Management of seizures in patients with primary mitochondrial diseases: consensus statement from the InterERNs Mitochondrial Working Group.

BACKGROUND AND PURPOSE: Primary mitochondrial diseases (PMDs) are common inborn errors of energy metabolism, with an estimated prevalence of one in 4300. These disorders typically affect tissues with high energy requirements, including heart, muscle and brain. Epilepsy may be the presenting feature of PMD, can be difficult to treat and often represents a poor prognostic feature. The aim of this study was to develop guidelines and consensus recommendations on safe medication use and seizure management in mitochondrial epilepsy. METHODS: A panel of 24 experts in mitochondrial medicine, pharmacology and epilepsy management of adults and/or children and two patient representatives from seven countries was established. Experts were members of five different European Reference Networks, known as the Mito InterERN Working Group. A Delphi technique was used to allow the panellists to consider draft recommendations on safe medication use and seizure management in mitochondrial epilepsy, using two rounds with predetermined levels of agreement. RESULTS: A high level of consensus was reached regarding the safety of 14 out of all 25 drugs reviewed, resulting in endorsement of National Institute for Health and Care Excellence guidelines for seizure management, with some modifications. Exceptions including valproic acid in POLG disease, vigabatrin in patients with γ-aminobutyric acid transaminase deficiency and topiramate in patients at risk for renal tubular acidosis were highlighted. CONCLUSIONS: These consensus recommendations describe our intent to improve seizure control and reduce the risk of drug-related adverse events in individuals living with PMD-related epilepsy.

7T MRI detects widespread brain iron deposition in neuroferritinopathy.

Neuroferritinopathy is a disorder of neurodegeneration with brain iron accumulation that has no proven disease-modifying treatments. Clinical trials require biomarkers of iron deposition. We examined brain iron accumulation in one presymptomatic FTL mutation carrier, two individuals with neuroferritinopathy and one healthy control using ultra-high-field 7T MRI. There was increased magnetic susceptibility, suggestive of iron deposition, in superficial and deep gray matter in both presymptomatic and symptomatic neuroferritinopathy. Cavitation of the putamen and globus pallidus increased with disease stage and at follow up. The widespread brain iron deposition in presymptomatic and early disease provides an opportunity for monitoring disease-modifying intervention.

The absorption-addiction model of celebrity worship: in search of a broader theoretical foundation.

BACKGROUND: A large body of evidence suggests that some people have a strong, obsessive attachment to a favorite celebrity. The absorption-addiction model attempts to account for this extreme attachment, sometimes labeled "celebrity worship." According to the model, a small portion of celebrity admirers ("celebrity worshipers") become absorbed in the personal lives of celebrities to compensate for perceived personal or social deficiencies. The purpose of this study is to examine how the absorption-addiction model relates to broader psychological theories that include non-celebrity contexts. Specifically, we examine how the absorption-addiction model relates to three theories: empty-self theory, extremism theory, and the dualistic model of passion. METHODS: Participants (N = 399; 77.94% women, Mage = 19.91 years, SD = 3.24) completed an online questionnaire measuring attraction to favorite celebrities. Constructs representing the three broader theories were compared to a measure of attraction to one's favorite celebrity. RESULTS: Sense of emptiness, obsessive passion, and extremism were positively associated with celebrity attraction. The strongest association was found with extremism, though the effect was moderate. CONCLUSIONS: These findings suggest that extremism theory is the best fit of the three broader theories explaining celebrity worship, although its contribution to understanding celebrity worship is modest.

Prevalence of celebrity worship: Development and application of the short version of the Celebrity Attitude Scale (CAS-7) on a large-scale representative sample.

Background and aims: Celebrity worship, defined as an excessive admiration towards celebrities, has generated considerable research and public interest. A widely used assessment instrument to measure celebrity worship is the 23-item Celebrity Attitude Scale. However, concerns have been raised regarding the measurement, including the inconsistent factor structure and lack of a cut-off point to identify "celebrity worshipers". The present study aims to address these concerns by testing the psychometric appropriateness of a short, 7-item version of the CAS (i.e., CAS-7) and estimating the prevalence of individuals with high-level celebrity admiration using a representative sample of Hungarian adults (between 18 and 64 years of age) according to gender, age, geographic location, and size of residence. Methods: The total sample comprised 2028 respondents, of which 769 valid responses were administered from participants who reported having a favorite celebrity (51.11% men, Mage = 36.38 years, SD = 13.36). Results: Results indicated an excellent model fit for the two-factor and bifactor model of the CAS-7. Based on the suggested cut-off score of 26, the prevalence of high-level celebrity admiration is 4.53% in the Hungarian adult population (18-64 years of age) and 8.51% among young adults (18-34 years of age). Individuals with this high level of admiration towards a favorite celebrity reported more symptoms of problematic Internet use, depression, anxiety, and stress than individuals with general celebrity admiration levels. Discussion and conclusions: The CAS-7 demonstrated sound psychometric properties, confirming its applicability in research and practice.

Variants in mitochondrial disease genes are common causes of inherited peripheral neuropathies.

BACKGROUND: Peripheral neuropathies in mitochondrial disease are caused by mutations in nuclear genes encoding mitochondrial proteins, or in the mitochondrial genome. Whole exome or genome sequencing enable parallel testing of nuclear and mtDNA genes, and it has significantly advanced the genetic diagnosis of inherited diseases. Despite this, approximately 40% of all Charcot-Marie-Tooth (CMT) cases remain undiagnosed. METHODS: The genome-phenome analysis platform (GPAP) in RD-Connect was utilised to create a cohort of 2087 patients with at least one Human Phenotype Ontology (HPO) term suggestive of a peripheral neuropathy, from a total of 10,935 patients. These patients' genetic data were then analysed and searched for variants in known mitochondrial disease genes. RESULTS: A total of 1,379 rare variants were identified, 44 of which were included in this study as either reported pathogenic or likely causative in 42 patients from 36 families. The most common genes found to be likely causative for an autosomal dominant neuropathy were GDAP1 and GARS1. We also detected heterozygous likely pathogenic variants in DNA2, MFN2, DNM2, PDHA1, SDHA, and UCHL1. Biallelic variants in SACS, SPG7, GDAP1, C12orf65, UCHL1, NDUFS6, ETFDH and DARS2 and variants in the mitochondrial DNA (mtDNA)-encoded MT-ATP6 and MT-TK were also causative for mitochondrial CMT. Only 50% of these variants were already reported as solved in GPAP. CONCLUSION: Variants in mitochondrial disease genes are frequent in patients with inherited peripheral neuropathies. Due to the clinical overlap between mitochondrial disease and CMT, agnostic exome or genome sequencing have better diagnostic yields than targeted gene panels.

EURO-NMD registry: federated FAIR infrastructure, innovative technologies and concepts of a patient-centred registry for rare neuromuscular disorders.

BACKGROUND: The EURO-NMD Registry collects data from all neuromuscular patients seen at EURO-NMD's expert centres. In-kind contributions from three patient organisations have ensured that the registry is patient-centred, meaningful, and impactful. The consenting process covers other uses, such as research, cohort finding and trial readiness. RESULTS: The registry has three-layered datasets, with European Commission-mandated data elements (EU-CDEs), a set of cross-neuromuscular data elements (NMD-CDEs) and a dataset of disease-specific data elements that function modularly (DS-DEs). The registry captures clinical, neuromuscular imaging, neuromuscular histopathology, biological and genetic data and patient-reported outcomes in a computer-interpretable format using selected ontologies and classifications. The EURO-NMD registry is connected to the EURO-NMD Registry Hub through an interoperability layer. The Hub provides an entry point to other neuromuscular registries that follow the FAIR data stewardship principles and enable GDPR-compliant information exchange. Four national or disease-specific patient registries are interoperable with the EURO-NMD Registry, allowing for federated analysis across these different resources. CONCLUSIONS: Collectively, the Registry Hub brings together data that are currently siloed and fragmented to improve healthcare and advance research for neuromuscular diseases.

Multi-level profiling unravels mitochondrial dysfunction in myotonic dystrophy type 2.

Myotonic dystrophy type 2 (DM2) is an autosomal-dominant multisystemic disease with a core manifestation of proximal muscle weakness, muscle atrophy, myotonia, and myalgia. The disease-causing CCTG tetranucleotide expansion within the CNBP gene on chromosome 3 leads to an RNA-dominated spliceopathy, which is currently untreatable. Research exploring the pathophysiological mechanisms in myotonic dystrophy type 1 has resulted in new insights into disease mechanisms and identified mitochondrial dysfunction as a promising therapeutic target. It remains unclear whether similar mechanisms underlie DM2 and, if so, whether these might also serve as potential therapeutic targets. In this cross-sectional study, we studied DM2 skeletal muscle biopsy specimens on proteomic, molecular, and morphological, including ultrastructural levels in two separate patient cohorts consisting of 8 (explorative cohort) and 40 (confirmatory cohort) patients. Seven muscle biopsy specimens from four female and three male DM2 patients underwent proteomic analysis and respiratory chain enzymology. We performed bulk RNA sequencing, immunoblotting of respiratory chain complexes, mitochondrial DNA copy number determination, and long-range PCR (LR-PCR) to study mitochondrial DNA deletions on six biopsies. Proteomic and transcriptomic analyses revealed a downregulation of essential mitochondrial proteins and their respective RNA transcripts, namely of subunits of respiratory chain complexes I, III, and IV (e.g., mt-CO1, mt-ND1, mt-CYB, NDUFB6) and associated translation factors (TACO1). Light microscopy showed mitochondrial abnormalities (e.g., an age-inappropriate amount of COX-deficient fibers, subsarcolemmal accumulation) in most biopsy specimens. Electron microscopy revealed widespread ultrastructural mitochondrial abnormalities, including dysmorphic mitochondria with paracrystalline inclusions. Immunofluorescence studies with co-localization of autophagy (p62, LC-3) and mitochondrial marker proteins (TOM20, COX-IV), as well as immunohistochemistry for mitophagy marker BNIP3 indicated impaired mitophagic flux. Immunoblotting and LR-PCR did not reveal significant differences between patients and controls. In contrast, mtDNA copy number measurement showed a reduction of mtDNA copy numbers in the patient group compared to controls. This first multi-level study of DM2 unravels thus far undescribed functional and structural mitochondrial abnormalities. However, the molecular link between the tetranucleotide expansion and mitochondrial dysfunction needs to be further elucidated.

A Homozygous NDUFS6 Variant Associated with Neuropathy and Optic Atrophy.

Background: The NADH dehydrogenase [ubiquinone] iron-sulfur protein 6 (NDUFS6) gene encodes for an accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (complex I). Bi-allelic NDUFS6 variants have been linked with a severe disorder mostly reported as a lethal infantile mitochondrial disease (LMID) or Leigh syndrome (LS). Objective: Here, we identified a homozygous variant (c.309 + 5 G > A) in NDUFS6 in one male patient with axonal neuropathy accompanied by loss of small fibers in skin biopsy and further complicated by optic atrophy and borderline intellectual disability. Methods: To address the pathogenicity of the variant, biochemical studies (mtDNA copy number quantification, ELISA, Proteomic profiling) of patient-derived leukocytes were performed. Results: The analyses revealed loss of NDUFS6 protein associated with a decrease of three further mitochondrial NADH dehydrogenase subunit/assembly proteins (NDUFA12, NDUFS4 and NDUFV1). Mitochondrial copy number is not altered in leukocytes and the mitochondrial biomarker GDF15 is not significantly changed in serum. Conclusions: Hence, our combined clinical and biochemical data strengthen the concept of NDUFS6 being causative for a very rare form of axonal neuropathy associated with optic atrophy and borderline intellectual disability, and thus expand (i) the molecular genetic landscape of neuropathies and (ii) the clinical spectrum of NDUFS6-associated phenotypes.

Correlation Between the SARA and A-T NEST Clinical Severity Scores in Adults with Ataxia-Telangiectasia.

Ataxia-Telangiectasia (A-T) is an autosomal recessive neurodegenerative disease associated with cerebellar ataxia and extrapyramidal features. A-T has a complex and diverse phenotype with varying rates of disease progression. The development of robust natural history studies and therapeutic trials relies on the accurate recording of phenotype using relevant and validated severity of illness indexes. We compared the commonly used Scale for the Assessment and Rating of Ataxia (SARA) and the disease-specific A-T Neurological Examination Scale Toolkit (A-T NEST), in our adult A-T cohort. We found a strong correlation between A-T NEST and the established SARA score, validating the use of A-T NEST and SARA in capturing the natural history of A-T patients.

Mitochondrial aminoacyl-tRNA synthetases trigger unique compensatory mechanisms in neurons.

Mitochondrial aminoacyl-tRNA synthetase (mt-ARS) mutations cause severe, progressive, and often lethal diseases with highly heterogeneous and tissue-specific clinical manifestations. This study investigates the molecular mechanisms triggered by three different mt-ARS defects caused by biallelic mutations in AARS2, EARS2, and RARS2, using an in vitro model of human neuronal cells. We report distinct molecular mechanisms of mitochondrial dysfunction among the mt-ARS defects studied. Our findings highlight the ability of proliferating neuronal progenitor cells (iNPCs) to compensate for mitochondrial translation defects and maintain balanced levels of oxidative phosphorylation (OXPHOS) components, which becomes more challenging in mature neurons. Mutant iNPCs exhibit unique compensatory mechanisms, involving specific branches of the integrated stress response, which may be gene-specific or related to the severity of the mitochondrial translation defect. RNA sequencing revealed distinct transcriptomic profiles showing dysregulation of neuronal differentiation and protein translation. This study provides valuable insights into the tissue-specific compensatory mechanisms potentially underlying the phenotypes of patients with mt-ARS defects. Our novel in vitro model may more accurately represent the neurological presentation of patients and offer an improved platform for future investigations and therapeutic development.

Clinical and genetic characterisation of a large Indian congenital myasthenic syndrome cohort.

Congenital myasthenic syndromes (CMS) are a rare group of inherited disorders caused by gene defects associated with the neuromuscular junction and potentially treatable with commonly available medications such as acetylcholinesterase inhibitors and ß2 adrenergic receptor agonists. In this study, we identified and genetically characterized the largest cohort of CMS patients from India to date. Genetic testing of clinically suspected patients evaluated in a South Indian hospital during the period 2014-19 was carried out by standard diagnostic gene panel testing or using a two-step method that included hotspot screening followed by whole-exome sequencing. In total, 156 genetically diagnosed patients (141 families) were characterized and the mutational spectrum and genotype-phenotype correlation described. Overall, 87 males and 69 females were evaluated, with the age of onset ranging from congenital to fourth decade (mean 6.6 ± 9.8 years). The mean age at diagnosis was 19 ± 12.8 (1-56 years), with a mean diagnostic delay of 12.5 ± 9.9 (0-49 years). Disease-causing variants in 17 CMS-associated genes were identified in 132 families (93.6%), while in nine families (6.4%), variants in genes not associated with CMS were found. Overall, postsynaptic defects were most common (62.4%), followed by glycosylation defects (21.3%), synaptic basal lamina genes (4.3%) and presynaptic defects (2.8%). Other genes found to cause neuromuscular junction defects (DES, TEFM) in our cohort accounted for 2.8%. Among the individual CMS genes, the most commonly affected gene was CHRNE (39.4%), followed by DOK7 (14.4%), DPAGT1 (9.8%), GFPT1 (7.6%), MUSK (6.1%), GMPPB (5.3%) and COLQ (4.5%). We identified 22 recurrent variants in this study, out of which eight were found to be geographically specific to the Indian subcontinent. Apart from the known common CHRNE variants p.E443Kfs*64 (11.4%) and DOK7 p.A378Sfs*30 (9.3%), we identified seven novel recurrent variants specific to this cohort, including DPAGT1 p.T380I and DES c.1023+5G>A, for which founder haplotypes are suspected. This study highlights the geographic differences in the frequencies of various causative CMS genes and underlines the increasing significance of glycosylation genes (DPAGT1, GFPT1 and GMPPB) as a cause of neuromuscular junction defects. Myopathy and muscular dystrophy genes such as GMPPB and DES, presenting as gradually progressive limb girdle CMS, expand the phenotypic spectrum. The novel genes MACF1 and TEFM identified in this cohort add to the expanding list of genes with new mechanisms causing neuromuscular junction defects.

Case report: Mutations in DNAJC30 causing autosomal recessive Leber hereditary optic neuropathy are common amongst Eastern European individuals.

Background: Leber Hereditary Optic Neuropathy (LHON) is the most common inherited mitochondrial disease characterized by bilateral, painless, subacute visual loss with a peak age of onset in the second to third decade. Historically, LHON was thought to be exclusively maternally inherited due to mutations in mitochondrial DNA (mtDNA); however, recent studies have identified an autosomal recessive form of LHON (arLHON) caused by point mutations in the nuclear gene, DNAJC30. Case Presentations: In this study, we report the cases of three Eastern European individuals presenting with bilateral painless visual loss, one of whom was also exhibiting motor symptoms. After a several-year-long diagnostic journey, all three patients were found to carry the homozygous c.152A>G (p.Tyr51Cys) mutation in DNAJC30. This has been identified as the most common arLHON pathogenic variant and has been shown to exhibit a significant founder effect amongst Eastern European individuals. Conclusion: This finding adds to the growing cohort of patients with arLHON and demonstrates the importance of DNAJC30 screening in patients with molecularly undiagnosed LHON, particularly in Eastern European individuals. It is of heightened translational significance as patients diagnosed with arLHON exhibit a better prognosis and response to therapeutic treatment with the co-enzyme Q10 analog idebenone.

The Medical Action Ontology: A tool for annotating and analyzing treatments and clinical management of human disease.

BACKGROUND: Navigating the clinical literature to determine the optimal clinical management for rare diseases presents significant challenges. We introduce the Medical Action Ontology (MAxO), an ontology specifically designed to organize medical procedures, therapies, and interventions. METHODS: MAxO incorporates logical structures that link MAxO terms to numerous other ontologies within the OBO Foundry. Term development involves a blend of manual and semi-automated processes. Additionally, we have generated annotations detailing diagnostic modalities for specific phenotypic abnormalities defined by the Human Phenotype Ontology (HPO). We introduce a web application, POET, that facilitates MAxO annotations for specific medical actions for diseases using the Mondo Disease Ontology. FINDINGS: MAxO encompasses 1,757 terms spanning a wide range of biomedical domains, from human anatomy and investigations to the chemical and protein entities involved in biological processes. These terms annotate phenotypic features associated with specific disease (using HPO and Mondo). Presently, there are over 16,000 MAxO diagnostic annotations that target HPO terms. Through POET, we have created 413 MAxO annotations specifying treatments for 189 rare diseases. CONCLUSIONS: MAxO offers a computational representation of treatments and other actions taken for the clinical management of patients. Its development is closely coupled to Mondo and HPO, broadening the scope of our computational modeling of diseases and phenotypic features. We invite the community to contribute disease annotations using POET (https://poet.jax.org/). MAxO is available under the open-source CC-BY 4.0 license (https://github.com/monarch-initiative/MAxO). FUNDING: NHGRI 1U24HG011449-01A1 and NHGRI 5RM1HG010860-04.

DPAGT1-CDG: Report of Two New Pediatric Patients and Brief Review of the Literature.

Introduction: Congenital glycosylation disorders are multisystem diseases with heterogeneous clinical manifestations caused by defects in the synthesis of the glycan moiety of glycoproteins or glycolipids or the binding of glycans to proteins and lipids. DPAGT1 (UDP-GlcNAc: dolichol phosphate N-acetylglucosamine-1-phosphotransferase) is an initiating protein in the biosynthetic pathway of dolichol-linked oligosaccharides required for protein N-glycosylation. Pathogenic variants in DPAGT1 (UDP-GlcNAc: dolichol phosphate N-acetylglucosamine-1-phosphotransferase) gene cause a rare type of congenital glycosylation disorder called DPAGT1-CDG (formerly CDG-Ij) (OMIM #608093). It is a rare autosomal recessive disease or a milder version with congenital myasthenic syndrome known as DPAGT1-CMS. A severe disease course with hypotonia, cataracts, skeletal deformities, resistant epilepsy, intellectual disability, global developmental delay, premature death has been described in most patients with DPAGT1-CDG. Patient Presentation: We describe two patients with variants in the DPAGT1 gene: an 8-month-old boy with a homozygous, missense DPAGT1:c.339T>G (p.Phe113Leu) novel variant and a 13-year-old female patient with compound heterozygous variants, DPAGT1:c.466C>T (p.Arg156Cys, R156C) and DPAGT1:c.161+5G>A. While the 8-month-old patient was diagnosed with congenital cataract at the age of 1 month, had dysmorphic findings, and epilepsy, clinical symptoms in the other patient appeared later but with more prominent muscle weakness, behavioral disorder, dysmorphic findings, and no epilepsy. Discussion: Cholinesterase inhibitor therapy was found to be effective in patients against muscle weakness, supporting DPAGT1 deficiency as the underlying etiology. We started pyridostigmine treatment in our patient with more pronounced muscle weakness, and we saw its benefit. We aimed to present our patients diagnosed with DPAGT1-CDG due to different variants in the same gene and different clinical presentations, treatment and to compare them with other patients in the literature.

Career intentions of medical students in the UK: a national, cross-sectional study (AIMS study).

OBJECTIVE: To determine current UK medical students' career intentions after graduation and on completing the Foundation Programme (FP), and to ascertain the motivations behind these intentions. DESIGN: Cross-sectional, mixed-methods survey of UK medical students, using a non-random sampling method. SETTING: All 44 UK medical schools recognised by the General Medical Council. PARTICIPANTS: All UK medical students were eligible to participate. The study sample consisted of 10 486 participants, approximately 25.50% of the medical student population. OUTCOME MEASURES: Career intentions of medical students postgraduation and post-FP, motivations behind these career intentions, characterising the medical student population and correlating demographic factors and propensity to leave the National Health Service (NHS). RESULTS: The majority of participating students (8806/10 486, 83.98%) planned to complete both years of the FP after graduation, with under half of these students (4294/8806, 48.76%) intending to pursue specialty training thereafter. A subanalysis of career intentions after the FP by year of study revealed a significant decrease in students' intentions to enter specialty training as they advanced through medical school. Approximately a third of surveyed students (3392/10 486, 32.35%) intended to emigrate to practise medicine, with 42.57% (n=1444) of those students not planning to return. In total, 2.89% of students intended to leave medicine altogether (n=303). Remuneration, work-life balance and working conditions were identified as important factors in decision-making regarding emigration and leaving the profession. Subgroup analyses based on gender, type of schooling, fee type and educational background were performed. Only 17.26% of surveyed students were satisfied or very satisfied with the overall prospect of working in the NHS. CONCLUSIONS: The Ascertaining the career Intentions of UK Medical Students study highlights UK students' views and career intentions, revealing a concerning proportion of those surveyed considering alternative careers or emigration. Addressing factors such as remuneration, work-life balance and working conditions may increase retention of doctors and improve workforce planning efforts.

The delivery of safe and effective test result communication, management and follow-up.

OBJECTIVES: This paper reports on a program of research funded by a National Health and Medical Research Council (NHRMC) partnership grant (2015-2021) entitled "Delivering safe and effective test result communication, management and follow-up". The project's objectives were to: 1) improve the effectiveness and safety of test-result management through the establishment of clear governance processes of communication, responsibility, and accountability; 2) harness health information technology to inform and monitor test-result management; and 3) enhance consumer contribution to the establishment of safe and effective test-result management systems. Type of program: The partnership project addressed its key objectives through: i) the development of a consumer-driven approach; ii) using diagnostic stewardship and digital health to enhance safety and quality; iii) identifying clinical workflows that can lead to timely and meaningful communication; and iv) contributing to the Royal College of Pathologists of Australasia and Australasian Association for Clinical Biochemistry and Laboratory Medicine's work on nationally harmonised alert thresholds for critical laboratory results. METHODS: The project employed a convergent mixed-methods approach using multistage studies across hospitals in South Eastern Sydney and Illawarra and Shoalhaven Local Health Districts. A consumer-centred approach, including patient reference groups and community forums, was used to identify mechanisms to enhance consumers' role in test-management governance processes and inform the direction of the research and interpretation of findings. Results and lessons learnt: The body of evidence generated by the project highlights the multilayered and interconnected components required to achieve safe and effective test results management. Addressing the significant patient safety risk associated with the failure to follow-up test results must include consideration of diagnostic clinical work tasks (involving multiple people across numerous clinical settings) and embrace patient-centred and digital health strategies for shared information and timely and meaningful communication.

The Medical Action Ontology: A Tool for Annotating and Analyzing Treatments and Clinical Management of Human Disease.

Navigating the vast landscape of clinical literature to find optimal treatments and management strategies can be a challenging task, especially for rare diseases. To address this task, we introduce the Medical Action Ontology (MAxO), the first ontology specifically designed to organize medical procedures, therapies, and interventions in a structured way. Currently, MAxO contains 1757 medical action terms added through a combination of manual and semi-automated processes. MAxO was developed with logical structures that make it compatible with several other ontologies within the Open Biological and Biomedical Ontologies (OBO) Foundry. These cover a wide range of biomedical domains, from human anatomy and investigations to the chemical and protein entities involved in biological processes. We have created a database of over 16000 annotations that describe diagnostic modalities for specific phenotypic abnormalities as defined by the Human Phenotype Ontology (HPO). Additionally, 413 annotations are provided for medical actions for 189 rare diseases. We have developed a web application called POET (https://poet.jax.org/) for the community to use to contribute MAxO annotations. MAxO provides a computational representation of treatments and other actions taken for the clinical management of patients. The development of MAxO is closely coupled to the Mondo Disease Ontology (Mondo) and the Human Phenotype Ontology (HPO) and expands the scope of our computational modeling of diseases and phenotypic features to include diagnostics and therapeutic actions. MAxO is available under the open-source CC-BY 4.0 license (https://github.com/monarch-initiative/MAxO).