Clinical Research Directory

Genetic Analysis of Uncommon Disease Presentations in Non-US Populations

Background: Genetics research over the past 20 years has helped researchers find the causes of many diseases. More powerful tools for genetic testing now exist. Researchers want to use these new tools to learn more about genetic diseases. They want to look for possible genetic causes of unusual diseases. They will focus on people who live outside of the United States and whose access to genetic testing has been limited. Objective: To look for potential genetic sources of diseases among children and their families. Eligibility: Children aged 2 to 18 years and their related family members who have or may have a genetic disease. They will reside primarily outside of the US. Design: Participants will be recruited at sites outside of the US. Participants will be screened. Their existing medical records will be reviewed. They will have a physical exam. They will answer questions about their family history and symptoms. Participants will provide samples for genetic testing. They may have blood drawn. They may spit saliva into a small container. They may have a cotton swab rubbed on the inside of the mouth. The samples will be shipped to the NIH for genetic testing. Participants will be notified if testing reveals a known disease. Participants may be asked to provide new samples to confirm the diagnosis. Local study teams will contact the participants about the results. Participants will also be notified if analysis yields gene variants that may cause disease.

BEhavioral and Adherence Model for Improving Quality, Health Outcomes and Cost-Effectiveness of healthcaRe

Lack of adherence to treatment is a widespread issue worldwide, which leads to higher healthcare utilisation rates and even premature death. While the level of adherence may differ based on the specific condition and treatment, studies estimate that approximately 50% of medications are not taken according to the prescribed instructions. In addition, adherence rates tend to decrease even further when the treatment requires a behavioural change. Literature reviews about factors that affect people's adherence show that it is challenging to predict whom can be considered to have adherent and non-adherent behaviours. In addition, the studies highlight that it is challenging to support a person to be adherent. Based on this knowledge the BEAMER project was established (Behavioural and Adherence Model for improving quality, health outcomes and cost-Effectiveness of healthcaRe). The overall goal of the project is to improve the quality of life of individuals, enhance healthcare accessibility and sustainability, thereby transforming the way healthcare stakeholders engage with patients to understand their condition and adherence levels throughout their healthcare journey. To address the overall goal, the BEAMER project has developed a disease agnostic model named "B-COMPASS: BEAMER-COmputational Model for Patient Adherence and Support Solutions". The aim of the B-COMPASS is to identify patients' needs and preferences which enables the creation of patient-specific supports, with the intention of improving their adherence to treatment within the heterogeneity of the different disease-areas and healthcare contexts. Based on the validated BEAMER questionnaire, the B-COMPASS predicts relative adherence and offers an elicitation process of patient needs and preferences to enable targeted supports to improve patient adherence. This results in an allocation of patients to different groups based on their needs and preferences. Overall, the B-COMPASS provides patient insights that will enable more effective design of patient support, most likely resulting in better patient experience, improved adherence and lower healthcare and societal costs. So far, several activities from a technical and user perspective have already been conducted in the project to refine the B-COMPASS. This has been done by applying an iterative mixed method approach were both stakeholders (regulator, pharma, academic/research and small and medium-sized enterprises) and end users (patients, health providers and health systems) have been involved. Despite the finetuning of the B-COMPASS, the effectiveness of the B-COMPASS hinges on empirical investigations into the structural elements that impact patient behaviour and the identification of predictive factors that can assist healthcare providers' (HCP) and Research Leads in designing more effective treatment plans (the term HCPs/Research Lead include both the individuals and the institutions where care is delivered). Therefore, validation studies will be conducted to assess the B-COMPASS's performance in six therapeutic areas (cardiovascular, endocrinology, immunology, neurology, oncology and rare diseases) with patients recruited in at least Italy (FISM), Portugal (APDP and MEDIDA) Norway (AHUS), Spain (FHUNJ and FIIBAP), The Netherlands (WDO), and Germany (UDUS). The collected data will be used to evaluate the B-COMPASS's capacity to attend to a variety of needs and challenges for adherence.

Longitudinal Studies of Patient With FPDMM

Background: Genes tell the body and its cells how to work. Familial platelet disease (FPD) or FPD with associated malignancies (FPDMM) is caused by a variant in the gene RUNX1. People with this disease may have problems with their blood and bleed for a long time when they are injured. Researchers want to learn more about RUNX1 variants and FPD. Objective: To learn more about FPD in people with RUNX1 variants to lead to better diagnosis, monitoring, and treatment. Eligibility: People any age with a suspected or confirmed RUNX1 variant People who have a family member with the variant Design: All participants will be screened with a phone call and a blood, saliva, or cheek cell sample. Participants with a suspected or confirmed variant will have 1 visit. It will last about 2 days. They will then have visits at least once a year. Visits will include: * Medical history and physical exam * Blood tests or saliva sample * Possible skin biopsy: A small piece of the participant s skin will be removed. * Bone marrow aspiration or biopsy: The participant s bone marrow will be removed by needle from a large bone such as the hip bone. * Possible apheresis: Blood will be removed from the body and certain blood cells will be taken out. The rest of the blood is returned to the body. Between visits, participants with a suspected or confirmed variant will keep a diary of disease symptoms and signs. Samples from all participants may be used for genetic testing

A Longitudinal Study on Family Adaptation and Relationship Dynamics in Pediatric Rare Diseases

Rare diseases in children can affect not only the child's health but also the well-being and relationships within the entire family. Parents often experience stress, uncertainty, and emotional strain, which may in turn influence their child's mental health and quality of life. However, little is known about how families adapt over time to living with a rare disease or how daily experiences and family interactions shape this process. This study aims to better understand how children with rare diseases and their caregivers adjust psychologically and emotionally over time. It will examine how factors such as parental stress, uncertainty, coping strategies, and family communication are linked to the mental health and quality of life of both children and parents. The study will include children and adolescents (ages 1-18) with a diagnosed rare disease and their caregivers. Participants will complete online questionnaires at four time points over one year. A subgroup of families will also take part in a two-week smartphone-based assessment, where parents report their daily experiences, such as stress, emotions, and worries, several times per day. Some children and adolescents will additionally participate in interviews to share their own perspectives. The main outcomes of interest are the child's mental health and quality of life. The study will also assess parental well-being and family functioning to understand how these factors influence each other over time. By combining long-term and daily data, this study will provide a detailed picture of how families cope with rare diseases in everyday life. The findings may help improve psychological support and guide the development of targeted interventions for families affected by rare pediatric conditions.

Epidemiological Study of Treatment Approaches in AChR-Antibody Positive Generalized Myasthenia Gravis in Russia

This is a multicenter, non-interventional, retrospective-prospective, single-arm observational study designed to describe real-world treatment approaches and clinical outcomes among adults with acetylcholine receptor (AChR) antibody-positive generalized myasthenia gravis (gMG) in routine clinical practice in Russia.

Rheopheresis as Adjuvant Treatment of Calciphylaxis

The investigators propose to set up a prospective randomized controlled trial to control the security and assess the efficacy of adjuvant treatment by rheopheresis in necrotizing-ulcered calciphylaxis in the hemodialysis population.

Implementation of Long-read Sequencing for the Diagnosis of Rare Diseases.

Following on from the third national plan for rare diseases (PNMR3), the main objectives of the PNMR4 are to reduce diagnostic uncertainty and dead ends and to strengthen translational research to promote diagnosis and the development of new treatments in the field of rare diseases. To this end, the French Genomic Medicine Plan 2025 (PFMG2025) is organizing the rollout of whole genome sequencing (WGS) for diagnostic purposes. This technological milestone, covering regions outside the coding regions, has recently enabled the identification of variations in the RNU4-2 gene as a major cause of Intellectual Developmental Disorder (IDD), accounting for approximately 0.4% of cases. RNU4-2 is a gene encoding a small nuclear RNA (snRNA), which is not translated into protein, and whose variations are not accessible to exome sequencing techniques. However, based on current knowledge, these techniques are based on short-read sequencing technology and can diagnose up to 50% of patients. It is therefore necessary to develop new techniques to detect variations not identified by these techniques. In this context, the development of third-generation sequencing, particularly using Nanopore technology, now makes it possible to combine genomic and post-genomic approaches through long-read whole genome sequencing coupled with the detection of methylated cytosines on native DNA. This new approach therefore enables the simultaneous detection of point or structural genomic variants, methylation abnormalities, and haplotype reconstruction. Numerous studies have shown that this strategy improves the diagnosis rate of rare diseases and could become a first-line genetic test. DNA methylation is an epigenetic modification that does not cause changes in the genomic sequence but regulates the transcription (RNA synthesis) of genes and therefore their expression. Methylation studies are performed either to establish an episignature or to search for methylation abnormalities. An episignature is the result of a variation in a gene known to regulate methylation marks. Methylation abnormalities are already known and sought after in targeted analysis for certain diseases such as Prader-Willi/Angelman syndromes and Beckwith-Wiedemann/Silver-Russell syndromes. The contribution of methylation analysis to the diagnosis of other diseases has recently been demonstrated. For example, in methylmalonic aciduria and homocystinuria type cblC associated with the autosomal recessive gene MMACHC, promoter methylation analysis revealed hypermethylation linked to the presence of an intronic variant of the PRDX1 gene. This intronic variant leads to the synthesis of an aberrant antisense RNA overlapping the promoter of the MMACHC gene, causing its hypermethylation. In 2024, combined whole-genome and methylation analysis in patients with porokeratosis led to the discovery of the FDFT1 gene. In general, the study of methylation profiles has shown its value in reducing diagnostic uncertainty in patients with rare diseases who have not been diagnosed after genome analysis. The search for methylation abnormalities (or epimutation) at the pan-genomic level in the context of molecular diagnosis of rare diseases remains largely inaccessible and poorly described in the literature. The techniques routinely used for their detection are most often based on bisulfite treatment and PCR amplification. The disadvantages of bisulfite treatment are that it degrades DNA, preventing long-read applications, that it does not distinguish between 5mC and 5hmC methylation, and that failure to treat unmethylated cytosines can lead to false positives . In addition, phase determination with a genomic variant identified in short reads requires complementary techniques such as SNP arrays. This approach therefore appears to be a major technological advance in the fight against diagnostic uncertainty in rare diseases and is part of the move towards precision medicine for patients. As part of our Reference Center for Developmental Anomalies and Malformation Syndromes of Southwest Occitanie Réunion (CRMR ADSOOR) at Bordeaux University Hospital, we have developed clinical and molecular expertise, particularly in the field of developmental anomalies with intellectual development disorders (particularly chromatinopathies and Rubinstein Taybi syndrome and albinism. In 2024, 2,300 consultations were carried out at the CRMR. In addition, 243 and 228 genome or exome analyses were interpreted in our molecular biology laboratory for albinism and intellectual development disorder and malformation syndrome, respectively. Our expertise in these two areas therefore represents the best starting point for the development of this pilot project using this innovative approach at Bordeaux University Hospital.

Genetic Study to Determine the Cause of Birth Defects in Newborns in Texas

The purpose of this study is to provide advanced genetic testing and virtual consultations for seriously ill newborns in hospitals in Texas with fewer resources, especially along the Texas-Mexico border. The researchers also want to know how well the virtual consultation tool, called Consultagene, works in these hospitals by gathering feedback from healthcare providers. Researchers will provide rapid whole genome sequencing (WGS) to 200 infants over a period of 5 years. Data will be collected via Consultagene, surveys, and qualitative interviews.

Institutional Registry of Rare Diseases

The goal of this observational study is to create a single macro registry system with data collection on common clinical features, grouping the different rare diseases (RD). Moreover, the specific goals are to generate an alert system for possible cases of RD with data from the electronic medical record, to describe the occurrence of RD in the evaluated population, to characterize the population, to describe patterns of diagnosis and treatment of RD present at the time, and to explore patient-reported outcomes.

Umbrella Study for Single Patient Treatments in Oncology

The purpose of this study is to collect data for assessing the improvement of the overall response rate for the overall cohorts and the proportion of patients accessing precision targeted therapy.

Rare and Undiagnosed Disease Research Biorepository

This research study is being done to find markers and identify causes of rare and undiagnosed diseases by analyzing patient's DNA (i.e., genetic material), RNA, plasma, urine, tissues, or other samples that could be informative of symptoms. Researchers are creating a biobank (library) of samples and information to learn more about treating rare and undiagnosed diseases.

Identification of Cellular Biomarkers of Rare Eye Diseases in Adults

The cornea is the outermost transparent 'window' of the eye allowing light to enter and serving as the first-line immune and mechanical barrier. It is a complex avascular tissue composed of cells, stem cells, nerves, and collagen layers organized in an exquisite manner to maintain its transparency and self-healing capacity. This delicately balanced interplay of corneal elements is disrupted in rare diseases of the cornea, resulting in non-healing wounds, corneal ulceration, inflammation, new vessel ingrowth (neovascularization), defective innervation, scarring, oedema and loss of transparency. For many Rare Eye Diseases (REDs), drug development has been relatively unsuccessful, delivering few to no new therapies. Current management is often prohibitively expensive, has low efficacy and leads to debilitating side effects. The RESTORE VISION project (https://restorevision-project.eu/) aims to improve eye health by using cutting-edge models for each rare disease to test novel and repurposed compounds (9 in total) and determine drug mechanisms of action, formulating compounds as safe eye drop suspensions, and performing several first-in-human trials of novel therapies. Thes drugs have solid preliminary data showing beneficial effects in restoring the cell physiology, immune, avascular, neural and signaling environment in the cornea. The current clinical study is part of Work package 2 within the RESTORE VISION EU grant agreement (''Validation of human drug targets of repurposed drugs and novel therapies'') and aims to ascertain the expression levels of genes and proteins and investigate pathways of interest in human tissue and fluid samples of REDs, that are targeted by the proposed experimental/repurposed substances. Therapeutic target gene and/or protein expression will be verified in human blood, tears and conjunctival cells collected from 7 RED patient groups. The RESTORE VISION Consortium know multiple putative genes and proteins involved in the REDs and/or affected by the drugs to be tested in RED models. These will be analyzed in patient samples from the 7 REDs to see if they are 1) expressed at all; 2) differ in expression between patient and control group and 3) are correlated with clinical endpoints and/or symptoms of REDs. The 7 REDs under investigation are briefly explained as follows: 1. AAK: genetic progressive limbal stem cell degeneration leading to corneal neovascularization, inflammation, recurrent erosions, chronic pain and vision loss. 2. OCP: autoimmune scarring of the conjunctiva leads to deficient wound healing, inflammation, scarring, blindness and pain. 3. EEC Syndrome: Ectodermal Dysplasia causes pathological corneal scarring and blindness. 4. NK: involves a corneal nerve deficit leading to reduction or loss of corneal sensitivity, impaired wound healing, corneal ulceration and loss of vision. 5. LSCD: acquired or hereditary stem cell deficiency inducing epithelial breakdown, neovascularization, scarring and inflammation leading to decreased vision, tearing and pain. 6. oGvHD: a severe side-effect of successful bone-marrow transplantation leads to painful and blinding ocular surface inflammation, neovascularization and delayed wound healing. 7. CN: in high-risk transplantation, pathologic inflammation, corneal blood and lymphatic vessels are key risk factors for high-risk corneal graft failure, leading to graft rejection and blindness.

Swiss Rare Disease Registry (SRDR)

The SRDR is a national registry that records rare diseases in people of any age who live in Switzerland. It serves as a platform for scientists, health professionals, affected people, and politicians.The SRDR aims to collect epidemiological data on rare diseases, and data on changes to the diagnosis over time. The SRDR will further serve as a research platform and facilitate patient participation in national and international studies. The SRDR will promote harmonization of data and method between the numerous existing disease-specific registries in Switzerland, will strengthen the exchange with international rare disease registries for research and policy, and will build a network for communication for patients and health care providers.

Retrospective Epidemiological Study of Patients in the National Cohort of the French TMA Center

Immune thrombotic thrombocytopenic purpura (iTTP) is a rare, life-threatening disorder characterized by microangiopathic hemolytic anemia, severe thrombocytopenia, and ischemic organ damage due to microvascular thrombosis. It results from a severe deficiency in the von Willeband factor (vWF)-cleaving protease ADAMTS13, primarily caused by autoantibodies that inhibit its activity. This deficiency leads to accumulation of ultra-large vWF multimers, triggering pathological platelet aggregation and widespread microthrombi. iTTP typically presents with acute neurological symptoms (e.g., confusion, seizures, coma), cardiac events (e.g., myocardial infarction), and multiorgan dysfunction. Without prompt treatment-plasma exchange, immunosuppression, and the vWF inhibitor caplacizumab-mortality exceeds 90%. Survivors face long-term risks, including cardiovascular complications, cognitive impairment, and reduced life expectancy. The TWI-LIGHT protocol is a national retrospective epidemiological study coordinated by the French Reference Center for Thrombotic Microangiopathies (CNR-MAT). It aims to analyze long-term outcome in \>1,200 iTTP patients diagnosed between October 2000 and June 2024. The study leverages pseudonymized data from the CNR-MAT registry, collected via a secure REDCap database. Key Objectives: 1. Primary: Assess the impact of cardiovascular risk factors (e.g., hypertension, diabetes) and ADAMTS13 activity on life expectancy in iTTP survivors. 2. Secondary: * Evaluate disease burden in underrepresented groups (pregnant/postpartum women, children, elderly patients). * Analyze the influence of new therapies (caplacizumab, rituximab, recombinant ADAMTS13) on care pathways. * Identify prognostic factors and treatment practices. * Characterize neurocognitive outcomes and quality of life post-iTTP. Methodology: * Design: Non-interventional, retrospective (MR-004 compliance), using data from standard care. * Inclusion: Patients with confirmed iTTP (thrombocytopenia, hemolytic anemia, ADAMTS13 \<10%), diagnosed within the study period, and ≥1 year of follow-up. * Exclusion: Cancer-associated iTTP, severe sepsis, or patient opposition to data reuse. * Data Collection: Clinical, biological, and therapeutic variables from hospital/consultation records, including cardiovascular events, ADAMTS13 activity, and neurocognitive assessments. * Analysis: Kaplan-Meier survival curves and Cox regression models to identify risk factors for non-iTTP-related death. Expected Outcomes: * Prevalence of cardiovascular comorbidities and their correlation with ADAMTS13 activity. * Insights into iTTP subtypes (e.g., gestational, pediatric) and therapeutic efficacy. * Evidence-based strategies for personalized long-term management. Ethical Framework: * AP-HP-sponsored, with oversight from Sorbonne University's ethics committee. * Patients informed of data reuse with opt-out rights; data archived for 15 years. This landmark study will inform clinical guidelines, optimize survivor care, and address unmet needs in iTTP management through comprehensive, real-world data analysis.

Marfan Syndrome and Quality of Life of Pediatric Patients

The goal of this observational study is to learn about the impact of Marfan syndrome (MFS) in paediatric affected subjects. the main questions it aims to answer are: * The assessment of quality of life in MFS Italian patients; * The impact of phenotypic manifestations on self-image and self-management skills; * Stratify patients according to the need of psychological support. Participants will take part in the study by completing four self-report questionnaires.

Investigation of the Neurovegetative Pattern in Patients With Thoracic Aortic Aneurysms (TAA)

The goal of this observational cross-sectional study is to learn about vagal features in patients with syndromic and non-syndromic TAA. The main question it aims to answer is to highlight a functional condition that could help stratify patients with TAA on the risk of aortic complications. Participant will take part by standing in supine position for 10 minutes and during active standing for 10 minutes. In this period of time, it will be possible to acquire the signals continuously and non invasively through recorded non-invasive blood pressure and piezoelectric sensor breathing belt.

Fibroblasts and Thoracic Aortic Aneurysms: in Vitro Characterization in With Marfan Syndrome and Genetic Aortic Diseases

The aim of the present study is to characterise the phenotype of fibroblasts and to classify different mechanisms involved in the onset and progression of TAAD in syndromic and non-syndromic subjects in order to evaluate potential markers related to TAAD.

Aortic Stiffness in Patients With Genetic Aortopathies

The goal of this observational study is to study arterial stiffness in patients with thoracic ascending aortic aneurysms (TAA), either syndromic or non-syndromic. The main questions it aims to answer are: * Stratification of aortic risk based on arterial stiffness; Compare measurements with morphological and haemodynamic features of the ascending thoracic aorta. Participants will be asked to undergo non-invasive evaluation of blood pressure and arterial stiffness.

Analysis of Muscular Properties in Patients With MFS and EDS

The goal of this observational study is to learn and assess muscle morphological and electromechanical properties in patients affected with Marfan syndrome (MFS) and Ehlers Danlos syndrome (EDS). the main questions it aims to answer are: * To assess the ability to develop muscle strength; * Muscle and tendon morphology involved in muscle contractions/relaxation; * Neuromuscular functionality. Participants will be take part in the study by performing a test for the assessment of the neuromuscular activity (voluntary muscle contractions) and undergoing a muscle ultrasound for the study of muscles and tendons. Researchers will compare the two groups with a control group to see potential differences in the morphological and neuromuscular structures of syndromic patients.

Structural Chromosome Rearrangements and Brain Disorders

The project is focused on the detailed study of structural genomic variants (SVs). Such genetic mutations are in fact alterations in the DNA molecule structure and include copy number variants, inversions and translocations. A single event may affect many genes as well as regulatory regions and the specific phenotypic consequences will depend on the location, genetic content and type of SV. Many times, the specific disease-causing mechanism is not known. Here, the plan is to study the molecular genetic behavior of structural variants as well as the underlying mutational mechanisms involved. First, genome sequencing will be done to pinpoint the chromosomal breakpoints at the nucleotide level, characterize the genomic architecture at the breakpoints and study the relationship between structural variants and SNVs. Second, the aim is to study how structural variants impact gene expression. Finally, disease mechanisms will be functionally explored in vivo using zebrafish and in vitro using primary patient cells and induced pluripotent stem cells. The studies will focus on the origin, structure and impact of structural variation on human disease. The results will directly lead to a higher mutation detection rate in genetic diagnostics. Through a better understanding of disease mechanisms the findings will also assist in the development of novel biomarkers and therapeutic strategies for patients with rare genetic disorders.

Baker Gordon Syndrome Natural History Study

The goal of this study is to conduct a prospective, longitudinal assessment of the natural clinical progression of children and adults with Synaptotagmin1-Associated Neurodevelopmental Disorder also known as Baker Gordon Syndrome (BAGOS). This will be performed by acquiring baseline measurements and developing effective outcome measures and diagnostic tools for the disorder, to prepare the healthcare system for future clinical trials.

DeciFace: Decipher the Influence of Ethnic Backgrounds on the Facial Dysmorphic Features of Rare Mendelian Disorders

There are more than 7000 known genetic disorders, and the number of affected is estimated to be about 6-10% of the population. Around 30 to 40% of genetic disorders have physical changes in the face and skull such as Down's syndrome or Fragile X syndrome. Therefore, the known facial phenotype of many genetic disorders is highly informative to clinical diagnosis. Since a large number of genetic diseases are associated with special facial phenotypes that are difficult to remember, automated facial analysis such as Face2Gene and GestaltMatcher can assist in the identification and diagnosis of facial phenotypes related to various genetic diseases. Although the current advances in whole exome sequencing (whole exome sequencing) or whole genome sequencing (whole genome sequencing) have greatly improved the diagnostic rate of genetic diseases, about half of the patients are still undiagnosed. For patients with special facial phenotypes, the investigators believe that by combining automated facial analysis and whole exome sequencing data, it should be possible to provide a fast and accurate diagnostic model of genetic mutations for genetic diseases. GestaltMatcher Database is a medical imaging database of rare diseases developed by Professor Peter Krawitz of the University of Bonn, Germany. The database's artificial intelligence module will infer a patient's possible diagnosis based on the patient's photo, age, gender, race, and clinical description. The database will be open to medical researchers in related fields to improve the diagnosis of rare diseases. The investigators will use GestaltMatcher to assist in the diagnosis of patients, and compare the accuracy and significant differences in facial deformities between Taiwanese patients and patients from different countries. And use Eye Tracker to analyze how doctors diagnose patients through facial photos, and compare whether there are significant differences between foreign patients and Taiwanese patients in the diagnosis literature of Taiwanese doctors. The project will also analyze how genetic doctors at the University of Bonn in Germany diagnose patients, and compare it with Taiwanese doctors to better understand the differences in the process of doctors diagnosing patients and ethnic backgrounds.

SLC13A5 Deficiency Natural History Study - United States Only

SLC13A5 deficiency (Citrate Transporter Disorder, EIEE 25) is a rare genetic disorder with neurodevelopmental delays and seizure onset in the first few days of life. This natural history study is designed to address the lack of understanding of disease progression. Additionally it will identify clinical and biomarker endpoints for use in future clinical trials.

Gait and Balance Impairment in Rare and Very Rare Neurological Diseases

Rare and very rare neurological diseases primarily or exclusively affect the nervous system with a prevalence of \< 5 out of 10'000 and 100'000 people, respectively. Besides these, there are undiagnosed neurological diseases: neurological conditions without a diagnosis after completing a full diagnostic examination. Rare, very rare, and undiagnosed neurological diseases are complicated and progressive and often cause variegated motor signs, impairments, and syndromes. Balance and gait are frequently affected in these conditions, already at the clinical examination. These balance and gait impairments limit activities and cause an increased risk of falling. Falls can eventually result in injuries, even severe. There are only a few studies about these diseases, likely because of their rarity. Hence, the clinical presentation and the course of rare and very rare diseases are poorly known or even unknown. Essential information for these conditions' diagnosis, prognosis, treatment and rehabilitation is missing. MaNeNeND is an observational study underway at the Fondazione IRCCS Istituto Neurologico "Carlo Besta" (Milano) aimed at detailing the clinical and biological features of very rare and undiagnosed neurological diseases. Research questions: 1. Do patients with rare (Ra), very rare (V) and undiagnosed (U) neurological diseases suffer a balance and gait impairment? 2. Is there a correlation between the clinical and instrumental severity of the balance and gait impairment in RaVU neurological diseases? 3. Are instrumental measures more sensitive in detecting balance and gait impairments in patients affected by a RaVU neurological disease than the clinical measures? 4. Do the balance and gait impairments in RaVU neurological diseases worsen in time? The current project aims at diagnosing, quantifying and detailing the balance and gait impairment in rare, very rare and undiagnosed neurological diseases. To this aim, questionnaires, clinical scales and instrumental tests will be administered to these patients to collect a wide range of balance and gait measures. These measures will also integrate those collected with MaNeNeND to provide a more detailed description of patients with rare, very rare and diagnosed neurological diseases. Participants will complete two questionnaires: the Dizziness Handicap Inventory - short form (DHI-sf, an ordinal score of self-perceived balance) and the Modified Fatigue Impact Scale (MFIS, an ordinal score of self-perceived fatigue). Moreover, a clinician will administer the Mini Balance Evaluation Systems Test (Mini-BESTest, an ordinal score of balance), the 10 m walking test (for measuring the gait speed and other gait parameters) and the Timed Up and Go test (an instrumental measure of mobility and balance). Walking and the Timed Up and Go tests will be recorded with a trunk-worn inertial measurement unit. Finally, participants will be asked to complete an instrumental upright stance and gait assessment, the first consisting of standing on posturographic plates and the second of walking on a treadmill equipped with force sensors. When walking on the treadmill, an optoelectronic system will also record the position in time of limbs and trunk. The quantification of the severity of the balance and gait impairment of the patients suffering a rare, very rare or undiagnosed neurological disease will highlight these persons' therapeutic and rehabilitative needs. Comparing the balance and gait impairment of rare, very rare and undiagnosed diseases with those of multiple sclerosis, Parkinson's disease and peripheral neuropathy will highlight if the formers' balance and gait impairment has unique characteristics that could help ease the diagnosis of these uncommon conditions. The longitudinal measurements on rare, very rare and undiagnosed diseases will be paramount to identifying prognostic factors. In addition, the data collected in the current study will be crucial for future studies, for example, for estimating the sample size in clinical trials.