Evidence of mitochondrial alterations in primary cardiac stromal cells from arrhythmogenic cardiomyopathy hearts

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): This research was funded by the Department of Innovation, Research and University of the Autonomous Province of Bolzano-South Tyrol (Italy), and by the Joint Project Südtirol- FWF (Italy-Austria) for A.R., J.T., A.M., R.P..

Background

Arrhythmogenic cardiomyopathy (ACM) is a genetic disease associated with sudden cardiac death and fibro-fatty replacement of myocardium. Recently, it has been demonstrated that oxidized lipid contributes to cardiac adipogenesis and that ACM hearts are characterized by an increase in oxidative stress.

Purpose

As mitochondria are an important source of reactive oxygen species (ROS) within mammalian cells, the present work aims to evaluate if increased oxidative stress observed in ACM hearts is associated with altered mitochondrial function.

Methods

The oxidative stress marker 4HNE was investigated together with the cardiomyocyte marker cardiac Troponin T on paraffin embedded human ventricular samples and analyzed by confocal microscopy.

Human primary cardiac stromal cells (CStCs), obtained from either right ventricle biopsies of ACM patients or healthy cadaveric tissue donor (CTR), were used as cellular model as they are known for their contribution to adipogenesis in the ACM pathology. CStCs were cultured either in basal medium or adipogenic medium (ADIPO) in presence or absence of 500 nM of the ROS scavenger MitoTEMPO.

After 7 days of adipogenic differentiation, intracellular lipid droplets accumulation and mitochondrial superoxide levels were measured in CStCs by confocal microscopy using BODIPY 493/503 (0.5 µM) and MitoSOX Red (5 µM) dyes, respectively.

The oxidative phosphorylation (OXPHOS) and fatty acid oxidation (FAO) were also evaluated in CStCs by high resolution respirometry.

Results

4HNE staining was increased in heart tissues from ACM patients compared to CTRs and particularly evident in non-cardiomyocyte cells. In agreement, a higher MitoSOX fluorescence intensity was found in ACM-CStCs compared to CTR-CStCs in ADIPO medium, confirming higher ROS presence in patient cells. The treatment with MitoTEMPO was efficient in reducing ROS abundance, strongly suggesting mitochondrial origin. Lipid accumulation in ACM-CStCs was also prevented by MitoTEMPO treatment.

Preliminary evidence further indicates that mitochondrial respiratory capacity is increased in ACM-CStCs versus CTR-CStCs exposed to adipogenic medium for 7 days. However, transmission electron microscopy analysis and Western blot analysis of Mfn1/2, Opa1, Fis1 and Drp1 did not show an evident alteration neither in mitochondria ultrastructure nor in the expression of proteins regulating mitochondrial dynamics.

Conclusions

Our data support an alteration of mitochondrial activity in CStCs from ACM patients, apparently not linked to a modified network or morphology of mitochondria but associated with a higher ROS production.

Are human induced pluripotent stem cell derived cardiomyocytes a good cellular model for studying incomplete penetrance in arrhythmogenic cardiomyopathy?

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Regional Development Fund and Interreg V-A Italy-Austria 2014-2020 and Department of Innovation, Research and University of the Autonomous Province of Bolzano-South Tyrol (Italy).

Background

Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) were previously used to model several inherited heart diseases (1). Among these, arrhythmogenic cardiomyopathy (ACM) is characterized by a fibrofatty myocardial replacement and severe ventricular arrhythmias (2). ACM is mainly caused by mutations affecting proteins of intercalated discs (3) and shows incomplete penetrance and variable expressivity (4).

Purpose

To evaluate whether hiPSC-CMs provide a good in vitro model to study incomplete penetrance in ACM.

Material and methods

hiPSCs were generated from buffy coats of 6 close relatives. Three of them were ACM patients carrying a deletion of exon 4 in the PKP2 gene causing a premature stop codon, 2 were asymptomatic (ASY) PKP2 mutation carriers and 1 was a healthy control (CTR). Whole exome sequencing of the 6 individuals was performed. The purified hiPSC-CMs were cultured in basal and adipogenic medium and examined by ddPCR, western blot, Wes™ immunoassay system, patch clamp and immunofluorescence.

Results

All family members tested negative for additional mutations in ACM genes. As expected, half the amount of wild type (wt) PKP2 mRNA was found in ACM and ASY than in CTR hiPSC-CMs (2.25±0.27vs4.29±0.70 wtPKP2/HPRT1; p=0.028) (2.08±0.38vs4.29±0.70 wtPKP2/HPRT1; p=0.052). Of note, the mutated (mut) PKP2 mRNA was detected and significantly more expressed in ACM than in ASY hiPSC-CMs (0.33±0.04vs0.11±0.06 mutPKP2/HPRT1; p=0.029). While we confirmed a reduced amount of wt plakophillin-2 protein in ACM and ASY compared to CTR hiPSC-CMs (0.19±0.07vs0.81±0.28 wtPKP2/GAPDH; p=0.016), (0.25±0.07vs0.81±0.28 wtPKP2/GAPDH; p=0.11), the truncated protein was not detected. Moreover, a significantly lower expression of the active form of β-catenin (ABC) has been shown in ACM and ASY than in CTR hiPSC-CMs (0.93±0.18vs1.30±0.09 ABC/GAPDH; p=0.057), (0.76±0.10vs1.30±0.09 ABC/GAPDH; p=0.0057). In basal medium, ACM hiPSC-CMs had a significant lower overall sodium current density compared to CTR (-49.82±2.8 vs -69.38±4.8 pA/pF; p<0.0001) and to ASY (-49.82±2.8 vs -68.92±4.3 pA/pF; p<0.0001) hiPSC-CMs. In adipogenic medium, ACM hiPSC-CMs showed a higher lipid accumulation and a higher sarcomere disorganization than CTR (1580±219vs615±199 intensity/nuclei; p=0.0351) (0.019±0.001vs0.028±0.003 myofibril alignment index; p=0.039) and ASY (1580±219vs689±146 intensity/nuclei; p=0.0059) (0.019±0.001vs0.027±0.001 myofibril alignment index; p=0.010) hiPSC-CMs.

Conclusions

Here we report that ACM express a significantly higher amount of mutated PKP2 mRNA than ASY iPSC-CMs. Even though no differences were detected for plakophilin-2 and active β-catenin proteins between ACM and ASY iPSCM-CMs, the ACM showed a fatty phenotype and altered electrical activity that differed significantly from the CTR as well as from the ASY hiPSC-CMs, demonstrating that these cells provide a valid model to study incomplete penetrance in ACM.

Set-up of a novel in vitro neurocardiac cell model for the in-depth study of heart disease

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Regional Development Fund and Interreg V-A Italy-Austria 2014-2020 and the Department of Innovation, Research and University of the Autonomous Province of Bolzano-South Tyrol (Italy).

Background

The autonomic nervous system (ANS) regulates the heart rate, conduction velocity, force of contraction, myocyte cohesion and relaxation of the heart [1]. The elucidation of how ANS and the heart interact and cooperate is at the basis of the comprehension of the mechanisms that participate in the development of many cardiac disorders including long QT and Brugada syndrome, ventricular tachyarrhythmia and arrhythmogenic cardiomyopathy [1]. However, the mechanisms of neuronal control of cardiac disease are still poorly characterized due to a lack of proper human cellular models.

Purpose

The aim of this work is to develop an in vitro neurocardiac model using sympathetic neurons (SNs) and cardiomyocytes (CMs) both derived from human induced pluripotent stem cells (iPSCs).

Methods

Commercial iPSCs were differentiated into SNs [2] and cardiomyocytes [3] using established protocols. Molecular and electrophysiological characterization of the generated cell populations was performed by qPCR, Western blot, flow cytometry, immunofluorescence and multielectrode array (MEA) analyses. Silicon-based two-well inserts with a defined cell-free gap were used for iPSC-derived SNs and CMs co-culture. SNs and CMs at approximately 30 days of differentiation were transferred in the two separated, matrigel-coated, wells of the silicon inserts, and cultured in a medium consisting of 1:1 of neural and cardiomyocyte medium.

Results

iPSC-derived CMs expressed typical cardiac markers such as α-actinin, troponin I and myosin heavy chain 7 and displayed spontaneous beating activity. iPSC-derived SNs were positive for pan-neuronal (TH) and sympathetic markers (PHOX2B, DBH). iPSC-derived SNs and CMs were separately cultured as monolayers (7x10^4 cells per chamber) for 3-5 days in the two chambers of the silicon inserts. After insert removal, neuronal axons sprouted towards the cardiomyocytes, forming connection in 3-5 days. The immunofluorescence staining of the neurocardiac co-culture displayed TH-positive axonal prolongation, punctuated varicosities and the presence of synaptic vesicles positive for the neuronal phosphoprotein Synapsin-I, indicating pre-synaptic cell contacts. Preliminary functional experiments performed using a MEA device seem to indicate an increase in the beat rate of iPSC-derived CMs after 14 days of co-culture with SNs (day 0: 44.26 beats per minute (bpm ); day 14: 87.61 bmp). This increase was not visible in monocultures of iPSC-derived CMs.

Conclusions

The establishment of this co-culture methodology and the preliminary observations collected in this work provide a promising in vitro cell model for a deeper investigation of the neurocardiac interconnection and future insights for drug screening and modelling of many cardiac disorders.

Association of mitochondrial DNA copy number with metabolic syndrome and type 2 diabetes in 14 176 individuals

BACKGROUND

Mitochondria play an important role in cellular metabolism, and their dysfunction is postulated to be involved in metabolic disturbances. Mitochondrial DNA is present in multiple copies per cell. The quantification of mitochondrial DNA copy number (mtDNA-CN) might be used to assess mitochondrial dysfunction.

OBJECTIVES

We aimed to investigate the cross-sectional association of mtDNA-CN with type 2 diabetes and the potential mediating role of metabolic syndrome.

METHODS

We examined 4812 patients from the German Chronic Kidney Disease (GCKD) study and 9364 individuals from the Cooperative Health Research in South Tyrol (CHRIS) study. MtDNA-CN was measured in whole blood using a plasmid-normalized qPCR-based assay.

RESULTS

In both studies, mtDNA-CN showed a significant correlation with most metabolic syndrome parameters: mtDNA-CN decreased with increasing number of metabolic syndrome components. Furthermore, individuals with low mtDNA-CN had significantly higher odds of metabolic syndrome (OR = 1.025; 95% CI = 1.011-1.039, P = 3.19 × 10-4 , for each decrease of 10 mtDNA copies) and type 2 diabetes (OR = 1.027; 95% CI = 1.012-1.041; P = 2.84 × 10-4 ) in a model adjusted for age, sex, smoking and kidney function in the meta-analysis of both studies. Mediation analysis revealed that the association of mtDNA-CN with type 2 diabetes was mainly mediated by waist circumference in the GCKD study (66%) and by several metabolic syndrome parameters, especially body mass index and triglycerides, in the CHRIS study (41%).

CONCLUSIONS

Our data show an inverse association of mtDNA-CN with higher risk of metabolic syndrome and type 2 diabetes. A major part of the total effect of mtDNA-CN on type 2 diabetes is mediated by obesity parameters.

32-channel time-correlated-single-photon-counting system for high-throughput lifetime imaging

Time-Correlated Single Photon Counting (TCSPC) is a very efficient technique for measuring weak and fast optical signals, but it is mainly limited by the relatively "long" measurement time. Multichannel systems have been developed in recent years aiming to overcome this limitation by managing several detectors or TCSPC devices in parallel. Nevertheless, if we look at state-of-the-art systems, there is still a strong trade-off between the parallelism level and performance: the higher the number of channels, the poorer the performance. In 2013, we presented a complete and compact 32 × 1 TCSPC system, composed of an array of 32 single-photon avalanche diodes connected to 32 time-to-amplitude converters, which showed that it was possible to overcome the existing trade-off. In this paper, we present an evolution of the previous work that is conceived for high-throughput fluorescence lifetime imaging microscopy. This application can be addressed by the new system thanks to a centralized logic, fast data management and an interface to a microscope. The new conceived hardware structure is presented, as well as the firmware developed to manage the operation of the module. Finally, preliminary results, obtained from the practical application of the technology, are shown to validate the developed system.

On the use of dense SNP marker data for the identification of distant relative pairs

There has been recent interest in the exploitation of readily available dense genome scan marker data for the identification of relatives. However, there are conflicting findings on how informative these data are in practical situations and, in particular, sets of thinned markers are often used with no concrete justification for the chosen spacing. We explore the potential usefulness of dense single nucleotide polymorphism (SNP) arrays for this application with a focus on inferring distant relative pairs. We distinguish between relationship estimation, as defined by a pedigree connecting the two individuals of interest, and estimation of general relatedness as would be provided by a kinship coefficient or a coefficient of relatedness. Since our primary interest is in the former case, we adopt a pedigree likelihood approach. We consider the effect of additional SNPs and data on an additional typed relative, together with choice of that relative, on relationship inference. We also consider the effect of linkage disequilibrium. When overall relatedness, rather than the specific relationship, would suffice, we propose an approximate approach that is easy to implement and appears to compete well with a popular moment-based estimator and a recent maximum likelihood approach based on chromosomal sharing. We conclude that denser marker data are more informative for distant relatives. However, linkage disequilibrium cannot be ignored and will be the main limiting factor for applications to real data.

A K(ATP) channel gene effect on sleep duration: from genome-wide association studies to function in Drosophila

Humans sleep approximately a third of their lifetime. The observation that individuals with either long or short sleep duration show associations with metabolic syndrome and psychiatric disorders suggests that the length of sleep is adaptive. Although sleep duration can be influenced by photoperiod (season) and phase of entrainment (chronotype), human familial sleep disorders indicate that there is a strong genetic modulation of sleep. Therefore, we conducted high-density genome-wide association studies for sleep duration in seven European populations (N=4251). We identified an intronic variant (rs11046205; P=3.99 × 10(-8)) in the ABCC9 gene that explains ≈5% of the variation in sleep duration. An influence of season and chronotype on sleep duration was solely observed in the replication sample (N=5949). Meta-analysis of the associations found in a subgroup of the replication sample, chosen for season of entry and chronotype, together with the discovery results showed genome-wide significance. RNA interference knockdown experiments of the conserved ABCC9 homologue in Drosophila neurons renders flies sleepless during the first 3 h of the night. ABCC9 encodes an ATP-sensitive potassium channel subunit (SUR2), serving as a sensor of intracellular energy metabolism.

Eye movement disorders are different in Parkin-linked and idiopathic early-onset PD

OBJECTIVES

Parkin gene mutations are the most common cause of early-onset parkinsonism. Patients with Parkin mutations may be clinically indistinguishable from patients with idiopathic early-onset Parkinson disease (EOPD) without Parkin mutations. Eye movement disorders have been shown to differentiate parkinsonian syndromes, but have never been systematically studied in Parkin mutation carriers.

METHODS

Eye movements were recorded in symptomatic (n = 9) and asymptomatic Parkin mutation carriers (n = 13), patients with idiopathic EOPD (n = 14), and age-matched control subjects (n = 27) during established oculomotor tasks.

RESULTS

Both patients with EOPD and symptomatic Parkin mutation carriers showed hypometric prosaccades toward visual stimuli, as well as deficits in suppressing reflexive saccades toward unintended targets (antisaccade task). When directing gaze toward memorized target positions, patients with EOPD exhibited hypometric saccades, whereas symptomatic Parkin mutation carriers showed normal saccades. In contrast to patients with EOPD, the symptomatic Parkin mutation carriers showed impaired tracking of a moving target (reduced smooth pursuit gain). The asymptomatic Parkin mutation carriers did not differ from healthy control subjects in any of the tasks.

CONCLUSIONS

Although clinically similarly affected, symptomatic Parkin mutation carriers and patients with idiopathic EOPD differed in several oculomotor tasks. This finding may point to distinct anatomic structures underlying either condition: dysfunctions of cortical areas involved in smooth pursuit (V5, frontal eye field) in Parkin-linked parkinsonism vs greater impairment of basal ganglia circuits in idiopathic Parkinson disease.

Heterozygous carriers of a Parkin or PINK1 mutation share a common functional endophenotype

OBJECTIVE

To use a combined neurogenetic-neuroimaging approach to examine the functional consequences of preclinical dopaminergic nigrostriatal dysfunction in the human motor system. Specifically, we examined how a single heterozygous mutation in different genes associated with recessively inherited Parkinson disease alters the cortical control of sequential finger movements.

METHODS

Nonmanifesting individuals carrying a single heterozygous Parkin (n = 13) or PINK1 (n = 9) mutation and 23 healthy controls without these mutations were studied with functional MRI (fMRI). During fMRI, participants performed simple sequences of three thumb-to-finger opposition movements with their right dominant hand. Since heterozygous Parkin and PINK1 mutations cause a latent dopaminergic nigrostriatal dysfunction, we predicted a compensatory recruitment of those rostral premotor areas that are normally implicated in the control of complex motor sequences. We expected this overactivity to be independent of the underlying genotype.

RESULTS

Task performance was comparable for all groups. The performance of a simple motor sequence task consistently activated the rostral supplementary motor area and right rostral dorsal premotor cortex in mutation carriers but not in controls. Task-related activation of these premotor areas was similar in carriers of a Parkin or PINK1 mutation.

CONCLUSION

Mutations in different genes linked to recessively inherited Parkinson disease are associated with an additional recruitment of rostral supplementary motor area and rostral dorsal premotor cortex during a simple motor sequence task. These premotor areas were recruited independently of the underlying genotype. The observed activation most likely reflects a "generic" compensatory mechanism to maintain motor function in the context of a mild dopaminergic deficit.

Premotor Gray Matter Volume is Associated with Clinical Findings in Idiopathic and Genetically Determined Parkinson's Disease

In the present voxel-based morphometric study, we investigated whether the severity and duration of disease are associated with alterations in gray matter volume (GMV) in symptomatic Parkin mutation carriers (sPARKIN-MC) and patients with idiopathic Parkinson’s disease (iPD). Regression analyses revealed different negative correlations between GMV in cortical motor areas and the severity as well as the disease duration in sPARKIN-MC and iPD patients. SPARKIN-MC showed a less involvement of cortical motor areas, in particular in the supplementary motor area (SMA) than iPD patients. Specifically, in iPD patients, but not in sPARKIN-MC, there was a negative correlation between the SMA degeneration and the UPDRS-II item freezing. The different degeneration patterns may mirror diverse kinetics of the disease progress in these two groups of PD patients with different underlying etiologies.

Haplotypes and gene expression implicate the MAPT region for Parkinson disease: the GenePD Study

BACKGROUND

Microtubule-associated protein tau (MAPT) has been associated with several neurodegenerative disorders including forms of parkinsonism and Parkinson disease (PD). We evaluated the association of the MAPT region with PD in a large cohort of familial PD cases recruited by the GenePD Study. In addition, postmortem brain samples from patients with PD and neurologically normal controls were used to evaluate whether the expression of the 3-repeat and 4-repeat isoforms of MAPT, and neighboring genes Saitohin (STH) and KIAA1267, are altered in PD cerebellum.

METHODS

Twenty-one single-nucleotide polymorphisms (SNPs) in the region of MAPT on chromosome 17q21 were genotyped in the GenePD Study. Single SNPs and haplotypes, including the H1 haplotype, were evaluated for association to PD. Relative quantification of gene expression was performed using real-time RT-PCR.

RESULTS

After adjusting for multiple comparisons, SNP rs1800547 was significantly associated with PD affection. While the H1 haplotype was associated with a significantly increased risk for PD, a novel H1 subhaplotype was identified that predicted a greater increased risk for PD. The expression of 4-repeat MAPT, STH, and KIAA1267 was significantly increased in PD brains relative to controls. No difference in expression was observed for 3-repeat MAPT.

CONCLUSIONS

This study supports a role for MAPT in the pathogenesis of familial and idiopathic Parkinson disease (PD). Interestingly, the results of the gene expression studies suggest that other genes in the vicinity of MAPT, specifically STH and KIAA1267, may also have a role in PD and suggest complex effects for the genes in this region on PD risk.

Differential gene expression analysis of ovarian cancer in a population isolate

Gene expression products represent candidate biomarkers with the potential for early screening and therapy of patients with ovarian serous carcinoma. The present study, using patients that originate from the population isolate of South Tyrol, Italy, substantiates the feasibility of differential gene expression analysis in a genetically isolated population for the identification of potential markers of ovarian cancer. Gene expression profiles of fresh-frozen ovarian serous papillary carcinoma samples were analyzed and compared to normal ovarian control tissues using oligonucleotide microarrays complementary to 14,500 human genes. Supervised analysis of gene expression profiling data identified 225 genes that are down-regulated and 635 that are up-regulated in malignant compared to normal ovarian tissues. Class-prediction analysis identified 40 differentially expressed genes for further investigation as potential classifiers for ovarian cancer, including 20 novel candidates. Our findings provide a glimpse into the potential of population isolate genomics in oncological research.

Morphometric fingerprint of asymptomatic Parkin and PINK1 mutation carriers in the basal ganglia

BACKGROUND

Mutations in the Parkin and PINK1 genes can cause parkinsonism. Since asymptomatic carriers of a single mutant allele of the Parkin or PINK1 gene display a presynaptic dopaminergic dysfunction in the striatum, they provide a unique in vivo model to study structural and functional reorganization in response to latent nigrostriatal dysfunction. We hypothesized that subclinical nigrostriatal neurodegeneration caused by these mutations would induce morphologic changes in the dysfunctional striatal gray matter.

METHODS

In asymptomatic carriers of a heterozygous Parkin (n = 13) or PINK1 (n = 10) mutation and 23 age-and sex-matched individuals without a mutation, we applied observer independent region-of-interest and voxel-based morphometry to high-resolution structural MRIs.

RESULTS

Relative to controls without a mutation, Parkin and PINK1 mutation carriers displayed a bilateral increase in gray matter volume in the putamen and the internal globus pallidus. In 8 of the 13 Parkin mutation carriers, the presynaptic dopaminergic function was studied with (18)F-DOPA PET. The metabolic-morphometric regression analysis revealed that the linear decrease in individual presynaptic striatal (18)F-DOPA uptake was linked to a reciprocal decrease in the striatal gray matter volume in the putamen bilaterally and in the left caudate nucleus.

CONCLUSIONS

The alternative causes of the increased striatal gray matter volume may be either due to excessive levels of neuronal activity caused by chronic dopaminergic dysfunction or due to long-term adaptation to chronic nigrostriatal dysfunction actively compensating for the dopaminergic denervation. In any case, the results indicate that a genetically driven regional dysfunction may be imprinted in the structure of the dysfunctional brain region, for example in the striatum.

Herbicide exposure modifies GSTP1 haplotype association to Parkinson onset age: the GenePD Study

BACKGROUND

Polymorphisms in the glutathione S-transferase pi gene (GSTP1), encoding GSTP1-1, a detoxification enzyme, may increase the risk of Parkinson disease (PD) with exposure to pesticides. Using the GenePD Study sample of familial PD cases, we explored whether GSTP1 polymorphisms were associated with the age at onset of PD symptoms and whether that relation was modified by exposure to herbicides.

METHODS

Seven single-nucleotide polymorphisms (SNPs) were genotyped and tested for association with PD onset age in men in three strata: no exposure to herbicides, residential exposure to herbicides, and occupational exposure to herbicides. Haplotypes were similarly evaluated in stratified analyses.

RESULTS

Three SNPs were associated with PD onset age in the group of men occupationally exposed to herbicides. Three additional SNPs had significant trends for the association of PD onset age across the herbicide exposure groups. Haplotype results also provided evidence that the relation between GSTP1 and onset age is modified by herbicide exposure. One haplotype was associated with an approximately 8-years-earlier onset in the occupationally exposed group and a 2.8-years-later onset in the nonexposed group.

CONCLUSIONS

Herbicide exposure may be an effect modifier of the relation between glutathione S-transferase pi gene polymorphisms and onset age in familial PD.

Population isolates in South Tyrol and their value for genetic dissection of complex diseases

The study of genetic isolates is a promising approach for the study of complex genetic traits. The small and constant population size, lack of migration, and multiple relationships between individuals in the isolate population could reduce the genetic diversity, and lead to increased levels of linkage disequilibrium (LD). We studied the extent of LD on Xq13 in six population isolates from South Tyrol in the Eastern Italian Alps. We found different levels of LD in our study samples, probably reflecting their degrees of isolation and their demographic histories. The highest values were obtained in Val Gardena (ranking among the highest levels of LD in Europe) and in Stelvio, which qualified as a microisolate according to historical information, and biodemographic and genealogical criteria. Phylogenetic analysis revealed that the two Ladin-speaking populations are genetically distant from each other, and from their German-speaking neighbours, and are characterized by a smaller effective population size than the neighbouring valleys. These peculiar characteristics suggest that South Tyrol could be a unique resource for the study of complex diseases, showing all the characteristics of isolated populations with the advantage of including, in a fairly homogeneous environment, two genetically differentiated sub-populations. This could allow investigators to gain an insight into the contribution of genetic heterogeneity in complex diseases.

Blink amplitude but not saccadic hypometria indicates carriers of Parkin mutations

We investigated saccades, eyelid blinks, and their interaction in symptomatic (n = 22) and asymptomatic (n = 31) subjects with (n = 19) and without (n = 34) Parkin mutations. Saccadic hypometria was correlated with clinical symptoms of Parkinson's disease, irrespective of mutational status. By contrast, blink amplitude was increased in carriers of Parkin mutations independent of their clinical status. Saccade main sequence and blink effects on saccades were normal. We propose that increased blink amplitude may serve as an endophenotype in carriers of Parkin mutations.

BDNF genetic variants are associated with onset age of familial Parkinson disease: GenePD Study

Brain-derived neurotrophic factor (BDNF) stimulates neuronal growth and protects nigral dopamine neurons in animal models of Parkinson disease (PD). Therefore, BDNF is a candidate gene for PD. The authors investigated five single-nucleotide polymorphisms in 597 cases of familial PD. Homozygosity for the rare allele of the functional BDNF G196A (Val66Met) variant was associated with a 5.3-year older onset age (p = 0.0001). These findings suggest that BDNF may influence PD onset age.

Absence of previously reported variants in the SCNA (G88C and G209A), NR4A2 (T291D and T245G) and the DJ-1 (T497C) genes in familial Parkinson's disease from the GenePD study

Parkinson's disease (PD) is a neurodegenerative disorder in which relatives of the probands are affected approximately 4 times as frequently as relatives of control subjects. Several genes have been implicated as genetic risk factors for PD. We investigated the presence of six reported genetic variations in the SCNA, NR4A2, and DJ-1 genes in 292 cases of familial Parkinson's disease from the GenePD study. None of the variants were found in the GenePD families. Our results suggest that other variants or genes account for the familial risk of PD within the GenePD study.

Motor reorganization in asymptomatic carriers of a single mutant Parkin allele: a human model for presymptomatic parkinsonism

Mutations in the Parkin gene are the most common known single cause of early-onset parkinsonism. It has been shown that asymptomatic carriers with a single mutant allele have latent presynaptic dopaminergic dysfunction in the striatum. Here we used functional MRI to map movement-related neuronal activity during internally selected or externally determined finger movements in 12 asymptomatic carriers of a Parkin mutation and 12 healthy non-carriers. Mean response times were 63 ms shorter during internally selected movements than during externally guided movements (P = 0.003). There were no differences in mean response times between groups (P > 0.2). Compared with externally determined movements, the internal selection of movements led to a stronger activation of rostral motor areas, including the rostral cingulate motor area (rCMA), rostral supplementary motor area, medial and dorsolateral prefrontal cortices. The genotype had a significant impact on movement-related activation patterns. Asymptomatic carriers showed a stronger increase in movement-related activity in the right rCMA and left dorsal premotor cortex, but only if movements relied on internal cues. In addition, synaptic activity in the rCMA had a stronger influence on activity in the basal ganglia in the context of internally selected movements in asymptomatic carriers relative to non-carriers. We infer that this reorganization of striatocortical motor loops reflects a compensatory effort to overcome latent nigrostriatal dysfunction.

Mutations in DYT1: extension of the phenotypic and mutational spectrum

BACKGROUND

Most cases of early-onset primary torsion dystonia (PTD) are caused by the same three-base pair (bp) (GAG) deletion in the DYT1 gene. Exon rearrangements are a common mutation type in other genes and have not yet been tested for in DYT1. Several lines of evidence suggest a relationship of the DYT1 gene with Parkinson disease (PD).

OBJECTIVE

To investigate the frequency and type of DYT1 mutations and explore the associated phenotypes in a mixed movement disorders patient cohort and in controls.

METHODS

The authors screened 197 patients with dystonia (generalized: n = 5; focal/segmental: n = 126; myoclonus-dystonia: n = 34; neuroleptic-induced: n = 32), 435 with PD, and 42 with various other movement disorders, along with 812 healthy controls, for small deletions in exon 5 of DYT1 and tested for exon rearrangements by quantitative, duplex PCR in 51 GAG deletion-negative dystonia cases.

RESULTS

The GAG deletion was detected in five patients: three with early-onset PTD, one with generalized jerky or clonic dystonia, and one with generalized dystonia and additional features (developmental delay, pyramidal syndrome). A novel out-of-frame four-bp deletion (934_937delAGAG) in exon 5 of the DYT1 gene was found in a putatively healthy blood donor. No exon rearrangements were identified in DYT1.

CONCLUSIONS

In this mixed patient sample, the GAG deletion was rare and in two out of five cases associated with an unusual phenotype. In addition, a novel DYT1 truncating mutation of unknown clinical relevance was found in a putatively unaffected individual. DYT1 exon rearrangements, however, do not seem to be associated with PTD.

DJ-1 (PARK7) mutations are less frequent than Parkin (PARK2) mutations in early-onset Parkinson disease

BACKGROUND

Mutations in the Parkin gene (PARK2) are the most commonly identified cause of recessively inherited early-onset Parkinson disease (EOPD) but account for only a portion of cases. DJ-1 (PARK7) was recently reported as a second gene associated with recessively inherited PD with a homozygous exon deletion and a homozygous point mutation in two families.

METHODS

To investigate the frequency of DJ-1 mutations, the authors performed mutational analysis of all six coding exons of DJ-1 in 100 EOPD patients. For the detection of exon rearrangements, the authors developed a quantitative duplex PCR assay. Denaturing high performance liquid chromatography analysis was used to screen for point mutations and small deletions. Further, Parkin analysis was performed as previously described.

RESULTS

The authors identified two carriers of single heterozygous loss-of-function DJ-1 mutations, including a heterozygous deletion of exons 5 to 7 and an 11-base pair deletion, removing the invariant donor splice site in intron 5. Interestingly, both DJ-1 mutations identified in this study were found in the heterozygous state only. The authors also detected a polymorphism (R98Q) in 1.5% of the chromosomes in both the patient and control group. In the same patient sample, 17 cases were detected with mutations in the Parkin gene.

CONCLUSIONS

Mutations in DJ-1 are less frequent than mutations in Parkin in EOPD patients but should be considered as a possible cause of EOPD. The effect of single heterozygous mutations in DJ-1 on the nigrostriatal system, as described for heterozygous changes in Parkin and PARK6, remains to be elucidated.

A haplotype at the PARK3 locus influences onset age for Parkinson's disease: the GenePD study

OBJECTIVE

To identify a haplotype influencing onset age for Parkinson's disease (PD) in the PARK3 region on chromosome 2p13.

METHODS

Single nucleotide polymorphisms (SNP) spanning 2.2 Mb and located in or near potential candidate genes were used to fine map the PARK3 region in 527 patients with familial PD, from 264 families.

RESULTS

TT homozygotes for rs1876487 (G/T) had a 7.4-year younger mean age at onset (p = 0.005) compared to patients with GT and GG genotypes. Furthermore, SNP flanking the sepiapterin reductase (7,8-dihydrobiopterin: NADP+ oxidoreductase) (SPR) gene, rs1876487 (p = 0.02) and rs1150500 (p = 0.04), were associated with younger onset age among persons who did not carry the 174 allele of D2S1394. The SPR gene is implicated in dopamine synthesis. Haplotype analysis of three SNP-rs2421095, rs1876487, rs1561244-revealed an association with onset age (p = 0.023) and a haplotype of A-T-G alleles was associated with younger onset for PD (p = 0.005).

CONCLUSIONS

A haplotype at the PARK3 locus, harboring the SPR gene, is associated with onset age of PD. This may suggest a role for the SPR gene in modifying the age at onset of PD.

Exon deletions in the GCHI gene in two of four Turkish families with dopa-responsive dystonia

Most cases of dopa-responsive dystonia (DRD) are thought to be caused by mutations in the GCHI gene; however, by sequencing, mutations are found in only 40% to 60%. Recently, a single report identified, via Southern blot analysis, a large genomic GCHI deletion in a "mutation-negative" case. This report describes four families with DRD, two of which carry large deletions, thus confirming that deletions are an important subtype of GCHI mutations. These deletions were detected by quantitative duplex PCR that is amenable to DNA diagnostics.

Novel three-stage ascertainment method: prevalence of PD and parkinsonism in South Tyrol, Italy

BACKGROUND

A number of community-based studies on the prevalence of PD have been conducted worldwide, but they are often extremely costly and time consuming.

OBJECTIVE

To assess the prevalence of PD and parkinsonism for the population aged between 60 and 85 years in South Tyrol, Northern Italy, using a novel population-based three-stage ascertainment method.

METHODS

Seven hundred fifty persons aged 60 to 85 years from South Tyrol received a validated screening mail questionnaire for parkinsonism. In the second stage of the ascertainment method, trained primary care physicians (PCP) identified all persons with possible parkinsonism among those screened positive. In the third stage, movement disorders specialists excluded or confirmed the diagnosis in all identified people.

RESULTS

The response rate was 87.6%. The prevalence rate per 100 population over 65 years of age was 1.5 (95% CI 0.6 to 2.3) for PD and 2.2 (95% CI 1.2 to 3.3) for parkinsonism after having been adjusted to the 1991 European standard population. Overall, 78% (95% CI 59 to 96%) of patients with parkinsonism were newly detected through the survey.

CONCLUSIONS

The prevalence of PD and parkinsonism in people aged over 65 in South Tyrol was similar to that observed in door-to-door surveys in other European countries. The novel three-stage case ascertainment method employed proved a useful tool to substitute for expensive door-to-door surveys for prevalence studies of parkinsonism, detecting a high number of undiagnosed cases, particularly in geographically remote areas.

Evaluation of 50 probands with early-onset Parkinson's disease for Parkin mutations

BACKGROUND

Early onset PD has been associated with different mutations in the Parkin gene, including exon deletions and duplications.

METHODS

The authors performed an extensive mutational analysis on 50 probands with onset of PD at younger than 50 years of age. Thirteen probands were ascertained from a registry of familial PD and 37 probands by age at onset at younger than 50 years, blind to family history. Mutational analysis was undertaken on the probands and available family members and included conventional techniques (single strand conformation polymorphism analysis and sequencing) and a newly developed method of quantitative duplex PCR to detect alterations of gene dosage (exon deletions and duplications) in PARKIN:

RESULTS

Using this new technique, the authors detected eight alterations of gene dosage in the probands, whereas 12 mutations were found by conventional methods among the probands and another different mutation in an affected family member. In total, the authors identified compound heterozygous mutations in 14%, heterozygous mutations in 12%, and no Parkin mutation in 74% of the 50 probands. We expanded the occurrence of Parkin mutations to another ethnic group (African-American).

CONCLUSION

The authors systematically screened all 12 Parkin exons by quantitative PCR and conventional methods in 50 probands. Eight mutations were newly reported, 2 of which are localized in exon 1, and 38% of the mutations were gene dosage alterations. These results underline the need to screen all exons and to undertake gene dosage studies. Furthermore, this study reveals a frequency of heterozygous mutation carriers that may signify a unique mode of inheritance and expression of the Parkin gene.

Parkin mutations in a patient with hemiparkinsonism-hemiatrophy: a clinical-genetic and PET study

The authors describe a 37-year-old woman with early-onset hemiparkinsonism (HP) and ipsilateral body hemiatrophy (HA). Genetic analysis revealed a missense mutation (Arg275Trp) and a duplication of exon 7 of parkin. The complementary metabolic and receptor pattern of PET ligands corresponded to that typically found in idiopathic PD, although tracer binding asymmetry was lacking. Parkin mutations should be considered in HPHA, particularly when there is a younger age at onset and dystonia is an early sign.

Epidemiologic study of 203 sibling pairs with Parkinson's disease: the GenePD study

OBJECTIVE

To examine patterns of familial aggregation and factors influencing onset age in a sample of siblings with PD.

METHODS

Sibling pairs (n = 203) with PD were collected as part of the GenePD study. Standardized family history, medical history, and risk factor data were collected and analyzed.

RESULTS

The mean age at onset was 61.4 years and did not differ according to sex, exposure to coffee, alcohol, or pesticides. Head trauma was associated with younger onset (p = 0.03) and multivitamin use with later onset (p = 0.007). Age at onset correlation between sibling pairs was significant (r = 0.56, p = 0.001) and was larger than the correlation in year of onset (r = 0.29). The mean difference in onset age between siblings was 8.7 years (range, 0 to 30 years). Female sex was associated with increased frequency of relatives with PD. The frequency of affected parents (7.0%) and siblings (5.1%) was increased when compared with frequency in spouses (2.0%).

CONCLUSIONS

The greater similarity for age at onset than for year of onset in sibling pairs with PD, together with increased risk for biological relatives over spouses of cases, supports a genetic component for PD. Risk to siblings in this series is increased over that seen in random series of PD cases; however, patients in this sample have similar ages at onset and sex distribution as seen for PD generally. These analyses suggest that factors influencing penetrance are critical to the understanding of this disease.

Genome-wide scan for Parkinson's disease: the GenePD Study

A genome-wide scan for idiopathic PD in a sample of 113 PD-affected sibling pairs is reported. Suggestive evidence for linkage was found for chromosomes 1 (214 cM, lod = 1.20), 9 (136 cM, lod = 1.30), 10 (88 cM, lod = 1.07), and 16 (114 cM, lod = 0.93). The chromosome 9 region overlaps the genes for dopamine beta-hydroxylase and torsion dystonia. Although no strong evidence for linkage was found for any locus, these results may be of value in comparison with similar studies by others.

The importance of gene dosage studies: mutational analysis of the parkin gene in early-onset parkinsonism

Early-onset parkinsonism (EOP) may be associated with different mutations in the parkin gene, including exon deletions and duplications. To test for gene dosage alterations, we developed a new method of quantitative duplex PCR using the fluorescence resonance energy transfer technique on the LightCycler (Roche Diagnostics). In 21 patients with EOP, three mutations (a single base pair substitution in exon 3 and small deletions in exon 9) were detected by conventional mutational screening (single-strand conformation polymorphism and sequence analysis), while alterations of gene dosage were found in seven patients. We identified heterozygous and compound heterozygous deletions of exons 2, 3, 5 and 7. The latter was also found in the homozygous state. In addition, two heterozygous duplications of exon 4 were observed. Remarkably, two patients carried more than two parkin mutations. This is the first study systematically screening all 12 exons of parkin by real-time, kinetic quantification and clearly shows that mutational analysis of the parkin gene should include gene dosage studies. Furthermore, our method of quantitative PCR is easily applicable to any other gene to be screened for deletions or duplications of whole exons.

Novel mutation in the TOR1A (DYT1) gene in atypical early onset dystonia and polymorphisms in dystonia and early onset parkinsonism

Dystonia is a movement disorder involving sustained muscle contractions and abnormal posturing with a strong hereditary predisposition and without a distinct neuropathology. In this study the TOR1A (DYT1) gene was screened for mutations in cases of early onset dystonia and early onset parkinsonism (EOP), which frequently presents with dystonic symptoms. In a screen of 40 patients, we identified three variations, none of which occurred in EOP patients. Two infrequent intronic single base pair (bp) changes of unknown consequences were found in a dystonia patient and the mother of an EOP patient. An 18-bp deletion (Phe323_Tyr328del) in the TOR1A gene was found in a patient with early onset dystonia and myoclonic features. This deletion would remove 6 amino acids close to the carboxy terminus, including a putative phosphorylation site of torsinA. This 18-bp deletion is the first additional mutation, beyond the GAG-deletion (Glu302/303del), to be found in the TOR1A gene, and is associated with a distinct type of early onset dystonia.

Positron emission tomographic analysis of the nigrostriatal dopaminergic system in familial parkinsonism associated with mutations in the parkin gene

A kindred from South Tyrol (northern Italy) with familial, adult-onset parkinsonism of pseudo-dominant inheritance and mutations in the parkin gene was recently described. To gain insight into basal ganglia dysfunction in this form of hereditary parkinsonism, positron emission tomography (PET) with 18-fluorodopa (FDOPA) and 11C-raclopride (RAC) was performed in 5 affected family members and 5 asymptomatic relatives with proven compound heterozygous or heterozygous parkin mutations. Results were compared to findings in healthy control subjects and patients with typical sporadic, idiopathic Parkinson's disease. Similar to findings in the sporadic Parkinson's disease group, presynaptic striatal FDOPA storage was decreased in patients with compound heterozygous parkin mutations, with the most prominent reduction in the posterior part of the putamen. Along with the presynaptic lowered FDOPA uptake, we found a uniform reduction of the striatal 11C-raclopride binding index in all affected family members as compared to asymptomatic family members carrying a heterozygous parkin mutation, sporadic Parkinson's disease, and control subjects. Our PET data provide evidence that parkinsonism in this family is associated with presynaptic dopaminergic dysfunction similar to idiopathic Parkinson's disease pathophysiology, along with alterations at the postsynaptic D2 receptor level. In asymptomatic carriers of a single parkin mutation with an apparently normal allele, we found a mild but statistically significant decrease of mean FDOPA uptake compared to control subjects in all striatal regions. These data indicate a preclinical disease process in these subjects.

Ante litteram description of atypical parkinsonian cases

We have searched in the neurological literature for cases of atypical parkinsonism published before the epidemic encephalitis era. Some of these cases can be recognized. Therefore the epidemic encephalitis has no etiological importance in these clinical syndromes.

Parkin deletions in a family with adult-onset, tremor-dominant parkinsonism: expanding the phenotype

A gene for autosomal recessive parkinsonism, PARK2 (parkin), has recently been identified on chromosome 6q and shown to be mutated in Japanese and European families, mostly with early-onset parkinsonism. Here we present a large pedigree from South Tyrol (a region of northern Italy) with adult-onset, clinically typical tremor-dominant parkinsonism of apparently autosomal dominant inheritance. Haplotype analysis excluded linkage to the chromosome 2p, 4p, and 4q regions that harbor genes associated with autosomal dominant parkinsonism, but implicated the parkin locus on chromosome 6q. Compound heterozygous deletions in the parkin gene (one large and one truncating) were identified in 4 affected male siblings. The patients were clinically indistinguishable from most patients with idiopathic Parkinson's disease. None of them displayed any of the clinical hallmarks described in patients with previously reported parkin mutations, including diurnal fluctuations, benefit from sleep, foot dystonia, hyperreflexia, and early susceptibility to levodopa-induced dyskinesias. Two affected female individuals carried one (truncating) of the two deletions in a heterozygous state with an apparently normal allele. We conclude that the phenotypic spectrum associated with mutations in the parkin gene is broader than previously reported, suggesting that this gene may be important in the etiology of the more frequent late-onset typical Parkinson's disease.

Neuronal loss in Onuf's nucleus in three patients with progressive supranuclear palsy

Disorders of micturition have been reported only sporadically in patients with progressive supranuclear palsy (PSP). We report the results of a clinicopathological study of 3 patients with a definite diagnosis of PSP at various stages of their illness with sphincter abnormalities. Electromyography of the sphincter muscles was performed in all 3 patients and was abnormal in 2. Morphological and morphometric evaluation of Onuf's nucleus in the sacral spinal cord, which is involved in sphincter control, showed severe cell loss, presence of neurofibrillary tangles, neuropil threads, and glial inclusions. We conclude that bladder dysfunction and abnormal sphincter electromyographic results are due to pathological changes in Onuf's nucleus, and we propose that sphincter abnormalities should be included in the list of possible symptoms of PSP.

[Genetics of dystonia]

To date, at least 12 types of primary dystonia can be distinguished on a genetic basis. A 3-bp deletion in the DYT1 gene causes early onset, generalized torsion dystonia (TD), and mutations in the GTP cyclohydrolase I and the tyrosine hydroxylase genes result in dopa-responsive dystonia (DYT5). A missense change in the D2 dopamine receptor in one large family (DYT11) has recently been implicated in myoclonus-dystonia. Furthermore, seven other loci for dystonia genes have been mapped to chromosomal regions, including a locus for a mixed dystonia phenotype (DYT6), one form of focal dystonia (DYT7), three types of paroxysmal dystonia (DYT8-10), X-linked dystonia-parkinsonism (DYT3), and rapid-onset dystonia-parkinsonism (DYT12). No positive linkage results have yet been obtained for autosomal recessive TD (DYT2) and several other families of different types of dominantly inherited TD (DYT4). In addition, hereditary secondary dystonia may occur as part of familial diseases of the basal ganglia, metabolic and storage disorders, and various X-linked and other familial neurodegenerative syndromes affecting the basal ganglia. It may be anticipated that the traditional clinical and etiological classifications of dystonia will increasingly be replaced by a genetic one and that the identification of more dystonia genes may lead to a better understanding of these largely nondegenerative disorders.

Corticobasal degeneration shares a common genetic background with progressive supranuclear palsy

Corticobasal degeneration is a sporadic form of tauopathy, involving the cerebral cortex and extrapyramidal motor system. A series of affected subjects was genotyped for a set of genetic markers along the tau protein gene. A specific haplotype is significantly overrepresented in patients versus controls. This haplotype is the same already reported in association with progressive supranuclear palsy. These data show that corticobasal degeneration and progressive supranuclear palsy, in addition to several clinical, pathological, and molecular features, may have the same genetic background.

Genetic testing for early-onset torsion dystonia (DYT1): introduction of a simple screening method, experiences from testing of a large patient cohort, and ethical aspects

Early-onset, generalized primary torsion dystonia (PTD) is an autosomal dominantly inherited disorder, characterized by involuntary movements and abnormal postures. The majority of cases are caused by a 3-bp deletion in the DYT1 gene on chromosome 9q34 that allows for specific genetic testing. We developed a simple, reliable, and cost-effective, PCR-based screening method for this mutation. Testing results from a cohort of 550 cases, including patients with different forms of dystonia and unclassified movement disorders, revealed that 72.2% of the patients with typical early-onset generalized PTD carried the GAG deletion in the DYT1 gene. Among 300 cases with late-onset focal/segmental dystonia, only 3 patients tested positive for the GAG deletion whereas 12.8% of the patients with an unclassified movement disorder were GAG positive. Our results confirm a genotype/phenotype correlation in early-onset PTD and show that application of strict clinical criteria leads to accurate prediction of carrier status in more than two-thirds of patients with this type of dystonia. Currently, we suggest that testing be recommended in individuals with age of onset of dystonia below 30 years and/or a positive family history of early-onset PTD. Testing is not recommended in patients with onset of symptoms after 30 years or in asymptomatic individuals under the age of 18.