probands than control probands reported relatives with PD (20.0 vs. 8.5%, p = 0.003), ET (11.5 vs. 2.8%, p = 0.002) and both ET and PD in different relatives (6.9 vs. 0.6%, p = 0.002).

CONCLUSIONS

This study provides evidence for the aggregation of ET in ET families and PD in PD families, and the familial co-aggregation of ET and PD.

Early-onset vs. Late-onset Parkinson's disease: A Clinical-pathological Study

BACKGROUND

Several studies have compared early-onset Parkinson disease (EOPD) and late-onset Parkinson disease (LOPD) but most are not based on autopsy confirmed cases.

METHODS

We compared clinical and pharmacological profiles, time to reach irreversible Hoehn and Yahr (H&Y) Stage 3 and levodopa motor complications in autopsy confirmed EOPD and LOPD cases.

RESULTS

At first clinic visit EOPD cases were younger but had longer disease duration and they died at a younger age (all p<0.0001). Anti-Parkinsonian drug use, including levodopa, was significantly delayed in EOPD. Lifetime use of amantadine (p<0.05) and dopamine agonists (p<0.01) were higher in EOPD. While lifetime use of levodopa was similar in the two groups, levodopa was used for a significantly longer period by EOPD (p< 0.0001). EOPD had a higher cumulative incidence of dyskinesias (p<0.01), wearing-off (p<0.01), and on-off (p<0.01). However, the time to dyskinesia onset was similar in the two groups. The threshold to wearing-off was much longer in EOPD (p<0.01). H&Y stage profile at first visit was similar in the two groups. The duration from disease onset to reach irreversible H&Y stage 3 was significantly longer in EOPD.

CONCLUSIONS

Our observations indicate that progression of PD is slower in EOPD and suggest that the pre-clinical interval in this group is longer. These findings can be used for case selection for drug trials and studies of the pathogenesis of PD.

DNAJC13 genetic variants in parkinsonism

BACKGROUND

A novel mutation (p.N855S) in DNAJC13 has been linked to familial, late-onset Lewy body parkinsonism in a Dutch-German-Russian Mennonite multi-incident kindred.

METHODS

DNAJC13 was sequenced in 201 patients with parkinsonism and 194 controls from Canada. Rare (minor allele frequency < 0.01) missense variants identified in patients were genotyped in two Parkinson's disease case-controls cohorts.

RESULTS

Eighteen rare missense mutations were identified; four were observed in controls, three were observed in both patients and controls, and eleven were identified only in patients. Subsequent genotyping showed p.E1740Q and p.L2170W to be more frequent in patients, and p.R1516H being more frequent in controls. Additionally, p.P336A, p.V722L, p.N855S, p.R1266Q were seen in one patient each, and p.T1895M was found in two patients.

CONCLUSION

Although the contribution of rare genetic variation in DNAJC13 to parkinsonisms remains to be further elucidated, this study suggests that, in addition to p.N855S, other rare variants might affect disease susceptibility.

Sequencing an Ashkenazi reference panel supports population-targeted personal genomics and illuminates Jewish and European origins

The Ashkenazi Jewish (AJ) population is a genetic isolate close to European and Middle Eastern groups, with genetic diversity patterns conducive to disease mapping. Here we report high-depth sequencing of 128 complete genomes of AJ controls. Compared with European samples, our AJ panel has 47% more novel variants per genome and is eightfold more effective at filtering benign variants out of AJ clinical genomes. Our panel improves imputation accuracy for AJ SNP arrays by 28%, and covers at least one haplotype in ≈67% of any AJ genome with long, identical-by-descent segments. Reconstruction of recent AJ history from such segments confirms a recent bottleneck of merely ≈350 individuals. Modelling of ancient histories for AJ and European populations using their joint allele frequency spectrum determines AJ to be an even admixture of European and likely Middle Eastern origins. We date the split between the two ancestral populations to ≈12–25 Kyr, suggesting a predominantly Near Eastern source for the repopulation of Europe after the Last Glacial Maximum.

Ashkenazi Jews are a genetically isolated population with distinct patterns of genetic diversity. Here, the authors sequence the genomes of 128 Ashkenazi Jewish individuals and use the sequence information to provide insight into the population's European and Middle Eastern origins.

Clinical profile of Parkinson's disease in the Gumei community of Minhang district, Shanghai

OBJECTIVE

We examined the demographic and clinical profiles of Parkinson's disease in Shanghai, China, to assist in disease management and provide comparative data on Parkinson's disease prevalence, phenotype, and progression among different regions and ethnic groups.

METHODS

A door-to-door survey and follow-up clinical examinations identified 180 community-dwelling Han-Chinese Parkinson's disease patients (104 males, 76 females).

RESULTS

The average age at onset was 65.16 ± 9.60 years. The most common initial symptom was tremor (112 patients, 62.22%), followed by rigidity (38, 21.11%), bradykinesia (28, 15.56%) and tremor plus rigidity (2, 1.11%). Tremor as the initial symptom usually began in a single limb (83.04% of patients). The average duration from onset to mild Parkinson's disease (Hoehn-Yahr phase 1-2) was 52.74 ± 45.64 months. Progression from mild to moderate/severe Parkinson's disease (phase ≥ 3) was significantly slower (87.07 ± 58.72 months; p<0.001), except for patients presenting initially with bradykinesia (53.83 ± 24.49 months). Most patients (149/180, 82.78%) took levodopa with or without other drugs. The Hamilton Anxiety Scale revealed symptoms of clinical anxiety in 35 patients, and the Hamilton Depression Scale revealed depressive symptoms in 88 patients. The depressed or anxious subgroup (123 patients) demonstrated a significantly younger age at onset (55.54 ± 7.68 years) compared with the overall mean (p<0.05).

CONCLUSION

Unilateral limb tremor was the most common initial symptom, and motor function deteriorated slowly over ≅4-9 years. Earlier-onset patients experience greater psychiatric dysfunction.

Genome-wide mapping of IBD segments in an Ashkenazi PD cohort identifies associated haplotypes

The recent series of large genome-wide association studies in European and Japanese cohorts established that Parkinson disease (PD) has a substantial genetic component. To further investigate the genetic landscape of PD, we performed a genome-wide scan in the largest to date Ashkenazi Jewish cohort of 1130 Parkinson patients and 2611 pooled controls. Motivated by the reduced disease allele heterogeneity and a high degree of identical-by-descent (IBD) haplotype sharing in this founder population, we conducted a haplotype association study based on mapping of shared IBD segments. We observed significant haplotype association signals at three previously implicated Parkinson loci: LRRK2 (OR = 12.05, P = 1.23 × 10(-56)), MAPT (OR = 0.62, P = 1.78 × 10(-11)) and GBA (multiple distinct haplotypes, OR > 8.28, P = 1.13 × 10(-11) and OR = 2.50, P = 1.22 × 10(-9)). In addition, we identified a novel association signal on chr2q14.3 coming from a rare haplotype (OR = 22.58, P = 1.21 × 10(-10)) and replicated it in a secondary cohort of 306 Ashkenazi PD cases and 2583 controls. Our results highlight the power of our haplotype association method, particularly useful in studies of founder populations, and reaffirm the benefits of studying complex diseases in Ashkenazi Jewish cohorts.

Genetic insights into sporadic Parkinson's disease pathogenesis

Intensive research over the last 15 years has led to the identification of several autosomal recessive and dominant genes that cause familial Parkinson’s disease (PD). Importantly, the functional characterization of these genes has shed considerable insights into the molecular mechanisms underlying the etiology and pathogenesis of PD. Collectively; these studies implicate aberrant protein and mitochondrial homeostasis as key contributors to the development of PD, with oxidative stress likely acting as an important nexus between the two pathogenic events. Interestingly, recent genome-wide association studies (GWAS) have revealed variations in at least two of the identified familial PD genes (i.e. α-synuclein and LRRK2) as significant risk factors for the development of sporadic PD. At the same time, the studies also uncovered variability in novel alleles that is associated with increased risk for the disease. Additionally, in-silico meta-analyses of GWAS data have allowed major steps into the investigation of the roles of gene-gene and gene-environment interactions in sporadic PD. The emergent picture from the progress made thus far is that the etiology of sporadic PD is multi-factorial and presumably involves a complex interplay between a multitude of gene networks and the environment. Nonetheless, the biochemical pathways underlying familial and sporadic forms of PD are likely to be shared.

Efficacy and safety of computer-assisted stereotactic transplantation of human retinal pigment epithelium cells in the treatment of Parkinson disease

OBJECTIVE

This study explores the efficacy and safety of computer-assisted stereotactic transplantation of human retinal pigment epithelium (hRPE) cells in the treatment of Parkinson disease (PD).

METHODS

Guided by computed tomography and magnetic resonance imaging image mergence, we transplanted 4 × 10 hRPE cells into the putamina and lateral ventricles of 17 PD cases by stereotactic surgery. The transplantation site was located in the contralateral side of the symptoms and signs.

RESULTS

At 3 months after operation, the effective rates of cell transplantation were 82.4% in the contralateral site and 64.7% in the ipsilateral site. Minority of the cases had mild dizziness and hemiparesis, but the durations were short.

CONCLUSIONS

Computer-assisted stereotactic transplantation of hRPE for the treatment of PD is safe and efficient.

Increased Rate of Sporadic and Recurrent Rare Genic Copy Number Variants in Parkinson's Disease Among Ashkenazi Jews

To date, only one genome-wide study has assessed the contribution of copy number variants (CNVs) to Parkinson's disease (PD). We conducted a genome-wide scan for CNVs in a case–control dataset of Ashkenazi Jewish (AJ) origin (268 PD cases and 178 controls). Using high-confidence CNVs, we examined the global genome wide burden of large (≥100 kb) and rare (≤1% in the dataset) CNVs between cases and controls. A total of 986 such CNVs were observed in our dataset of 432 subjects. Overall global burden analyses did not reveal significant differences between cases and controls in CNV rate, distribution of deletions or duplications or number of genes affected by CNVs. Overall deletions (total CNV size and ≥2× frequency) were found 1.4 times more often in cases than in controls (P = 0.019). The large CNVs (≥500 kb) were also significantly associated with PD (P = 0.046, 1.24-fold higher in cases than in controls). Global burden was elevated for rare CNV regions. Specifically, for OVOS2 on Chr12p11.21, CNVs were observed only in PD cases (n = 7) but not in controls (P = 0.028) and this was experimentally validated. A total of 81 PD cases carried a rare genic CNV that was absent in controls. Ingenuity pathway analysis (IPA) identified ATXN3, FBXW7, CHCHD3, HSF1, KLC1, and MBD3 in the same disease pathway with known PD genes.

Systematic review and UK-based study of PARK2 (parkin), PINK1, PARK7 (DJ-1) and LRRK2 in early-onset Parkinson's disease

Approximately 3.6% of patients with Parkinson's disease develop symptoms before age 45. Early-onset Parkinson's disease (EOPD) patients have a higher familial recurrence risk than late-onset patients, and 3 main recessive EOPD genes have been described. We aimed to establish the prevalence of mutations in these genes in a UK cohort and in previous studies. We screened 136 EOPD probands from a high-ascertainment regional and community-based prevalence study for pathogenic mutations in PARK2 (parkin), PINK1, PARK7 (DJ-1), and exon 41 of LRRK2. We also carried out a systematic review, calculating the proportion of cases with pathogenic mutations in previously reported studies. We identified 5 patients with pathogenic PARK2, 1 patient with PINK1, and 1 with LRRK2 mutations. The rate of mutations overall was 5.1%. Mutations were more common in patients with age at onset (AAO) < 40 (9.5%), an affected first-degree relative (6.9%), an affected sibling (28.6%), or parental consanguinity (50%). In our study EOPD mutation carriers were more likely to present with rigidity and dystonia, and 6 of 7 mutation carriers had lower limb symptoms at onset. Our systematic review included information from >5800 unique cases. Overall, the weighted mean proportion of cases with PARK2 (parkin), PINK1, and PARK7 (DJ-1) mutations was 8.6%, 3.7%, and 0.4%, respectively. PINK1 mutations were more common in Asian subjects. The overall frequency of mutations in known EOPD genes was lower than previously estimated. Our study shows an increased likelihood of mutations in patients with lower AAO, family history, or parental consanguinity.

Age-specific Parkinson disease risk in GBA mutation carriers: information for genetic counseling

PURPOSE

We sought to estimate age-specific risk of Parkinson disease in relatives of patients with Gaucher disease, who are obligate carriers of GBA mutations and who were not ascertained by family history of Parkinson disease.

METHODS

A validated family history of Parkinson disease questionnaire was administered to 119 patients with Gaucher disease who were evaluated at the Mount Sinai School of Medicine from 2009 to 2012; the ages of their parents, siblings, and children, history of Parkinson disease, age at onset of Parkinson disease, and ethnic background were obtained. Kaplan-Meier survival curves were used to estimate age-specific Parkinson disease penetrance among parents of patients with Gaucher disease, who are obligatory GBA mutation carriers.

RESULTS

Two participants with Gaucher disease were affected by Parkinson disease (5.4% of those who were 60 years or older). Of the 224 informative parents of patients with Gaucher disease, 11 had Parkinson disease (4.9%). Among the parents (obligatory carriers), cumulative risk of Parkinson disease by ages 65 and 85 was estimated to be 2.2% ±2.1% and 10.9% ±7.2%, respectively.

CONCLUSION

We provide useful age-specific estimates of Parkinson disease penetrance in patients with Gaucher disease and GBA heterozygous carriers for genetic counseling. Although GBA mutations may increase the risk for PD, the vast majority of patients with Gaucher disease and heterozygotes may not develop the disease. Further studies are needed to identify what modifies the risk of Parkinson disease in GBA mutation carriers.

Gene-environment interactions in Parkinson's disease: specific evidence in humans and mammalian models

Interactions between genetic factors and environmental exposures are thought to be major contributors to the etiology of Parkinson's disease. While such interactions are poorly defined and incompletely understood, recent epidemiological studies have identified specific interactions of potential importance to human PD. In this review, the most current data on gene-environment interactions in PD from human studies are critically discussed. Animal models have also highlighted the importance of genetic susceptibility to toxicant exposure and data of potential relevance to human PD are discussed. Goals and needs for the future of the field are proposed.

Cooperative genome-wide analysis shows increased homozygosity in early onset Parkinson's disease

Parkinson's disease (PD) occurs in both familial and sporadic forms, and both monogenic and complex genetic factors have been identified. Early onset PD (EOPD) is particularly associated with autosomal recessive (AR) mutations, and three genes, PARK2, PARK7 and PINK1, have been found to carry mutations leading to AR disease. Since mutations in these genes account for less than 10% of EOPD patients, we hypothesized that further recessive genetic factors are involved in this disorder, which may appear in extended runs of homozygosity.

We carried out genome wide SNP genotyping to look for extended runs of homozygosity (ROHs) in 1,445 EOPD cases and 6,987 controls. Logistic regression analyses showed an increased level of genomic homozygosity in EOPD cases compared to controls. These differences are larger for ROH of 9 Mb and above, where there is a more than three-fold increase in the proportion of cases carrying a ROH. These differences are not explained by occult recessive mutations at existing loci. Controlling for genome wide homozygosity in logistic regression analyses increased the differences between cases and controls, indicating that in EOPD cases ROHs do not simply relate to genome wide measures of inbreeding. Homozygosity at a locus on chromosome19p13.3 was identified as being more common in EOPD cases as compared to controls. Sequencing analysis of genes and predicted transcripts within this locus failed to identify a novel mutation causing EOPD in our cohort.

There is an increased rate of genome wide homozygosity in EOPD, as measured by an increase in ROHs. These ROHs are a signature of inbreeding and do not necessarily harbour disease-causing genetic variants. Although there might be other regions of interest apart from chromosome 19p13.3, we lack the power to detect them with this analysis.

The relation between depression and parkin genotype: the CORE-PD study

BACKGROUND

Mutations in parkin are a known genetic risk factor for early onset Parkinson's disease (EOPD) but their role in non-motor manifestations is not well established. Genetic factors for depression are similarly not well characterized. We investigate the role of parkin mutations in depression among those with EOPD and their relatives.

METHODS

We collected psychiatric information using the Patient Health Questionnaire and Beck Depression Inventory II on 328 genotyped individuals including 88 probands with early onset PD (41 with parkin mutations, 47 without) and 240 first and second-degree relatives without PD.

RESULTS

Genotype was not associated with depression risk among probands. Among unaffected relatives of EOPD cases, only compound heterozygotes (n = 4), and not heterozygotes, had significantly increased risk of depressed mood (OR = 14.1; 95% CI 1.2-163.4), moderate to severe depression (OR = 17.8; 95% CI 1.0-332.0), depression (score ≥ 15) on the Beck Depression Inventory II (BDI-II) (OR = 51.9; 95% CI 4.1-657.4), and BDI-II total depression score (β = 8.4; 95% CI 2.4-11.3) compared to those without parkin mutations.

CONCLUSIONS

Relatives of EOPD cases with compound heterozygous mutations and without diagnosed PD may have a higher risk of depression compared to relatives without parkin mutations. These findings support evidence of a genetic contribution to depression and may extend the phenotypic spectrum of parkin mutations to include non-motor manifestations that precede the development of PD.

Genome-wide association study identifies candidate genes for Parkinson's disease in an Ashkenazi Jewish population

Background

To date, nine Parkinson disease (PD) genome-wide association studies in North American, European and Asian populations have been published. The majority of studies have confirmed the association of the previously identified genetic risk factors, SNCA and MAPT, and two studies have identified three new PD susceptibility loci/genes (PARK16, BST1 and HLA-DRB5). In a recent meta-analysis of datasets from five of the published PD GWAS an additional 6 novel candidate genes (SYT11, ACMSD, STK39, MCCC1/LAMP3, GAK and CCDC62/HIP1R) were identified. Collectively the associations identified in these GWAS account for only a small proportion of the estimated total heritability of PD suggesting that an 'unknown' component of the genetic architecture of PD remains to be identified.

Methods

We applied a GWAS approach to a relatively homogeneous Ashkenazi Jewish (AJ) population from New York to search for both 'rare' and 'common' genetic variants that confer risk of PD by examining any SNPs with allele frequencies exceeding 2%. We have focused on a genetic isolate, the AJ population, as a discovery dataset since this cohort has a higher sharing of genetic background and historically experienced a significant bottleneck. We also conducted a replication study using two publicly available datasets from dbGaP. The joint analysis dataset had a combined sample size of 2,050 cases and 1,836 controls.

Results

We identified the top 57 SNPs showing the strongest evidence of association in the AJ dataset (p < 9.9 × 10^-5). Six SNPs located within gene regions had positive signals in at least one other independent dbGaP dataset: LOC100505836 (Chr3p24), LOC153328/SLC25A48 (Chr5q31.1), UNC13B (9p13.3), SLCO3A1(15q26.1), WNT3(17q21.3) and NSF (17q21.3). We also replicated published associations for the gene regions SNCA (Chr4q21; rs3775442, p = 0.037), PARK16 (Chr1q32.1; rs823114 (NUCKS1), p = 6.12 × 10^-4), BST1 (Chr4p15; rs12502586, p = 0.027), STK39 (Chr2q24.3; rs3754775, p = 0.005), and LAMP3 (Chr3; rs12493050, p = 0.005) in addition to the two most common PD susceptibility genes in the AJ population LRRK2 (Chr12q12; rs34637584, p = 1.56 × 10^-4) and GBA (Chr1q21; rs2990245, p = 0.015).

Conclusions

We have demonstrated the utility of the AJ dataset in PD candidate gene and SNP discovery both by replication in dbGaP datasets with a larger sample size and by replicating association of previously identified PD susceptibility genes. Our GWAS study has identified candidate gene regions for PD that are implicated in neuronal signalling and the dopamine pathway.

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.

Parkinson's disease: genetics and pathogenesis

Recent investigation into the mechanisms of Parkinson's disease (PD) has generated remarkable insight while simultaneously challenging traditional conceptual frameworks. Although the disease remains defined clinically by its cardinal motor manifestations and pathologically by midbrain dopaminergic cell loss in association with Lewy bodies, it is now recognized that PD has substantially more widespread impact, causing a host of nonmotor symptoms and associated pathology in multiple regions throughout the nervous system. Further, the discovery and validation of PD-susceptibility genes contradict the historical view that environmental factors predominate, and blur distinctions between familial and sporadic disease. Genetic advances have also promoted the development of improved animal models, highlighted responsible molecular pathways, and revealed mechanistic overlap with other neurodegenerative disorders. In this review, we synthesize emerging lessons on PD pathogenesis from clinical, pathological, and genetic studies toward a unified concept of the disorder that may accelerate the design and testing of the next generation of PD therapies.

Genetic testing and Parkinson disease: assessment of patient knowledge, attitudes, and interest

The most common genetic contributor to late-onset Parkinson disease (PD) is the LRRK2 gene. In order to effectively integrate LRRK2 genetic testing into clinical practice, a strategy tailored to the PD population must be developed. We assessed 168 individuals with PD for baseline knowledge of genetics, perceived risk, and interest and opinions regarding genetic counseling and testing. Most participants felt that they were familiar with general genetics terms but overall knowledge levels were low, with an average score of 55%. The majority of participants thought it was likely they inherited a PD gene (72%), believed genetic testing for PD would be useful (86%), and were interested in genetic testing (59%) and genetic counseling (56%). However, only a few participants had heard of any genetic tests for PD (29%) or LRRK2 (10%). There appears to be a significant level of interest in genetics and genetic testing within the PD population, but a considerable deficit in genetics knowledge and an over-estimation of risk. Genetic education and counseling tools to address these needs were developed to provide patients with the ability to make informed and knowledgeable genetic testing decisions.

Familial aggregation of panic disturbances in Parkinson's disease

Panic disorder has an elevated prevalence in Parkinson's disease (PD). To explore the basis for this co-occurrence, the familial aggregation of panic disorder was examined in patients with PD. Probands and relatives of patients with PD and panic disorder (PD-PANIC; N=20, N=115) and control probands with PD and no active psychiatric illness (PD-NA; N=17, N=108) were interviewed by phone, using a structured interview to determine panic status. Lifetime prevalence of panic and "panic-like" disorders was higher in PD-PANIC than in PD-NA relatives. Panic and "panic-like" disorders are familial disorders in PD.

Neuropsychological Profile of Parkin Mutation Carriers with and without Parkinson Disease: The CORE-PD Study

The cognitive profile of early onset Parkinson's disease (EOPD) has not been clearly defined. Mutations in the parkin gene are the most common genetic risk factor for EOPD and may offer information about the neuropsychological pattern of performance in both symptomatic and asymptomatic mutation carriers. EOPD probands and their first-degree relatives who did not have Parkinson's disease (PD) were genotyped for mutations in the parkin gene and administered a comprehensive neuropsychological battery. Performance was compared between EOPD probands with (N = 43) and without (N = 52) parkin mutations. The same neuropsychological battery was administered to 217 first-degree relatives to assess neuropsychological function in individuals who carry parkin mutations but do not have PD. No significant differences in neuropsychological test performance were found between parkin carrier and noncarrier probands. Performance also did not differ between EOPD noncarriers and carrier subgroups (i.e., heterozygotes, compound heterozygotes/homozygotes). Similarly, no differences were found among unaffected family members across genotypes. Mean neuropsychological test performance was within normal range in all probands and relatives. Carriers of parkin mutations, whether or not they have PD, do not perform differently on neuropsychological measures as compared to noncarriers. The cognitive functioning of parkin carriers over time warrants further study.

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.

Predictors of parkin mutations in early-onset Parkinson disease: the consortium on risk for early-onset Parkinson disease study

BACKGROUND

Mutations in the parkin gene are the most common genetic cause of early-onset Parkinson disease (PD). Results from a multicenter study of patients with PD systematically sampled by age at onset have not been reported to date.

OBJECTIVE

To determine risk factors associated with carrying parkin mutations.

DESIGN

Cross-sectional observational study.

SETTING

Thirteen movement disorders centers.

PARTICIPANTS

A total of 956 patients with early-onset PD, defined as age at onset younger than 51 years.

MAIN OUTCOME MEASURES

Presence of heterozygous, homozygous, or compound heterozygous parkin mutations.

RESULTS

Using a previously validated interview, 14.7% of patients reported a family history of PD in a first-degree relative. Sixty-four patients (6.7%) had parkin mutations (3.9% heterozygous, 0.6% homozygous, and 2.2% compound heterozygous). Copy number variation was present in 52.3% of mutation carriers (31.6% of heterozygous, 83.3% of homozygous, and 81.0% of compound heterozygous). Deletions in exons 3 and 4 and 255delA were common among Hispanics (specifically Puerto Ricans). Younger age at onset (<40 years) (odds ratio [OR], 5.0; 95% confidence interval [CI], 2.8-8.8; P = .001), Hispanic race/ethnicity (OR compared with white non-Hispanic race/ethnicity, 2.7; 95% CI, 1.3-5.7; P = .009), and family history of PD in a first-degree relative (OR compared with noncarriers, 2.8; 95% CI, 1.5-5.3; P = .002) were associated with carrying any parkin mutation (heterozygous, homozygous, or compound heterozygous). Hispanic race/ethnicity was associated with carrying a heterozygous mutation (OR compared with white non-Hispanic race/ethnicity, 2.8; 95% CI, 1.1-7.2; P = .03) after adjustment for covariates.

CONCLUSIONS

Age at onset, Hispanic race/ethnicity, and family history of PD are associated with carrying any parkin mutation (heterozygous, homozygous, or compound heterozygous) and heterozygous mutations alone. The increased odds of carrying a parkin mutation among Hispanics warrants further study.

The heritability of risk and age at onset of Parkinson's disease after accounting for known genetic risk factors

We questioned whether the evidence for the genetic component in Parkinson's disease (PD) in Caucasians could be explained by the causative and susceptibility genes that have already been identified. We estimated heritability of risk and age at onset of PD in a well-characterized sample of 504 nuclear families (2828 individuals). After excluding families with known pathogenic mutations and accounting for the major susceptibility genes, the heritability of risk of developing PD was 0.41 (P=0.01). These data suggest that approximately 40% of the variation in susceptibility to PD is due to as-yet unidentified genes, the remainder is likely environmental.

Motor phenotype of LRRK2 G2019S carriers in early-onset Parkinson disease

OBJECTIVE

To determine the motor phenotype of LRRK2 G2019S mutation carriers. LRRK2 mutation carriers were previously reported to manifest the tremor dominant motor phenotype, which has been associated with slower motor progression and less cognitive impairment compared with the postural instability and gait difficulty (PIGD) phenotype.

DESIGN

Cross-sectional observational study.

SETTING

Thirteen movement disorders centers.

PARTICIPANTS

Nine hundred twenty-five early-onset Parkinson disease cases defined as age at onset younger than 51 years.

MAIN OUTCOME MEASURES

LRRK2 mutation status and Parkinson disease motor phenotype: tremor dominant or PIGD. Demographic information, family history of Parkinson disease, and the Unified Parkinson's Disease Rating Scale score were collected on all participants. DNA samples were genotyped for LRRK2 mutations (G2019S, I2020T, R1441C, and Y1699C). Logistic regression was used to examine associations of G2019S mutation status with motor phenotype adjusting for disease duration, Ashkenazi Jewish ancestry, levodopa dose, and family history of Parkinson disease.

RESULTS

Thirty-four cases (3.7%) (14 previously reported) were G2019S carriers. No other mutations were found. Carriers were more likely to be Ashkenazi Jewish (55.9% vs 11.9%; P < .001) but did not significantly differ in any other demographic or disease characteristics. Carriers had a lower tremor score (P = .03) and were more likely to have a PIGD phenotype (92.3% vs 58.9%; P = .003). The association of the G2019S mutation with PIGD phenotype remained after controlling for disease duration and Ashkenazi Jewish ancestry (odds ratio, 17.7; P < .001).

CONCLUSION

Early-onset Parkinson disease G2019S LRRK2 carriers are more likely to manifest the PIGD phenotype, which may have implications for disease course.

MDPD: an integrated genetic information resource for Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder affecting millions of people. Both environmental and genetic factors play important roles in its causation and development. Genetic analysis has shown that over 100 genes are correlated with the etiology and pathology of PD. However, accessing genetic information in a consistent and fruitful way is not an easy task. The Mutation Database for Parkinson's Disease (MDPD) is designed to fulfill the need for information integration so that users can easily retrieve, inspect and enhance their knowledge on PD. The database contains 2391 entries on 202 genes extracted from 576 publications and manually examined by biomedical researchers. Each genetic substitution and the resulting impact are clearly labelled and linked to its primary reference. Every reported gene has a summary page that provides information on the variation impact, mutation type, the studied population, mutation position and reference collection. In addition, MDPD provides a unique functionality for users to compare the differences on the type of mutations among ethnic groups. As such, we hope that MDPD will serve as a valuable tool to bridge the gap between genetic analysis and clinical practice. MDPD is publicly accessible at http://datam.i2r.a-star.edu.sg/mdpd/.

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.

Risk of Parkinson disease in carriers of parkin mutations: estimation using the kin-cohort method

OBJECTIVE

To estimate the risk of Parkinson disease (PD) in individuals with mutations in the Parkin gene.

DESIGN

We assessed point mutations and exon deletions and duplications in the Parkin gene in 247 probands with PD (age at onset < or =50 years) and 104 control probands enrolled in the Genetic Epidemiology of Parkinson's Disease (GEPD) study. For each first-degree relative, a consensus diagnosis of PD was established. The probability that each relative carried a mutation was estimated from the proband's Parkin carrier status using Mendelian principles and from the relationship of the relative to the proband.

SETTING

Tertiary care movement disorders center. Patients Cases, controls, and their first-degree relatives were enrolled in the GEPD study.

MAIN OUTCOME MEASURES

Estimated age-specific penetrance in first-degree relatives.

RESULTS

Parkin mutations were identified in 25 probands with PD (10.1%), 18 (72.0%) of whom were heterozygotes. One Parkin homozygote was reported in 2 siblings with PD. The cumulative incidence of PD to age 65 years in carrier relatives (age-specific penetrance) was estimated to be 7.0% (95% confidence interval, 0.4%-71.9%), compared with 1.7% (95% confidence interval, 0.8%-3.4%) in noncarrier relatives of the cases (P = .59) and 1.1% (95% confidence interval, 0.3%-3.4%) in relatives of the controls (compared with noncarrier relatives, P = .52).

CONCLUSIONS

The cumulative risk of PD to age 65 years in a noncarrier relative of a case with an age at onset of 50 years or younger is not significantly greater than the general population risk among controls. Age-specific penetrance among Parkin carriers, in particular heterozygotes, deserves further study.

Mutations in the glucocerebrosidase gene are associated with early-onset Parkinson disease

OBJECTIVE

To evaluate the frequency of glucocerebrosidase (GBA) mutations in cases and controls enrolled in the Genetic Epidemiology of Parkinson's Disease (GEPD) study.

METHODS

We sequenced all exons of the GBA gene in 278 Parkinson disease (PD) cases and 179 controls enrolled in GEPD, with a wide range of age at onset (AAO), and that included a subset of 178 Jewish cases and 85 Jewish controls. Cases and controls were recruited without knowledge of family history of PD, and cases were oversampled in the AAO < 50 years category.

RESULTS

13.7% of PD cases (38/278) carried GBA mutations, compared with 4.5% of controls (8/179) (odds ratio [OR] 3.4, 95% CI 1.5 to 7.4). The frequency of GBA mutations was 22.2% in 90 cases with AAO < or = 50 years, compared with 9.7% in 185 cases with AAO > 50 years (OR 2.7, 95% CI 1.3 to 5.3). Adjusting for age at the time of evaluation, sex, family history of PD, and Jewish ancestry, GBA carriers had a 1.7-year-earlier AAO of PD (95% CI 0.5 to 3.3, p < 0.04) than noncarriers. The average AAO of PD was 2.5 years earlier in carriers with an AAO < or = 50 years compared with noncarriers (95% CI 0.6 to 4.5, p < 0.01) and this was not seen in the AAO > 50 years group. The frequency of GBA mutations was higher in a subset of 178 cases that reported four Jewish grandparents (16.9%) than in cases who did not report Jewish ancestry (8.0%) (p < 0.01). Nine different GBA mutations were identified in PD cases, including 84insGG, E326K, T369M, N370S, D409H, R496H, L444P, RecNciI, and a novel mutation, P175P.

CONCLUSIONS

This study suggests that the Glucocerebrosidase gene may be a susceptibility gene for Parkinson disease and that Glucocerebrosidase mutations may modify age at onset.

Evidence of shared risk for Alzheimer's disease and Parkinson's disease using family history

This case-control study examined the potential for a common etiology of Parkinson's disease (PD) and Alzheimer's disease (AD) using reported family history. Structured interviews were used to collect AD and PD family history from subjects (n = 1,531) with AD, PD, AD/PD, or controls. Intergroup analysis compared reported AD and PD family histories in the three case groups to the histories reported in the control group. Intragroup analysis stratified each diagnostic group based on positive family history of AD, then compared the subgroups for a family history of PD. Subjects with AD had a higher risk of having a family history of AD [odds ratio (OR) 2.3; 1.5-3.4] and subjects with PD had a higher risk of having a family history of PD (OR 2.2; 1.2-4.0) as compared to control subjects. Intergroup analyses revealed no significant crossed risk, increased risk of subjects with AD having a family history of PD vs controls and vice versa. Intragroup analysis found that subjects with PD and a family history of AD were more likely to have a family history of PD (OR 1.7; 1.1-2.6) when compared to subjects with PD and no family history of AD. A similar trend was found for subjects with AD (OR 1.7; 0.9-3.1). AD and PD cases each have an increased familial risk of their respective disease. Probands with AD or PD and a family history of either disease have a higher crossed risk of a family history of the other disease. These findings suggest the existence of common genetic and/or environmental factors that predispose to both AD and PD in the subset of cases with positive family history of both neurodegenerative diseases.

Construction and validation of a Parkinson's disease mutation genotyping array for the Parkin gene

Parkin mutations account for the majority of familial and sporadic early onset Parkinson's disease (EOPD) cases with a known genetic association. More than 100 mutations have been described in the Parkin gene that includes homozygous, compound heterozygous, and single heterozygous mutations. We have designed a Parkin mutation genotyping array (gene chip) that includes published Parkin sequence variants and allows their simultaneous detection. The chip was validated by screening 85 PD cases and 47 controls previously tested for Parkin mutations. Similar genotyping microarrays have been developed for other genetically heterogeneous diseases including age-related macular degeneration. Here, we show the utility of a genotyping array for Parkinson's disease by analysis of 60 subjects from the Genetic Epidemiology of Parkinson Disease (GEPD) study that includes 15 early-onset PD case probands and 45 relatives.

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.