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Background Remethylation defects are rare inherited disorders in which impaired remethylation of homocysteine to methionine leads to accumulation of homocysteine and perturbation of numerous methylation reactions. Objective To summarise clinical and biochemical characteristics of these severe disorders and to provide guidelines on diagnosis and management. Data sources Review, evaluation and discussion of the medical literature (Medline, Cochrane databases) by a panel of experts on these rare diseases following the GRADE approach. Key recommendations We strongly recommend measuring plasma total homocysteine in any patient presenting with the combination of neurological and/or visual and/or haematological symptoms, subacute spinal cord degeneration, atypical haemolytic uraemic syndrome or unexplained vascular thrombosis. We strongly recommend to initiate treatment with parenteral hydroxocobalamin without delay in any suspected remethylation disorder; it significantly improves survival and incidence of severe complications. We strongly recommend betaine treatment in individuals with MTHFR deficiency; it improves the outcome and prevents disease when given early.

Background The number of market approvals of orphan medicinal products (OMPs) has been increasing steadily in the last 3 decades. While OMPs can offer a unique chance for patients suffering from rare diseases, they are usually very expensive. The growing number of approved OMPs increases their budget impact despite their low prevalence, making it pressing to find solutions to ethical challenges on how to fairly allocate scarce healthcare resources under this context. One potential solution could be to grant OMPs special status when considering them for reimbursement, meaning that they are subject to different, and less stringent criteria than other drugs. This study aims to provide a systematic analysis of moral reasons for and against such a special status for the reimbursement of OMPs in publicly funded healthcare systems from a multidisciplinary perspective. Results With a systematic review of reasons, we identified 39 reasons represented in 243 articles (scientific and grey literature) for and against special status for the reimbursement of OMPs, then categorized them into nine topics. Taking a multidisciplinary perspective, we found that most articles came from health policy (n = 103) and health economics (n = 49). More articles took the position for a special status of OMPs (n = 97) than those against it (n = 31) and there was a larger number of reasons identified in favour (29 reasons) than against (10 reasons) this special status. Conclusion Results suggest that OMP reimbursement issues should be assessed and analysed from a multidisciplinary perspective. Despite the higher occurrence of reasons and articles in favour of a special status, there is no clear-cut solution for this ethical challenge. The binary perspective of whether or not OMPs should be granted special status oversimplifies the issue: both OMPs and rare diseases are too heterogeneous in their characteristics for such a binary perspective. Thus, the scientific debate should focus less on the question of disease prevalence but rather on how the important variability of different OMPs concerning e.g. target population, cost-effectiveness, level of evidence or mechanism of action could be meaningfully addressed and implemented in Health Technology Assessments.

Methylmalonic and propionic acidemia (MMA/PA) are inborn errors of metabolism characterized by accumulation of propionic acid and/or methylmalonic acid due to deficiency of methylmalonyl-CoA mutase (MUT) or propionyl-CoA carboxylase (PCC). MMA has an estimated incidence of ~ 1: 50,000 and PA of ~ 1:100-000 -150,000. Patients present either shortly after birth with acute deterioration, metabolic acidosis and hyperammonemia or later at any age with a more heterogeneous clinical picture, leading to early death or to severe neurological handicap in many survivors. Mental outcome tends to be worse in PA and late complications include chronic kidney disease almost exclusively in MMA and cardiomyopathy mainly in PA. Except for vitamin B 12 responsive forms of MMA the outcome remains poor despite the existence of apparently effective therapy with a low protein diet and carnitine. This may be related to under recognition and delayed diagnosis due to nonspecific clinical presentation and insufficient awareness of health care professionals because of disease rarity. These guidelines aim to provide a trans-European consensus to guide practitioners, set standards of care and to help to raise awareness. To achieve these goals, the guidelines were developed using the SIGN methodology by having professionals on MMA/PA across twelve European countries and the U.S. gather all the existing evidence, score it according to the SIGN evidence level system and make a series of conclusive statements supported by an associated level of evidence. Although the degree of evidence rarely exceeds level C (evidence from non-analytical studies like case reports and series), the guideline should provide a firm and critical basis to guide practice on both acute and chronic presentations, and to address diagnosis, management, monitoring, outcomes, and psychosocial and ethical issues. Furthermore, these guidelines highlight gaps in knowledge that must be filled by future research. We consider that these guidelines will help to harmonize practice, set common standards and spread good practices, with a positive impact on the outcomes of MMA/PA patients.

Deregulation of mitochondrial network in terminally differentiated cells contributes to a broad spectrum of disorders. Methylmalonic acidemia (MMA) is one of the most common inherited metabolic disorders, due to deficiency of the mitochondrial methylmalonyl-coenzyme A mutase (MMUT). How MMUT deficiency triggers cell damage remains unknown, preventing the development of disease–modifying therapies. Here we combine genetic and pharmacological approaches to demonstrate that MMUT deficiency induces metabolic and mitochondrial alterations that are exacerbated by anomalies in PINK1/Parkin–mediated mitophagy, causing the accumulation of dysfunctional mitochondria that trigger epithelial stress and ultimately cell damage. Using drug–disease network perturbation modelling, we predict targetable pathways, whose modulation repairs mitochondrial dysfunctions in patient–derived cells and alleviate phenotype changes in mmut –deficient zebrafish. These results suggest a link between primary MMUT deficiency, diseased mitochondria, mitophagy dysfunction and epithelial stress, and provide potential therapeutic perspectives for MMA. Methylmalonic acidemia is an inherited metabolic disease caused by loss or mutation of the enzyme MMUT. Here the authors use cell and animal models to show that MMUT mutations lead to defective mitophagy and stress in kidney cells, contributing to the pathogenesis in methylmalonic acidemia patients.

The folate and methionine cycles are crucial for biosynthesis of lipids, nucleotides and proteins, and production of the methyl donor S-adenosylmethionine (SAM). 5,10-methylenetetrahydrofolate reductase (MTHFR) represents a key regulatory connection between these cycles, generating 5-methyltetrahydrofolate for initiation of the methionine cycle, and undergoing allosteric inhibition by its end product SAM. Our 2.5 Å resolution crystal structure of human MTHFR reveals a unique architecture, appending the well-conserved catalytic TIM-barrel to a eukaryote-only SAM-binding domain. The latter domain of novel fold provides the predominant interface for MTHFR homo-dimerization, positioning the N-terminal serine-rich phosphorylation region near the C-terminal SAM-binding domain. This explains how MTHFR phosphorylation, identified on 11 N-terminal residues (16 in total), increases sensitivity to SAM binding and inhibition. Finally, we demonstrate that the 25-amino-acid inter-domain linker enables conformational plasticity and propose it to be a key mediator of SAM regulation. Together, these results provide insight into the molecular regulation of MTHFR. The human enzyme MTHFR links the folate and methionine cycles, which are essential for the biosynthesis of nucleotides and proteins. Here, the authors present the crystal structure and biochemical analysis of human MTHFR, providing molecular insights into its function and regulation in higher eukaryotes.

Acute liver failure (ALF) has been reported in ornithine transcarbamylase deficiency (OTCD) and other urea cycle disorders (UCD). The frequency of ALF in OTCD is not well-defined and the pathogenesis is not known. To evaluate the prevalence of ALF in OTCD, we analyzed the Swiss patient cohort. Laboratory data from 37 individuals, 27 females and 10 males, diagnosed between 12/1991 and 03/2015, were reviewed for evidence of ALF. In parallel, we performed cell culture studies using human primary hepatocytes from a single patient treated with ammonium chloride in order to investigate the inhibitory potential of ammonia on hepatic protein synthesis. More than 50% of Swiss patients with OTCD had liver involvement with ALF at least once in the course of disease. Elevated levels of ammonia often correlated with (laboratory) coagulopathy as reflected by increased values for international normalized ratio (INR) and low levels of hepatic coagulation factors which did not respond to vitamin K. In contrast, liver transaminases remained normal in several cases despite massive hyperammonemia and liver involvement as assessed by pathological INR values. In our in vitro studies, treatment of human primary hepatocytes with ammonium chloride for 48 hours resulted in a reduction of albumin synthesis and secretion by approximately 40%. In conclusion, ALF is a common complication of OTCD, which may not always lead to severe symptoms and may therefore be underdiagnosed. Cell culture experiments suggest an ammonia-induced inhibition of hepatic protein synthesis, thus providing a possible pathophysiological explanation for hyperammonemia-associated ALF.

Increased propionylcarnitine levels in newborn screening are indicative for a group of potentially severe disorders including propionic acidemia (PA), methylmalonic acidemias and combined remethylation disorders (MMACBL). This alteration is relatively non-specific, resulting in the necessity of confirmation and differential diagnosis in subsequent tests. Thus, we aimed to develop a multiplex approach for concurrent determination of 3-hydroxypropionic acid, methylmalonic acid and methylcitric acid from the same dried blood spot (DBS) as in primary screening (second-tier test). We also set out to validate the method using newborn and follow-up samples of patients with confirmed PA or MMACBL. The assay was developed using liquid chromatography-tandem mass spectrometry and clinically validated with retrospective analysis of DBS samples from PA or MMACBL patients. Reliable determination of all three analytes in DBSs was achieved following simple and fast (<20 min) sample preparation without laborious derivatization or any additional pipetting steps. The method clearly distinguished the pathological and normal samples and differentiated between PA and MMACBL in all stored newborn specimens. Methylcitric acid was elevated in all PA samples; 3-hydroxypropionic acid was also high in most cases. Methylmalonic acid was increased in all MMACBL specimens; mostly together with methylcitric acid. A liquid chromatography-tandem mass spectrometry assay allowing simultaneous determination of the biomarkers 3-hydroxypropionic acid, methylmalonic acid and methylcitric acid in DBSs has been developed. The assay can use the same specimen as in primary screening (second-tier test) which may reduce the need for repeated blood sampling. The presented preliminary findings suggest that this method can reliably differentiate patients with PA and MMACBL in newborn screening. The validated assay is being evaluated prospectively in a pilot project for extension of the German newborn screening panel (‟Newborn screening 2020\"; Newborn Screening Center, University Hospital Heidelberg).

Brian Fowler, David Rosenblatt and colleagues show that mutations in the ABC transporter gene ABCD4 cause a new inborn error of vitamin B 12 metabolism. ABCD4 colocalizes with the lysosomal proteins LAMP1 and LMBD1 and may be involved in intracellular processing of vitamin B 12 . Inherited disorders of vitamin B 12 (cobalamin) have provided important clues to how this vitamin, which is essential for hematological and neurological function, is transported and metabolized. We describe a new disease that results in failure to release vitamin B 12 from lysosomes, which mimics the cblF defect caused by LMBRD1 mutations. Using microcell-mediated chromosome transfer and exome sequencing, we identified causal mutations in ABCD4 , a gene that codes for an ABC transporter, which was previously thought to have peroxisomal localization and function. Our results show that ABCD4 colocalizes with the lysosomal proteins LAMP1 and LMBD1, the latter of which is deficient in the cblF defect. Furthermore, we show that mutations altering the putative ATPase domain of ABCD4 affect its function, suggesting that the ATPase activity of ABCD4 may be involved in intracellular processing of vitamin B 12 .

This study aims to determine clusters of access to healthcare among adults with rare diseases in Switzerland, identify associated individual characteristics of access, and impact on health-related quality of life (HRQoL). Swiss adults ( = 341) diagnosed with a rare disease completed an online survey including the Perception of Access to Healthcare Questionnaire (PAHQ) and Short Form Health Survey (SF-12). We employed partition around medoids algorithm to identify patient clusters based on the PAHQ. Various sociodemographic/disease-related factors and HRQoL were assessed. We identified two patient clusters: higher ( = 227) and lower access ( = 114). Significantly associated with lower access were an unstable disease course ( < 0.05), increased number of misdiagnoses ( < 0.05), and diseases affecting the nervous system ( < 0.01). Membership in the lower access cluster was significantly associated with worse HRQoL ( < 0.05). Findings highlight the need for comprehensive assessment of healthcare access in adults with rare diseases and identifies potential targets for tailored interventions.

Background Acute intoxication-type inborn errors of metabolism (IT-IEM) such as urea cycle disorders and non-acute IT-IEM such as phenylketonuria (PKU) and their treatment have a major impact on the life of affected children and families. Yet patients’ and parents’ perspectives on the burdens of IT-IEM and its effects on everyday functioning and well-being have rarely been addressed. Patient- and observer-reported outcomes (PROs/ObsROs) are critically important to evaluate and target health care and treatment efficacy. Therefore, it is mandatory to define PROs/ObsROs relevant to patients with IT-IEM, their families, and health care professionals and to provide valid, standardised and reliable measuring instruments. To achieve consensus we performed a two-round, electronic-based modification of a Delphi survey including 27 parents of affected children, nine teenage patients and 35 health professionals (physicians, nutritionists, psychologists). The final set of PROs/ObsROs was discussed and defined in an online consensus meeting with a subsample of three health professionals, three parents and two patients. For this final set, appropriate measures (PROMs/ObsROMs) were assembled. Results Seventeen PROs/ObsROs constitute the final core set for paediatric IT-IEM. They cover social (e.g. social participation), emotional (e.g. positive affect), and disease-related aspects (e.g. attitude towards treatment) of patients’ lives as well as the experience of parents (e.g. parental stress). Conclusion To promote a holistic treatment approach, this consensus-driven set of relevant PROs/ObsROs should be incorporated into daily IT-IEM care and considered as the key psychological outcomes in clinical trials. We have identified existing—psychometrically and contextual—appropriate PROMs/ObsROMs with open access to facilitate this process.