Multidimensional definition of the interferonopathy of Down syndrome and its response to JAK inhibition

Mechanistic insights into Down syndrome comorbidities via convergent RNA-seq and TWAS signals

Down syndrome (DS) is caused by trisomy of chromosome 21 and is associated with diverse clinical manifestations, yet the molecular pathways linking chromosome-21 dosage effects to DS comorbidities remain poorly defined. Here we address this gap by applying a network-based, integrative framework that combines whole-blood transcriptomic data with gene-trait associations to uncover mechanistic insights into DS-associated conditions. First, we performed matrix factorization using PLIER on Human Trisome Project (HTP) RNA-Seq profiles from 304 trisomy-21 (T21) and 95 euploid (D21) individuals, deriving 156 biologically interpretable gene modules. We then identified 92 modules whose activity differed significantly between T21 and D21 and annotated these with prior-knowledge and KEGG pathways. To connect modules to clinical traits, we integrated PrediXcan-derived TWAS results from the UK Biobank, revealing 25 T21-specific modules with significant gene-trait associations (FDR < 0.1), including modules linked to cardiovascular, hematological, immune, metabolic, and neurological phenotypes relevant to DS. Using HTP clinical records as a replication cohort, 13 of these modules reliably predicted comorbidity status (AUC > 0.65, mAPS > 0.65). Most notably module 37, an interferon-stimulated gene network, whose elevated expression robustly distinguished DS individuals with pulmonary hypertension (AUC = 0.76, mAPS = 0.73). Overall, our study demonstrates that integrating blood-derived gene modules with population-scale genetic data uncovers coherent molecular signatures underlying DS comorbidities, identifies candidate biomarkers and therapeutic targets (e.g., ISG15, IFITs, MX1 ), and highlights the power of combining transcriptomic and genetic evidence to elucidate complex disease mechanisms.

DYRK1A in blood and immune function: implications in leukemia, inflammatory disorders, infection and Down syndrome

Down syndrome (DS) is the most frequent autosomal aneuploidy, and it arises due to an extra copy of human chromosome 21. Individuals with trisomy 21 (T21) exhibit an increased predisposition towards a wide number of developmental and physiological alterations, often referred to as DS co-occurring conditions, including congenital heart disease, leukemia, intellectual disability, neurodegenerative disorders or autoimmune diseases, among many others. The overexpression of several genes encoded on chromosome 21 have been linked to many of such T21-associated disorders, but we are still very far from grasping a full picture of the contributions and interconnections of such genes in the pathophysiology of DS. DYRK1A is a versatile and ubiquitous kinase encoded on human chromosome 21, and as such, its activity has been linked to many alterations that characterize DS. Although most of the attention has been focused on DYRK1A's roles in neural development, function and degeneration, accumulating reports are expanding the scope towards other tissues and conditions where this kinase also performs critical functions, such as the cardiovascular system, diabetes, inflammation and immune homeostasis. Here, we present a detailed review of the literature summarizing all the information linking DYRK1A to blood and immune function, as well as leukemia, inflammation and viral infections, with a special focus on their potential associations to T21. This article synthesizes evidence that supports several novel hypotheses on previously unsuspected roles for DYRK1A in specific DS alterations, opening new pathways for the research community to explore and therefore, contributing to future innovative diagnostic or therapeutic interventions. This article will hopefully inspire and guide the advancement of our knowledge leading to much needed treatments for individuals with Down syndrome, but also for the general population.

Type I interferon signalling and interferon-responsive microglia in health and disease

Recent evidence suggests that type I interferon (IFN-I) signalling extends beyond its canonical roles in antiviral defence and immunomodulation. Over the past decade, dysregulated IFN-I signalling has been linked to genetic disorders and neurodegenerative diseases, where it may contribute to neurological impairments. Microglia have emerged as key mediators of IFN-I responses in the central nervous system. A distinct transcriptional state responsive to interferons has recently been identified in microglia. The activation of the IFN-I pathway in these cells is now recognised as pivotal in both development and neurodegeneration. This review is divided into two main sections: the first examines the broader role of IFN-I signalling in the central nervous system, particularly its contribution to neurological dysfunction; the second focuses on the specific state of interferon-responsive microglia, exploring its mechanisms and relevance in neurodegenerative conditions. Finally, we discuss how these areas intersect and their implications for both healthy and diseased states.

The emerging concept of ANCA-associated vasculitis related to inborn errors of immunity

ANCA-associated vasculitis (AAV) is a group of rare small vessels vasculitis that preferentially affect the kidneys, lungs and upper airways. Although the detailed pathophysiology remains unclear, genetic background has been shown to play a role in sporadic forms of AAV. The discovery of these susceptibility genes (and associated biological pathways) involved in AAV have shaped the current understanding of AAV pathophysiology. In addition to common genetic polymorphisms, specific rare inborn errors of immunity (IEI) have been described with a high frequency of ANCA (antineutrophil cytoplasmic antibodies) positivity and vasculitis features in young individuals (in addition to other manifestations). A systematic literature search revealed that patients with pathogenic variants in COPA, STING1, DNASE1L3, and PIK3CD are at increased risk of developing ANCA and AAV features, including alveolar hemorrhage, interstitial lung disease, pauciimmune glomerulonephritis, and upper airways involvement (septum perforation, saddle-nose deformity, chronic nasal/sinuses ulceration). Some of these IEI may also present with a mixed phenotype and/or auto-antibodies profile associating features of AAV and other autoimmune diseases (in particular systemic lupus erythematosus). Notably, a proportion of reports and series lack serological (ANCA specificity and titers) and/or histopathological data, making challenging to assess the likelihood for ANCA pathogenicity in some patients with IEI (as opposed to unspecific signs of biologic autoimmunity). This point is nonetheless essential to make appropriate therapeutic decisions. In addition, since most of the genes mentioned above are involved in the type 1 interferon signaling, the role of this pathway in AAV etiopathogenesis deserves further investigation. In this review, we will describe these IEI, their overlap with sporadic AAV, and their evocative features. Next, we will discuss how these monogenic conditions might inform our general understanding of AAV pathophysiology. We also propose some directions for future research in order to better define the link between ANCA and IEI. Finally, we will consider how making the diagnosis of an IEI in a patient with AAV features might impact individual management.

Evidence of blood-brain barrier dysfunction and CSF immunoglobulin synthesis in Down Syndrome Regression Disorder

OBJECTIVES

This study sought to evaluate proteomic, metabolomic, and immune signatures in the cerebrospinal fluid of individuals with Down Syndrome Regression Disorder (DSRD).

METHODS

A prospective case-control study comparing proteomic, metabolomic, and immune profiles in individuals with DSRD was performed. Samples were obtained from a biorepository of affected individuals and compared to clinically available data and previously obtained neurodiagnostic studies. Individuals with DSRD were compared to individuals with established neuroinflammatory conditions (e.g., multiple sclerosis), and neurotypical controls undergoing a lumbar puncture for headaches. Samples underwent high-throughput proteomic, metabolomic, and immune marker profiling. Data was compared across groups and clinical phenotypes. Gene set enrichment analysis and pathway analyses were utilized to analyze the data.

RESULTS

In total, 34 individuals with DSRD, 22 neuroinflammatory controls, and 27 neurotypical controls were enrolled in the study. We observed a highly significant concordance in dysregulated proteomics signatures in DSRD and neuroinflammatory controls versus healthy controls, most prominently upregulation of many immunoglobulin sequences. In addition, individuals with DSRD displayed strong upregulation of liver-derived plasma proteins and erythrocyte proteins in the CSF, indicating poor blood-brain barrier integrity. The immune marker profile of DSRD is clearly similar to other neuroimmunological conditions, including strong elevation of MIP3-α, eotaxin, and IFN-γ.

INTERPRETATION

Individuals with DSRD have unique CSF proteomic and metabolomic signatures consistent with neuroinflammation and increased blood-brain barrier permeability. The CSF of individuals with DSRD was more comparable to individuals with neuroinflammatory disorders than neurotypical controls, indicating the potential for an immune etiology of disease.

NF-κB signaling directs a program of transient amplifications at innate immune response genes

The cellular response to pathogens involves an intricate response directed by key innate immune signaling pathways which is characterized by cell-to-cell heterogeneity. How this heterogeneity is established and regulated remains unclear. We describe a program of transient site-specific gains (TSSG) producing extrachromosomal DNA (ecDNA) of immune-related genes in response to innate immune signaling. Activation of NF-κB drives TSSG of the interferon receptor gene cluster through inducible recruitment of the transcription factor RelA and the pre-replication complex member MCM2 to an epigenetically regulated TSSG control element. Targeted recruitment of RelA or p300 are sufficient to induce TSSG formation. RelA and MCM2 specify a program of TSSG for at least six and as many as 179 regions enriched in innate immune response genes. Identification of this program reveals regulated production of ecDNA as a mechanism of heterogeneity in the host response.

Mediator kinase inhibition suppresses hyperactive interferon signaling in Down syndrome

Hyperactive interferon (IFN) signaling is a hallmark of Down syndrome (DS), a condition caused by Trisomy 21 (T21); strategies that normalize IFN signaling could benefit this population. Mediator-associated kinases CDK8 and CDK19 drive inflammatory responses through incompletely understood mechanisms. Using sibling-matched cell lines with/without T21, we investigated Mediator kinase function in the context of hyperactive IFN in DS over a 75 min to 24 hr timeframe. Activation of IFN-response genes was suppressed in cells treated with the CDK8/CDK19 inhibitor cortistatin A (CA), via rapid suppression of IFN-responsive transcription factor (TF) activity. We also discovered that CDK8/CDK19 affect splicing, a novel means by which Mediator kinases control gene expression. To further probe Mediator kinase function, we completed cytokine screens and metabolomics experiments. Cytokines are master regulators of inflammatory responses; by screening 105 different cytokine proteins, we show that Mediator kinases help drive IFN-dependent cytokine responses at least in part through transcriptional regulation of cytokine genes and receptors. Metabolomics revealed that Mediator kinase inhibition altered core metabolic pathways in cell type-specific ways, and broad upregulation of anti-inflammatory lipid mediators occurred specifically in kinase-inhibited cells during hyperactive IFNγ signaling. A subset of these lipids (e.g. oleamide, desmosterol) serve as ligands for nuclear receptors PPAR and LXR, and activation of these receptors occurred specifically during hyperactive IFN signaling in CA-treated cells, revealing mechanistic links between Mediator kinases, lipid metabolism, and nuclear receptor function. Collectively, our results establish CDK8/CDK19 as context-specific metabolic regulators, and reveal that these kinases control gene expression not only via TFs, but also through metabolic changes and splicing. Moreover, we establish that Mediator kinase inhibition antagonizes IFN signaling through transcriptional, metabolic, and cytokine responses, with implications for DS and other chronic inflammatory conditions.

Hospital-based Introduction of Untested High-risk Foods for Down Syndrome Infant with Severe Food Protein-induced Enterocolitis Syndrome: A Case Report

Down syndrome (DS) is a risk factor for severe food protein-induced enterocolitis syndrome (FPIES), with DS patients tending to have multiple-food FPIES. This is the first case where a DS infant with a history of severe chronic FPIES to milk and soy could effectively be introduced with some untested high-risk foods through hospital-based oral food challenges (OFCs). The infant is a 20-month-old girl with DS, who was diagnosed with milk- and soy-induced FPIES. Considering her history of intensive care unit care for severe FPIES reactions, we considered that introducing other high-risk foods, such as wheat and hen's egg (white and yolk), at home was not appropriate for her. We offered hospital-based OFCs effectively and safely by introducing wheat and hen's egg as high-risk foods against FPIES to the 20-month-old infant. As a result, she tolerated soy-based seasoning, wheat, and egg whites without any symptoms, but she developed frequent vomiting after ingesting egg yolk. We did a prompt intervention with intravenous fluid replacement to prevent severe adverse conditions. After discharge, she exhibited an FPIES symptom as a consequence of ingesting green peas and miso; hence, we recommended the elimination of peas, in addition to soy, milk, and egg yolk, from her diet. She remained symptom-free since adhering to this dietary regimen. In severe FPIES children, it is encouraged to introduce unconsumed high-risk foods in the hospital safely to avoid severe reactions at home and prevent unnecessary food eliminations.

A Pathway-Level Information ExtractoR (PLIER) framework to gain mechanistic insights into obesity in Down syndrome

Down syndrome (DS), caused by the triplication of chromosome 21 (T21), is a prevalent genetic disorder with a higher incidence of obesity. Traditional approaches have struggled to differentiate T21-specific molecular dysregulation from general obesity-related processes. This study introduces the omni-PLIER framework, combining the Pathway-Level Information ExtractoR (PLIER) with the omnigenic model, to uncover molecular mechanisms underlying obesity in DS. The PLIER framework aligns gene expression data with biological pathways, facilitating the identification of relevant molecular patterns. Using RNA sequencing data from the Human Trisome Project, omni-PLIER identified latent variables (LVs) significantly associated with both T21 and body mass index (BMI). Elastic net regression and causal mediation analysis revealed LVs mediating the effect of karyotype on BMI. Notably, LVs involving glutathione peroxidase-1 (GPX1) and MCL1 apoptosis regulator, BCL2 family members emerged as crucial mediators. These findings provide insights into the molecular interplay between DS and obesity. The omni-PLIER model offers a robust methodological advancement for dissecting complex genetic disorders, with implications for understanding obesity-related processes in both DS and the general population.

JAK inhibition decreases the autoimmune burden in Down syndrome

Background

Individuals with Down syndrome (DS), the genetic condition caused by trisomy 21 (T21), display clear signs of immune dysregulation, including high rates of autoimmunity and severe complications from infections. Although it is well established that T21 causes increased interferon responses and JAK/STAT signaling, elevated autoantibodies, global immune remodeling, and hypercytokinemia, the interplay between these processes, the clinical manifestations of DS, and potential therapeutic interventions remain ill defined.

Methods

We report a comprehensive analysis of immune dysregulation at the clinical, cellular, and molecular level in hundreds of individuals with DS, including autoantibody profiling, cytokine analysis, and deep immune mapping. We also report the interim analysis of a Phase II clinical trial investigating the safety and efficacy of the JAK inhibitor tofacitinib through multiple clinical and molecular endpoints.

Results

We demonstrate multi-organ autoimmunity of pediatric onset concurrent with unexpected autoantibody-phenotype associations in DS. Importantly, constitutive immune remodeling and hypercytokinemia occur from an early age prior to autoimmune diagnoses or autoantibody production. Analysis of the first 10 participants to complete 16 weeks of tofacitinib treatment shows a good safety profile and no serious adverse events. Treatment reduced skin pathology in alopecia areata, psoriasis, and atopic dermatitis, while decreasing interferon scores, cytokine scores, and levels of pathogenic autoantibodies without overt immune suppression.

Conclusions

JAK inhibition is a valid strategy to treat autoimmune conditions in DS. Additional research is needed to define the effects of JAK inhibition on the broader developmental and clinical hallmarks of DS.

Funding

NIAMS, Global Down Syndrome Foundation.

Clinical trial number

NCT04246372.

Infantile Spasms in Pediatric Down Syndrome: Potential Mechanisms Driving Therapeutic Considerations

Infantile spasms are common in Down Syndrome (DS), but the mechanisms by which DS predisposes to this devastating epilepsy syndrome are unclear. In general, neuronal excitability and therefore seizure predisposition results from an imbalance of excitation over inhibition in neurons and neural networks of the brain. Animal models provide clues to mechanisms and thereby provide potential therapeutic approaches. Ts65Dn mice have been the most widely used animal model of DS. In this model, there is evidence for both abnormal cerebral excitation and inhibition: infantile spasms-like clinical and electrographic activity can be elicited by the administration of gamma-aminobutyric acid (GABA)-B receptor agonist, gamma-butyrolactone (GBL), and depolarizing GABA-A responses persist beyond the age of their usual switch to hyperpolarized responses. But despite its widespread use, the Ts65Dn model may be suboptimal because of the absence of numerous genes that are triplicated in human DS and the presence of numerous genes that are not triplicated in human DS. Recently, a transchromosomic mouse artificial chromosome 21 (TcMAC21) mouse model has been developed, which carries a copy of human chromosome 21 and therefore has a genetic composition more similar to human DS. As in Ts65Dn mice, exposure of TcMAC21 mice to GBL results in epileptic spasms, and aberrant excitation has also been demonstrated. This review summarizes excitatory and inhibitory dysfunction in models of DS that may play a role in the generation of seizures and infantile spasms, providing a perspective on past studies and a prelude for future ones. Further elucidation will hopefully lead to rational therapeutic options for DS children with infantile spasms.

Integrated analysis of immunometabolic interactions in Down syndrome

Down syndrome (DS), caused by trisomy 21 (T21), results in immune and metabolic dysregulation. People with DS experience co-occurring conditions at higher rates than the euploid population. However, the interplay between immune and metabolic alterations and the clinical manifestations of DS are poorly understood. Here, we report an integrated analysis of immunometabolic pathways in DS. Using multi-omics data, we infered cytokine-metabolite relationships mediated by specific transcriptional programs. We observed increased mediation of immunometabolic interactions in those with DS compared to euploid controls by genes in interferon response, heme metabolism, and oxidative phosphorylation. Unsupervised clustering of immunometabolic relationships in people with DS revealed subgroups with different frequencies of co-occurring conditions. Across the subgroups, we observed distinct mediation by DNA repair, Hedgehog signaling, and angiogenesis. The molecular stratification associates with the clinical heterogeneity observed in DS, suggesting that integrating multiple omic profiles reveals axes of coordinated dysregulation specific to DS co-occurring conditions.

Dysregulated airway epithelial antiviral immunity in Down Syndrome impairs type III IFN response and amplifies airway inflammation during RSV infection

Trisomy 21 (TS21), also known as Down syndrome (DS), increases pediatric mortality risk from respiratory syncytial virus (RSV) by nine-fold, yet its underlying immunological basis remains unclear. Here, we investigated RSV-induced immunological responses in TS21 airway epithelial cells (AECs), the primary site of respiratory virus entry and host defense. TS21 AECs exhibit hyperactive interferon (IFN) signaling and reduced RSV infectivity, but they also show impaired type-III IFN responses during viral infection. Furthermore, TS21 AECs demonstrate heightened production of proinflammatory mediators CXCL5 and CXCL10 both before and after RSV exposure. Infants with DS suffering from severe viral bronchiolitis demonstrate dysregulated airway immune responses in vivo, characterized by diminished type-III IFN levels and increased CXCL5/CXCL10 secretion. Our results indicate that RSV severity in DS is not due to impaired viral control but to dysregulated airway proinflammatory responses, offering new therapeutic opportunities to mitigate the severity of RSV infection in children with DS.

CNS disease associated with enhanced type I interferon signalling

The ability to mount an interferon-mediated innate immune response is essential in protection against neurotropic viruses, but antiviral type I interferons also have neurotoxic potential. The production of type I interferons can be triggered by self-derived nucleic acids, and the brain can be susceptible to inappropriate upregulation of type I interferon signalling. Homoeostatic dysregulation of type I interferons has been implicated in rare inborn errors of immunity (referred to as type I interferonopathies) and more common neurodegenerative disorders (eg, Parkinson's disease, Alzheimer's disease, and amyotrophic lateral sclerosis). Recent developments include new insights into the pathogenesis of these disorders that involve dysregulated type I interferon signalling, as well as advances in their diagnosis and management. The role of type I interferons in brain cellular health suggests the future therapeutic potential of approaches that target these interferons and their signalling.

JAK inhibition decreases the autoimmune burden in Down syndrome

Individuals with Down syndrome (DS), the genetic condition caused by trisomy 21 (T21), display clear signs of immune dysregulation, including high rates of autoimmune disorders and severe complications from infections. Although it is well established that T21 causes increased interferon responses and JAK/STAT signaling, elevated autoantibodies, global immune remodeling, and hypercytokinemia, the interplay between these processes, the clinical manifestations of DS, and potential therapeutic interventions remain ill defined. Here, we report a comprehensive analysis of immune dysregulation at the clinical, cellular, and molecular level in hundreds of individuals with DS. We demonstrate multi-organ autoimmunity of pediatric onset concurrent with unexpected autoantibody-phenotype associations. Importantly, constitutive immune remodeling and hypercytokinemia occur from an early age prior to autoimmune diagnoses or autoantibody production. We then report the interim analysis of a Phase II clinical trial investigating the safety and efficacy of the JAK inhibitor tofacitinib through multiple clinical and molecular endpoints. Analysis of the first 10 participants to complete the 16-week study shows a good safety profile and no serious adverse events. Treatment reduced skin pathology in alopecia areata, psoriasis, and atopic dermatitis, while decreasing interferon scores, cytokine scores, and levels of pathogenic autoantibodies without overt immune suppression. Additional research is needed to define the effects of JAK inhibition on the broader developmental and clinical hallmarks of DS. ClinicalTrials.gov identifier: NCT04246372.

Overview of secondary immunodeficiency

In contrast to inborn errors of immunity (IEI), which are inherited disorders of the immune system that predispose to infections, malignancy, atopy, and immune dysregulation, secondary immunodeficiencies and immune dysregulation states (SID) are acquired impairments in immune cell function and/or regulation, and may be transient, reversible, or permanent. SIDs can derive from a variety of medical comorbidities, including protein-losing conditions, malnutrition, malignancy, certain genetic syndromes, prematurity, and chronic infections. Medications, including immunosuppressive and chemotherapeutic drugs, can have profound effects on immunity and biologic agents used in rheumatology, neurology, and hematology/oncology practice are increasingly common causes of SID. Iatrogenic factors, including surgical procedures (thymectomy, splenectomy) can also contribute to SID. A thorough case history, medication review, and laboratory evaluation are necessary to identify the primary driver and determine proper management of SID. Careful consideration should be given to whether a primary IEI could be contributing to autoimmunity, malignancy, and posttreatment complications (e.g., antibody deficiency). SID management consists of addressing the driving condition and/or removing the offending agent if feasible. If SID is suspected to be permanent, then antibiotic prophylaxis, additional immunization, and immunoglobulin replacement should be considered.

Multimodal analysis of dysregulated heme metabolism, hypoxic signaling, and stress erythropoiesis in Down syndrome

Down syndrome (DS), the genetic condition caused by trisomy 21 (T21), is characterized by delayed neurodevelopment, accelerated aging, and increased risk of many co-occurring conditions. Hypoxemia and dysregulated hematopoiesis have been documented in DS, but the underlying mechanisms and clinical consequences remain ill defined. We report an integrative multi-omic analysis of ∼400 research participants showing that people with DS display transcriptomic signatures indicative of elevated heme metabolism and increased hypoxic signaling across the lifespan, along with chronic overproduction of erythropoietin, elevated biomarkers of tissue-specific hypoxia, and hallmarks of stress erythropoiesis. Elevated heme metabolism, transcriptional signatures of hypoxia, and stress erythropoiesis are conserved in a mouse model of DS and associated with overexpression of select triplicated genes. These alterations are independent of the hyperactive interferon signaling characteristic of DS. These results reveal lifelong dysregulation of key oxygen-related processes that could contribute to the developmental and clinical hallmarks of DS.

Human life within a narrow range: The lethal ups and downs of type I interferons

The past 20 years have seen the definition of human monogenic disorders and their autoimmune phenocopies underlying either defective or enhanced type I interferon (IFN) activity. These disorders delineate the impact of type I IFNs in natural conditions and demonstrate that only a narrow window of type I IFN activity is beneficial. Insufficient type I IFN predisposes humans to life-threatening viral diseases (albeit unexpectedly few) with a central role in immunity to respiratory and cerebral viral infection. Excessive type I IFN, perhaps counterintuitively, appears to underlie a greater number of autoinflammatory and/or autoimmune conditions known as type I interferonopathies, whose study has revealed multiple molecular programs involved in the induction of type I IFN signaling. These observations suggest that the manipulation of type I IFN activity to within a physiological range may be clinically relevant for the prevention and treatment of viral and inflammatory diseases.

Variegated overexpression of chromosome 21 genes reveals molecular and immune subtypes of Down syndrome

Individuals with Down syndrome, the genetic condition caused by trisomy 21, exhibit strong inter-individual variability in terms of developmental phenotypes and diagnosis of co-occurring conditions. The mechanisms underlying this variable developmental and clinical presentation await elucidation. We report an investigation of human chromosome 21 gene overexpression in hundreds of research participants with Down syndrome, which led to the identification of two major subsets of co-expressed genes. Using clustering analyses, we identified three main molecular subtypes of trisomy 21, based on differential overexpression patterns of chromosome 21 genes. We subsequently performed multiomics comparative analyses among subtypes using whole blood transcriptomes, plasma proteomes and metabolomes, and immune cell profiles. These efforts revealed strong heterogeneity in dysregulation of key pathophysiological processes across the three subtypes, underscored by differential multiomics signatures related to inflammation, immunity, cell growth and proliferation, and metabolism. We also observed distinct patterns of immune cell changes across subtypes. These findings provide insights into the molecular heterogeneity of trisomy 21 and lay the foundation for the development of personalized medicine approaches for the clinical management of Down syndrome.

Cryo-EM structures reveal tau filaments from Down syndrome adopt Alzheimer's disease fold

Down syndrome (DS) is a common genetic condition caused by trisomy of chromosome 21. Among their complex clinical features, including musculoskeletal, neurological, and cardiovascular disabilities, individuals with DS have an increased risk of developing progressive dementia and early-onset Alzheimer's disease (AD). This dementia is attributed to the increased gene dosage of the amyloid-β (Aβ) precursor protein gene, the formation of self-propagating Aβ and tau prion conformers, and the deposition of neurotoxic Aβ plaques and tau neurofibrillary tangles. Tau amyloid fibrils have previously been established to adopt many distinct conformations across different neurodegenerative conditions. Here, we report the characterization of brain samples from four DS cases spanning 36-63 years of age by spectral confocal imaging with conformation-specific dyes and cryo-electron microscopy (cryo-EM) to determine structures of isolated tau fibrils. High-resolution structures revealed paired helical filament (PHF) and straight filament (SF) conformations of tau that were identical to those determined from AD cases. The PHFs and SFs are made of two C-shaped protofilaments, each containing a cross-β/β-helix motif. Similar to filaments from AD cases, most filaments from the DS cases adopted the PHF form, while a minority (approximately 20%) formed SFs. Samples from the youngest individual with no documented dementia had sparse tau deposits. To isolate tau for cryo-EM from this challenging sample we used a novel affinity-grid method involving a graphene oxide surface derivatized with anti-tau antibodies. This method improved isolation and revealed that primarily tau PHFs and a minor population of chronic traumatic encephalopathy type II-like filaments were present in this youngest case. These findings expand the similarities between AD and DS to the molecular level, providing insight into their related pathologies and the potential for targeting common tau filament folds by small-molecule therapeutics and diagnostics.

Malignant progression of preleukemic disorders

ABSTRACT

The spectrum of myeloid disorders ranges from aplastic bone marrow failure characterized by an empty bone marrow completely lacking in hematopoiesis to acute myeloid leukemia in which the marrow space is replaced by undifferentiated leukemic blasts. Recent advances in the capacity to sequence bulk tumor population as well as at a single-cell level has provided significant insight into the stepwise process of transformation to acute myeloid leukemia. Using models of progression in the context of germ line predisposition (trisomy 21, GATA2 deficiency, and SAMD9/9L syndrome), premalignant states (clonal hematopoiesis and clonal cytopenia of unknown significance), and myelodysplastic syndrome, we review the mechanisms of progression focusing on the hierarchy of clonal mutation and potential roles of transcription factor alterations, splicing factor mutations, and the bone marrow environment in progression to acute myeloid leukemia. Despite major advances in our understanding, preventing the progression of these disorders or treating them at the acute leukemia phase remains a major area of unmet medical need.

Cryo-EM Structures Reveal Tau Filaments from Down Syndrome Adopt Alzheimer's Disease Fold

Down syndrome (DS) is a common genetic condition caused by trisomy of chromosome 21. Among the complex clinical features including musculoskeletal, neurological and cardiovascular disabilities, individuals with DS have an increased risk of developing progressive dementia and early onset Alzheimer's Disease (AD). This is attributed to the increased gene dosage of amyloid-β (Aβ) precursor protein gene, the formation of self-propagating Aβ and tau prion conformers, and the deposition of neurotoxic Aβ plaques and tau neurofibrillary tangles. Tau amyloid fibrils have previously been established to adopt many distinct conformations across different neurodegenerative conditions. Here we report the characterization of brain samples from four DS cases spanning 36 to 63 years of age by spectral confocal imaging with conformation-specific dyes and cryo-electron microscopy (cryo-EM) to determine structures of isolated tau fibrils. High-resolution structures reveal paired helical filament (PHF) and straight filament (SF) conformations of tau that are identical to those determined from AD. The PHFs and SFs are made of two C-shaped protofilaments with a cross-β/β-helix motif. Similar to filaments from AD cases, most filaments from the DS cases adopted the PHF form, while a minority (~20%) formed SFs. Samples from the youngest individual with no documented dementia had sparse tau deposits. To isolate tau for cryo-EM from this challenging sample we used a novel affinity-grid method involving a graphene-oxide surface derivatized with anti-tau antibodies. This improved isolation and revealed primarily tau PHFs and a minor population of chronic traumatic encephalopathy type II-like filaments were present in this youngest case. These findings expand the similarities between AD and DS to the molecular level, providing insight into their related pathologies and the potential for targeting common tau filament folds by small-molecule therapeutics and diagnostics.