Top ten discoveries of the year

This review highlights a collection of both diverse and highly impactful studies published in the previous year selected by the author from the neurodegenerative neuropathology literature. As with previous reviews in this series, the focus is, to the best of my ability, to highlight human tissue-based experimentation most relevant to experimental and clinical neuropathologists. A concerted effort was made to balance the selected studies across neurodegenerative disease categories, approaches, and methodologies to capture the breadth of the research landscape. These studies employ a range of classical and state-of-the-art methodologies ranging from clinical pathoanatomical correlative studies to single-cell RNA sequencing, artificial intelligence, and patient-derived human induced pluripotent stem cell models. Key studies include demonstration of the earliest pathological changes in young patients with repetitive head impacts (RHI), elucidation of the longitudinal trajectory of extrapyramidal symptoms in Lewy body disease subtypes, mapping of cell-type specific polygenic risk in Alzheimer’s disease to neuropathology, a novel measure of histological brain age acceleration using artificial intelligence, trends in cerebrovascular pathologies over 25 years, associations between RHI and TDP-43 / hippocampal sclerosis, microglia / T-cell interaction in neurodegeneration, the impact of viral exposures on neurodegenerative disease risk, and polyglutamine repeat expansion disorders. This sampling of the literature collectively displays the breadth of the progress being made in the neuropathology of neurodegenerative diseases.

2023 was an important year for research in traumatic brain injury (TBI), particularly as it concerned interests in neuropathology. After reviewing the literature, we present the advancements that we felt were of particular importance to the neuropathology community. Highlighted are articles that report upon: (1) the first large-cohort assessment for the neuropathology of intimate partner violence, (2) the assessment of chronic traumatic encephalopathy (CTE) in young athletes, (3) the observation of cortical sulcal depth vascular changes in CTE, (4) a proposal for a tau immunohistochemical panel to evaluate complex cases of CTE in the context of multiple tauopathies, (5) the relationship of TBI and/or CTE with TDP-43 pathology, (6) repetitive TBI inducing pathology in C9orf72-transgenic mice, (7) radiologic patterns of head and neck injury following vehicular underbody blast exposure, (8) chronic alterations in brain metal content following repetitive impact TBI, (9) neurovascular unit injury following low-level blast exposure, and finally (10) an assessment of Muhammad Ali’s clinical history leading to the conclusion that he suffered from young-onset, idiopathic Parkinson Disease. We close our writing with in memoriam to Dr. Byron A. Kakulas, a renowned figure in the neuropathology of spinal cord injury who we lost in 2023.

As in previous years, including 2023, a major focus in the neurooncological area of neuropathology was put on more precise and constantly faster diagnostic procedures, even reaching the level of ultra-fast intraoperative diagnostics based on methylation profiling. Neuropathological diagnostic precision and clinical follow-up treatment has been further increased by combining DNA methylation profiling with targeted panel sequencing. A few new, molecularly defined tumor subtypes have been proposed, among others, a glioneuronal tumor with ATRX alteration, kinase fusion and anaplastic features (in its abbreviated form named GTAKA) and the de novo replication repair deficient glioblastoma, IDH-wildtype both having either distinct prognostic or therapeutic implications. Regarding the understanding of brain tumor development and progression, several novel mechanisms have been presented which might also be considered as treatment targets in the future, such as a) autonomous rhythmical Ca²⁺ oscillations in interconnected glioma cell networks driving tumor growth; b) transfer of mitochondria from normal astrocytes to glioma cells enhancing proliferation and self-renewal; c) brain endothelial cell remodeling upon matrix-metalloprotease 9 secretion by tumor cells metastasizing into the CNS and d) anti-tumor activity of microglia in CNS metastasis of breast cancer. Finally, in contrast to previous years, several very promising neurooncological treatment studies have been conducted, focusing on specific targets such as H3K27M or IDH1/2 mutations for which a proper neuropathological assessment is key. The continuous translation of potential new treatment targets using faster and precise diagnostic procedures will further pave the way for better individualized clinical care of neurooncological patients.

Neurodevelopmental disorders encompass a range of conditions such as intellectual disability, autism spectrum disorder, rare genetic disorders and developmental and epileptic encephalopathies, all manifesting during childhood. Over 1,500 genes involved in various signaling pathways, including numerous transcriptional regulators, spliceosome elements, chromatin-modifying complexes and de novo variants have been recognized for their substantial role in these disorders. Along with new machine learning tools applied to neuroimaging, these discoveries facilitate genetic diagnoses, providing critical insights into neuropathological mechanisms and aiding in prognosis, and precision medicine. Also, new findings underscore the importance of understanding genetic contributions beyond protein-coding genes and emphasize the role of RNA and non-coding DNA molecules but also new players, such as transposable elements, whose dysregulation generates gene function disruption, epigenetic alteration, and genomic instability. Finally, recent developments in analyzing neuroimaging now offer the possibility of characterizing neuronal cytoarchitecture in vivo, presenting a viable alternative to traditional post-mortem studies. With a recently launched digital atlas of human fetal brain development, these new approaches will allow answering complex biological questions about fetal origins of cognitive function in childhood. In this review, we present ten fascinating topics where major progress has been made in the last year.

Neuropathology-based studies in neurosurgically resected brain tissue obtained from carefully examined patients with focal epilepsies remain a treasure box for excellent insights into human neuroscience, including avenues to better understand the neurobiology of human brain organization and neuronal hyperexcitability at the cellular level including glio-neuronal interaction. It also allows to translate results from animal models in order to develop personalized treatment strategies in the near future. A nice example of this is the discovery of a new disease entity in 2017, termed mild malformation of cortical development with oligodendroglial hyperplasia in epilepsy or MOGHE, in the frontal lobe of young children with intractable seizures. In 2021, a brain somatic missense mutation of the galactose transporter SLC35A2 leading to altered glycosylation of lipoproteins in the Golgi apparatus was detected in 50 % of MOGHE samples. In 2023, the first clinical trial evaluated galactose supplementation in patients with histopathologically confirmed MOGHE carrying brain somatic SLC35A2 mutations that were not seizure free after surgery. The promising results of this pilot trial are an example of personalized medicine in the arena of epileptology. Besides this, neuropathological studies of epilepsy samples have revealed many other fascinating results for the main disease categories in focal epilepsies, such as the first deep-learning based classifier for Focal Cortical Dysplasia, or the genomic landscape of cortical malformations showing new candidate genes such as PTPN11, which is associated with ganglioglioma and adverse clinical outcome. This update will also ask why common pathogenic variants accumulate in certain brain regions, e.g., MTOR in the frontal lobe, and BRAF in the temporal lobe. Finally, I will highlight the ongoing discussion addressing commonalities between temporal lobe epilepsy and Alzheimer's disease, the impact of adult neurogenesis and gliogenesis for the initiation and progression of temporal lobe seizures in the human brain as well as the immunopathogenesis of glutamic acid decarboxylase antibody associated temporal lobe epilepsy as a meaningful disease entity. This review will update the reader on some of these fascinating publications from 2022 and 2023 which were selected carefully, yet subjectively, by the author.

2022 was a productive year for research in traumatic brain injury (TBI) and resultant neuropathology. After an extensive review, we present related studies and publications which we felt were of particular importance to the neuropathology community. First, 2022 was highlighted by important advancements in the diagnosis and, moreover, our understanding of chronic traumatic encephalopathy (CTE). Important publications include a pair concluding that CTE primarily concerns neuronal accumulation of phosphorylated tau (ptau), but that glial ptau accumulation often helps to facilitate diagnosis. In addition, a new large community study from Australia continues the indication that CTE is relatively uncommon in the community, and the first large-cohort study on brains of military personnel similarly demonstrates that CTE appears to be uncommon among service members and does not appear to explain high rates of neuropsychiatric sequelae suffered by the warfighter. The causation of CTE by impact-type TBI was supported by the application of the Bradford Hill criteria, within the brains of headbutting bovids, and interestingly within an artificial head model exposed to linear impact. Finally, a large-scale analysis of APOE genotypes contends that gene status may influence CTE pathology and outcomes. In experimental animal work, a study using mouse models provided important evidence that TDP-43 facilitates neurodegenerative pathology and is implicated in cognitive dysfunction following TBI, and another study using a swine model for concussion demonstrated that evidence that axonal sodium channel disruption may be a driver of neurologic dysfunction after concussion. Finally, we end with memoriam to Dr. John Q. Trojanowski, a giant of neurodegenerative research and an important contributor to the neurotrauma literature, who we lost in 2022.

This paper reviews ten highly impactful studies published in the previous year selected by the author from the neurodegenerative neuropathology literature. As in previous years, the focus is to highlight human tissue-based experimentation most relevant to neuropathologists. A concerted effort was made to balance the selected studies across disease categories, approaches, and methodologies to capture the breadth of the research landscape. Studies include an integrated proteomic and transcriptomic study of Alzheimer disease (AD) and new consensus diagnostic neuropathological criteria for progressive supranuclear palsy. A number of studies looking at TAR DNA-binding protein 43 (TDP-43) are highlighted. One examined interaction between AD and limbic age-related TDP-43 encephalopathy (LATE) and yet another demonstrated how TDP-43 represses cryptic exon inclusion in UNC13A, suggesting a novel pathogenic mechanism. Most surprisingly, three cryogenic electron microscopy (cryo-EM) studies showed that TMEM106B filaments form the core of TDP-43-positive inclusions. Cryo-EM revealed a prion protein amyloid structure from aggregates in Gerstmann-Sträussler-Scheinker disease. There was an elegant functional genomic study cataloging microglial gene expression in the human brain. A study shed light on how APOE influences chronic traumatic encephalopathy. A pathoanatomical study tested the dual hit hypothesis of Lewy body progression throughout the nervous system. And finally, deep learning continues to show its promise with application of a weakly supervised multiple instance learning paradigm to assess aging post-mortem brains.

Several advances in the field of neurodevelopmental diseases (NDDs) have been reported by 2022. Of course, NDDs comprise a diverse group of disorders, most of which with different aetiologies. However, owing to the development and consolidation of technological approaches, such as proteomics and RNA-sequencing, and to the improvement of brain organoids along with the introduction of artificial intelligence (AI) for biodata analysis, in 2022 new aetiological mechanisms for some NDDs have been proposed. Here, we present hints of some of these findings. For instance, centrioles regulate neuronal migration and could be behind the aetiology of periventricular heterotopia; also, the accumulation of misfolded proteins could explain the neurological effects in COVID-19 patients; and, autism spectrum disorders (ASD) could be the expression of altered cortical arealization. We also cover other interesting aspects as the description of a new NDD characterized by deregulation of genes involved in stress granule (SG) assemblies, or the description of a newly discovered neural progenitor that explains the different phenotypes of tumours and cortical tubers in tuberous sclerosis complex (TSC) disease; and how it is possible to decipher the aetiology of sudden unexplained death in childhood (SUDC) or improve the diagnosis of cortical malformations using formalin-fixed paraffin-embedded samples.

This article presents some of the author’s neuropathological highlights in the field on neuro-oncology research encountered in 2022. Major advances were made in the development of more precise, faster, easier, less invasive and unbiased diagnostic tools ranging from immunohistochemical prediction of 1p/19q loss in diffuse glioma, methylation analyses in CSF samples, molecular profiling for CNS lymphoma, proteomic analyses of recurrent glioblastoma, integrated molecular diagnostics for better stratification in meningioma, intraoperative profiling making use of Raman effect or methylation analysis, to finally, the assessment of histological slides by means of machine learning for the prediction of molecular tumor features. In addition, as the discovery of a new tumor entity may also be a highlight for the neuropathology community, the newly described high-grade glioma with pleomorphic and pseudopapillary features (HPAP) has been selected for this article. Regarding new innovative treatment approaches, a drug screening platform for brain metastasis is presented. Although diagnostic speed and precision is steadily increasing, clinical prognosis for patients with malignant tumors affecting the nervous system remains largely unchanged over the last decade, therefore future neuro-oncological research focus should be put on how the amazing developments presented in this article can be more sustainably applied to positively impact patient prognosis.

Multiple sclerosis (MS) is the most frequent inflammatory and demyelinating disease of the Central Nervous System (CNS). Significant progress has been made during recent years in preventing relapses by using systemic immunomodulatory or immunosuppressive therapies. However, the limited effectiveness of such therapies for controlling the progressive disease course indicates there is a continuous disease progression independent of relapse activity which may start very early during the disease course. Dissecting the underlying mechanisms and developing therapies for preventing or stopping this disease progression represent, currently, the biggest challenges in the field of MS. Here, we summarize publications of 2022 which provide insight into susceptibility to MS, the basis of disease progression and features of relatively recently recognized distinct forms of inflammatory/demyelinating disorders of the CNS, such as myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD).

This review highlights ten important advances in the neuromuscular disease field that were reported in 2022. As with prior updates in this article series, the overarching topics include (i) advances in understanding of fundamental neuromuscular biology; (ii) new / emerging diseases; (iii) advances in understanding of disease etiology and pathogenesis; (iv) diagnostic advances; and (v) therapeutic advances. Within this general framework, the individual disease entities that are discussed in more detail include neuromuscular complications of COVID-19 (another look at the topic first covered in the 2021 and 2022 reviews), DNAJB4-associated myopathy, NMNAT2-deficient hereditary axonal neuropathy, Guillain-Barré syndrome, sporadic inclusion body myositis, and amyotrophic lateral sclerosis. In addition, the review highlights a few other advances (including new insights into mechanisms of fiber maturation during muscle regeneration and fiber rebuilding following reinnervation, improved genetic testing methods for facioscapulohumeral and myotonic muscular dystrophies, and the use of SARM1 inhibitors to block Wallerian degeneration) that will be of significant interest for clinicians and researchers who specialize in neuromuscular disease.

The year 2021 was highlighted by many notable advancements in the field of neurotrauma and associated neuropathology. After a thorough review of the new literature, we call attention to what we feel are among the most impactful studies and publications. In brief, 2021 was marked by published consensus papers related to the diagnosis of chronic traumatic encephalopathy (CTE) and its clinical counterpart, traumatic encephalopathy syndrome. There was also progress toward our understanding of the impact of traumatic brain injury (TBI) on the general population, and how strongly CTE pathology may, or may not, commonly underlie long term clinical sequelae following TBI. Next, a critical new study has identified that acetylated tau protein, which has been found to be increased in the brains of Alzheimer’s disease and CTE patients, can be induced by TBI, is neurotoxic, and that its reduction via already-existent therapeutics is neuroprotective. There are also several important updates that pertain to military and blast TBI, particularly as they pertain to establishing causality of interface astroglial scarring. In addition, and for the first time, a specific signature for diffuse axonal injury has been identified in ex vivo tissues using multidimensional magnetic resonance imaging, providing promise for the clinical diagnosis of this lesion. Finally, several important radiologic studies from 2021 have highlighted long-standing structural reductions in a number of brain regions following both mild and severe TBI, emphasizing the need for neuropathologic correlation. We end by highlighting an editorial piece discussing how

In this update we present a series of papers focused on topics that have emerged in vascular disease over the prior year. The first two papers focus on the pathogenesis of vascular malformations, the first on brain arteriovenous malformations, and the second on cerebral cavernous malformations. These disorders can lead to significant brain injuries from intracerebral hemorrhage (if they rupture) or other neurological complications, including seizures. The next set of papers reflects work that has advanced our understanding of how the brain and the immune system “communicate” after brain injury, including stroke (papers 3-6). The first of these shows that T cells are involved in white matter repair after ischemic injury, an effect dependent on microglia, demonstrating the important cross-talk between innate and adaptive immunity. The next two papers focus on B cells, which have been relatively understudied in the context of brain injury. The contribution of antigen-experienced B cells from the meninges and skull bone marrow, rather than blood-derived B cells in neuroinflammation opens up a very novel area of investigation. The possibility that antibody secreting B cells may contribute to vascular dementia will certainly be an active area for future investigations. Similarly, in paper 6, investigators found that CNS-infiltrating myeloid cells can originate from brain borders tissues. These cells have unique transcriptional signatures that are distinct from their blood-derived counterparts, and likely contribute to myeloid cell infiltration from bone-marrow niches in close proximity to the brain. The contribution of microglia, the primary innate immune cell of the brain, to amyloid deposition and propagation is then discussed, followed by work on how perivascular Aβ is potentially cleared along the cerebral vessels in patients with cerebral amyloid angiopathy. The final two papers focus on the contribution of senescent endothelial cells and pericytes. The first used a model of accelerated senescence (Hutchinson-Gilford progeria syndrome; HGPS) and shows the translational potential of an approach to reduce telomere shortening to slow aging. The final paper demonstrates how capillary pericytes contribute to basal blood flow resistance and slow modulation of blood flow throughout the brain. Interestingly, several of the papers identified therapeutic strategies that could be potentially translated into clinical populations.

Here, we review a collection of recent manuscripts and research trends on the neuropathology of neurodegeneration that are considered by the author to be among the potentially most impactful. To the greatest extent possible, we chose to focus on histopathological studies that are most relevant to experimental and diagnostic neuropathology. While there has been an abundance of important recent discoveries and developments in neurodegenerative disease research, there was a deliberate effort here to provide balance to prevent disease categories and experimental approaches from overshadowing the others. The result is a diverse series of outstanding studies, together showing the landscape of progress across neurodegenerative disorders. One is a stereological study examining dystrophic microglia in aging. We highlight the first large genetic study of primary age-related tauopathy, showing convergence and divergence from classical Alzheimer’s disease. There were further advances in the neuropathological criteria and staging of chronic traumatic encephalopathy. Links suggesting a causal role for TMEM106B in TDP-43 proteinopathy emerged. Attempts to subtype Alzheimer’s disease on the molecular level were made. Evidence for a role for the VEGF family in cognitive impairment was advanced. Comparison of gene expression profiles from myeloid cells in peripheral blood and brain tissues from Parkinson’s disease patients revealed pathways that may lead to new mechanistic insights and biomarkers. A large autopsy series identified an increased frequency of central nervous system developmental malformations in Huntington’s disease. A robust and reliable system for assessing Lewy body pathology was proposed. Finally, we continue to be plagued by the COVID-19 pandemic, with lingering concerns of a long-term link with neurodegeneration.

The impact of a precise histopathology diagnosis and molecular workup for surgical patient management remains a controversial issue in epileptology with a lack of diagnostic agreement as root cause. Very recent advances in genotype-phenotype characterization of epilepsy-associated developmental brain lesions, including the first diagnostically useful DNA methylation studies, opened new avenues and will help to finally resolve these issues. A series of most recent articles were decisively selected by the author to exemplify the areas of improvement in neuropathology and epilepsy surgery. These topics include the progress in genotype-phenotype association studies of Focal Cortical Dysplasia (FCD) leading to the discovery of new molecularly defined entities, i.e. mild malformation of cortical development with oligodendroglial hyperplasia in epilepsy (MOGHE), SLC35A2 altered. These studies also triggered the first update of the international FCD consensus classification scheme from 2011, which will hopefully support diagnostic agreement in clinical practice and research. The dilemma of new tumor entities proposed by the 5^th edition of the WHO classification primarily associated with early seizure onset yet not well introduced to the epileptology community will also be discussed in the light of emerging experimental evidence when transfecting the developing murine brain with the single most important genetic alteration for both carcino- and epileptogenesis, i.e. BRAF V600E.

With a prevalence of 2-4% of the worldwide population, neurodevelopmental disorders (NDDs) comprise a heterogeneous group of disorders associated with neurodevelopmental dysfunction, including intellectual disability (ID), autism spectrum disorder (ASD), Down syndrome (DS) and attention-deficit/hyperactivity disorder (ADHD) among others. However, due to their heterogeneity and overlapping clinical features, NDDs such as ASD are often misdiagnosed, while for others with more distinct symptoms, such as Rett syndrome or DS, the mechanisms underlying their pathogenesis remain elusive. Last year, important steps in the mechanistic understanding of several NDDs have been achieved. New preclinical models demonstrated causality between PAK3 mutations and disorders associated with social deficiencies. ARID1B mutations have been linked to neuroectoderm specification in Coffin-Siris syndrome and DNA damage was established as an important pathologic mechanism in Aicardi-Goutières syndrome. Moreover, alterations in basic molecular processes including translation and histone acetylation have been established as major traits in the pathology of X-linked ID and Rett syndrome, revealing new pathogenetic mechanisms. Last year, advances in bioinformatics have begun to shed light on the human repeatome, a largely unexplored part of our genome, and how alterations in these sequences have a central role in ASD. The role of mitochondria in neuropathology was clarified last year with the discovery of previously unknown vesicles derived from mitochondria with a putative role in DS. An interesting discovery in the field of basic neurodevelopment showed that during postnatal brain development, changes in genome architecture and transcriptional dynamics progress independently of sensory experience. Finally, our neurocentric views of NDDs are changing as new players such as astrocytes are revealed to be crucial in neuropathology. The role of astrocytes has been clarified for some pathologies such as ASD and DS, linking well-known genetic mutations to impaired astrocyte function.

This review highlights ten important advances in the neuromuscular disease field that were reported in 2021. As with prior updates in this article series, the overarching topics include (i) advances in understanding of fundamental neuromuscular biology; (ii) new / emerging diseases; (iii) advances in understanding of disease etiology and pathogenesis; (iii) diagnostic advances; and (iv) therapeutic advances. Within this general framework, the individual disease entities that are discussed in more detail include neuromuscular complications of COVID-19 (another look at the topic first covered in the 2021 review), autosomal recessive myopathy caused by MLIP mutations, autosomal recessive neuromuscular disease caused by VWA1 mutations, Leber’s hereditary optic neuropathy, myopathies with autophagic defects, tRNA synthetase-associated Charcot-Marie-Tooth disease, systemic sclerosis-associated myopathy, humoral immune endoneurial microvasculopathy, and late-onset Pompe disease. In addition, the review highlights a few other advances (including new insights into mechanisms of muscle and nerve regeneration and the use of gene expression profiling to better characterize different subtypes of immune-mediated myopathies) that will be of significant interest for clinicians and researchers who specialize in neuromuscular disease.

This ‘Neurooncology: 2022 update’ presents topics that were selected by the authors as top ten discoveries published in 2021 in the broader field of neurooncological pathology. This time, the spectrum of topics includes: papers with a direct impact on daily diagnostic practice of CNS tumors in general and with information on how to improve grading of meningiomas; studies shedding new light on the oncogenesis of gliomas (in particular ‘optic gliomas’ and H3-mutant gliomas); several ‘multi-omic’ investigations unraveling the intra-tumoral heterogeneity of especially glioblastomas further; a study indicating the potential of ‘repurposing’ Prozac®; for the treatment of glioblastomas; liquid biopsy using CSF for assessment of residual medulloblastoma. In the last part of this review some other papers are mentioned that didn’t make it to this (quite subjective) top ten list.

Besides important progress in the understanding of the pathological substrate of COVID-19-associated brain disease, major insights into mechanisms of neurodegeneration in human disease have been provided in neuropathological studies published in 2021. Recently developed techniques, which allow the simultaneous detection of a large battery of different molecules within single cells, have proven useful in the analysis of disease mechanisms in experimental and human neuroinflammatory conditions. They have elucidated protective and detrimental effects of activated microglia, which act in a stage and context-dependent manner in the induction and propagation of neurodegeneration. In addition, they emphasize the importance of synaptic damage and of selective neuronal vulnerability in the respective diseases. The results provide important new insights with high clinical relevance.

This article reviews a collection of manuscripts in the field of neurodegenerative disease chosen from what are considered by the author to be among the 10 most important and potentially impactful topics or research trends of 2020 relevant to the field of experimental and diagnostic neuropathology. A deliberate effort was made to provide balance among disease categories covered. The result is a varied selection that includes not just individual papers but also research topics and trends. The association of COVID-19 with longer-term neurological symptoms has launched a research trend fueled by speculation that the SARS-CoV-2 might trigger neurodegenerative changes. The onslaught of transcriptomic studies has begun to give way to proteomics, with three transformative studies published examining glial contributions to Alzheimer disease, cerebral atherosclerosis in cognitive decline, and the complex sequence of post-translational modifications of the tau protein. Plasma biomarkers for Alzheimer disease have continued to make rapid advances, especially around highly sensitive assays capable of detecting different forms of abnormal hyperphosphorylated tau in peripheral blood. Two studies using cryo-electron microscopy showed the power of the approach by continuing to elucidate the diversity of filamentous tau inclusions, and a third study gave the first glimpse of α-synuclein aggregates at near atomic resolution. Another study continued to delineate how different α-synuclein conformers (“strains”) target specific brain regions and lead to neurodegeneration. In Huntington’s disease, we saw compelling molecular data showing how cells adapt to endoplasmic reticulum stress through the unfolded protein response. Finally, the role of astrocytes in chronic traumatic encephalopathy has emerged as a critical area of interest.

One of the current challenges in the field of neurodevelopmental disorders (NDDs) is still to determine their underlying aetiology and risk factors. NDDs comprise a diverse group of disorders primarily related to neurodevelopmental dysfunction including autism spectrum disorder (ASD), developmental delay, intellectual disability (ID), and attention-deficit/hyperactivity disorder (ADHD) that may present with a certain degree of cognitive dysfunction and high prevalence of neuropsychiatric outcomes. Last year, advances in human genomics have begun to shed light on the genetic architecture of these disorders and large-scale sequencing studies are starting to reveal mechanisms that range from unique genomic DNA methylation patterns (i.e. “episignatures”) to highly polygenic conditions. In addition, the contribution of de novo somatic mutations to neurodevelopmental diseases is being recognized. However, progressing from genetic findings to underlying neuropathological mechanisms has proved challenging, due to the increased resolution of the molecular and genetic assays. Advancement in modelling tools is likely to improve our understanding of the origin of neurodevelopmental disorders and provide insight into their developmental mechanisms. Also, combined in vivo editing of multiple genes and single-cell RNA-sequencing (scRNA-seq) are bringing us into a new era of understanding the molecular neuropathology of NDDs.

This article briefly presents 10 topics that were selected by the author as ‘top 10 discoveries’ published in 2020 in the broader field of neurooncological pathology including neurosciences as well as clinical neurooncology of interest for neurooncological pathology. The selected topics concern new information on the molecular characteristics of gliomas (infratentorial IDH-mutant diffuse astrocytomas, pediatric low-grade gliomas, infant-type high-grade gliomas, hypermutation in gliomas), the immunological aspects of the brain tumor microenvironment (TME), the impact of the TME on preclinical glioma models, and the importance of lymphatic drainage on brain tumor surveillance. Furthermore, important papers were published on two ‘new’ genetic syndromes predisposing to medulloblastoma, on liquid biopsy-based diagnosis of central nervous system (CNS) tumors, and on the ‘microbiome’ in glioblastomas (and other cancers). In the last part of this review, a dozen of papers are given as examples of papers that did not make it to the top 10 list of the author, underscoring the subjective component in the selection process. Acknowledging that 2020 will be remembered as the year in which the world changed because of the COVID-19 pandemic, some of the consequences of this pandemic for neurooncological pathology are briefly discussed as well. Hopefully, this review forms an incentive to appreciate the wealth of information provided by the papers that were used as building blocks for the present manuscript.

Despite the interruptions and restrictions to the progress of science that the COVID-19 pandemic has introduced, 2020 was marked by a number of important advances in the field of neurotrauma. Here, I will highlight what I believe are among the most important contributions. This year there were notable advances towards providing clinically useful information on neurotrauma outcome through the use of fluid biomarkers. I also introduce fascinating approaches to studying the role of microglia in nervous system repair and neuroinflammatory mechanisms leading to dysfunction through the use of colony-stimulating factor 1 receptor inhibitors, especially Plexxikon 5622 (PLX5622). Oral administration of this compound is able to deplete microglial elements and then, following withdrawal from the drug, a new population of microglia then repopulates the brain. Use of this approach in traumatic brain injury experimental models has produced important insights into the pathogenetic role of microglia in responding to this process. Important new data on the nature and distribution of tau involvement of neurons and astrocytes in cases of chronic traumatic encephalopathy (CTE) also appeared suggesting differences and similarities to Alzheimer’s disease. Additionally, the use of tau-specific PET scan ligands in at-risk populations has suggested that this approach may be able to identify cases with CTE. Lastly, we note the death in the past year of a major contributor to the field of neurotrauma neuropathology, Professor J. Hume Adams.

This review highlights ten important advances in the neuromuscular disease field that were first reported in 2020. The overarching topics include (i) advances in understanding of fundamental neuromuscular biology; (ii) new / emerging diseases; (iii) advances in understanding of disease etiology and pathogenesis; (iv) diagnostic advances; and (v) therapeutic advances. Within this broad framework, the individual disease entities that are discussed in more detail include neuromuscular complications of COVID-19, supervillin-deficient myopathy, 19p13.3-linked distal myopathy, vasculitic neuropathy due to eosinophilic granulomatosis with polyangiitis, spinal muscular atrophy, idiopathic inflammatory myopathies, and transthyretin neuropathy/myopathy. In addition, the review highlights several other advances (such as the revised view of the myofibrillar architecture, new insights into molecular and cellular mechanisms of muscle regeneration, and development of new electron microscopy tools) that will likely have a significant impact on the overall neuromuscular disease field going forward.

Key requirements for the validity of a neuropathological study are the inclusion of large numbers of biopsy or autopsy cases and proper controls, the rigorous classification of the basic neuropathology and the selection of the most suitable technologies for investigation. Whether the studies are performed with the fanciest, new, and state of the art technology or with rather conventional methodology is of minor importance. Following these criteria, a spectrum of neuropathological studies has been published in 2020, which provides new insights on important questions related to neurological disease. They include the pathological substrate of brain disease in COVID-19 infected patients, the nature of the adaptive and innate inflammatory response, or the type and mechanisms of tissue injury and repair in multiple sclerosis, and diagnostically relevant or mechanistic new insights into antibody-mediated diseases of the central nervous system. Other studies describe in detail the dynamic changes of brain inflammation in patients with trisomy 21 as a disease model for Alzheimer’s disease, or the presence and consequences of vascular comorbidities in a chronic inflammatory disease, such as multiple sclerosis. All these contributions have provided important, highly relevant clues for basic and translational neuroscience.

Developmental brain disorders, a highly heterogeneous group of disorders with a prevalence of around 3% of worldwide population, represent a growing medical challenge. They are characterized by impaired neurodevelopmental processes leading to deficits in cognition, social interaction, behavior and motor functioning as a result of abnormal development of brain. This can include developmental brain dysfunction, which can manifest as neuropsychiatric problems or impaired motor function, learning, language or non-verbal communication. Several of these phenotypes can often co-exist in the same patient and characterize the same disorder. Here I discuss some contributions in 2019 that are shaking our basic understanding of the pathogenesis of neurodevelopmental disorders. Recent developments in sophisticated in-utero imaging diagnostic tools have raised the possibility of imaging the fetal human brain growth, providing insights into the developing anatomy and improving diagnostics but also allowing a better understanding of antenatal pathology. On the other hand, advances in our understanding of the pathogenetic mechanisms reveal a remarkably complex molecular neuropathology involving a myriad of genetic architectures and regulatory elements that will help establish more rigorous genotype-phenotype correlations.

As we embark on a new year of scientific inquiry in neurodegenerative disease research, it is helpful to take a look back and consider the contributions in the field with the potential to be the most impactful. The purpose of this review is to highlight recent advances in 2019 which have the potential to be transformative in the field of neurodegenerative neuropathology. Substantive scientific progress rarely occurs as a “eureka moment”, and when possible, we opted to highlight collaborative efforts and research trends. We also included groundbreaking methodologies and tools. The generous increases in federal funding in the United States and elsewhere have massively expanded the total number of active programs researching Alzheimer’s disease. This exacerbates an imbalance, and an effort was made to highlight innovations across disease categories, and not to permit dementia to crowd out movement disorders, motor neuron disease, ataxias, etc. Thus, our overall goal was to highlight some of the most important discoveries, tools or methods that we feel will most likely directly enhance our ability to understand and diagnose neurodegenerative brain diseases. Given space limitations and the targeted readership of this journal, we selected ten topics most relevant to neuropathologists and clinical neuroscientists: 1. A new neurodegenerative disease category, 2. A new approach to probing gene expression on the single cell level, 3. A new approach merging histology and gene expression profiling, 4. A new computational approach using deep machine learning and computer vision, 5. A neuropathological substrate for sleep disturbance in Alzheimer’s disease, 6. A candidate pathogenic agent for Alzheimer’s disease, 7. A comprehensive approach to morphometric analysis of cerebellar neurodegeneration, 8. The strongest evidence yet linking neurodegeneration to contact sports, 9. Mounting evidence for gut to central nervous system transmission in Parkinson’s disease, and 10. A spotlight on glia in Huntington’s disease.

Neurotrauma represents a major public health problem and is one of the leading causes of death and disability worldwide. Despite its high prevalence, there are major gaps in our understanding of the underlying pathophysiology leading to the substantial morbidity and mortality associated with this problem. Here, ten studies published in 2019 are reviewed that addressed issues related to the acute and long-term effects of neurotrauma. These studies can be broken down into three separate categories, namely, the importance of neurotrauma-based damage to the cerebrovascular unit, white matter damage following neurotrauma, and research related to the long-term neurodegenerative consequences of repeated head trauma, especially chronic traumatic encephalopathy. The advances highlighted here indicate that progress has been made. However, major gaps in knowledge remain which will require additional neuropathologic studies of clinical specimens, as well as the development and investigation of a wide range of relevant pre-clinical models. Further efforts in this field are clearly needed if there are to emerge better clinical outcomes for the numerous patients that suffer neurotrauma each year as well as those currently suffering from its long-term effects.

This article briefly discusses 10 topics that were selected by the author as top 10 discoveries published in 2019 in the broader field of neuro-oncological pathology (so including neurosciences as well as clinical neuro-oncology but with implications for neuro-oncological pathology). Some topics concern new information on immunohistochemical and molecular markers that enable improved diagnosis of particular tumors of the cen-tral nervous system (CNS) and information on a refined classification of medulloblastomas. Subsequently, several papers are discussed that further elucidate some pathobiological aspects of especially medulloblastomas (histogenesis, molecular evolution) and diffuse gliomas (mechanisms involved in CNS infiltration, role of cancer stem(-like) cells, longitudinal molecular evolution). The remaining topics concern progress made in vaccination therapy for glioblastomas and in using cerebrospinal fluid for liquid biopsy diagnosis of gliomas. Clearly, substantial, and sometimes even amazing progress has been made in increasing our understanding in several areas of neuro-oncological pathology. At the same time, almost every finding raises new questions, and translation of new insights in improving the outcome for patients suffering from CNS tumors remains a huge challenge.

The aim of this review is to highlight novel findings in 2019 in the area of neurovascular disease. Experimental studies have provided insight into disease development, molecular determinants of pathology, and putative novel therapeutic targets. Studies in genetic experimental models as well as monogenic forms of human cerebrovascular diseases identified pathogenic molecules that may also be relevant to sporadic cases. There have been advances in understanding the development of cerebral cavernous angiomas and arteriovenous malformations, and putative curative treatments have been suggested from experimental models. Key pathogenic pathways involved in vessel calcification and stiffness have also been identified. At the cellular level, studies showed that proper function of endothelial and mural cells, particularly pericytes, is crucial to ensure full endothelial differentiation and blood-brain barrier integrity. Moreover, recent discoveries support the existence of a homeostatic crosstalk between vascular cells and other neural cells, including neurons. Cerebrovascular diseases are strongly associated with inflammation. Beyond pathogenic roles of specific components of the inflammatory response, new discoveries showed interesting interactions between inflammatory molecules and regulators of vascular function. Clinical investigation on cerebrovascular diseases has progressed by combining advanced imaging and genome-wide association studies. Finally, vascular cognitive impairment and dementia are receiving increasing attention. Recent findings suggest that high-salt intake may cause cerebrovascular dysfunction and cognitive impairment independent of hypoperfusion and hypertension. These and other recent reports will surely inspire further research in the field of cerebrovascular disease that will hopefully contribute to improved prevention and treatment.

This review highlights ten important advances in the neuromuscular disease field that either were first reported in 2019, or have reached a broad consensus during that year. The overarching topics include (i) new / emerging diseases; (ii) advances in understanding of disease etiology and pathogenesis; (iii) diagnostic advances; and (iv) therapeutic advances. Within this broad framework, the individual disease entities that are discussed in more detail include myoglobinopathy, POPDC3-mutated limb-girdle muscular dystrophy, neuromuscular adverse events associated with the immune checkpoint inhibition therapy, neuroglial stem cell-derived inflammatory pseudotumor of the spinal cord and spinal cord roots, acute flaccid myelitis, congenital myopathies, idiopathic inflammatory myopathies (with particular emphasis on immune-mediated necrotizing myopathies and sporadic inclusion body myositis), spinal muscular atrophy, and Duchenne muscular dystrophy. In addition, the review highlights several diagnostic advances (such as diagnostic RNA sequencing and development of digital diagnostic tools) that will likely have a significant impact on the overall neuromuscular disease field going forward.

Ten neuropathological studies, published in 2019, are discussed, which address important aspects of neuroimmunology and inflammatory brain disease. They include topics related to new mechanisms of inflammation and immune mediated neurodegeneration, which are relevant for multiple sclerosis (publications 1 to 4) and discuss the role of specific autoantibodies against myelin oligodendrocyte glycoprotein or aquaporin 4 in neuromyelitis optica spectrum disorders (publications 5 and 6). Other studies highlight the discovery of new virus induced diseases of the nervous system and their relevance for clinical neurology and diagnostic neuropathology (publications 7 and 8). Finally, very interesting studies are discussed dealing with microglia and immune mechanisms in neurodegeneration (publication 9) and the neuropathological long-term outcome of Aß vaccination in Alzheimer’s disease (publication 10). All these studies highlight the central role of neuropathology in neurological disease research.