Vera Tadic

Association of LRRK2 exonic variants with susceptibility to Parkinson's disease: A case-control study

BACKGROUND Background The leucine-rich repeat kinase 2 gene (LRRK2) harbours highly penetrant mutations that are linked to familial parkinsonism. However, the extent of its polymorphic variability in relation to risk of Parkinsons disease (PD) has not been assessed systematically. We therefore assessed the frequency of LRRK2 exonic variants in individuals with and without PD, to investigate the role of the variants in PD susceptibility. METHODS LRRK2 was genotyped in patients with PD and controls from three series (white, Asian, and Arab-Berber) from sites participating in the Genetic Epidemiology of Parkinsons Disease Consortium. Genotyping was done for exonic variants of LRRK2 that were identified through searches of literature and the personal communications of consortium members. Associations with PD were assessed by use of logistic regression models. For variants that had a minor allele frequency of 0·5% or greater, single variant associations were assessed, whereas for rarer variants information was collapsed across variants. FINDINGS 121 exonic LRRK2 variants were assessed in 15 540 individuals: 6995 white patients with PD and 5595 controls, 1376 Asian patients and 962 controls, and 240 Arab-Berber patients and 372 controls. After exclusion of carriers of known pathogenic mutations, new independent risk associations were identified for polymorphic variants in white individuals (M1646T, odds ratio 1·43, 95% CI 1·15-1·78; p=0·0012) and Asian individuals (A419V, 2·27, 1·35-3·83; p=0·0011). A protective haplotype (N551K-R1398H-K1423K) was noted at a frequency greater than 5% in the white and Asian series, with a similar finding in the Arab-Berber series (combined odds ratio 0·82, 0·72-0·94; p=0·0043). Of the two previously reported Asian risk variants, G2385R was associated with disease (1·73, 1·20-2·49; p=0·0026), but no association was noted for R1628P (0·62, 0·36-1·07; p=0·087). In the Arab-Berber series, Y2189C showed potential evidence of risk association with PD (4·48, 1·33-15·09; p=0·012). INTERPRETATION The results for LRRK2 show that several rare and common genetic variants in the same gene can have independent effects on disease risk. LRRK2, and the pathway in which it functions, is important in the cause and pathogenesis of PD in a greater proportion of patients with this disease than previously believed. These results will help discriminate those patients who will benefit most from therapies targeted at LRRK2 pathogenic activity. FUNDING Michael J Fox Foundation and National Institutes of Health.

ATP13A2 variants in early-onset Parkinson's disease patients and controls.

Four genes responsible for recessively inherited forms of Parkinsons disease (PD) have been identified, including the recently discovered ATP13A2 (PARK9) gene. Our objective was to investigate the role of this gene in a large cohort of PD patients and controls. We extensively screened all 29 exons of the ATP13A2 coding region in 112 patients with early‐onset PD (EOPD; <40 years) of mostly European ethnic origin and of 55 controls. We identified four carriers (3.6%) of novel single heterozygous ATP13A2 missense changes that were absent in controls. Interestingly, the carrier of one of these variants also harbored two mutations in the Parkin gene. None of the carriers had atypical features previously described in patients with two mutated ATP13A2 alleles (Kufor–Rakeb syndrome). Our data suggest that two mutated ATP13A2 alleles are not a common cause of PD. Although heterozygous variants are present in a considerable number of patients, they are—based on this relatively small sample—not significantly more frequent in patients compared to controls.

Impaired sense of smell and color discrimination in monogenic and idiopathic Parkinson's disease†

Olfaction is typically impaired in idiopathic Parkinsons disease (IPD), but its role is uncertain in monogenic PD. Diminished color discrimination has been suggested as another early sign of dopaminergic dysfunction but not been systematically studied. Furthermore, it is unknown whether both deficits are linked. We examined 100 patients with IPD, 27 manifesting mutation carriers (MC), 20 nonmanifesting mutation carriers (NMC), and 110 controls. Participants underwent a standardized neurological examination, the University of Pennsylvania Smell Identification Test (UPSIT), the Farnsworth‐Munsell (FM) color discrimination test, and mutation testing in known PD genes. The monogenic group consisted of 15 Parkin (6MC/9NMC), 17 PINK1 (10MC/7NMC), 8 LRRK2 (4MC/4NMC), 3 SNCA (MC), and 4 ATP13A2 (MC) carriers. Olfaction was most impaired in IPD (UPSIT percentiles 10.1 ± 13.5) compared with all other groups (MC 13.8 ± 11.9, NMC 19.6 ± 13.0, controls 33.8 ± 22.4). Within MC, carriers of two mutations in Parkin and PINK1 showed higher UPSIT percentiles than LRRK2 and SNCA carriers. Color discrimination was reduced in IPD (FM total error score 134.8 ± 92.7). In MC (122.4 ± 142.4), the reduction was most pronounced in LRRK2, NMC (80.0 ± 38.8) were comparable with controls (97.2 ± 61.1). UPSIT and FM scores were correlated in the control (r = −0.305; P = 0.002) and the IPD group (r = −0.303; P = 0.006) but not among mutation carriers. First, we confirmed olfaction and color discrimination to be impaired in IPD and suggest olfaction to be a premotor sign. Second, olfaction differed between carriers with one and two mutations in Parkin/PINK1‐associated PD. Third, olfaction and color discrimination impairment do not necessarily evolve in parallel.

Structural imaging in the presymptomatic stage of genetically determined parkinsonism.

Several genes associated with monogenic forms of Parkinsons disease (PD) have been discovered, opening up new avenues for the investigation of presymptomatic stages of PD. Using voxel-based morphometry in 30 asymptomatic mutation carriers (MC) with mutations in four different genes for PD and 100 healthy controls, we identified an increase in gray matter volume (GMV) in the striatum in asymptomatic Parkin, PINK1, ATP13A2 and, to a much lesser extent, in LRRK2 MC. Moreover, an increase in GMV was found in the parieto-temporo-occipital association cortex in asymptomatic Parkin and ATP13A2 MC. The observed striatal GMV increase might be the common structural correlate of compensatory mechanisms due to the latent dopaminergic deficit, reflecting the different, but probably interrelated pathogenic pathways resulting in nigral cell death. Asymptomatic PINK1 and LRRK2 MC also revealed smaller GMV in the hippocampal region, which might play a role in the observed psychiatric disorders.

Nonmotor Symptoms in Parkin Gene-Related Parkinsonism

The aim of the study was to explore the prevalence and differences of nonmotor symptoms (NMSs) in patients with young‐onset Parkinsons disease (YOPD) with and without mutations in the Parkin gene and late‐onset Parkinsons disease (LOPD). Twenty‐seven patients with YOPD and 27 with LOPD, as well as 16 patients with homozygous or compound heterozygote Parkin mutations filled in the nonmotor symptoms questionnaire, a 30‐item self‐completed questionnaire that addresses various NMSs. Overall, NMSs were more prevalent in YOPD (12.07 ± 3.9; P = 0.009) and LOPD (13.26 ± 5.8; P = 0.001) compared with Parkin mutation carriers (7.38 ± 4.2). Dribbling of saliva, vivid dreams, loss of smell, and urinary urgency were more prevalent in YOPD compared with Parkin mutation carriers. Only anxiety was more prevalent in the latter. Apart from anxiety, NMSs appear to be less prevalent in Parkin gene‐related parkinsonism. Although these results need further study, the presented data might be helpful in the clinical recognition of specific phenotypes and genotypes in YOPD. The data are in keeping with a different pathological disease process in Parkin gene‐related parkinsonism.

Primary Familial Brain Calcification With Known Gene Mutations: A Systematic Review and Challenges of Phenotypic Characterization

IMPORTANCE In the past 2 years, 3 genes (SLC20A2, PDGFRB, and PDGFB) were identified as causative of primary familial brain calcification (PFBC), enabling genotype-specific phenotyping. OBJECTIVES To provide a systematic literature review on the neuroimaging and clinical phenotype of genetically confirmed PFBC and summarize known pathophysiological mechanisms, to improve and harmonize future phenotype description and reporting by addressing data gaps, and to develop uniform definitions for clinical characterization. EVIDENCE REVIEW We systematically searched the MEDLINE database among articles published from January 1, 2012, through May 31, 2014, for the 3 genes and selected 25 articles from all records (n=75) and from sources cited in the reference lists. Only genetically confirmed cases with individual clinical information were included, leaving 15 reports. Predefined categories for data extraction were different neurologic and psychiatric symptoms, imaging results, and age at onset (AAO). We also assessed availability of information to estimate possible bias. FINDINGS We included a total of 179 cases, 162 of which belong to 25 families. Availability of information ranged from 96.6% for ethnicity to 24.4% for AAO. All cases had calcifications on comprehensive cranial computed tomography, most frequently located in the basal ganglia (70.6%), subcortical white matter (40.8%), cerebellum (34.1%), or thalamus (28.5%). Mean (SD) AAO was 27.9 (22.3) years, and the AAO was comparable across genes (P=.77). The most frequently described signs were movement disorders, such as parkinsonism (12%) and dystonia (19%). Penetrance of the imaging phenotype was 100% compared with only 61% of the clinical phenotype. We propose a novel definition of disease status by specifying PFBC into genetic, clinical, and imaging phenotypes. Pathophysiological pathways converge on impaired phosphorus homeostasis and integrity of the blood-brain barrier. CONCLUSIONS AND RELEVANCE Especially in rare conditions, meta-analyses are the most suitable tool to extract reliable information on the natural course of a disease. For future analyses, we provide a minimal data set that can be used for systematic clinical and imaging data collection in PFBC and that will also improve informed counseling of patients.

Clinical neuroimaging and electrophysiological assessment of three DYT6 dystonia families.

The purpose of the study was to delineate clinical and electrophysiological characteristics as well as laryngoscopical and transcranial ultrasound (TCS) findings in THAP1 mutation carriers (MutC). According to recent genetic studies, DYT6 (THAP1) gene mutations are an important cause of primary early‐onset dystonia. In contrast to DYT1 mutations, THAP1 mutations are associated with primary early‐onset segmental or generalised dystonia frequently involving the craniocervical region and the larynx. Blood samples from twelve individuals of three German families with DYT6 positive index cases were obtained to test for THAP1 mutations. Eight THAP1 MutC were identified. Of these, six (three symptomatic and three asymptomatic) THAP1 MutC could be clinically evaluated. Laryngoscopy was performed to evaluate laryngeal dysfunction in patients. Brainstem echogenicity was investigated in all MutC using TCS. Two of the patients had undergone bilateral pallidal DBS. In all three symptomatic MutC, early‐onset laryngeal dystonia was a prominent feature. Laryngeal assessment demonstrated adductor‐type dystonia in all of them. On clinical examination, the three asymptomatic MutC also showed subtle signs of focal or segmental dystonia. TCS revealed increased substantia nigra (SN) hyperechogenicity in all MutC. Intraoperative microelectrode recordings under general anesthesia in two of the patients showed no difference between THAP1 and previously operated DYT1 MutC. The presence of spasmodic dysphonia in patients with young‐onset segmental or generalised dystonia is a hallmark of DYT6 dystonia. SN hyperechogenicity on TCS may represent an endophenotype in these patients. Pallidal DBS in two patients was unsatisfactory.

Depression and Quality of Life in Monogenic Compared to Idiopathic, Early-Onset Parkinson's Disease

Quality of life (QoL) is decreased in PD and is linked with depression and anxiety. However, little is known about QoL in monogenic PD. Subjects with mutations in PD genes were recruited from ongoing family and genetic studies (manifesting carriers, n = 23; nonmanifesting carriers, n = 19). For comparison purposes, we included patients with idiopathic PD (IPD; n = 128; early onset, n = 38; late onset, n = 90), healthy controls (n = 127), and data on depressive symptoms of 144 patients with major depression (treated controls). Depression affected 31% of early‐onset PD cases, 21% of late‐onset cases, and 44% of manifesting carriers of mutations in PD genes, but was rare in the nonmanifesting carriers (7%) and healthy controls (5%). Subjects with Parkinson‐associated depression reported fewer feelings of guilt or self‐doubt than treated controls, but the occurrence of suicidal ideation was associated with severity of depression only. Social phobia (P = 0.018) and agoraphobia (P = 0.059) were more common in manifesting carriers than in any other group. QoL was decreased in the Parkinson groups, particularly in the early‐onset cases (P < 0.001), and QoL correlated with depression in all analyses. In our study, monogenic and IPD cases were comparable in QoL and depression characteristics. The QoL and, possibly, overall prognosis of all PD patients can be improved by appropriate attention and treatment for depression, sleep impairments, and anxiety, even if the treatment of the motor problems cannot be further optimized.

The protective effect of LRRK2 p.R1398H on risk of Parkinson’s disease is independent of MAPT and SNCA variants

The best validated susceptibility variants for Parkinsons disease are located in the α-synuclein (SNCA) and microtubule-associated protein tau (MAPT) genes. Recently, a protective p.N551K-R1398H-K1423K haplotype in the leucine-rich repeat kinase 2 (LRRK2) gene was identified, with p.R1398H appearing to be the most likely functional variant. To date, the consistency of the protective effect of LRRK2 p.R1398H across MAPT and SNCA variant genotypes has not been assessed. To address this, we examined 4 SNCA variants (rs181489, rs356219, rs11931074, and rs2583988), the MAPT H1-haplotype-defining variant rs1052553, and LRRK2 p.R1398H (rs7133914) in Caucasian (n = 10,322) and Asian (n = 2289) series. There was no evidence of an interaction of LRRK2 p.R1398H with MAPT or SNCA variants (all p ≥ 0.10); the protective effect of p.R1398H was observed at similar magnitude across MAPT and SNCA genotypes, and the risk effects of MAPT and SNCA variants were observed consistently for LRRK2 p.R1398H genotypes. Our results indicate that the association of LRRK2 p.R1398H with Parkinsons disease is independent of SNCA and MAPT variants, and vice versa, in Caucasian and Asian populations.

Does Uncoupling Protein 2 Expression Qualify as Marker of Disease Status in LRRK2-Associated Parkinson's Disease?

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common known genetic cause of late-onset Parkinsons disease (PD). However, the penetrance of the disease is below 50% at 60 years of age. LRRK2 is associated with the mitochondrial membrane, and mutant forms impair the function of the organelle and autophagosome clearance in human cells, including induced pluripotent stem cell-derived neurons. Elevated expression of uncoupling proteins has been identified as the cause of mitochondrial depolarization in human fibroblasts with G2019S LRRK2. To identify factors that contribute to the penetrance of LRRK2 mutations, we studied respiratory chain function, markers of mitochondrial uncoupling, oxidative stress, and autophagy in fibroblasts from affected and unaffected carriers of the G2019S mutation. Independent of disease status, all mutation carriers showed reduced mitochondrial membrane potential, increased proton leakage, and more fragmented mitochondria. However, a significant increase in the expression of uncoupling protein 2 (UCP2) was only detected in affected individuals with the G2019S mutation in LRRK2. Since oxidative stress and autophagic markers were selectively increased in some of the PD patients, we hypothesize that UCP2 expression is upregulated in response to elevated reactive oxygen species generation in affected mutation carriers and that UCP2 mRNA levels might, therefore, serve as markers of disease status in LRRK2-associated PD.