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Department of Biomedical EngineeringIn the brain, iron is an essential element in oxygen supply through blood vessels, energy metabolism, myelin formation, and neurotransmitter synthesis for brain development with maintaining homeostasis. However, even in healthy people, as they grow older, iron levels increase steadily in some regions of the brain. Among the inevitable iron deposits with aging, the unbound labile iron generates reactive oxygen and free radicals, which produce stress on the brain tissue and necrosis of cells, which are closely associated with neurodegenerative diseases. These finally promote neurodegenerative diseases, including Parkinson???s disease and Alzheimer???s disease, which accompany the damage in behavior and cognitive function. Therefore, developing magnetic resonance imaging-based biomarkers to detect various iron clusters deposited in the brain is crucial work for diagnosing and monitoring related diseases. However, it???s still impossible to classify the states of iron and separate the various forms of iron deposited in the brain. The aim of this study was to develop multi-color iron magnetic resonance imaging and the investigation of its in vivo feasibility through translation research from the preclinical trials including postmortem magnetic resonance imaging with histopathological validation to clinical application. In the first section, it was discovered that the neuromelanin pigment within the human substantia nigra is only sensitive to T2* than other magnetic resonance contrast due to its paramagnetic property. Subsequently, the technique for specific visualization of neuromelanin-iron clusters in postmortem substantia nigra tissue was developed using combined T2 and T2* (T2*/T2 or T2*/T22) with histopathological validation supported by the Monte Carlo simulation. Separate segmentations of the areas of iron detected in the T2 map and neuromelanin observed in the T2*/T2 map (or T2*/T22 map) were available within the substantia nigra. The dorsal linear mismatch of T2 and T2* was consistently detected in the brains of healthy controls. However, it was shortened in the diseased brains. In vivo feasibility and implication of developed technique as a clinical biomarker were quantitatively demonstrated in the patients of Parkinson???s disease compared to healthy subjects. In the second section, the iron deposition along the myelinated fiber of white matter was identified in the diseased brains. The iron-rich white matter at the frontal subcortical area contributes to the positive susceptibility in the patients of Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia. Susceptibility-weighted imaging presented the noticeable phase signal showing the tree-like structure in the white matter of the frontal brain, with striking atrophy. This kind of rare tissue contrast in susceptibility-weighted imaging can aid to define Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia. Besides, the deposited iron was verified on the myelinated fibers of the 3rd cranial nerve, which is the oculomotor nerve within the brain of progressive supranuclear palsy. Our results demonstrated the enhanced magnetic resonance susceptibility value between the area of substantia nigra and red nucleus shown in the brain of progressive supranuclear palsy derives from exaggerated iron concentration on the myelinated fibers of the nerves between two structures. In conclusion, the developed techniques of multi-color iron magnetic resonance imaging in this thesis can be useful imaging biomarkers to evaluate the progressive change of several iron-related neurodegenerative diseases, such as Perry syndrome, progressive supranuclear palsy, Parkinson???s disease, and Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia. The advanced research will be implemented to validate the alteration of magnetic resonance signal with the presence of iron molecules chelated to beta-amyloid or tau with Alzheimer???s disease progression.ope

Magnetic resonance imaging of the substantia nigra in parkinson’s disease : neuromelanin, iron and diffusion tensor imaging

Tese de doutoramento, Medicina (Imagiologia), Universidade de Lisboa, Faculdade de Medicina, 2015In the last years, extensive developments in neuroimaging MR techniques have profoundly changed the study of Parkinson’s disease (PD), evolving from the role of excluding secondary parkinsonism to the emergence as a disease biomarker. MR advanced sequences in high field magnets opened the possibility to visualize in vivo the substantia nigra (SN) and to investigate specific PD pathological changes, enabling the development of high accuracy tools for disease diagnosis in early stages and for the comprehension of disease pathophysiology. Our work was centered on the application of new MR imaging techniques to study the SN in PD, early in the disease course, mainly focusing on untreated patients at the time of clinical diagnosis. The primary objectives were centered on the application of high field MR imaging sequences in two main areas: diagnosis of PD in early disease stages and differential diagnosis with Essential tremor (ET). The development and application of neuromelanin sensitive MR imaging in 3.0 Tesla allowed the detection of significant changes in the SN of PD patients, with high sensitivity and specificity for disease diagnosis, even in early disease stages (namely at the time of clinical diagnosis). These imaging findings reproduced in vivo the characteristic pathological changes of PD with greater alteration in the ventrolateral SN region and preservation of the dorsal segment. These results were obtained with several image evaluation methods: semi-automated area assessments, manual width measurements and simple visual inspection by Neuroradiologists, corroborating the reproducibility of the data and enabling wider applications of this image technique in the clinical practice. The MR correlation of neuromelanin with iron in the SN of PD patients allowed the in vivo investigation of the influence of local iron concentration in the SN on the signal of neuromelanin-sensitive sequences. A quantification T2-relaxometry study showed that the SN paramagnetic iron effects do not seem to influence significantly the neuromelanin MR signal reduction in PD patients. Several studies with diffusion tensor MR imaging (DTI) have allowed the detection of microstructural changes in the SN of PD patients in early disease changes, emerging as a possible disease biomarker. So, the reproducibility of DTI metrics in this specific brain area was particularly relevant for future applications of this MR technique. We conducted a reproducibility DTI study in PD patients that showed a good reproducibility of DTI metrics supporting the use of these measurements in further studies, namely longitudinal within-subject evaluation, and cross-sectional comparisons. The differential diagnosis of PD with ET is particularly relevant and there was the need of high accurate tools to aid the clinical assessment. The application of neuromelanin-sensitive MR techniques was able to discriminate ET from early stage tremor-dominant PD with high sensitivity and specificity values, in the same range as nuclear medicine techniques and may become a useful clinical tool in the evaluation of tremor disorders. Our research showed an important role of neuromelanin sensitive MR imaging for the diagnosis PD in early disease stages and its differential diagnosis with ET. A multi-modal MR approach with iron assessment and diffusion tensor imaging can further elucidate the SN disease changes and aid future research of disease pathophysiology.Nos últimos anos, o extenso desenvolvimento das técnicas de neuroimagem modificou profundamente a investigação da Doença de Parkinson (PD), evoluindo de um simples papel na exclusão de parkinsonismo secundário para a emergência de biomarcadores imagiológicos da doença. Sequências avançadas de RM em aparelhos de alto campo magnético abriram a possibilidade de visualizar in vivo a substantia nigra (SN) e a investigação de alterações patológicas específicas da PD, permitindo o desenvolvimento de ferramentas com elevada fiabilidade para o diagnóstico em fases precoces da evolução da doença e para a compreensão da sua fisiopatologia. A nossa investigação centrou-se na aplicação de novas técnicas de imagem RM para estudar a SN na PD, em fases precoces da doença, com enfoque especial em doentes não tratados na altura do diagnóstico clínico. Os objectivos principais centraram-se na aplicação de sequências de RM em alto campo em duas áreas major: diagnóstico da PD em fases precoces da doença e o diagnóstico diferencial com o Tremor essencial (ET). O desenvolvimento e aplicação da imagem RM sensível à neuromelanina em 3.0T permitiu a detecção de alterações significativas na SN de doentes com PD, com elevada sensibilidade e especificidade para o diagnóstico da doença, mesmo em fases precoces da sua evolução dela (nomeadamente na altura do diagnóstico clínico). Estes achados de imagem reproduziram in vivo as alterações patológicas características da PD, com uma maior alteração na região ventero-lateral da SN e preservação do segmento dorsal. Estes resultados foram obtidos com vários métodos de avaliação de imagem: avaliação semi-automática da área, medição manual da espessura e avaliação visual por neurorradiologistas, corroborando a reproductibilidade dos dados e permitindo uma aplicação abrangente desta técnica de imagem na prática clínica. A correlação por RM da neuromelanina com o ferro, na SN de doentes com PD, permitiu a investigação in vivo da influência da concentração local de ferro na SN com o sinal das sequências sensíveis à neuromelanina. Um estudo quantitativo de relaxometria T2* mostrou que os efeitos paramagnéticos do ferro não influenciam significativamente a redução de sinal RM da neuromelanina em doentes com PD. Vários estudos com tensores de difusão (DT) permitiram a detecção de alterações microestruturais na SN de doentes com PD em fases precoces de doença, emergindo como um possível biomarcador de doença. Assim, a reproductibilidade das métricas de DTI, nesta área específica do encéfalo, é particularmente relevante para aplicações futuras desta técnica de RM. Conduzimos um estudo de reproductibilidade de DTI em doentes com PD que demonstrou uma boa reproductibilidade das métricas de DTI, suportando a utilização destas medidas em estudos futuros, nomeadamente avaliações longitudinais “within-subject” e comparações “cross-sectional”. O diagnóstico diferencial da PD com ET é particularmente relevante e ferramentas fiáveis para auxiliar a avaliação clínica eram necessárias. A aplicação de técnicas de RM sensíveis à neuromelanina possibilitou a discriminação de ET de PD “tremor-dominant” em fases precoces com elevados valores de sensibilidade e especificidade, no mesmo espectro das técnicas de medicina nuclear e pode tornar-se uma ferramenta clínica útil para a avaliação do tremor. A nossa investigação demonstrou um importante papel das técnicas de RM sensíveis à neuromelanina para o diagnóstico de PD em fases precoces da doença e para o seu diagnóstico diferencial com ET. Uma abordagem multi-modal de RM com avaliação do ferro e DTI pode, adicionalmente, permitir estudar as alterações da SN e auxiliar a investigação futura da fisiopatologia da doença

Personalized translational epilepsy research - Novel approaches and future perspectives: Part I: Clinical and network analysis approaches.

Despite the availability of more than 15 new "antiepileptic drugs", the proportion of patients with pharmacoresistant epilepsy has remained constant at about 20-30%. Furthermore, no disease-modifying treatments shown to prevent the development of epilepsy following an initial precipitating brain injury or to reverse established epilepsy have been identified to date. This is likely in part due to the polyetiologic nature of epilepsy, which in turn requires personalized medicine approaches. Recent advances in imaging, pathology, genetics and epigenetics have led to new pathophysiological concepts and the identification of monogenic causes of epilepsy. In the context of these advances, the First International Symposium on Personalized Translational Epilepsy Research (1st ISymPTER) was held in Frankfurt on September 8, 2016, to discuss novel approaches and future perspectives for personalized translational research. These included new developments and ideas in a range of experimental and clinical areas such as deep phenotyping, quantitative brain imaging, EEG/MEG-based analysis of network dysfunction, tissue-based translational studies, innate immunity mechanisms, microRNA as treatment targets, functional characterization of genetic variants in human cell models and rodent organotypic slice cultures, personalized treatment approaches for monogenic epilepsies, blood-brain barrier dysfunction, therapeutic focal tissue modification, computational modeling for target and biomarker identification, and cost analysis in (monogenic) disease and its treatment. This report on the meeting proceedings is aimed at stimulating much needed investments of time and resources in personalized translational epilepsy research. Part I includes the clinical phenotyping and diagnostic methods, EEG network-analysis, biomarkers, and personalized treatment approaches. In Part II, experimental and translational approaches will be discussed (Bauer et al., 2017) [1]

Differentiating the Substantia Nigra and Ventral Tegmental Area in Early-stage Parkinson\u27s Disease Using Iron Imaging

Excessive midbrain iron accumulation in Parkinson’s Disease (PD) contributes to degeneration of the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA). Despite this understanding, there are no validated PD biomarkers. Magnetic resonance imaging (MRI) can localize and quantify brain iron for diagnosis of PD. Seventeen early-stage PD patients and twenty-one controls were scanned at 3T and 7T MRI. Using quantitative susceptibility mapping (QSM) and R2* relaxometry, we analyzed the average iron content in the SNc, substantia nigra pars reticulata (SNr), and VTA. QSM detected significantly higher SNc iron content in PD patients compared to controls at both field strengths. R2* only detected differences at 7T and showed lower sensitivity and diagnostic accuracy in diagnostic biomarker analyses. As predicted, the SNr and VTA were spared from iron accumulation. SNc iron overload in early-stage PD, best detected using QSM, could be the first diagnostic biomarker of PD following validation

Gradient echo-based quantitative MRI of human brain at 7T : Mapping of T1, MT saturation and local flip angle

Quantitative MRI (qMRI) refers to the process of deriving maps of MR contrast parameters, such as relaxation times, from conventional images. If the qMRI maps have a high degree of precision and a low degree of bias, they can be compared longitudinally, across subjects, and (ideally) between measurement protocols and research sites. They also provide a more direct biophysical interpretation of the pixel intensities. The increased magnetization of spins at ultra-high field (UHF) strengths of 7T and above could potentially be translated into higher spatial resolution and/or reduced scan time. This thesis tackles UHF-related challenges in qMRI, namely the increased inhomogeneity of the radio frequency (RF) field (B1) and increased specific absorption rate (SAR). The changing relaxation times (i.e. prolonged T1 and shortened T2) also needs to be accounted for.Here, spoiled gradient-recalled echo (GRE) techniques are employed to map (primarily) two structural MR parameters, i.e. the longitudinal relaxation time (T1) and the magnetization transfer (MT) saturation (MTsat). Because of its influence at UHF, emphasis is also put on mapping of the local flip angle. Primarily, qMRI is performed by the inversion of analytical signal equations, as opposed to numerical approaches.The process of implementing and modifying the dual flip angle (DFA) technique in conjunction with an MT-weighted GRE for 7T is described. Implementation is performed within the well-established multi-parameter mapping (MPM) framework and special attention is afforded to the reduction of biases as well as overcoming saftey restrictions imposed by SAR. An approach to obtain high-SNR low-bias flip angle maps at 7T, using the dual refocusing echo acquisition mode (DREAM) technique is also presented. This is important since high fidelity flip angle maps are a prerequisite in DFA-based T1-mapping and recommended for correcting MTsat at UHF. Furthermore, MPRAGE-based techniques are discussed. Firstly, it is demonstrated how to most effectively obtain B1-corrected MPRAGE images of “pure” T1 contrast using a sequential protocol This is followed by a description of T1-mapping using MP2RAGE. Finally, an innovative technique for simultaneous mapping of T1 and the local flip angle is introduced, dubbed “MP3RAGE”

Relaxometria no estudo da doença de Parkinson

Dissertação para obtenção do Grau de Mestre em Engenharia BiomédicaA doença de Parkinson (DP) é uma doença neurodegenerativa que afecta cerca de 1-2% dos indivíduos com idade superior a 65 anos, num total de 5 milhões em todo o mundo. Durante os próximos 20 anos prevê-se que a incidência da DP duplique. A alteração do conteúdo de ferro em certas estruturas cerebrais parece estar relacionada com distúrbios neurodegenerativos. A quantificação do conteúdo de ferro in vivo através da Imagem por Ressonância Magnética (IRM) tem sido estudada como biomarcador destas doenças. Uma vez que a presença de ferro afecta o campo magnético local, medições de variáveis físicas dos tecidos, nomeadamente da constante T2*, através de técnicas de relaxometria, podem levar a algumas conclusões indirectas sobre o conteúdo de ferro nos tecidos. O presente estudo teve como objectivo desenvolver um programa com interface gráfica que permitisse a medição da constante T2* de uma forma prática, aplicável na clínica, e utilizá-lo num conjunto de imagens para comparar valores da constante de T2* em determinadas regiões cerebrais, entre grupos de indivíduos com DP e controlos. Participaram neste estudo um total de 32 indivíduos, tendo sido medida a constante de T2* em três regiões da substantia nigra, através da delimitação de ROIs. Efectuaram-se simulações computacionais de forma a determinar qual o método mais robusto na obtenção dos valores de T2*. Após a análise e tratamento dos resultados obtidos observou-se uma ligeira diminuição do valor de T2* (33%) na região rostral da SN, entre o grupo de doentes com DP e os controlos, de acordo com o esperado. Analisando a gravidade da doença, esta correlacionou-se com a assimetria característica da DP. No entanto, os resultados obtidos não foram estatisticamente significativos, sendo necessário no futuro aumentar a amostra em estudo ou alterar a abordagem de aquisição de imagens, de forma a que esta metodologia possa ser aplicável em ambiente clínico e constituir uma ferramenta no auxílio ao diagnóstico da DP

Unveiling the impact of neuromotor disorders on speech: a structured approach combining biomechanical fundamentals and statistical machine learning

Speech has been shown to convey clinically useful information in the study of Neurodegenerative Disorders (NDs), such as Parkinson’s Disease (PD). Traditionally the use of speech as an exploratory tool in People with Parkinson’s (PwP) has focused on the estimation of acoustic characteristics and their study at face value, analysing the physio-acoustical markers and using them as features for the differentiation between Healthy Controls (HC) and PwP. The present work takes a step further, given the intricate interoperation between neuromotor activity, responsible for both planning and driving the system, and the production of the acoustic speech signal; by the study of speech, this relationship may be properly exploited and analysed, providing a non-invasive method for the diagnosis, analysis, and observation of NDs. This work aims to introduce a working model that is capable of linking both domains and serves as a projection tool to provide insights about a speaker’s neuromotor state. This is based on a review of the neurophysiological background of the structure and function of the nervous system, and a review of the main nervous system dysfunctions involved in PD and other related neuromotor disorders. The role of the respiratory, phonatory, and articulatory systems is reviewed in the production of voice and speech under normal and pathological circumstances. This setting might allow for speech to be considered a useful trait within the precision medicine framework, as it provides a personal biometric marker that is innate and easy to elicit, can be recorded remotely with inexpensive equipment, is non-invasive, cost-effective, and easy to process. The problem can be divided into two main categories: firstly, a binary detection task distinguishing between healthy controls and individuals with NDs based on the projection model and phonatory estimates; secondly, a progression and tracking task providing a set of quantitative indices that enable clinically interpretable scores. This study aims to define a set of features and models that help to characterise hypokinetic dysarthria (HD). These incorporate the neuroscientific knowhow semantically and quantitatively to be used in clinical decision support tools that provide mechanistic insight on the processes involved in speech production, incorporating into the algorithmic element neuromotor considerations that add to better interpretability, consequently leading to improved clinical decisions and diagnosis. An overview of the acoustic signal processing algorithms for use in speech articulation and phonation system inversion regarding neuromotor disorder assessment is provided. An algorithmic methodology for model inversion and exploration has been proposed for the functional characterization and system inversion of each subsystem involved under the neuro-biomechanical foundations exposed before. A description of the vocal fold biomechanics using the glottal source, and formant dynamics provides the base for specific mapping to articulation kinematics. The statistical methods used in performance evaluation are based on three-way comparisons and transversal and longitudinal assessment by classical hypothesis testing. Three related experimental studies are shown to empirically illustrate the potential of phonation and articulation analysis: the characterization of PD from glottal biomechanics based on the amplitude distributions of the glottal flow and on the vocal fold body stiffness in assessing the efficiency of transcranial magnetic stimulation, and the description of PD dysarthria through an articulation projection model. The results from the biomechanical analysis of phonation showed that the behaviour of glottal source amplitude distributions from PD and healthy controls using three-way comparisons and hierarchical clustering were essentially distinguishable from those from normative young participants with the best accuracy scores produced by SVM classifiers of 94.8% (males) and 92.2% (females). Nevertheless, PD participants were barely separable from age-matched controls, possibly pointing to confounding factors due to age. The outcomes from using vocal fold stiffness in assessing the efficiency of transcranial magnetic stimulation showed mixed results, as some PD participants reflected clear improvements in phonation stability after stimulation, whereas some others did not. Some cases of sham controls experienced also minor improvements of unknown origin, possibly expressing a placebo effect. The overall results on the efficiency of stimulation showed an accuracy global score of 67% over the 18 cases studied. The results from articulation projection modelling showed the possibility of formulating personalised models for PD and control participants to transform acoustic formant dynamics into articulation kinematics. This might open the possibility of characterising PD dysarthria based on speech audio records. The most remarkable findings of the study include the determination of the glottal source amplitude distribution behaviour of normative and PD participants; the impact of age effects in phonation as a confounding factor in neuromotor disorder characterization; the importance of ensuring that the classification of speech dysarthria is based on principles that can be explained and interpreted; the need of taking into account the effects of medication when framing new classification experiments; the potential of using EEG-band decomposition to analyse vocal fold stiffness correlates, as well as the possibility of using these descriptions in longitudinal monitoring of treatment efficiency; the feasibility of establishing a relationship between acoustic and kinematic variables by projection model inversion; and the potential of these descriptions for estimating neuromotor activities in midbrain related to phonation and articulation activity. The most important outcome to be brought forth from the thesis is that the methodology used throughout the project uses a bottom-up approach based on speech model inversion at the acoustical, biomechanical, and neuromotor levels allowing to estimate glottal signals, biomechanical correlates, and neuromotor activity from speech alone, establishing a common neuromechanical characterisation framework on its own

Biomarcadores diagnósticos y de deterioro cognitivo en la enfermedad de Parkinson

262 p.La enfermedad de Parkinson es una enfermedad neurodegenerativa en la que, como en otras, el proceso fisiopatológico que conduce a la muerte de neuronas está presente desde tiempo antes del diagnóstico. Las manifestaciones clínicas cardinales son temblor, bradicinesia, rigidez y pérdida de reflejos posturales, denominadas síntomas motores. Aun hoy, doscientos años después de la detallada descripción que hizo James Parkinson en "An essay on the shaking palsy", el diagnóstico de la enfermedad se basa en criterios clínicos. Esto hace que, incluso entre expertos, puedan existan errores diagnósticos, dado que otras enfermedades cursan con manifestaciones similares.Por otro lado, además de los síntomas motores, existe otro grupo de manifestaciones clínicas conocidas como "síntomas no motores" que contribuyen de manera sustancial al empeoramiento de la calidad de vida de los pacientes. Ente ellas se encuentran las alteraciones del sueño, las alteraciones del sistema nervioso autónomo, los trastornos psiquiátricos o las alteraciones del tracto digestivo. El deterioro cognitivo es una manifestación no motora frecuente en la enfermedad de Parkinson. De hecho, con el curso de la enfermedad, una proporción importante de pacientes termina desarrollando demencia, con consecuencias muy del etéreas sobre el individuo y su entorno. El deterioro cognitivo leve en la enfermedad de Parkinson es un constructo definido para etiquetar a aquellos pacientes que, teniendo déficit cognitivo, no presentan alteraciones de su funcionalidad en el día a día. Aunque se sabe que éste es un factor de riesgo para desarrollar demencia, no todos los pacientes con deterioro cognitivo leve acaban desarrollándola.Por tanto, el disponer de biomarcadores capaces de ayudar en el diagnóstico de la enfermedad de Parkinson o de detectar pacientes con mayor riesgo de desarrollar demencia, es una necesidad crucial aún sin resolver. La investigación de biomarcadores ha de ser paralela al desarrollo de tratamientos neuroprotectores que, según las corrientes de evidencia actuales, sólo serían útiles en las fases más tempranas de la enfermedad. El presente trabajo de Tesis Doctoral se centra en la investigación de biomarcadores, tanto para el diagnóstico como para la detección de pacientes con más riesgo de desarrollar demencia asociada a la enfermedad de Parkinson. El trabajo se ha basado en el estudio exhaustivo desde el punto de vista clínico y neuropsicológico de una cohorte de pacientes con enfermedad de Parkinson sin demencia y una cohorte de controles. La búsqueda de biomarcadores se ha realizado en líquido cefalorraquídeo y sangre (plasma). Como aproximación se han tenido en cuenta tres de los procesos fisiopatológicos implicados en la enfermedad de Parkinson: agregación de proteínas, inflamación, y autofagia. Por ello, se han evaluado en líquido cefalorraquídeo las proteínas que se encuentran en los agregados patológicos cerebrales (ß-amiloide, tau, tau fosforilada y -sinucleína) y diversas citoquinas en líquido cefalorraquídeo y en sangre. Además, se ha medido la actividad de diversos enzimas lisosomales en líquido cefalorraquídeo. Como forma de validar y ampliar parte de nuestros resultados, se ha explorado una base de datos internacional disponible de forma pública del estudio Parkinson's Progression Markers Initiative.Con los resultados de la presente Tesis Doctoral se ha demostrado que la combinación en forma de ratios de los niveles de diversas proteínas en líquido cefalorraquídeo tiene un mayor valor como herramienta diagnóstica para diferenciar pacientes de controles que los niveles de las proteínas por separado. Así, por ejemplo, la ratio formada por tau fosforilada/¿-sinucleína diferencia a pacientes de controles con un área bajo la curva de 0,85. Por otro lado, el factor de necrosis tumoral se ha encontrado elevado en líquido cefalorraquídeo de pacientes, y en conjunción con la ratio anterior presenta unos valores de precisión diagnóstica mejores, por lo que podría servir como biomarcador diagnóstico de la enfermedad. Además, niveles crecientes de interleuquina 6 en plasma se asocian a mayor gravedad de la enfermedad, por lo que podría tener utilidad como biomarcador pronóstico de la misma. En relación al deterioro cognitivo, algunas de las ratios formadas por las proteínas de agregación, presentan correlación con la integridad de algunos dominios cognitivos, como memoria o función visuoespacial, por lo que podrían servir como biomarcador para diferenciar subtipos de deterioro cognitivo leve. Además, explorando la base de datos del estudio Parkinson¿s Progression Markers Initiative, que dispone de datos de seguimiento, se ha comprobado que la elevación de algunas de esas ratios (tau total/ß-amiloide, tau total/¿-sinucleína y tau total/ß-amiloide+-sinucleína) predicen el desarrollo de demencia a los tres años de evolución. Por último, en relación a los enzimas lisosomales, la actividad de la catepsina D, se ha encontrado elevada en pacientes con deterioro cognitivo leve al compararlos con los cognitivamente normales. Por otro lado, la actividad de la ß-hexosaminidasa se asocia con los niveles en líquido cefalorraquídeo de las proteínas de agregación, por lo que la actividad de este enzima podría estar implicada en el depósito de dichas proteínas. Con todo, los resultados de esta tesis sugieren varios candidatos como biomarcadores para el diagnóstico y para la detección de la progresión del deterioro cognitivo. Queda patente a lo largo del trabajo la idea de que, dado que el sustrato fisiopatológico de la enfermedad es complejo y en el intervienen diferentes mecanismos, parece poco probable, que un único biomarcador sea capaz de alcanzar una precisión suficiente. Los resultados encontrados, aportan evidencia sobre la utilidad de diversos biomarcadores que pueden guiar las líneas a seguir en futuros estudios