Laura Parkkinen

Cerebrospinal fluid β-amyloid 42 and tau proteins as biomarkers of Alzheimer-type pathologic changes in the brain

BACKGROUND There is a clear need to develop an objective diagnostic test for Alzheimer disease (AD). Changes in the levels of cerebrospinal fluid (CSF) tau protein and beta-amyloid 42 (Abeta42) peptide in patients with AD have been well documented, but the relationship between these biomarkers and neuropathologic changes in the brain is not established. OBJECTIVE To study the relationship between antemortem CSF biomarker levels and Alzheimer-type neuropathologic changes in the brain. DESIGN Cross-sectional study to correlate levels of CSF Abeta42, total tau, and phosphorylated tau protein with neuropathologic changes in the brain. SETTING Academic research. Patients The study included 123 patients (79 with clinically diagnosed AD, 29 with other dementia, and 15 with other neurologic disease). All underwent clinical evaluation and provided antemortem lumbar CSF samples, and neuropathologic data were collected from September 11, 1990, to March 13, 2003, in the Department of Neuroscience and Neurology, University of Kuopio, Kuopio, Finland. MAIN OUTCOME MEASURES Levels of CSF Abeta42, total tau, and phosphorylated tau protein were measured using standard commercial immunoassays. Neuropathologic evaluations included the classic silver impregnation method and immunohistochemistry for Abeta, hyperphosphorylated tau, and alpha-synuclein. RESULTS Cerebrospinal fluid Abeta42 and tau protein levels were related to amyloid load and the presence of neurofibrillary pathologic abnormalities in the brain. Cerebrospinal fluid Abeta42 level correlated inversely with total Abeta load in the brain, and CSF tau level correlated with results of immunohistochemistry for hyperphosphorylated tau and with the presence of neocortical neurofibrillary tangles. In multivariate logistic regression analysis, the number of neuritic plaques in the brain remained a significant predictor of decreased CSF Abeta42 level and of increased CSF tau level. Based on the ratio of phosphorylated tau level to Abeta42 level, sensitivity was 91.6%, and specificity was 85.7%, with an overall accuracy of 90.2% for the presence of pathologic neuritic plaque in the brain. CONCLUSIONS Cerebrospinal fluid Abeta42 and tau proteins are biomarkers of AD-associated pathologic changes in the brain. The combination of abnormally low CSF Abeta42 level and abnormally high CSF tau level predicted the presence of AD pathologic features with high accuracy. This combination assay may be helpful in diagnosing the presence of AD pathologic changes in the brain.

Glucocerebrosidase mutations in clinical and pathologically proven Parkinson's disease

Mutations in the glucocerebrosidase gene (GBA) are associated with Gauchers disease, the most common lysosomal storage disorder. Parkinsonism is an established feature of Gauchers disease and an increased frequency of mutations in GBA has been reported in several different ethnic series with sporadic Parkinsons disease. In this study, we evaluated the frequency of GBA mutations in British patients affected by Parkinsons disease. We utilized the DNA of 790 patients and 257 controls, matched for age and ethnicity, to screen for mutations within the GBA gene. Clinical data on all identified GBA mutation carriers was reviewed and analysed. Additionally, in all cases where brain material was available, a neuropathological evaluation was performed and compared to sporadic Parkinsons disease without GBA mutations. The frequency of GBA mutations among the British patients (33/790 = 4.18%) was significantly higher (P = 0.01; odds ratio = 3.7; 95% confidence interval = 1.12-12.14) when compared to the control group (3/257 = 1.17%). Fourteen different GBA mutations were identified, including three previously undescribed mutations, K7E, D443N and G193E. Pathological examination revealed widespread and abundant alpha-synuclein pathology in all 17 GBA mutation carriers, which were graded as Braak stage of 5-6, and had McKeiths limbic or diffuse neocortical Lewy body-type pathology. Diffuse neocortical Lewy body-type pathology tended to occur more frequently in the group with GBA mutations compared to matched Parkinsons disease controls. Clinical features comprised an early onset of the disease, the presence of hallucinations in 45% (14/31) and symptoms of cognitive decline or dementia in 48% (15/31) of patients. This study demonstrates that GBA mutations are found in British subjects at a higher frequency than any other known Parkinsons disease gene. This is the largest study to date on a non-Jewish patient sample with a detailed genotype/phenotype/pathological analyses which strengthens the hypothesis that GBA mutations represent a significant risk factor for the development of Parkinsons disease and suggest that to date, this is the most common genetic factor identified for the disease.

Alpha-synuclein pathology does not predict extrapyramidal symptoms or dementia.

Intracytoplasmic aggregation of α‐synuclein protein as Lewy bodies in the brainstem neurons is diagnostic for Parkinsons disease, whereas if this process also occurs in the cortical neurons, it is considered pathognomonic for dementia with Lewy bodies. However, the link between α‐synuclein incorporation into inclusions, neuronal dysfunction, and clinical symptoms needs to be clarified. Another important issue of the pathogenetic puzzle is to understand where α‐synuclein pathology begins and how it progresses in the brain. To study this, we collected all cases from autopsy material (N = 904) that had α‐synuclein pathology in the dorsal motor nucleus of vagus, substantia nigra, and/or basal forebrain nuclei. In this way, our study has a unique design because the selection of material is entirely based on the presence of α‐synuclein pathology regardless of clinical phenotype. Retrospective clinical assessment then showed that only 32 (30%) of 106 α‐synuclein–positive cases were diagnosed with a neurodegenerative disorder. The distribution or load of α‐synuclein pathology did not permit a dependable postmortem diagnosis of extrapyramidal symptoms or cognitive impairment. Some neurologically unimpaired cases had a reasonable burden of α‐synuclein pathology in both brainstem and cortical areas, suggesting that α‐synuclein–positive structures are not definite markers of neuronal dysfunction. Ann Neurol 2004

Staging/typing of Lewy body related α-synuclein pathology: a study of the BrainNet Europe Consortium

When 22 members of the BrainNet Europe (BNE) consortium assessed 31 cases with α-synuclein (αS) immunoreactive (IR) pathology applying the consensus protocol described by McKeith and colleagues in 2005, the inter-observer agreement was 80%, being lowest in the limbic category (73%). When applying the staging protocol described by Braak and colleagues in 2003, agreement was only 65%, and in some cases as low as 36%. When modifications of these strategies, i.e., McKeith’s protocol by Leverenz and colleagues from 2009, Braak’s staging by Müller and colleagues from 2005 were applied then the agreement increased to 78 and 82%, respectively. In both of these modifications, a reduced number of anatomical regions/blocks are assessed and still in a substantial number of cases, the inter-observer agreement differed significantly. Over 80% agreement in both typing and staging of αS pathology could be achieved when applying a new protocol, jointly designed by the BNE consortium. The BNE-protocol assessing αS-IR lesions in nine blocks offered advantages over the previous modified protocols because the agreement between the 22 observers was over 80% in most cases. Furthermore, in the BNE-protocol, the αS pathology is assessed as being present or absent and thus the quality of staining and the assessment of the severity of αS-IR pathology do not alter the inter-observer agreement, contrary to other assessment strategies. To reach these high agreement rates an entity of amygdala-predominant category was incorporated. In conclusion, here we report a protocol for assessing αS pathology that can achieve a high inter-observer agreement for both the assignment to brainstem, limbic, neocortical and amygdala-predominant categories of synucleinopathy and the Braak stages.

Deficits in dopaminergic transmission precede neuron loss and dysfunction in a new Parkinson model

Significance Elevated expression of the presynaptic protein α-synuclein underlies familial and sporadic Parkinson disease (PD). However, our understanding of how increases in α-synuclein levels drive the sequence of events leading to PD is incomplete. Here, we apply a multidisciplinary longitudinal analysis to a new α-synuclein transgenic mouse model. We show that early-stage decreases in dopamine release and vesicle reclustering precede late-stage changes in neuronal firing properties, measured by in vivo recordings from vulnerable neurons. Accumulated deficits in dopamine neurotransmission and altered neuronal firing are associated with cell death and motor abnormalities, in the absence of protein aggregation in the substantia nigra. These findings have important implications for developing therapies. The pathological end-state of Parkinson disease is well described from postmortem tissue, but there remains a pressing need to define early functional changes to susceptible neurons and circuits. In particular, mechanisms underlying the vulnerability of the dopamine neurons of the substantia nigra pars compacta (SNc) and the importance of protein aggregation in driving the disease process remain to be determined. To better understand the sequence of events occurring in familial and sporadic Parkinson disease, we generated bacterial artificial chromosome transgenic mice (SNCA-OVX) that express wild-type α-synuclein from the complete human SNCA locus at disease-relevant levels and display a transgene expression profile that recapitulates that of endogenous α-synuclein. SNCA-OVX mice display age-dependent loss of nigrostriatal dopamine neurons and motor impairments characteristic of Parkinson disease. This phenotype is preceded by early deficits in dopamine release from terminals in the dorsal, but not ventral, striatum. Such neurotransmission deficits are not seen at either noradrenergic or serotoninergic terminals. Dopamine release deficits are associated with an altered distribution of vesicles in dopaminergic axons in the dorsal striatum. Aged SNCA-OVX mice exhibit reduced firing of SNc dopamine neurons in vivo measured by juxtacellular recording of neurochemically identified neurons. These progressive changes in vulnerable SNc neurons were observed independently of overt protein aggregation, suggesting neurophysiological changes precede, and are not driven by, aggregate formation. This longitudinal phenotyping strategy in SNCA-OVX mice thus provides insights into the region-specific neuronal disturbances preceding and accompanying Parkinson disease.

Genetic analysis implicates APOE, SNCA and suggests lysosomal dysfunction in the etiology of dementia with Lewy bodies

Clinical and neuropathological similarities between dementia with Lewy bodies (DLB), Parkinsons and Alzheimers diseases (PD and AD, respectively) suggest that these disorders may share etiology. To test this hypothesis, we have performed an association study of 54 genomic regions, previously implicated in PD or AD, in a large cohort of DLB cases and controls. The cohort comprised 788 DLB cases and 2624 controls. To minimize the issue of potential misdiagnosis, we have also performed the analysis including only neuropathologically proven DLB cases (667 cases). The results show that the APOE is a strong genetic risk factor for DLB, confirming previous findings, and that the SNCA and SCARB2 loci are also associated after a study-wise Bonferroni correction, although these have a different association profile than the associations reported for the same loci in PD. We have previously shown that the p.N370S variant in GBA is associated with DLB, which, together with the findings at the SCARB2 locus, suggests a role for lysosomal dysfunction in this disease. These results indicate that DLB has a unique genetic risk profile when compared with the two most common neurodegenerative diseases and that the lysosome may play an important role in the etiology of this disorder. We make all these data available.

Testing an aetiological model of visual hallucinations in Parkinson's disease.

The exact pathogenesis of visual hallucinations in Parkinsons disease is not known but an integrated model has been proposed that includes impaired visual input and central visual processing, impaired brainstem regulation of sleep-wake cycle with fluctuating vigilance, intrusion of rapid eye movement dream imagery into wakefulness and emergence of internally generated imagery, cognitive dysfunction and influence of dopaminergic drugs. In a clinical study, we assessed motor and non-motor function, including sleep, mood, autonomic and global, frontal and visuoperceptive cognitive function in patients with and without visual hallucinations. A subgroup of patients underwent detailed ophthalmological assessment. In a separate pathological study, histological specimens were obtained from cases of pathologically proven Parkinsons disease and a retrospective case notes review was made for reporting of persistent formed visual hallucinations. An assessment of Lewy body and Lewy neurite pathology was carried out in five cortical regions as recommended by diagnostic criteria for dementia with Lewy Bodies and in brainstem nuclei. Ninety-four patients (mean age 67.5 ± 9.5 years) participated in the clinical study of whom 32% experienced visual hallucinations. When corrected for multiple comparisons, patients with visual hallucinations had significantly greater disease duration, treatment duration, motor severity and complications, sleep disturbances, in particular excessive daytime somnolence and rapid eye movement sleep behavioural disorder, disorders of mood, autonomic dysfunction and global, frontal and visuoperceptive cognitive dysfunction. Of the 94 patients, 50 (53%) underwent ophthalmological assessment. There were no differences in ocular pathology between the visual hallucination and non-visual hallucination groups. In a logistic regression model the four independent determinants of visual hallucinations were rapid eye movement sleep behavioural disorder (P = 0.026), autonomic function (P = 0.004), frontal cognitive function (P = 0.020) and a test of visuoperceptive function (object decision; P = 0.031). In a separate study, post-mortem analysis was performed in 91 subjects (mean age at death 75.5 ± 8.0 years) and persistent visual hallucinations were documented in 63%. Patients in the visual hallucinations group had similar disease duration but had significantly higher Lewy body densities in the middle frontal (P = 0.002) and middle temporal gyri (P = 0.033) and transentorhinal (P = 0.005) and anterior cingulate (P = 0.020) cortices but not parietal cortex (P = 0.22). Using a comprehensive assessment of the clinical, demographic and ophthalmological correlates of visual hallucinations in Parkinsons disease, the combined data support the hypothesized model of impaired visual processing, sleep-wake dysregulation and brainstem dysfunction, and cognitive, particularly frontal, impairment all independently contributing to the pathogenesis of visual hallucinations in Parkinsons disease. These clinical data are supported by the pathological study, in which higher overall cortical Lewy body counts, and in particular areas implicated in visuoperception and executive function, were associated with visual hallucinations.

Assessment of alpha-synuclein pathology: A study of the BrainNet Europe consortium

To determine the reliability of assessment of &agr;-synuclein-immunoreactive (&agr;S-IR) structures by neuropathologists, 28 evaluators from 17 centers of BrainNet Europe examined current methods and reproducibility of &agr;S-IR evaluation using a tissue microarray (TMA) technique. Tissue microarray blocks were constructed of samples from the participating centers that contained &agr;S-IR structures. Slides from these blocks were stained in each center and assessed for neuronal perikaryal inclusions, neurites, and glial cytoplasmic inclusions. The study was performed in 2 phases. First, the TMA slides were stained with the antibody of the centers choice. In this phase, 59% of the sections were of good or acceptable quality, and 4 of 9 antibodies used performed consistently. Differences in interpretation and categorization of &agr;S-IR structures, however, led to differing results between the laboratories. Prior to the second phase, the neuropathologists participated in a training session on the evaluation of &agr;S-IR structures. Based on the results of the first phase, selected antibodies using designated antigen retrieval methods were then applied to TMA slides in the second phase. When the designated methods of both staining and evaluation were applied, all 26 subsequently stained TMA sections evaluated were of good/acceptable quality, and a high level of concordance in the assessment of the presence or absence of specific &agr;S-IR structures was achieved. A semiquantitative assessment of &agr;S-IR neuronal perikaryal inclusions yielded agreements ranging from 49% to 82%, with best concordance in cortical core samples. These results suggest that rigorous methodology and dichotomized assessment (i.e. determining the presence or absence of &agr;S-IR) should be applied, and that semiquantitative assessment can be recommended only for the cortical samples. Moreover, the study demonstrates that there are limitations in the scoring of &agr;S-IR structures.

Parkin disease: A clinicopathologic entity?

IMPORTANCE Mutations in the gene encoding parkin (PARK2) are the most common cause of autosomal recessive juvenile-onset and young-onset parkinsonism. The few available detailed neuropathologic reports suggest that homozygous and compound heterozygous parkin mutations are characterized by severe substantia nigra pars compacta neuronal loss. OBJECTIVE To investigate whether parkin-linked parkinsonism is a different clinicopathologic entity to Parkinson disease (PD). DESIGN, SETTING, AND PARTICIPANTS We describe the clinical, genetic, and neuropathologic findings of 5 unrelated cases of parkin disease and compare them with 5 pathologically confirmed PD cases and 4 control subjects. The PD control cases and normal control subjects were matched first for age at death then disease duration (PD only) for comparison. RESULTS Presenting signs in the parkin disease cases were hand or leg tremor often combined with dystonia. Mean age at onset was 34 years; all cases were compound heterozygous for mutations of parkin. Freezing of gait, postural deformity, and motor fluctuations were common late features. No patients had any evidence of cognitive impairment or dementia. Neuronal counts in the substantia nigra pars compacta revealed that neuronal loss in the parkin cases was as severe as that seen in PD, but relative preservation of the dorsal tier was seen in comparison with PD (P = .04). Mild neuronal loss was identified in the locus coeruleus and dorsal motor nucleus of the vagus, but not in the nucleus basalis of Meynert, raphe nucleus, or other brain regions. Sparse Lewy bodies were identified in 2 cases (brainstem and cortex). CONCLUSIONS AND RELEVANCE These findings support the notion that parkin disease is characterized by a more restricted morphologic abnormality than is found in PD, with predominantly ventral nigral degeneration and absent or rare Lewy bodies.

alpha-Synuclein pathology is highly dependent on the case selection

Lewy bodies and dystrophic neurites have been considered a common substrate for dementia, but they are also frequently found in the normal elderly population. The primary component of this pathology involves α‐synuclein. The main objective of the present study was to estimate the prevalence of α‐synuclein pathology in aged population, and to assess its relative significance in relation to dementia. The study also investigated whether differences could be detected in α‐synuclein pathology in relation to age, gender or concomitant Alzheimers pathology. Furthermore, the influence of sampling strategies was analysed. α‐Synuclein pathology was assessed using immunohistochemistry in well‐characterized post‐mortem material. The investigation included patients from a longitudinal study of dementia of Alzheimers type (n = 103, 85% demented), subjects from a prospective longitudinal clinical study of ageing (n = 69, 29% demented), a cohort of consecutive clinical post‐mortem cases collected for 1 year (n = 262, 12% demented), a sample of forensic post‐mortem cases collected for 6 months (n = 121, 15% demented) and a sample of Brain Bank material (n = 234, 26% demented). Overall, α‐synuclein pathology was found in 14% of all 774 subjects over 40 years of age, and this percentage varied from 8% to 27% according to sampling strategies. These results indicate that the prevalence of α‐synuclein pathology clearly depends on the selection of material. Furthermore α‐synuclein pathology was found in 23% of clinically demented patients and in 11% of non‐demented subjects. The load of α‐synuclein pathology was significantly greater in the demented patients versus non‐demented subjects indicating that α‐synuclein pathology is indeed of importance in the pathogenesis of dementia.