Guidelines for the diagnosis and management of methylmalonic acidaemia and propionic acidaemia: First revision

Clinical and laboratory characteristics of propionic acidemia in a Turkish cohort

OBJECTIVES

Propionic acidemia (PA) is an autosomal recessive multisystem disorder caused by the deficiency of propionyl-CoA carboxylase, encoded by PCCA and PCCB genes. This retrospective study presents the clinical and laboratory characteristics of PA patients followed up in our center.

METHODS

Included in the study were 50 patients diagnosed in a single center with propionic acidemia between 1984 and 2020, whose electronic and written hospital records regarding demographic, clinical, and laboratory features, along with diagnostic and therapeutic approaches, were reviewed retrospectively.

RESULTS

This cohort had a median age at diagnosis of 18 days and 91.1 % (n=41) were born at term. Consanguinity was notably prevalent (91.1 %), and a family history of PA was reported in 14 % of cases. No significant relationships were observed between clinical and laboratory parameters and mortality. Laboratory findings at the time of diagnosis revealed significant metabolic abnormalities, including low levels of free carnitine, elevated C3 propionyl carnitine, and varied amino acid imbalances. Twenty-three patients exhibited developmental delay and/or intellectual disability. Brain magnetic resonance imaging unveiled white matter involvement and ventricular dilatation in 9/25 patients. Furthermore, dilated cardiomyopathy (26 %) was noted in patients who had cardiac assessments. Among the study cohort, 27 patients survived, 23 patients died during follow-up. No significant relationships were observed between clinical and laboratory parameters and mortality.

CONCLUSIONS

Despite improvements in the understanding of the pathophysiology and advances in diagnostic and treatment approaches, propionic acidemia and its long-term complications can still lead to severe consequences. This comprehensive evaluation offers valuable insights into the multifaceted nature of PA.

Correlation between toxic organic acid fluctuations and neurodevelopment in patients with methylmalonic acidemia

BACKGROUND

Methylmalonic acidemia (MMA) is a rare autosomal recessive disorder, that causes multisystem damage by accumulating toxic metabolites. These metabolites, particularly affecting nerve cells, contribute to suboptimal neurodevelopment in MMA patients. While fluctuations in these toxic metabolites are common in MMA patients, their precise impact on neurodevelopment remains unclear.

RESULTS

This study enrolled 20 MMA patients, comprising 14 vitamin B12 non-responsive (B12-NR) type and 6 vitamin B12 responsive (B12-R) type. Diverse parameters were assessed, including methylmalonic acid (MA), methylcitric acid (MCA), propionylcarnitine (C3), acetylcarnitine (C2), ammonia, glycine, and lactate. Cognitive function was evaluated using the Bayley-III and Wechsler intelligence scale, and brain imaging was conducted through magnetic resonance spectroscopy (MRS). The frequency and extent of fluctuations in toxic organic acids were computed based on blood test results. B12-NR type patients exhibited elevated levels of MA, MCA, C3, C3/C2 ratio and lactate, with more frequent and significant MA, MCA and C3 fluctuation than B12-R type patients. Brain imaging revealed central nervous system demyelination in B12-NR type patients, while B12-R type patients displayed normal MRS results. B12-R type patients exhibited significantly better neurocognitive outcomes, with higher scores in all domains.

CONCLUSION

Patients with B12-NR type MMA exhibit worse neurodevelopmental outcomes and more pronounced biochemical imbalances compared to those with B12-R type. Significant correlations were observed between higher fluctuation frequencies of toxic metabolites and lower developmental and IQ scores. These findings emphasize the importance of targeted strategies to manage organic acid fluctuations for improving neurodevelopmental outcomes in MMA.

Clinical development of therapeutic mRNA applications

mRNA therapeutics are emerging as a transformative approach in modern medicine, providing innovative, highly adaptable solutions for a wide range of diseases, from viral infections to cancer. Since the approval of the first mRNA therapeutic-the coronavirus disease 2019 vaccines in 2021-we have identified more than 70 current clinical trials utilizing mRNA for various diseases. We propose classifying mRNA therapeutics into four main categories: vaccines, protein replacement therapies, antibodies, and mRNA-based cell and gene therapies. Each category can be further divided into subcategories. Vaccines include those targeting viral antigens, bacterial or parasitic antigens, general and individualized cancer antigens, and self-antigens. Protein replacement therapies include maintenance therapeutics designed to treat genetic disorders and interventional therapeutics, where delivering therapeutic proteins could improve patient outcomes, such as vascular endothelial growth factor A for ischemic heart disease or proinflammatory cytokines in cancer. Therapeutic antibodies are based on mRNA sequences encoding the heavy and light chains of clinically relevant antibodies, enabling patient cells to produce them directly, bypassing the costly and complex process of manufacturing protein-ready antibodies. Another category of mRNA-based therapeutics encompasses cell and gene therapies, including CRISPR with mRNA-mediated delivery of Cas9 and the in vivo generation of cells expressing CAR through mRNA. We discuss examples of mRNA therapeutics currently in clinical trials within each category, providing a comprehensive overview of the field's progress and highlighting key advancements as of the end of 2024.

The Arg108Cys Variant of Methylmalonyl-CoA Mutase: Clinical Implications for the Mexican Population Based on Molecular Dynamics and Docking

Methylmalonic acidemia (MMA) is a genetic condition associated with intellectual disability and a high mortality rate. It is caused by pathogenic variants in the MMUT gene, which codes methylmalonyl-CoA mutase enzyme (MUT). In the Mexican population, the variant NM_000255.4:c.322C>T or p.(Arg108Cys) is the most frequently found, but its structural pathogenic effect is scarcely studied. To describe the clinical picture of p.(Arg108Cys) homozygous patients and to predict its structural pathogenic effect, we performed an analysis of the medical files from six MMA Mexican p.(Arg108Cys) homozygous patients. The structural changes in MUT caused by this variant were analyzed through molecular dynamics simulations (MDS) and docking and compared with the wild-type (Wt) enzyme. The main clinical symptoms presented by the patients were feeding difficulties, lethargy, and neurodevelopmental delay, with a predominance of early-onset phenotype and a mortality rate of 83%. We found significant structural changes in MUT structure, particularly in the catalytic domain, with increased volume cavity, shortening of the binding substrate tunnel, and aberrant accommodation. Also, the dimerization interface area increased from 1343 Å2 in the Wt to 3386 Å2, and the dimer formation involved a different set of amino acids. The NM_000255.4:c.322C>T or p.(Arg108Cys) MMUT variant is associated with a severe outcome in MMA Mexican patients, and the enzyme was associated with ostentatious topological changes in the secondary and tertiary structure, which impacted the catalytic domain, the accommodation of the substrate, and the dimerization interface. Further ex vivo functional studies are needed to confirm these predictions, such as enzymatic activity measurements in fibroblasts of patients.

Clinical and biochemical footprints of inherited metabolic diseases: Ia. Movement disorders, updated

Movement disorders are a common manifestation of inherited metabolic diseases (IMDs), categorized into hyperkinetic movement disorders, hypokinetic-rigid syndromes, ataxia, and spasticity. We reviewed and updated the list of known metabolic disorders associated with movement disorders, identifying a total of 559 IMDs. We outlined the more common and treatable causes, sorted by the dominant movement disorder phenomenology, and provided a practical clinical approach for suspected IMDs presenting with movement disorders. This work represents an updated catalog in a series of articles aimed at creating and maintaining a comprehensive list of clinical and metabolic differential diagnoses based on system involvement.

Six Chinese patients with propionic acidemia: from asymptomatic to death in the neonatal period

BACKGROUND

Propionic acidemia (PA) is a severe organic acidemia that can result in multi-organ damage and is potentially fatal. The rarity of this disease and the limited number of reported cases contribute to a lack of comprehensive knowledge, particularly concerning the genotype-phenotype correlation. This study aims to report on PA cases in Beijing and Ningxia, China, identify the pathogenic genetic factors involved, and explore the relationship between genotype and phenotype.

METHODS

We calculated the positive screening rates of PA in Beijing and Ningxia and summarized data from six Chinese patients with PA identified at the Beijing Newborn Screening Center and Ningxia Newborn Screening Center. Clinical examinations included blood tandem mass spectrometry, urine gas chromatography-mass spectrometry, and the next-generation sequencing (NGS) technology. Candidate mutations were validated using polymerase chain reaction and Sanger sequencing technology. Bioinformatics software was used to analyze the pathogenicity of the variants, and Swiss PDB Viewer software was employed to predict the effect of mutations on PCCA and PCCB proteins.

RESULTS

The updated incidence of PA was 1 in 114,820 in Beijing and 1 in 189,671 in Ningxia. We reported five patients diagnosed with PA through newborn screening (NBS) and one additional patient diagnosed clinically. Among the five patients diagnosed by NBS, the two late-onset patients exhibited normal neurodevelopment, while all three early-onset patients succumbed between 4 days and 18 months of age. The patient diagnosed clinically passed away at 20 days of age. NGS showed one patient carries compound mutations in the PCCA gene and three patients carry compound heterozygous or homozygous mutations in the PCCB gene. A total of two mutations in PCCA (c.985T > A and c.1195 C > T) and five mutations in PCCB (c.1076 C > T, c.1087T > C, c.224 A > C, c.1339 C> T, and c.1033G > C)were identified, including one novel PCCA mutation (c.985T > A) and four novel PCCB mutations (c.1076 C > T, c.224 A > C, c.1339 C> T, and c.1033G > C). Bioinformatics analysis indicated these mutations are pathogenic, and Swiss PDB Viewer predictions suggest that these variations affect protein conformation.

CONCLUSIONS

The updated incidence rates of PA in Beijing and Ningxia provide new epidemiological insights. We reported six patients with PA, and identified one novel mutation (c.985T > A) in PCCA and four novel mutations (c.1076 C > T, c.224 A > C, c.1339 C> T, and c.1033G > C) in PCCB, which expands the spectrum of clinical features and genetic mutations associated with PA. The c.985T > A mutation in PCCA and the c.1076 C > T mutation in PCCB may be associated with late-onset PA, while the c.224 A > C, c.1339 C > T, and c.1033G > C mutations in PCCB are related to early-onset PA.

Mitochondrial dysfunction drives a neuronal exhaustion phenotype in methylmalonic aciduria

Methylmalonic aciduria (MMA) is an inborn error of metabolism resulting in loss of function of the enzyme methylmalonyl-CoA mutase (MMUT). Despite acute and persistent neurological symptoms, the pathogenesis of MMA in the central nervous system is poorly understood, which has contributed to a dearth of effective brain specific treatments. Here we utilised patient-derived induced pluripotent stem cells and in vitro differentiation to generate a human neuronal model of MMA. We reveal strong evidence of mitochondrial dysfunction caused by deficiency of MMUT in patient neurons. By employing patch-clamp electrophysiology, targeted metabolomics, and bulk transcriptomics, we expose an altered state of excitability, which is exacerbated by application of dimethyl-2-oxoglutarate, and we suggest may be connected to metabolic rewiring. Our work provides first evidence of mitochondrial driven neuronal dysfunction in MMA, which through our comprehensive characterisation of this paradigmatic model, enables first steps to identifying effective therapies.

An atypical presentation in a child with propionic acidemia? Better think twice!

This report details the case of an infant with confirmed propionic acidemia who presented with progressive neurological deterioration and recurrent episodes of metabolic decompensation with elevated lactate levels, but without hyperammonemia. The child's clinical course and neuroradiological findings increasingly deviated from the known clinical and neuroradiological spectrum of propionic acidemia. A rapid trio exome sequencing identified SLC19A3-related thiamine metabolism dysfunction syndrome 2 as a second genetic disease. The pathomechanisms of both diseases synergize in the impairment of brain energy metabolism, and the associated clinical phenotypes partially overlap, which explains the severe and atypical course of propionic acidemia in the reported case.

Human Milk Feeding in Inherited Metabolic Disorders: A Systematic Review of Growth, Metabolic Control, and Neurodevelopment Outcomes

Human milk (HM) is the optimal source of nutrition for infants. Yet the suitability of HM macronutrient composition, paired with the challenge of regulating HM intake, may deserve some consideration for infants with inherited metabolic disorders (IMDs) requiring restrictive and controlled dietary management. Except for classic galactosemia, HM feeding is expected to be feasible, allowing infants to maintain metabolic stability, while growing and developing optimally. However, information about HM feeding in nonphenylketonuria (PKU) literature is scarce. In this systematic review, 52 studies were included, representing 861 infants (86% PKU) receiving HM after IMD diagnosis (mean duration 4-10 months depending on the IMD). For non-PKU IMDs (e.g., other amino acidopathies, urea cycle disorders, organic acidemias, fatty acid oxidation disorders), outcomes of HM feeding were available for few infants, except for medium-chain acyl-CoA dehydrogenase (MCAD) deficiency (n = 48). In PKU, HM feeding combined with phenylalanine-free formula, led to adequate metabolic control (25 studies), growth (15 studies), and neurodevelopment (10 studies). For other IMDs, more evidence is required, but the limited data suggest that HM feeding is possible, with attentive monitoring and disease-specific formula supplementation where applicable. In MCAD deficiency, ensuring adequate HM intake is essential, as symptoms were more frequently reported in exclusively breastfed infants. No IMD-specific articles were found on the relationship between HM feeding and many other outcomes of interest (e.g., immune status or comorbidity risk later in life). With the exception of galactosemia, HM feeding is expected to benefit infants with IMD. More data should be published for IMDs other than PKU.

Emergency Management of Intoxication-Type Inherited Metabolic Disorders

In many intoxication-type inherited metabolic disorders, the accumulation of the toxic chemical can cause acute life-threatening emergencies. Sometimes this is the inevitable consequence of a severe metabolic defect, but it is often triggered by catabolism. In this article, we consider the acute management when these conditions cause encephalopathy, seizures, stroke-like episodes, thromboses, liver failure, cardiac failure, arrhythmias and rhabdomyolysis. Treatment is available for most intoxication-type disorders, though it is seldom entirely satisfactory. The emergency management involves general measures for the immediate problem (such as liver failure, thrombosis or an arrhythmia) and specific treatment for the metabolic disorder. The latter usually aims to reduce the accumulation of the toxic small molecule. Often this involves preventing or reversing catabolism. Sometimes the formation of the toxic chemical can be reduced by removing dietary precursors, by diverting precursors to alternative pathways, or by inhibiting an earlier step in the affected pathway. Another strategy is to remove the toxic chemical by binding it to a drug or by extracorporeal blood purification. Occasionally, the block in the pathway can be ameliorated and some disorders, specific treatment may prevent the consequences of the accumulating chemical. Despite all these treatment strategies, outcomes are often disappointing, particularly if an intoxication disorder first presents as an emergency. Newborn screening has greatly improved the prognosis for some disorders. For others, outcomes can only be improved by earlier recognition and treatment.

Methylmalonic acidemia with homocystinuria in acute myeloid leukemia: a case report

BACKGROUND

Methylmalonic acidaemia (MMA) is a genetic metabolic disorder caused by congenital defects that may result in multisystem damage. However, MMA complicated with acute myeloid leukemia (AML) is very rare.

CASE PRESENTATION

Here, we report a case of MMA with AML in a boy aged 7 years and 6 months. The boy was screened for MMA after birth and received long-term treatment with dietary control, vitamin B12, and L-carnitine. He was readmitted at the age of 7 years and 6 months with systemic bleeding spots and was diagnosed with AML by bone marrow cytology. When the diagnosis was clear, the patient received chemotherapy in addition to maintenance treatment for MMA. His blood routine, liver and kidney function, blood biochemistry, blood glucose, blood lipids, lactic acid and blood ammonia were monitored continuously. Bone marrow cytology one month after starting chemotherapy showed complete remission. Sorafenib was also added during chemotherapy and was discontinued 1 year after completion of chemotherapy. At the end of chemotherapy, he chose venetoclax for consolidation, and to date, the patient's condition is stable, with sustained CR and no relapse.

CONCLUSION

MMA combined with AML is rare. The prevention of infection, comprehensive assessment of nutritional status, continuous monitoring of related indicators and overall situation should be prioritized and comprehensive and individualized treatment approaches are paramount.

The emerging role of dysregulated propionate metabolism and methylmalonic acid in metabolic disease, aging, and cancer

Propionate metabolism dysregulation has emerged as a source of metabolic health alterations linked to aging, cardiovascular and renal diseases, obesity and diabetes, and cancer. This is supported by several large cohort population studies and recent work revealing its role in cancer progression. Mutations in several enzymes of this metabolic pathway are associated with devastating inborn errors of metabolism, resulting in severe methylmalonic and propionic acidemias. Beyond these rare diseases, however, the broader pathological significance of propionate metabolism and its metabolites has been largely overlooked. Here, we summarize earlier studies and new evidence that the alteration of this pathway and associated metabolites are involved in the development of various metabolic diseases and link aging to cancer progression and metastasis.

Evidence That Long-Term Treatment Prevents Tissue Oxidative Damage in Patients With Inherited Disorders of the Propionate Pathway

Propionic and methylmalonic acidemias (PAcidemia and MMAcidemia, respectively) are genetic disorders clinically characterized by metabolic decompensation associated with life-threatening encephalopathic episodes in the neonatal period. Adequate and rapid therapeutic management is essential for patients' survival and prognosis. In this study, a restricted protein diet associated with L-carnitine (LC) supplementation was shown to decrease mortality and morbidity in patients affected by these disorders probably by decreasing the accumulation of the major metabolites and therefore their toxicity. Since oxidative stress was proposed as a contributing mechanism of tissue damage in PAcidemia and MMAcidemia and LC has potent antioxidant properties, our objective in this work was to investigate the effects of a long-term therapy consisting of reduced protein intake associated with LC supplementation on oxidative damage markers in patients affected by these diseases. We measured urinary isoprostanes, di-tyrosine, and oxidized guanine species, which reflect oxidative damage to lipids, proteins, and DNA/RNA, respectively, as well as the concentrations of NO products (nitrate plus nitrite) in patients untreated or submitted to short-term or a long-term treatment. Results revealed significant increases of isoprostanes, di-tyrosine, and oxidized guanine species, as well as a moderate nonsignificant increase of NO levels in the untreated patients, relatively to controls. Furthermore, these altered markers were attenuated after short-term treatment and normalized after prolonged treatment. In conclusion, data from this work show for the first time that long-standing treatment of patients with disorders of the propionate pathway can protect against oxidative damage. However, it remains to be elucidated whether oxidative stress identified in this study directly correlates with the clinical conditions of the affected patients.

Syndromic Retinitis Pigmentosa: A Narrative Review

Retinitis pigmentosa (RP) encompasses inherited retinal dystrophies, appearing either as an isolated eye condition or as part of a broader systemic syndrome, known as syndromic RP. In these cases, RP includes systemic symptoms impacting other organs, complicating diagnosis and management. This review highlights key systemic syndromes linked with RP, such as Usher, Bardet-Biedl, and Alström syndromes, focusing on genetic mutations, inheritance, and clinical symptoms. These insights support clinicians in recognizing syndromic RP early. Ocular signs like nystagmus and congenital cataracts may indicate systemic disease, prompting genetic testing. Conversely, systemic symptoms may necessitate eye exams, even if vision symptoms are absent. Understanding the systemic aspects of these syndromes emphasizes the need for multidisciplinary collaboration among ophthalmologists, pediatricians, and other specialists to optimize patient care. The review also addresses emerging genetic therapies aimed at both visual and systemic symptoms, though more extensive studies are required to confirm their effectiveness. Overall, by detailing the genetic and clinical profiles of syndromic RP, this review seeks to aid healthcare professionals in diagnosing and managing these complex conditions more effectively, enhancing patient outcomes through timely, specialized intervention.

Caregiver's experiences with a mobile-based educational program and its impact on dietary treatment compliance of children with methylmalonic acidemia: an online survey

BACKGROUND

Compliance to highly restrictive diets is critical for children with Methylmalonic Acidemia (MMA), and their caregivers play a prominent role in children's dietary treatment from early childhood through to adulthood. Despite lots of efforts by the multidisciplinary medical team to ensure the smooth implementation of dietary treatment, restricting dietary protein remains particularly challenging for children with MMA. This study aimed to assess dietary treatment compliance in children with MMA and evaluate the impact of WeChat-based parent education on compliance.

METHODS

A sample of 151 caregiver-child dyads was obtained through online recruitment using convenience sampling from February to March 2023. At least one month following the enrollment of MMA caregivers in the WeChat public account "Methylmalonic Acidemia Diet Manager", structured questionnaires were distributed to them through the electronic platform "Questionnaire Star" in collaboration with the Chinese National Alliance of Rare Diseases. Subsequently, the collected data was analyzed using quantitative methods.

RESULTS

Children with MMA aged over 5 years were more likely to present a lower level of dietary treatment compliance compared to those under 1 year old. Besides, the levels of children's dietary treatment compliance were higher when their caregivers had higher levels of satisfaction and benefit from using the public account.

CONCLUSION

Our findings highlighted the significance of age-related challenges in dietary treatment compliance among children with MMA and the promising impact of utilizing WeChat public accounts as a supportive education tool.

Identification of a biallelic MMUT variant (p.Thr230Arg) and its global perspective on clinical management

BACKGROUND

Methylmalonic acidemia (MMA), type mut (0) is a rare type of genetic inborn error of metabolism (IEM) that is caused by aberrant malonyl-CoA mutase activity. Diagnosing IEM can be challenging due to its inherited onset and varying degrees of severity.

METHODS AND RESULTS

In the present study, a consanguineous Pakistani family suspected of IEM was genetically analyzed using whole exome sequencing. A biallelic variant c.689 C > G (p.Thr230Arg) in MMUT was identified to be the causative factor of the disease, which helped in establishing the accurate diagnosis in the family to be MMA mut(0) type. On the basis of the genetic findings, the patient's condition was appropriately managed through a supportive nutrition plan and administration of oral L-carnitine.

CONCLUSIONS

Identification of MMUT mutation through whole exome sequencing was helpful in solving the family and devising targeted management strategies. This study highlights the utility of genetic analysis in diagnosing and treating metabolic disorders like MMA in Pakistani inbred population.

Paediatric Personalized Research Network Switzerland (SwissPedHealth): a joint paediatric national data stream

INTRODUCTION

Children represent a large and vulnerable patient group. However, the evidence base for most paediatric diagnostic and therapeutic procedures remains limited or is often inferred from adults. There is an urgency to improve paediatric healthcare provision based on real-world evidence generation. Digital transformation is a unique opportunity to shape a data-driven, agile, learning healthcare system and deliver more efficient and personalised care to children and their families. The goal of Paediatric Personalized Research Network Switzerland (SwissPedHealth) is to build a sustainable and scalable infrastructure to make routine clinical data from paediatric hospitals in Switzerland interoperable, standardised, quality-controlled, and ready for observational research, quality assurance, trials and health-policy creation. This study describes the design, aims and current achievements of SwissPedHealth.

METHODS AND ANALYSIS

SwissPedHealth was started in September 2022 as one of four national data streams co-funded by the Swiss Personalized Health Network (SPHN) and the Personalized Health and Related Technologies (PHRT). SwissPedHealth develops modular governance and regulatory strategies and harnesses SPHN automatisation procedures in collaboration with clinical data warehouses, the Data Coordination Center, Biomedical Information Technology Network, and other SPHN institutions and funded projects. The SwissPedHealth consortium is led by a multisite, multidisciplinary Steering Committee, incorporating patient and family representatives. The data stream contains work packages focusing on (1) governance and implementation of standardised data collection, (2) nested projects to test the feasibility of the data stream, (3) a lighthouse project that enriches the data stream by integrating multi-omics data, aiming to improve diagnoses of rare diseases and 4) engagement with families through patient and public involvement activities and bioethics interviews.

ETHICS AND DISSEMINATION

The health database regulation of SwissPedHealth was approved by the ethics committee (AO_2022-00018). Research findings will be disseminated through national and international conferences and publications in peer-reviewed journals, and in lay language via online media and podcasts.

Role of carglumic acid in the long-term management of propionic and methylmalonic acidurias

Propionic aciduria (PA) and methylmalonic aciduria (MMA) are rare inherited disorders caused by defects in the propionate metabolic pathway. PA due to propionyl coenzyme A carboxylase deficiency results in accumulation of propionic acid, while in MMA, deficiency in methylmalonyl coenzyme A mutase leads to accumulation of methylmalonic acid. Hyperammonemia is related to a secondary deficiency of N-acetylglutamate (NAG), the activator of carbamoyl phosphate synthetase 1, which is an irreversible rate-limiting enzyme in the urea cycle. Carglumic acid (CGA) is a synthetic structural analog of human NAG and is approved for the treatment of patients with hyperammonemia due to PA or MMA. CGA is well tolerated and its use in normalizing ammonia levels during acute hyperammonemic episodes in patients with PA and MMA is well established. This expert opinion analyzed clinical evidence for CGA and discussed its place, along with other management strategies, in the long-term management of PA or MMA. A literature search of PubMed was undertaken to identify publications related to the chronic use of CGA, transplantation, dietary management, ammonia scavengers, and gene therapy for treatment of patients with PA or MMA. The authors selected the most relevant studies for inclusion. Four clinical studies, one single center case series, and three case reports show that CGA is safe and effective in the chronic treatment of PA and MMA. In particular, the addition of CGA is associated with a reduction in hyperammonemic decompensation episodes and admission to hospital, compared with conventional dietary treatment alone. Current treatment guidelines and recommendations include the use of CGA mainly in acute decompensation, however, lag in considering the benefits of long-term CGA treatment on clinical and biochemical outcomes in patients with PA or MMA. CGA is safe and effective in the chronic treatment of PA and MMA and may help to resolve some of the issues associated with other strategies used to treat these disorders. Thus, CGA appears to have potential for the chronic management of patients with PA and MMA and should be recommended for inclusion in the chronic treatment of these disorders.

Renal phenotyping in a hypomorphic murine model of propionic aciduria reveals common pathomechanisms in organic acidurias

Mutations in the mitochondrial enzyme propionyl-CoA carboxylase (PCC) cause propionic aciduria (PA). Chronic kidney disease (CKD) is a known long-term complication. However, good metabolic control and standard therapy fail to prevent CKD. The pathophysiological mechanisms of CKD are unclear. We investigated the renal phenotype of a hypomorphic murine PA model (Pcca-/-(A138T)) to identify CKD-driving mechanisms. Pcca-/-(A138T) mice show elevated retention parameters and express markers of kidney damage progressing with time. Morphological assessment of the Pcca-/-(A138T) mouse kidneys indicated partial flattening of tubular epithelial cells and focal tubular-cystic dilation. We observed altered renal mitochondrial ultrastructure and mechanisms acting against oxidative stress were active. LC-MS/MS analysis confirmed disease-specific metabolic signatures and revealed disturbances in mitochondrial energy generation via the TCA cycle. Our investigations revealed altered mitochondrial networks shifted towards fission and a marked reduction of mitophagy. We observed a steep reduction of PGC-1-α, the key mediator modulating mitochondrial functions and a counter actor of mitochondrial fission. Our results suggest that impairment of mitochondrial homeostasis and quality control are involved in CKD development in PA. Therapeutic targeting of the identified pathways might help to ameliorate CKD in addition to the current treatment strategies.

Clinical Practice Recommendations on Kidney Management in Methylmalonic Acidemia: an Expert Consensus Statement From ERKNet and MetabERN

Methylmalonic acidemias (MMAs) are rare inherited metabolic diseases with multiorgan involvement. Chronic kidney disease (CKD) is a common complication, leading to kidney failure, dialysis, and kidney transplantation (KT). The objective of these guidelines was to develop clinical practice recommendations focusing on specific aspects of the kidney management of this disease. Development of these clinical practice recommendations is an initiative of the European Reference Network for Rare Kidney Diseases in collaboration with the European Reference Network for Hereditary Metabolic Disorders and included pediatric and adult nephrologists, metabolic specialists, as well as liver and kidney transplant specialists. CKD has become a significant clinical issue that requires specific follow-up in both pediatric and adult departments. Creatinine-based formulae significantly overestimate kidney function and the estimation of estimated glomerular filtration rate (eGFR) is more accurate using cystatin C. Besides usual kidney indications, acute dialysis may be required in emergency in case of acute metabolic decompensation to clear metabolic toxins. Long-term dialysis may be initiated for clearance of toxic metabolites. Long hours on hemodialysis (HD) and/or daily dialysis are required. The indications for transplantation in MMA are a high rate of metabolic decompensations, a high burden of disease and difficult metabolic control. Transplantation is also indicated in case of long-term complications. Combined liver-kidney transplantation (LKT) should be preferred in patients with MMA with CKD. Possible calcineurin inhibitors (CNIs) induced neurotoxicity was described in patients with MMA requiring immunosuppressive treatment monitoring and adaptation. Overall, 13 statements were produced to provide guidance on the management of CKD, dialysis, and transplantation in pediatric and adult patients with MMA.

Isolated methylmalonic acidemia in Mexico: Genotypic spectrum, report of two novel MMUT variants and a possible synergistic heterozygosity effect

Isolated methylmalonic acidemia (iMMA) is a group of monogenic metabolic disorders affecting methylmalonate and cobalamin metabolism. Five iMMA-responsible genes have been described to date: MMUT (MIM *609058), MMAA (MIM *607481, MMAB (MIM *607568), MMADHC (MIM *611935), and MCEE (MIM *608419). Although iMMA is the most common form of organic acidemia reported in Mexico, its genotypic spectrum is still largely unknown. We performed a clinical exome analysis on 42 unrelated Mexican patients with iMMA. MMUT deficiency accounted for 73.8 % of all cases, followed by MMAA (14.2 %), MMAB (7.2 %), and MMADHC (2.4 %) deficiencies. One patient presented MMUT and MMAA double heterozygosity, which should be further experimentally confirmed to prove that synergistic heterozygosity could be another inheritance mechanism in iMMA. The most frequent MMUT genotype involved the Hispanic variant NM_000255.4:c. [322C > T];[322C > T] or p.[Arg108Cys];[Arg108Cys] (14.3 %). Two novel MMUT variants, NM_000255.4:c.589G > A or p.(Ala197Thr) and c.1476C > A or p.(Tyr492*), were identified in a deceased newborn presenting the neonatal-onset severe form of the disease. In silico protein modeling of the p.(Arg108Cys) and novel p.(Ala197Thr) MMUT variants suggested disruption of the substrate-binding and catalytic domains of the protein, respectively. This study expands the current knowledge on the molecular spectrum of iMMA in the Mexican population and reinforces the importance of genetic analysis in guiding clinical management.

The Impact of Early Indication of Living Donor Liver Transplantation on the Outcomes of Patients With Propionic Acidemia: A Single-Center Experience

BACKGROUND

Liver transplantation has been indicated for propionic acidemia (PA) patients with frequent metabolic decompensation and performed as an enzyme replacement therapy. We retrospectively evaluated the outcomes of patients with PA and analyze the appropriate timing of living donor liver transplantation (LDLT).

METHODS

We reviewed 12 children with PA who underwent LDLT, who were divided into early (period from the first episode of metabolic decompensation to LDLT < 1 year; n = 6) and late (> 1 year; n = 6) indication groups depending on the timing of LDLT.

RESULTS

The patient and graft survival rates were 100% in 12 children with PA, and the median observation period was 61 months (5-193 months). None of the patients experienced any episodes of metabolic decompensation after LDLT. The timing of LDLT did not influence the incidence of surgical complications. Two patients in the late indication group had episodes of cardiac arrest and long QT syndrome before LDLT, and one patient showed prolongation of QT interval after LDLT. Two of the six patients in the late indication group had findings of metabolic stroke of the brain on MRI before LDLT. Although LDLT improved the findings of metabolic stroke, a decrease in development quotient score was shown in the post-LDLT course.

CONCLUSIONS

LDLT may be an effective therapeutic option for improving metabolic control. Early LDLT might be help prevent cardiomyopathy and neurological impairment.

Associations between elevated uric acid and brain imaging abnormalities in pediatric patients with methylmalonic acidemia under 5 years of age

Methylmalonic acidemia (MMA) is the most common inborn organic acidemia, presenting multisystemic complications. Uric acid may have neurotoxic or neuroprotective effects due to its antioxidant or pro-inflammatory properties; however, its role in MMA brain injury remains unclear. We examined the correlation between the serum uric acid levels and brain imaging features of MMA. Data were collected from a cross-sectional study of 216 patients with MMA and 216 healthy matched controls aged 0-5 years in China. Serum uric acid levels were measured, and magnetic resonance imaging and computed tomography findings were retrieved from hospital records. Overall, 74.1% patients had brain abnormalities. Patients in the MMA group with abnormal brain imaging had higher serum uric acid levels than those in the MMA normal brain imaging and control groups. The area under the curve of serum uric acid was 0.74, 0.91, and 0.93 for MMA diagnosis with abnormal brain images, basal ganglia changes, and globus pallidus changes, respectively. Higher serum uric acid levels were independently associated with abnormal brain images. Children aged < 5 years with abnormal brain images in MMA exhibit elevated serum uric acid levels, serving as an effective auxiliary diagnostic indicator and independent risk factor for brain tissue injury.

Survival of propionic acidemia patients with liver transplant

Propionic acidemia (PA) is a rare metabolic disorder affecting amino acid metabolism. Liver transplantation improves some outcomes, but the impact on long-term survival remains unclear. A systematic literature review and survival analysis, identifying 94 PA patients who underwent transplantation, revealed a survival probability of 62% at age 33; while median survival was estimated at 40 years. These findings highlight a substantial survival deficit of PA patients compared to the general population despite liver transplantation.

Development of a signs and symptoms outcome measure for caregivers of patients with methylmalonic acidemia and propionic acidemia (MMAPAQ)

BACKGROUND AND OBJECTIVE

Methylmalonic acidemia (MMA) and propionic acidemia (PA) are rare inborn errors of metabolism with shared signs and symptoms that are associated with significant morbidity and mortality. No disease-specific clinical outcomes assessment instruments for MMA and/or PA currently exist to capture the patient perspective in clinical trials. Because patients with these conditions are generally young and have cognitive impairments, an observer-reported outcome (ObsRO) instrument is crucial. We report results from qualitative research supporting development of the Methylmalonic Acidemia and Propionic Acidemia Questionnaire (MMAPAQ), a signs and symptoms ObsRO measure for caregivers of patients with MMA and/or PA.

METHODS

Concept elicitation (CE) interviews were conducted with 35 participants across 2 studies who were aged ≥18 years and caregivers of patients with a confirmed diagnosis of MMA or PA, and an additional 5 patients aged ≥6 years with MMA or PA in Study 1, to identify core signs/symptoms for inclusion in the MMAPAQ. All interviews were conducted in English. Study 2 included cognitive interviews (CI) with caregivers and clinical experts to further assess content validity. CE and a conceptual framework review were also conducted with clinical experts to further support findings.

RESULTS

A consistent set of signs/symptoms of MMA and PA were reported by eligible caregivers interviewed in study 1 (n = 21) and study 2 (n = 14), representing 11 patients with MMA and 20 with PA. Based on concepts reported in study 1, a draft instrument was constructed and compared with the Pediatric Quality of Life Inventory™ (PedsQL™) and Family Impact module, demonstrating face validity for measuring key signs/symptoms important to patients and caregivers. The PedsQL™ and Family Impact modules were preferred to assess patient and caregiver impacts. Two waves of CE and CIs were conducted in study 2, with wave 1 resulting in removal of 7 items and other revisions to improve clarity, and wave 2 resulting in modification of examples used for 2 items. The final instrument consisted of the following 7 items assessed over the past 7 days using a Likert-type response scale ranging from "never" to "very often": uncontrollable or involuntary movements, dehydration, rapid breathing at rest, appearing lethargic, appearing disinterested in eating, refusing to eat, and vomiting.

CONCLUSIONS

This study establishes the content validity of the MMAPAQ as the first ObsRO questionnaire for measuring core signs and symptoms of MMA and PA in clinical trials and community research. Scoring and psychometric measurement properties of the MMAPAQ will be established in future studies. The PedsQL™ was found to have face validity in measuring concepts that affect the MMA and PA patient populations and should also be considered for use in clinical trials in MMA and PA.

Aminotransferase trends in propionic acidemia

Propionic acidemia is a metabolic condition with multiple serious acute and chronic presentations that require strict monitoring. Literature on liver function abnormalities in propionic acidemia is scarce, and the mechanism of liver impairment in this condition remains unclear. Currently, there is no indication for liver-function tests during follow-up and their clinical or prognostic utility is unknown. This study aimed to determine aminotransferase trends in individuals with propionic acidemia at a single institution. We retrospectively evaluated and classified the aminotransferases of 12 patients with propionic acidemia during hospital admissions and routine office visits. The present findings suggest that aminotransferase elevations are very common in this population and can persist beyond acute illness. During hospitalization events, aminotransferases were not a predictor of severity, duration of stay, and readmission within 1 month. Understanding aminotransferase trends in these patients will help clinicians make decisions in the acute setting and potentially in the follow-up of new therapies.

Long-Term Outcomes of Living Donor Liver Transplantation for Methylmalonic Acidemia

BACKGROUND

Despite early diagnosis and medical interventions, patients with methylmalonic acidemia (MMA) suffer from multi-organ damage and recurrent metabolic decompensations.

METHODS

We conducted the largest retrospective multi-center cohort study so far, involving five transplant centers (NCCHD, KUH, KUHP, ATAK, and EMC), and identified all MMA patients (n = 38) undergoing LDLT in the past two decades. Our primary outcome was patient survival, and secondary outcomes included death-censored graft survival and posttransplant complications.

RESULTS

The overall 10-year patient survival and death-censored graft survival rates were 92% and 97%, respectively. Patients who underwent LDLT within 2 years of MMA onset showed significantly higher 10-year patient survival compared to those with an interval more than 2 years (100% vs. 81%, p = 0.038), although the death-censored graft survival were not statistically different (100% vs. 93%, p = 0.22). Over the long-term follow-up, 14 patients (37%) experienced intellectual disability, while two patients developed neurological complications, three patients experienced renal dysfunction, and one patient had biliary anastomotic stricture. The MMA level significantly decreased from 2218.5 mmol/L preoperative to 307.5 mmol/L postoperative (p = 0.038).

CONCLUSIONS

LDLT achieves favorable long-term patient and graft survival outcomes for MMA patients. While not resulting in complete cure, our findings support the consideration of early LDLT within 2 years of disease onset. This approach holds the potential to mitigate recurrent metabolic decompensations, and preserve the long-term renal function.

Improved therapeutic efficacy in two mouse models of methylmalonic acidemia (MMA) using a second-generation mRNA therapy

Isolated methylmalonic acidemia/aciduria (MMA) due to MMUT enzyme deficiency is an ultra-rare pediatric disease with high morbidity and mortality, with no approved disease-altering therapies. Previous publications showed that systemic treatment with a codon-optimized mRNA encoding wild-type human MMUT (MMUT) is a promising strategy for treatment of MMA. We developed a second-generation drug product, mRNA-3705, comprised of an mRNA encoding the MMUT enzyme formulated in a lipid nanoparticle (LNP) with incorporation of enhancements over the previous clinical candidate mRNA-3704. Both drug products produced functional MMUT in rat livers when dosed IV, and showed long-term safety and efficacy in two mouse models of MMA. mRNA-3705 produced 2.1-3.4-fold higher levels of hepatic MMUT protein expression than the first-generation drug product mRNA-3704 when given at an identical dose level, which resulted in greater and more sustained reductions in plasma methylmalonic acid. The data presented herein provide comprehensive preclinical pharmacology to support the clinical development of mRNA-3705.

Disorders of organic acid metabolism and epilepsy

Epilepsy can be caused by a variety of causes, such as inborn errors of metabolism, organic acid disorders are the most significant type of metabolic disorders that cause seizures. The clinical manifestations of these diseases are generally nonspecific, and the types of seizures are different. Screening for multisystem clinical symptoms and identifying the underlying etiology are crucial for early treatment of epileptic seizures. This article provides a comprehensive summary of the pathogenesis, clinical features, diagnosis and treatment of epilepsy associated with organic acid metabolism disorders. Furthermore, relevant literature has also been reviewed to assist clinicians in the diagnosis of cases characterized by the coexistence of multisystemic symptoms and epileptic manifestations.

Propionic Acidemia, Methylmalonic Acidemia, and Cobalamin C Deficiency: Comparison of Untargeted Metabolomic Profiles

Methylmalonic acidemia (MMA), propionic acidemia (PA), and cobalamin C deficiency (cblC) share a defect in propionic acid metabolism. In addition, cblC is also involved in the process of homocysteine remethylation. These three diseases produce various phenotypes and complex downstream metabolic effects. In this study, we used an untargeted metabolomics approach to investigate the biochemical differences and the possible connections among the pathophysiology of each disease. The significantly changed metabolites in the untargeted urine metabolomic profiles of 21 patients (seven MMA, seven PA, seven cblC) were identified through statistical analysis (p < 0.05; log2FC > |1|) and then used for annotation. Annotated features were associated with different metabolic pathways potentially involved in the disease's development. Comparative statistics showed markedly different metabolomic profiles between MMA, PA, and cblC, highlighting the characteristic species for each disease. The most affected pathways were related to the metabolism of organic acids (all diseases), amino acids (all diseases), and glycine and its conjugates (in PA); the transsulfuration pathway; oxidative processes; and neurosteroid hormones (in cblC). The untargeted metabolomics study highlighted the presence of significant differences between the three diseases, pointing to the most relevant contrast in the cblC profile compared to MMA and PA. Some new biomarkers were proposed for PA, while novel data regarding the alterations of steroid hormone profiles and biomarkers of oxidative stress were obtained for cblC disease. The elevation of neurosteroids in cblC may indicate a potential connection with the development of ocular and neuronal deterioration.

Variable phenotypes and outcomes associated with the MMACHC c.482G > A mutation: follow-up in a large CblC disease cohort

BACKGROUND

The aim of this study was to characterize the variable phenotypes and outcomes associated with the methylmalonic aciduria and homocystinuria type C protein gene (MMACHC) c.482G > A mutation in 195 Chinese cases with CblC disease.

METHODS

We carried out a national, retrospective multicenter study of 195 Chinese patients with CblC disease attributable to the MMACHC c.482G > A variant either in a homozygous or compound heterozygous state. The control group consisted of 200 patients diagnosed with CblC disease who did not possess the c.482G > A mutation. Clinical features, including disease onset, symptoms, biochemical metabolites, gene mutation, and follow-up outcomes were reviewed and analyzed in detail. The median follow-up period spanned 3 years and 8 months, with a range of 1 year and 2 months to 12 years and 10 months.

RESULTS

Among 195 patients carrying the c.482G > A variant, 125 (64.1%) cases were diagnosed by newborn screening (NBS), 60 (30.8%) cases were detected due to disease onset, and 10 (5.1%) cases were identified from sibling diagnoses. One hundred and seventeen (93.6%) individuals who were diagnosed by NBS, and nine patients who came from sibling diagnoses remained asymptomatic in this study. From 69 symptomatic patients of the c.482G > A group, more patients presented with later onset, and the top six common clinical symptoms at disease onset were developmental delay (59.4%), lower limb weakness and poor exercise tolerance (50.7%), cognitive decline (37.7%), gait instability and abnormal posture (36.2%), seizures (26.1%), and psychiatric and behavioral disturbances (24.6%). In the 159 symptomatic patients lacking c.482G > A variants, the most frequently observed clinical manifestations at disease onset included developmental delay (81.8%), lethargy and feeding difficulty (62.9%), lower limb weakness and poor exercise tolerance (54.7%), prolonged neonatal jaundice (51.6%), vomiting (47.2%), and seizures (32.7%). Before treatment, the levels of blood propionylcarnitine, propionylcarnitine/acetylcarnitine ratio, and homocysteine in the c.482G > A group were significantly lower (P < 0.05) than those in the non-c.482G > A group, while the concentration of urinary methylmalonic acid was slightly lower (P > 0.05). The degree of decline in the above metabolites after treatment in different groups significantly differed in both plasma total homocysteine values and urinary methylmalonic acid levels (P < 0.05). In patients carrying the c.482G > A variant compared with the non-c.428G > A group, there were markedly lower rates of mortality (0.5% vs. 2.0%) and developmental delay (20.5% vs. 65.5%). When compared with individuals diagnosed due to disease onset, those identified through NBS in either group exhibited a reduced proportion of disease onset (6.7% vs. 100% in the c.482G > A group, 54.4% vs. 100% in the non-c.482G > A group), lower mortality (0.0% vs. 1.7% in the c.482G > A group, 0.0% vs. 3.6% in the non-c.482G > A group), and had a higher percentage of patients exhibiting normal psychomotor and language development (99.3% vs. 33.3% in the c.482G > A group, 58.9% vs. 10.9% in the non-c.482G > A group).

CONCLUSIONS

The c.482G > A variant in MMACHC is associated with late-onset and milder phenotypes of CblC disease. Patients with this mutation tend to have a relatively better response to hydroxocobalamin, better metabolic control, and more favorable neurological outcomes. NBS and other appropriate pre-symptomatic treatments seem to be helpful in early diagnosis, resulting in favorable clinical outcomes. Video Abstract (MP4 136794 kb).

Long-term clinical outcomes and health-related quality of life in patients with isolated methylmalonic acidemia after liver transplantation: experience from the largest cohort study in China

BACKGROUND

Liver transplantation (LT) has been proposed as a viable treatment option for selected methylmalonic acidemia (MMA) patients. However, there are still controversies regarding the therapeutic value of LT for MMA. The systematic assessment of health-related quality of life (HRQoL)-targeted MMA children before and after LT is also undetermined. This study aimed to comprehensively assess the long-term impact of LT on MMA, including multiorgan sequelae and HRQoL in children and families.

METHODS

We retrospectively evaluated 15 isolated MMA patients undergoing LT at our institution between June 2013 and March 2022. Pre- and post-transplant data were compared, including metabolic profiles, neurologic consequences, growth parameters, and HRQoL. To further assess the characteristics of the HRQoL outcomes in MMA, we compared the results with those of children with biliary atresia (BA).

RESULTS

All patients had early onset MMA, and underwent LT at a mean age of 4.3 years. During 1.3-8.2 years of follow-up, the patient and graft survival rates were 100%. Metabolic stability was achieved in all patients with liberalized dietary protein intake. There was a significant overall improvement in height Z scores (P = 0.0047), and some preexisting neurological complications remained stable or even improved after LT. On the Pediatric Quality of Life Inventory (PedsQL™) generic core scales, the mean total, physical health, and psychosocial health scores improved significantly posttransplant (P < 0.05). In the family impact module, higher mean scores were noted for all subscales post-LT, especially family function and daily activities (P < 0.01). However, the total scores on the generic core scales and transplant module were significantly lower (Cohen's d = 0.57-1.17) when compared with BA recipients. In particular, social and school functioning (Cohen's d = 0.86-1.76), treatment anxiety, and communication (Cohen's d = 0.99-1.81) were far behind, with a large effect size.

CONCLUSIONS

This large single-center study of the mainland of China showed an overall favorable impact of LT on isolated MMA in terms of long-term survival, metabolic control, and HRQoL in children and families. The potential for persistent neurocognitive impairment and inherent metabolic fragility requires long-term special care. Video Abstract (MP4 153780 KB).

Clinical outcomes of patients with mut-type methylmalonic acidemia identified through expanded newborn screening in China

BACKGROUND

Isolated methylmalonic acidemia, an autosomal recessive disorder of propionate metabolism, is usually caused by mutations in the methylmalonyl-CoA mutase gene (mut-type). Because no universal consensus was made on whether mut-type methylmalonic acidemia should be included in newborn screening (NBS), we aimed to compare the outcome of this disorder detected by NBS with that detected clinically and investigate the influence of NBS on the disease course.

DESIGN & METHODS

In this study, 168 patients with mut-type methylmalonic acidemia diagnosed by NBS were compared to 210 patients diagnosed after disease onset while NBS was not performed. Clinical data of these patients from 7 metabolic centers in China were analyzed retrospectively, including initial manifestations, biochemical metabolites, the responsiveness of vitamin B12 therapy, and gene variation, to explore different factors on the long-term outcome.

RESULTS

By comparison of the clinically-diagnosed patients, NBS-detected patients showed younger age at diagnosis, less incidence of disease onset, better responsiveness of vitamin B12, younger age at start of treatment, lower levels of biochemical features before and after treatment, and better long-term prognosis (P < 0.01). Onset of disease, blood C3/C2 ratio and unresponsiveness of vitamin B12 were more positively associated with poor outcomes of patients whether identified by NBS. Moreover, the factors above as well as older age at start of treatment were positively associated with mortality.

CONCLUSIONS

This research highly demonstrated NBS could prevent major disease-related events and allow an earlier treatment initiation. As a key prognostic factor, NBS is beneficial for improving the overall survival of infants with mut-type methylmalonic acidemia.

An In Vivo Model of Propionic Acid-Rich Diet-Induced Gliosis and Neuro-Inflammation in Mice (FVB/N-Tg(GFAPGFP)14Mes/J): A Potential Link to Autism Spectrum Disorder

Evidence shows that Autism Spectrum Disorder (ASD) stems from an interplay of genetic and environmental factors, which may include propionic acid (PPA), a microbial byproduct and food preservative. We previously reported that in vitro treatment of neural stem cells with PPA leads to gliosis and neuroinflammation. In this study, mice were exposed ad libitum to a PPA-rich diet for four weeks before mating. The same diet was maintained through pregnancy and administered to the offspring after weaning. The brains of the offspring were studied at 1 and 5 months postpartum. Glial fibrillary acidic protein (astrocytic marker) was significantly increased (1.53 ± 0.56-fold at 1 M and 1.63 ± 0.49-fold at 5 M) in the PPA group brains. Tubulin IIIβ (neuronal marker) was significantly decreased in the 5 M group. IL-6 and TNF-α expression were increased in the brain of the PPA group (IL-6: 2.48 ± 1.25-fold at 5 M; TNF-α: 2.84 ± 1.16-fold at 1 M and 2.64 ± 1.42-fold, at 5 M), while IL-10 was decreased. GPR41 and p-Akt were increased, while PTEN (p-Akt inhibitor) was decreased in the PPA group. The data support the role of a PPA-rich diet in glia over-proliferation and neuro-inflammation mediated by the GPR41 receptor and PTEN/Akt pathway. These findings strongly support our earlier study on the role of PPA in ASD.

Biochemical Pattern of Methylmalonyl-CoA Epimerase Deficiency Identified in Newborn Screening: A Case Report

Methylmalonyl-CoA epimerase enzyme (MCEE) is responsible for catalyzing the isomeric conversion between D- and L-methylmalonyl-CoA, an intermediate along the conversion of propionyl-CoA to succinyl-CoA. A dedicated test for MCEE deficiency is not included in the newborn screening (NBS) panels but it can be incidentally identified when investigating methylmalonic acidemia and propionic acidemia. Here, we report for the first time the biochemical description of a case detected by NBS. The NBS results showed increased levels of propionylcarnitine (C3) and 2-methylcitric acid (MCA), while methylmalonic acid (MMA) and homocysteine (Hcy) were within the reference limits. Confirmatory analyses revealed altered levels of metabolites, including MCA and MMA, suggesting a block in the propionate degradation pathway. The analysis of methylmalonic pathway genes by next-generation sequencing (NGS) allowed the identification of the known homozygous nonsense variation c.139C>T (p.R47X) in exon 2 of the MCE gene. Conclusions: Elevated concentrations of C3 with a slight increase in MCA and normal MMA and Hcy during NBS should prompt the consideration of MCEE deficiency in differential diagnosis. Increased MMA levels may be negligible at NBS as they may reach relevant values beyond the first days of life and thus could be identified only in confirmatory analyses.

Outcomes after newborn screening for propionic and methylmalonic acidemia and homocystinurias

The current German newborn screening (NBS) panel includes 13 inherited metabolic diseases (IMDs). In addition, a NBS pilot study in Southwest Germany identifies individuals with propionic acidemia (PA), methylmalonic acidemia (MMA), combined and isolated remethylation disorders (e.g., cobalamin [cbl] C and methylenetetrahydrofolate reductase [MTHFR] deficiency), cystathionine β-synthase (CBS) deficiency, and neonatal cbl deficiency through one multiple-tier algorithm. The long-term health benefits of screened individuals are evaluated in a multicenter observational study. Twenty seven screened individuals with IMDs (PA [N = 13], MMA [N = 6], cblC deficiency [N = 5], MTHFR deficiency [N = 2] and CBS deficiency [N = 1]), and 42 with neonatal cbl deficiency were followed for a median of 3.6 years. Seventeen screened IMD patients (63%) experienced at least one metabolic decompensation, 14 of them neonatally and six even before the NBS report (PA, cbl-nonresponsive MMA). Three PA patients died despite NBS and immediate treatment. Fifteen individuals (79%) with PA or MMA and all with cblC deficiency developed permanent, mostly neurological symptoms, while individuals with MTHFR, CBS, and neonatal cbl deficiency had a favorable clinical outcome. Utilizing a combined multiple-tier algorithm, we demonstrate that NBS and specialized metabolic care result in substantial benefits for individuals with MTHFR deficiency, CBS deficiency, neonatal cbl deficiency, and to some extent, cbl-responsive MMA and cblC deficiency. However, its advantage is less evident for individuals with PA and cbl-nonresponsive MMA. SYNOPSIS: Early detection through newborn screening and subsequent specialized metabolic care improve clinical outcomes and survival in individuals with MTHFR deficiency and cystathionine-β-synthase deficiency, and to some extent in cobalamin-responsive methylmalonic acidemia (MMA) and cblC deficiency while the benefit for individuals with propionic acidemia and cobalamin-nonresponsive MMA is less evident due to the high (neonatal) decompensation rate, mortality, and long-term complications.

The utility of methylmalonic acid, methylcitrate acid, and homocysteine in dried blood spots for therapeutic monitoring of three inherited metabolic diseases

Backgroud

Routine metabolic assessments for methylmalonic acidemia (MMA), propionic acidemia (PA), and homocysteinemia involve detecting metabolites in dried blood spots (DBS) and analyzing specific biomarkers in serum and urine. This study aimed to establish a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the simultaneous detection of three specific biomarkers (methylmalonic acid, methylcitric acid, and homocysteine) in DBS, as well as to appraise the applicability of these three DBS metabolites in monitoring patients with MMA, PA, and homocysteinemia during follow-up.

Methods

A total of 140 healthy controls and 228 participants were enrolled, including 205 patients with MMA, 17 patients with PA, and 6 patients with homocysteinemia. Clinical data and DBS samples were collected during follow-up visits.

Results

The reference ranges (25th-95th percentile) for DBS methylmalonic acid, methylcitric acid, and homocysteine were estimated as 0.04-1.02 μmol/L, 0.02-0.27 μmol/L and 1.05-8.22 μmol/L, respectively. Following treatment, some patients achieved normal metabolite concentrations, but the majority still exhibited characteristic biochemical patterns. The concentrations of methylmalonic acid, methylcitric acid, and homocysteine in DBS showed positive correlations with urine methylmalonic acid (r = 0.849, p < 0.001), urine methylcitric acid (r = 0.693, p < 0.001), and serum homocysteine (r = 0.721, p < 0.001) concentrations, respectively. Additionally, higher levels of DBS methylmalonic acid and methylcitric acid may be associated with increased cumulative complication scores.

Conclusion

The LC-MS/MS method established in this study reliably detects methylmalonic acid, methylcitric acid, and homocysteine in DBS. These three DBS metabolites can be valuable for monitoring patients with MMA, PA, and homocysteinemia during follow-up. Further investigation is required to determine the significance of these DBS biomarkers in assessing disease burden over time.

Hypogammaglobulinemia Class G Is Present in Compensated and Decompensated Patients with Propionate Defects, Independent of Their Nutritional Status

Propionate defects (PDs) mainly include methylmalonic (MMA) and propionic acidemia (PA) defects. Lifelong PD patients progress from the compensated to the decompensated stages, the latter of which are characterized by life-threatening acidemia and hyperammonemia crises. PD patients can suffer immunocompromise, especially during the decompensation stage. There is a significant gap in the research regarding the humoral immune response in PD patients. Here, we analyzed serum immunoglobulin concentrations and hemograms across compensated and decompensated stages in PD patients. Nutritional status and crisis triggers of decompensation were also explored. Twenty patients were studied, and 25 decompensation events (DE) and 8 compensation events (CE) were recorded. Compared with those in the CE group, the IgG levels in the DE group (513.4 ± 244.5 mg/dL) were significantly lower than those in the CE group (860.8 ± 456.5 mg/dL) (p < 0.0087). The mean hemoglobin concentration was significantly lower in the DE group (11.8 g/dL) than in the CE group (13.4 g/dL) (p < 0.05). The most frequent (48%) possible decompensation trigger factor was infection. Most of the events were registered in eutrophic patients (87.9%), despite which 65.2% and 50% of patients who experienced decompensated and compensated events, respectively, presented with hypogammaglobulinemia G. These findings provide evidence of the immunodeficiency of PD patients, independent of their nutritional status. We suggest that PD patients be managed as immunocompromised independently of their nutritional status or metabolic state (compensated or decompensated).

Full-left/Full-right Liver Splitting With Middle Hepatic Vein and Caval Partition During Dual Hypothermic Oxygenated Machine Perfusion

BACKGROUND

Split liver transplantation is a valuable means of mitigating organ scarcity but requires significant surgical and logistical effort. Ex vivo splitting is associated with prolonged cold ischemia, with potentially negative effects on organ viability. Machine perfusion can mitigate the effects of ischemia-reperfusion injury by restoring cellular energy and improving outcomes.

METHODS

We describe a novel technique of full-left/full-right liver splitting, with splitting and reconstruction of the vena cava and middle hepatic vein, with dual arterial and portal hypothermic oxygenated machine perfusion. The accompanying video depicts the main surgical passages, notably the splitting of the vena cava and middle hepatic vein, the parenchymal transection, and the venous reconstruction.

RESULTS

The left graft was allocated to a pediatric patient having methylmalonic aciduria, whereas the right graft was allocated to an adult patient affected by hepatocellular carcinoma and cirrhosis.

CONCLUSIONS

This technique allows ex situ splitting, counterbalancing prolonged ischemia with the positive effects of hypothermic oxygenated machine perfusion on graft viability. The venous outflow is preserved, safeguarding both grafts from venous congestion; all reconstructions can be performed ex situ, minimizing warm ischemia. Moreover, there is no need for highly skilled surgeons to reach the donor hospital, thereby simplifying logistical aspects.

Fasting alleviates metabolic alterations in mice with propionyl-CoA carboxylase deficiency due to Pcca mutation

Propionic acidemia (PA), resulting from Pcca or Pccb gene mutations, impairs propionyl-CoA metabolism and induces metabolic alterations. While speculation exists that fasting might exacerbate metabolic crises in PA patients by accelerating the breakdown of odd-chain fatty acids and amino acids into propionyl-CoA, direct evidence is lacking. Our investigation into the metabolic effects of fasting in Pcca-/-(A138T) mice, a PA model, reveals surprising outcomes. Propionylcarnitine, a PA biomarker, decreases during fasting, along with the C3/C2 (propionylcarnitine/acetylcarnitine) ratio, ammonia, and methylcitrate. Although moderate amino acid catabolism to propionyl-CoA occurs with a 23-h fasting, a significant reduction in microbiome-produced propionate and increased fatty acid oxidation mitigate metabolic alterations by decreasing propionyl-CoA synthesis and enhancing acetyl-CoA synthesis. Fasting-induced gluconeogenesis further facilitates propionyl-CoA catabolism without changing propionyl-CoA carboxylase activity. These findings suggest that fasting may alleviate metabolic alterations in Pcca-/-(A138T) mice, prompting the need for clinical evaluation of its potential impact on PA patients.

Comparative analysis of inherited metabolic diseases in normal newborns and high-risk children: Insights from a 10-year study in Shanghai

BACKGROUND

Compare the differences between normal newborns and high-risk children with inherited metabolic diseases. The disease profile includes amino acidemias, fatty acid oxidation disorders, and organic acidemias.

METHODS

Data was collected on newborns and children from high-risk populations in Shanghai from December 2010 to December 2020.

RESULTS

232,561 newborns were screened for disorders of organic, amino acid, and fatty acid metabolism. The initial positive rate was 0.66 % (1,526/232,561) and the positive recall rate was 77.85 %. The positive predictive value is 4.71 %. Among them, 56 cases were diagnosed as metabolic abnormalities. The total incidence rate is 1:4153. Hyperphenylalaninemia and short-chain acyl-CoA dehydrogenase are the most common diseases in newborns. In addition, in 56 children, 39 (69.42 %) were diagnosed by genetic sequencing. Some hotspot mutations in 14 IEMs have been observed, including PAH gene c.728G > A, c.611A > G, and ACADS gene c. 1031A > G, c.164C > T. A total of 49,860 symptomatic patients were screened, of which 185 were diagnosed with IEM, with a detection rate of 0.37 %. The most commonly diagnosed diseases in high-risk infants aremethylmalonic acidemia and hyperphenylalaninemia.

CONCLUSION

There are more clinical cases of congenital metabolic errors diagnosed by tandem mass spectrometry than newborn screening. The spectrum of diseases, prevalence, and genetic characteristics of normal newborns and high-risk children are quite different.

Clinical and genetic analysis of methylmalonic aciduria in 60 patients from Southern China: a single center retrospective study

BACKGROUND

Methylmalonic aciduria (MMA) is a group of rare genetic metabolic disorders resulting from defects in methylmalonyl coenzyme A mutase (MCM) or intracellular cobalamin (cbl) metabolism. MMA patients show diverse clinical and genetic features across different subtypes and populations.

METHODS

We retrospectively recruited 60 MMA patients from a single center and diagnosed them based on their clinical manifestations and biochemical assays. We then performed genetic analysis to confirm the diagnosis and identify the causal variants.

RESULTS

We confirmed the common clinical manifestations of MMA reported previously. We also described four rare MMA cases with unusual symptoms or genetic variants, such as pulmonary hypertension or limb weakness in late-onset patients. We identified 15 MMACHC and 26 MMUT variants in 57 patients, including 6 novel MMUT variants. Two patients had only one MMAA variant each, and one patient had mild MMA due to mitochondrial DNA depletion syndrome caused by a SUCLA2 variant. Among 12 critically ill patients, isolated MMA was associated with higher C3, blood ammonia, and acidosis, while combined MMA was linked to hydrocephalus on skull MRI. MMACHC c.658-660delAAG and MMUT c.1280G > A variants were correlated with more severe phenotypes.

CONCLUSIONS

Our study demonstrates the clinical and genotypic heterogeneity of MMA patients and indicates that metabolic screening and genetic analysis are useful tools to identify rare cases.

Characterizing the mechanism of action for mRNA therapeutics for the treatment of propionic acidemia, methylmalonic acidemia, and phenylketonuria

Messenger RNA (mRNA) therapeutics delivered via lipid nanoparticles hold the potential to treat metabolic diseases caused by protein deficiency, including propionic acidemia (PA), methylmalonic acidemia (MMA), and phenylketonuria (PKU). Herein we report results from multiple independent preclinical studies of mRNA-3927 (an investigational treatment for PA), mRNA-3705 (an investigational treatment for MMA), and mRNA-3210 (an investigational treatment for PKU) in murine models of each disease. All 3 mRNA therapeutics exhibited pharmacokinetic/pharmacodynamic (PK/PD) responses in their respective murine model by driving mRNA, protein, and/or protein activity responses, as well as by decreasing levels of the relevant biomarker(s) when compared to control-treated animals. These preclinical data were then used to develop translational PK/PD models, which were scaled allometrically to humans to predict starting doses for first-in-human clinical studies for each disease. The predicted first-in-human doses for mRNA-3927, mRNA-3705, and mRNA-3210 were determined to be 0.3, 0.1, and 0.4 mg/kg, respectively.

mRNA therapies: Pioneering a new era in rare genetic disease treatment

Rare genetic diseases, often referred to as orphan diseases due to their low prevalence and limited treatment options, have long posed significant challenges to our medical system. In recent years, Messenger RNA (mRNA) therapy has emerged as a highly promising treatment approach for various diseases caused by genetic mutations. Chemically modified mRNA is introduced into cells using carriers like lipid-based nanoparticles (LNPs), producing functional proteins that compensate for genetic deficiencies. Given the advantages of precise dosing, biocompatibility, transient expression, and minimal risk of genomic integration, mRNA therapies can safely and effectively correct genetic defects in rare diseases and improve symptoms. Currently, dozens of mRNA drugs targeting rare diseases are undergoing clinical trials. This comprehensive review summarizes the progress of mRNA therapy in treating rare genetic diseases. It introduces the development, molecular design, and delivery systems of mRNA therapy, highlighting their research progress in rare genetic diseases based on protein replacement and gene editing. The review also summarizes research progress in various rare disease models and clinical trials. Additionally, it discusses the challenges and future prospects of mRNA therapy. Researchers are encouraged to join this field and collaborate to advance the clinical translation of mRNA therapy, bringing hope to patients with rare genetic diseases.

NMR Spectroscopy in Diagnosis and Monitoring of Methylmalonic and Propionic Acidemias

Although both localized nuclear magnetic resonance spectroscopy (MRS) and non-localized nuclear magnetic resonance spectroscopy (NMR) generate the same information, i.e., spectra generated by various groups from the structure of metabolites, they are rarely employed in the same study or by the same research group. As our review reveals, these techniques have never been applied in the same study of methylmalonic acidemia (MMA), propionic acidemia (PA) or vitamin B12 deficiency patients. On the other hand, MRS and NMR provide complementary information which is very valuable in the assessment of the severity of disease and efficiency of its treatment. Thus, MRS provides intracellular metabolic information from localized regions of the brain, while NMR provides extracellular metabolic information from biological fluids like urine, blood or cerebrospinal fluid. This paper presents an up-to-date review of the NMR and MRS studies reported to date for methylmalonic and propionic acidemias. Vitamin B12 deficiency, although in most of its cases not inherited, shares similarities in its metabolic effects with MMA and it is also covered in this review.

Clinical Genetic and Genomic Testing in Congenital Heart Disease and Cardiomyopathy

Congenital heart disease (CHD) and cardiomyopathies are the leading cause of morbidity and mortality worldwide. These conditions are often caused by genetic factors, and recent research has shown that genetic and genomic testing can provide valuable information for patient care. By identifying genetic causes, healthcare providers can screen for other related health conditions, offer early interventions, estimate prognosis, select appropriate treatments, and assess the risk for family members. Genetic and genomic testing is now the standard of care in patients with CHD and cardiomyopathy. However, rapid advances in technology and greater availability of testing options have led to changes in recommendations for the most appropriate testing method. Several recent studies have investigated the utility of genetic testing in this changing landscape. This review summarizes the literature surrounding the clinical utility of genetic evaluation in patients with CHD and cardiomyopathy.

Serum methylmalonic acid concentrations at breast cancer diagnosis significantly correlate with clinical frailty

Methylmalonic acid (MMA), a by-product of propionate metabolism, is known to increase with age. This study investigates the potential of serum MMA concentrations as a biomarker for age-related clinical frailty in older patients with breast cancer. One hundred nineteen patients ≥ 70 years old with early-stage breast cancer were included (median age 76 years). G8 screening, full geriatric assessment, clinical parameters (i.e., estimated glomerular filtration rate (eGFR) and body mass index (BMI)), and serum sample collection were collected at breast cancer diagnosis before any therapy was administered. MMA concentrations were measured via liquid chromatography with tandem mass spectrometry. MMA concentrations significantly increased with age and eGFR (all P < 0.001) in this older population. The group with an abnormal G8 (≤ 14, 51% of patients) had significantly higher MMA levels than the group with normal G8 (> 14, 49%): 260 nmol/L vs. 188 nmol/L, respectively (P = 0.0004), even after correcting for age and eGFR (P = 0.001). Furthermore, in the detailed assessment, MMA concentrations correlated most with mobility (Eastern Cooperative Oncology Group (ECOG) Performance Status and Activities of Daily Living (ADL) tools, all P ≤ 0.02), comorbidity (Charlson Comorbidity Index (CCI) tool, P = 0.005), and polypharmacy (P < 0.001), whereas no significant associations were noted for instrumental ADL (IADL), Mini-Mental State Examination (MMSE), Geriatric Depression Scale-15 (GDS15), Mini Nutritional Assessment-Short Form (MNA-SF), and pain (all P > 0.1). In addition, our results showed that higher MMA levels correlate with poor overall survival in breast cancer patients (P = 0.003). Elevated serum MMA concentrations at initial diagnosis are significantly associated, not only with age but also independently with clinical frailty, suggesting a possible influence of MMA on clinical frailty in older patients with early-stage breast cancer.