Karin D. van Dijk

Genome-wide association study confirms extant PD risk loci among the Dutch.

In view of the population-specific heterogeneity in reported genetic risk factors for Parkinsons disease (PD), we conducted a genome-wide association study (GWAS) in a large sample of PD cases and controls from the Netherlands. After quality control (QC), a total of 514 799 SNPs genotyped in 772 PD cases and 2024 controls were included in our analyses. Direct replication of SNPs within SNCA and BST1 confirmed these two genes to be associated with PD in the Netherlands (SNCA, rs2736990: P=1.63 × 10−5, OR=1.325 and BST1, rs12502586: P=1.63 × 10−3, OR=1.337). Within SNCA, two independent signals in two different linkage disequilibrium (LD) blocks in the 3′ and 5′ ends of the gene were detected. Besides, post-hoc analysis confirmed GAK/DGKQ, HLA and MAPT as PD risk loci among the Dutch (GAK/DGKQ, rs2242235: P=1.22 × 10−4, OR=1.51; HLA, rs4248166: P=4.39 × 10−5, OR=1.36; and MAPT, rs3785880: P=1.9 × 10−3, OR=1.19).

CSF α-Synuclein Does Not Discriminate Dementia with Lewy Bodies from Alzheimer's Disease

In this study, we assessed whether cerebrospinal fluid (CSF) levels of the biomarker α-synuclein have a diagnostic value in differential diagnosis of dementia with Lewy bodies (DLB) and Alzheimers disease (AD). We also analyzed associations between CSF biomarkers and cognitive performance in DLB and in AD. We included 35 DLB patients, 63 AD patients, 18 patients with Parkinsons disease (PD), and 34 patients with subjective complaints (SC). Neuropsychological performance was measured by means of the Mini-Mental Status Examination (MMSE), Visual Association Test (VAT), VAT object-naming, Trail Making Test, and category fluency. In CSF, levels of α-synuclein, amyloid-β 1-42 (Aβ1-42), total tau (tau), and tau phosphorylated at threonine 181 (ptau-181) were measured. CSF α-synuclein levels did not differentiate between diagnostic groups (p=0.16). Higher ptau-181 and higher tau levels differentiated AD from DLB patients (p< 0.05). In DLB patients, lower Aβ1-42 and higher total tau levels were found than in SC and PD patients (p< 0.05). In DLB patients, linear regression analyses of CSF biomarkers showed that lower α-synuclein was related to lower MMSE-scores (β (SE) = 6(2) and p< 0.05) and fluency (β (SE) = 4(2), p< 0.05). Ultimately, CSF α-synuclein was not a useful diagnostic biomarker to differentiate DLB and/or PD (α-synucleinopathies) from AD or SC. In DLB patients maybe lower CSF α-synuclein levels are related to worse cognitive performance.

Diagnostic cerebrospinal fluid biomarkers for Parkinson's disease: A pathogenetically based approach

Abstract The inaccuracy of the early diagnosis of Parkinsons disease (PD) has been a major incentive for studies aimed at the identification of biomarkers. Brain-derived cerebrospinal fluid (CSF) proteins are potential biomarkers considering the major role that proteins play in PD pathogenesis. In this review, we discuss the current hypotheses about the pathogenesis of PD and identify the most promising candidate biomarkers among the CSF proteins studied so far. The list of potential markers includes proteins involved in various pathogenetic processes, such as oxidative stress and protein aggregation. This list will undoubtedly grow in the near future by application of CSF proteomics and subsequent validation of identified proteins. Probably a single biomarker will not suffice to reach high sensitivity and specificity, because PD is pathogenetically heterogeneous and shares etiological factors with other neurodegenerative diseases. Furthermore, identified candidate biomarkers will have to be thoroughly validated before they can be implemented as diagnostic aids.

Oligomeric and phosphorylated alpha-synuclein as potential CSF biomarkers for Parkinson’s disease

BackgroundDespite decades of intensive research, to date, there is no accepted diagnosis for Parkinson’s disease (PD) based on biochemical analysis of blood or CSF. However, neurodegeneration in the brains of PD patients begins several years before the manifestation of the clinical symptoms, pointing to serious flaw/limitations in this approach.ResultsTo explore the potential use of alpha-synuclein (α-syn) species as candidate biomarkers for PD, we generated specific antibodies directed against wide array of α-syn species, namely total-, oligomeric- and phosphorylated-Ser129-α-syn (t-, o- and p-S129-α-syn). Next we sought to employ our antibodies to develop highly specific ELISA assays to quantify α-syn species in biological samples. Finally we verified the usefulness of our assays in CSF samples from 46 PD patients and 48 age-matched healthy controls. We also assessed the discriminating power of combining multiple CSF α-syn species with classical Alzheimer’s disease biomarkers. The combination of CSF o-/t-α-syn, p-S129-α-syn and p-tau provided the best fitting predictive model for discriminating PD patients from controls. Moreover, CSF o-α-syn levels correlated significantly with the severity of PD motor symptoms (r = -0.37).ConclusionOur new ELISA assays can serve as research tools to address the unmet need for reliable CSF biomarkers for PD and related disorders.

Is Disturbed Intracortical Excitability a Stable Trait of Chronic Insomnia? A Study Using Transcranial Magnetic Stimulation Before and After Multimodal Sleep Therapy

BACKGROUND Chronic insomnia is a poorly understood disorder. Risk factors for developing chronic insomnia are largely unknown, yet disturbances in brain indexes of arousal seem to accompany the disorder. We here investigate whether insomnia patients and control participants differ with respect to brain responses to direct stimulation, i.e., cortical excitability. Transcranial magnetic stimulation (TMS) offers a method to directly investigate the excitability level of the human cerebral cortex in psychiatric and neurological disease. METHODS We investigated cortical excitability in 16 insomnia patients and 14 carefully matched control participants using absolute and relative amplitudes of motor evoked potentials in response to single- and paired-pulse stimulation using TMS. RESULTS Nonmedicated insomnia patients showed, first, an exaggerated absolute response to both suprathreshold single- and paired-pulse stimulation compared with control participants and second, a reduced relative response to paired-pulse stimulation at long interpulse intervals (i.e., a reduced intracortical facilitation). The abnormal excitability persisted despite sleep therapy that effectively improved sleep quality as well as behavioral and neuroimaging indexes of brain function. CONCLUSIONS The results suggest that a subtly disturbed intracortical excitability characterizes patients with chronic insomnia: a relatively reduced intracortical facilitation in the context of a globally increased absolute excitability. The findings do not resemble TMS findings after sleep deprivation or in sleep apnea and thus seem specific to insomnia. They may offer diagnostic value and implications for assessment of risk to develop this common and disabling disorder.

Changes in endolysosomal enzyme activities in cerebrospinal fluid of patients with Parkinson's disease

Parkinsons disease (PD) is characterized neuropathologically by the cytoplasmic accumulation of misfolded α‐synuclein in specific brain regions. The endolysosomal pathway appears to be involved in α‐synuclein degradation and, thus, may be relevant to PD pathogenesis. This assumption is further strengthened by the association between PD and mutations in the gene encoding for the lysosomal hydrolase glucocerebrosidase. The objective of the present study was to determine whether endolysosomal enzyme activities in cerebrospinal fluid (CSF) differ between PD patients and healthy controls. Activity levels of 6 lysosomal enzymes (β‐hexosaminidase, α‐fucosidase, β‐mannosidase, β‐galactosidase, β‐glucocerebrosidase, and cathepsin D) and 1 endosomal enzyme (cathepsin E) were measured in CSF from 58 patients with PD (Hoehn and Yahr stages 1–3) and 52 age‐matched healthy controls. Enzyme activity levels were normalized against total protein levels. Normalized cathepsin E and β‐galactosidase activity levels were significantly higher in PD patients compared with controls, whereas normalized α‐fucosidase activity was reduced. Other endolysosomal enzyme activity levels, including β‐glucocerebrosidase activity, did not differ significantly between PD patients and controls. A combination of normalized α‐fucosidase and β‐galactosidase discriminated best between PD patients and controls with sensitivity and specificity values of 63%. In conclusion, the activity of a number of endolysosomal enzymes is changed in CSF from PD patients compared with healthy controls, supporting the alleged role of the endolysosomal pathway in PD pathogenesis. The usefulness of CSF endolysosomal enzyme activity levels as PD biomarkers, either alone or in combination with other markers, remains to be established in future studies.

The Proteome of the Locus Ceruleus in Parkinson's Disease: Relevance to Pathogenesis

The locus ceruleus is among the earliest affected brain regions in Parkinsons disease (PD) showing Lewy body pathology and neuronal loss. To improve our understanding of the pathogenesis of PD, we performed the first proteomic analysis ever of post‐mortem locus ceruleus tissue of six pathologically confirmed PD patients, and six age‐ and gender‐matched non‐neurological controls. In total 2495 proteins were identified, of which 87 proteins were differentially expressed in the locus ceruleus of PD patients compared with controls. The majority of these differentially expressed proteins are known to be involved in processes that have been implicated in the pathogenesis of PD previously, including mitochondrial dysfunction, oxidative stress, protein misfolding, cytoskeleton dysregulation and inflammation. Several individual proteins were identified that have hitherto not been associated with PD, such as regucalcin, which plays a role in maintaining intracellular calcium homeostasis, and isoform 1 of kinectin, which is involved in transport of cellular components along microtubules. In addition, pathway analysis suggests a pathogenetic role for aminoacyl‐tRNA‐biosynthesis. These findings indicate that the proteome of the locus ceruleus of PD patients and non‐neurological controls provides data that are relevant to the pathogenesis of PD, reflecting both known and potentially novel pathogenetic pathways.

Clusterin Levels in Plasma Predict Cognitive Decline and Progression to Alzheimer’s Disease

BACKGROUND Increased clusterin levels have been reported in brain, cerebrospinal fluid (CSF), and plasma of Alzheimers disease (AD) patients. Because changes are also observed in mild cognitive impairment (MCI), a possible relationship between clusterin levels and early neurodegenerative changes in AD was suggested. OBJECTIVES To determine whether clusterin concentrations could 1) serve as a diagnostic marker for AD, 2) predict disease progression in MCI, and 3) correlate with AD-biomarkers. METHODS Clusterin levels in CSF and plasma, as well as AD biomarker levels of Aβ42, Tau, and pTau in CSF and Mini-Mental State Examination scores (MMSE) were determined in 67 controls, 50 MCI, and 107 AD patients. Repeated MMSE was obtained for 44 MCI and 72 AD patients after, on average, 2.7 years. RESULTS Elevated clusterin concentrations in plasma, but not in CSF, were a risk factor for AD (HR 18.6; 95% CI 2.8-122), and related to cognitive decline in MCI (r =-0.38; p <  0.01). An inverse relation between plasma clusterin levels and cognitive decline was observed in AD patients (r = 0.23; p≤0.05). In CSF, but not in plasma, clusterin levels correlated with Tau and pTau in all groups. CONCLUSION Elevated plasma clusterin levels in MCI confer an increased risk for progression to AD, and more rapid cognitive decline. We speculate that clusterin levels in CSF may reflect its involvement in the earliest neurodegenerative processes associated with AD pathology. Whereas neither clusterin levels in CSF nor in plasma had diagnostic value, plasma clusterin levels may serve as a prognostic marker for AD.

Diagnosis and management of aspergillosis in the Netherlands: a national survey

A survey of diagnosis and treatment of invasive aspergillosis was conducted in eight University Medical Centers (UMCs) and eight non‐academic teaching hospitals in the Netherlands. Against a background of emerging azole resistance in Aspergillus fumigatus routine resistance screening of clinical isolates was performed primarily in the UMCs. Azole resistance rates at the hospital level varied between 5% and 10%, although rates up to 30% were reported in high‐risk wards. Voriconazole remained first choice for invasive aspergillosis in 13 out of 16 hospitals. In documented azole resistance 14 out of 16 centres treated patients with liposomal amphotericin B.

Beneficial effect of transcranial magnetic stimulation on sleep in Parkinson's disease.

Sleep disorders are common in Parkinsons disease (PD) and have profound negative influences on quality of life. Sleep structure in healthy participants can be changed by repetitive transcranial magnetic stimulation (rTMS), but this has never been studied systematically in PD. Therefore, we characterized sleep in PD patients and examined effects of rTMS using a combination of actigraphy and a pressure sensitive pad. Thirteen PD patients received 5 Hz rTMS over the motor or parietal cortex. Actigraphic sleep estimates were obtained before, during and after rTMS, as well as compared with 8 healthy, age‐matched controls. Motor symptoms and mood were evaluated before and after rTMS. Mixed‐model regression analyses indicated that PD patients slept shorter (350 ± 17 vs. 419 ± 24 min., P = 0.02), more fragmented (fragmentation index 41 ± 4 vs. 22 ± 2, P = 0.0004) and had a lower sleep efficiency (77 ± 2 vs. 86 ± 2%, P = 0.002) and longer nocturnal awakenings (3.4 ± 0.2 vs. 2.3 ± 0.2 min., P = 0.003) than healthy controls. rTMS over the parietal, but not over the motor cortex improved sleep fragmentation (P = 0.0002) and sleep efficiency (P = 0.0002) and reduced the average duration of nocturnal awakenings (P = 0.02). No change of motor symptoms or mood was observed. Disturbed sleep in PD patients may partly be reversed by parietal rTMS, without affecting motor symptoms or mood.