Impact of age at onset and newborn screening on outcome in organic acidurias

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.

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.

Clinical and Molecular Spectrum of Patients with Methylmalonic Acidemia

OBJECTIVES

To study the clinical and molecular spectrum of Methylmalonic acidemia (MMA).

METHODS

In this retrospective study, the records of 30 MMA patients were evaluated for their phenotype, biochemical abnormalities, genotype, and outcomes.

RESULTS

Thirty patients with MMA (age range 0-21 y) from 27 unrelated families were enrolled. Family history and consanguinity were noted in 10/27 (37%) and 11/27 (41%) families respectively. Acute metabolic decompensation was more common (57%) than chronic presentation. Biochemical work-up was suggestive of isolated MMA (n = 18) and MMA with homocystinuria (n = 9) respectively. Molecular testing in 24 families showed 21 pathogenic or likely pathogenic variants with MMA cblC as the commonest molecular subtype (n = 8). B12 responsiveness, an important determinant of long-term outcome, was observed in eight patients [MMAA (n = 3) and MMACHC (n = 5)]. Mortality was 30% (n = 9/30) with a high proportion of early-onset severe disease and fatal outcome in isolated MMA mut0 (4/4) and MMA cblB (3/3), as compared to MMA cblA (1/5) and MMA cblC (1/10).

CONCLUSIONS

This study cohort had MMA cblC subtype as the most common type of MMA followed by the MMA mutase defect. Outcomes in MMA are influenced by the type of molecular defect, age, and severity of presentation. Early detection and management is likely to result in better outcomes.

Cardiac Involvement in Classical Organic Acidurias: Clinical Profile and Outcome in a Pediatric Cohort

BACKGROUND

Cardiac involvement is reported in a significant proportion of patients with classical organic acidurias (OAs), contributing to disability and premature death. Different cardiac phenotypes have been described, among which dilated cardiomyopathy (DCM) is predominant. Despite recent progress in diagnosis and treatment, the natural history of patients with OAs remains unresolved, specifically with regard to the impact of cardiac complications. We therefore performed a retrospective study to address this issue at our Referral Center for Pediatric Inherited Errors of Metabolism.

METHODS

Sixty patients with OAs (propionic (PA), methylmalonic (MMA) and isovaleric acidemias and maple syrup urine disease) diagnosed from 2000 to 2022 were systematically assessed at baseline and at follow-up.

RESULTS

Cardiac anomalies were found in 23/60 OA patients, all with PA or MMA, represented by DCM (17/23 patients) and/or acquired long QT syndrome (3/23 patients). The presence of DCM was associated with the worst prognosis. The rate of occurrence of major adverse cardiac events (MACEs) at 5 years was 55% in PA with cardiomyopathy; 35% in MMA with cardiomyopathy; and 23% in MMA without cardiomyopathy. Liver transplantation was performed in seven patients (12%), all with PA or MMA, due to worsening cardiac impairment, and led to the stabilization of metabolic status and cardiac function.

CONCLUSIONS

Cardiac involvement was documented in about one third of children diagnosed with classical OAs, confined to PA and MMA, and was often associated with poor outcome in over 50%. Etiological diagnosis of OAs is essential in guiding management and risk stratification.

[Evaluation and optimization of newborn screening by structured long-term follow-up-using the example of inherited metabolic diseases]

Newborn screening (NBS) is a highly successful secondary prevention program with the goal of preventing severe sequelae of congenital, mostly genetic, diseases by identifying them as early as possible, ideally in the pre-symptomatic period. Studies to date have shown the important achievements of NBS programs but also reveal a number of relevant weaknesses. These include the often incompletely understood natural history and phenotypic diversity of rare diseases as well as the inadequate ability to accurately predict individual disease severity at an early stage and thus the uncertainties in case definition, risk stratification, and treatment indication.In light of the rapid developments in high-throughput genetic technologies and the associated opportunities for substantial future expansion of NBS programs, it seems overdue to make structured long-term follow-up and the subsequent evaluation of the long-term health benefits mandatory for individuals with rare diseases identified through NBS. This article explains the importance of long-term follow-up for the evaluation and continuous optimization of the screening. Long-term clinical outcomes of people with inherited metabolic diseases identified by NBS are presented as examples.

Collaborative evaluation study on 18 candidate diseases for newborn screening in 1.77 million samples

Analytical and therapeutic innovations led to a continuous but variable extension of newborn screening (NBS) programmes worldwide. Every extension requires a careful evaluation of feasibility, diagnostic (process) quality and possible health benefits to balance benefits and limitations. The aim of this study was to evaluate the suitability of 18 candidate diseases for inclusion in NBS programmes. Utilising tandem mass spectrometry as well as establishing specific diagnostic pathways with second-tier analyses, three German NBS centres designed and conducted an evaluation study for 18 candidate diseases, all of them inherited metabolic diseases. In total, 1 777 264 NBS samples were analysed. Overall, 441 positive NBS results were reported resulting in 68 confirmed diagnoses, 373 false-positive cases and an estimated cumulative prevalence of approximately 1 in 26 000 newborns. The positive predictive value ranged from 0.07 (carnitine transporter defect) to 0.67 (HMG-CoA lyase deficiency). Three individuals were missed and 14 individuals (21%) developed symptoms before the positive NBS results were reported. The majority of tested candidate diseases were found to be suitable for inclusion in NBS programmes, while multiple acyl-CoA dehydrogenase deficiency, isolated methylmalonic acidurias, propionic acidemia and malonyl-CoA decarboxylase deficiency showed some and carnitine transporter defect significant limitations. Evaluation studies are an important tool to assess the potential benefits and limitations of expanding NBS programmes to new diseases.

The challenge of understanding and predicting phenotypic diversity in urea cycle disorders

The Urea Cycle Disorders Consortium (UCDC) and the European registry and network for Intoxication type Metabolic Diseases (E-IMD) are the worldwide largest databases for individuals with urea cycle disorders (UCDs) comprising longitudinal data from more than 1100 individuals with an overall long-term follow-up of approximately 25 years. However, heterogeneity of the clinical phenotype as well as different diagnostic and therapeutic strategies hamper our understanding on the predictors of phenotypic diversity and the impact of disease-immanent and interventional variables (e.g., diagnostic and therapeutic interventions) on the long-term outcome. A new strategy using combined and comparative data analyses helped overcome this challenge. This review presents the mechanisms and relevant principles that are necessary for the identification of meaningful clinical associations by combining data from different data sources, and serves as a blueprint for future analyses of rare disease registries.

Isovaleric aciduria identified by newborn screening: Strategies to predict disease severity and stratify treatment

Newborn screening (NBS) allows early identification of individuals with rare disease, such as isovaleric aciduria (IVA). Reliable early prediction of disease severity of positively screened individuals with IVA is needed to guide therapeutic decision, prevent life-threatening neonatal disease manifestation in classic IVA and over-medicalization in attenuated IVA that may remain asymptomatic. We analyzed 84 individuals (median age at last study visit 8.5 years) with confirmed IVA identified by NBS between 1998 and 2018 who participated in the national, observational, multicenter study. Screening results, additional metabolic parameters, genotypes, and clinical phenotypic data were included. Individuals with metabolic decompensation showed a higher median isovalerylcarnitine (C5) concentration in the first NBS sample (10.6 vs. 2.7 μmol/L; p < 0.0001) and initial urinary isovalerylglycine concentration (1750 vs. 180 mmol/mol creatinine; p = 0.0003) than those who remained asymptomatic. C5 was in trend inversely correlated with full IQ (R = -0.255; slope = -0.869; p = 0.0870) and was lower for the "attenuated" variants compared to classic genotypes [median (IQR; range): 2.6 μmol/L (2.1-4.0; 0.7-6.4) versus 10.3 μmol/L (7.4-13.1; 4.3-21.7); N = 73]. In-silico prediction scores (M-CAP, MetaSVM, and MetaLR) correlated highly with isovalerylglycine and ratios of C5 to free carnitine and acetylcarnitine, but not sufficiently with clinical endpoints. The results of the first NBS sample and biochemical confirmatory testing are reliable early predictors of the clinical course of IVA, facilitating case definition (attenuated versus classic IVA). Prediction of attenuated IVA is supported by the genotype. On this basis, a reasonable algorithm has been established for neonates with a positive NBS result for IVA, with the aim of providing the necessary treatment immediately, but whenever possible, adjusting the treatment to the individual severity of the disease.

Late-onset cblC defect: clinical, biochemical and molecular analysis

BACKGROUND

cblC defect is the most common type of methylmalonic acidemia in China. Patients with late-onset form (>1 year) are often misdiagnosed due to heterogeneous symptoms. This study aimed to describe clinical characteristics and evaluate long-term outcomes of Chinese patients with late-onset cblC defect.

METHODS

A total of 85 patients with late-onset cblC defect were enrolled. Clinical data, including manifestations, metabolites, molecular diagnosis, treatment and outcome, were summarized and analyzed.

RESULTS

The age of onset ranged from 2 to 32.8 years old (median age 8.6 years, mean age 9.4 years). The time between first symptoms and diagnosis ranged from a few days to 20 years (median time 2 months, mean time 20.7 months). Neuropsychiatric symptoms were presented as first symptoms in 68.2% of cases, which were observed frequently in schoolchildren or adolescents. Renal involvement and cardiovascular disease were observed in 20% and 8.2% of cases, respectively, which occurred with the highest prevalence in preschool children. Besides the initial symptoms, the disease progressed in most patients and cognitive decline became the most frequent symptom overall. The levels of propionylcarnitine, propionylcarnitine / acetylcarnitine ratio, methylmalonic acid, methylcitric acid and homocysteine, were decreased remarkably after treatment (P<0.001). Twenty-four different mutations of MMACHC were identified in 78 patients, two of which were novel. The c.482G>A variant was the most frequent mutated allele in this cohort (25%). Except for 16 patients who recovered completely, the remaining patients were still left with varying degrees of sequelae in a long-term follow-up. The available data from 76 cases were analyzed by univariate analysis and multivariate logistic regression analysis, and the results showed that the time from onset to diagnosis (OR = 1.025, P = 0. 024) was independent risk factors for poor outcomes.

CONCLUSIONS

The diagnosis of late-onset cblC defect is often delayed due to poor awareness of its various and nonspecific symptoms, thus having an adverse effect on the prognosis. It should be considered in patients with unexplained neuropsychiatric and other conditions such as renal involvement, cardiovascular diseases or even multiple organ damage. The c.482G>A variant shows the highest frequency in these patients. Prompt treatment appears to be beneficial.

Combined Newborn Screening Allows Comprehensive Identification also of Attenuated Phenotypes for Methylmalonic Acidurias and Homocystinuria

Newborn screening (NBS) programs are effective measures of secondary prevention and have been successively extended. We aimed to evaluate NBS for methylmalonic acidurias, propionic acidemia, homocystinuria, remethylation disorders and neonatal vitamin B12 deficiency, and report on the identification of cofactor-responsive disease variants. This evaluation of the previously established combined multiple-tier NBS algorithm is part of the prospective pilot study "NGS2025" from August 2016 to September 2022. In 548,707 newborns, the combined algorithm was applied and led to positive NBS results in 458 of them. Overall, 166 newborns (prevalence 1: 3305) were confirmed (positive predictive value: 0.36); specifically, methylmalonic acidurias (N = 5), propionic acidemia (N = 4), remethylation disorders (N = 4), cystathionine beta-synthase (CBS) deficiency (N = 1) and neonatal vitamin B12 deficiency (N = 153). The majority of the identified newborns were asymptomatic at the time of the first NBS report (total: 161/166, inherited metabolic diseases: 9/14, vitamin B12 deficiency: 153/153). Three individuals were cofactor-responsive (methylmalonic acidurias: 2, CBS deficiency: 1), and could be treated by vitamin B12, vitamin B6 respectively, only. In conclusion, the combined NBS algorithm is technically feasible, allows the identification of attenuated and severe disease courses and can be considered to be evaluated for inclusion in national NBS panels.

Methylmalonic acidemia: Neurodevelopment and neuroimaging

Methylmalonic acidemia (MMA) is a genetic disease of abnormal organic acid metabolism, which is one of the important factors affecting the survival rate and quality of life of newborns or infants. Early detection and diagnosis are particularly important. The diagnosis of MMA mainly depends on clinical symptoms, newborn screening, biochemical detection, gene sequencing and neuroimaging diagnosis. The accumulation of methylmalonic acid and other metabolites in the body of patients causes brain tissue damage, which can manifest as various degrees of intellectual disability and severe neurological dysfunction. Neuroimaging examination has important clinical significance in the diagnosis and prognosis of MMA. This review mainly reviews the etiology, pathogenesis, and nervous system development, especially the neuroimaging features of MMA.

How guideline development has informed clinical research for organic acidurias (et vice versa)

Organic acidurias, such as glutaric aciduria type 1 (GA1), methylmalonic (MMA), and propionic aciduria (PA) are a prominent group of inherited metabolic diseases involving accumulation of eponymous metabolites causing endogenous intoxication. For all three conditions, guidelines for diagnosis and management have been developed and revised over the last years, resulting in three revisions for GA1 and one revision for MMA/PA. The process of clinical guideline development in rare metabolic disorders is challenged by the scarcity and limited quality of evidence available. The body of literature is often fragmentary and where information is present, it is usually derived from small sample sizes. Therefore, the development of guidelines for GA1 and MMA/PA was initially confronted with a poor evidence foundation that hindered formulation of concrete recommendations in certain contexts, triggering specific research projects and initiation of longitudinal, prospective observational studies using patient registries. Reversely, these observational studies contributed to evaluate the value of newborn screening, phenotypic diversities, and treatment effects, thus significantly improving the quality of evidence and directly influencing formulation and evidence levels of guideline recommendations. Here, we present insights into interactions between guideline development and (pre)clinical research for GA1 and MMA/PA, and demonstrate how guidelines gradually improved from revision to revision. We describe how clinical studies help to unravel the relative impact of therapeutic interventions on outcome and conclude that despite new and better quality of research data over the last decades, significant shortcomings of evidence regarding prognosis and treatment remain. It appears that development of clinical guidelines can directly help to guide research, and vice versa.

Newborn screening for propionic, methylmalonic acidemia and vitamin B12 deficiency. Analysis of 588,793 newborns

OBJECTIVES

We present the results of our experience in the diagnosis and follow up of the positive cases for propionic, methylmalonic acidemias and cobalamin deficiencies (PA/MMA/MMAHC) since the Expanded Newborn Screening was implemented in Madrid Region.

METHODS

Dried blood samples were collected 48 h after birth. Amino acids and acylcarnitines were quantitated by MS/MS. Newborns with alterations were referred to the clinical centers for follow-up. Biochemical and molecular genetic studies for confirmation of a disease were performed.

RESULTS

In the period 2011-2020, 588,793 children were screened, being 953 of them were referred to clinical units for abnormal result (192 for elevated C3 levels). Among them, 88 were false positive cases, 85 maternal vitamin B12 deficiencies and 19 were confirmed to suffer an IEM (8 PA, 4 MMA, 7 MMAHC). Ten out 19 cases displayed symptoms before the NBS results (6 PA, 1 MMA, 3 MMAHC). C3, C16:1OH+C17 levels and C3/C2 and C3/Met ratios were higher in newborns with PA/MMA/MMAHC. Cases diagnosed with B12 deficiency had mean B12 levels of 187.6 ± 76.9 pg/mL and their mothers 213.7 ± 95.0; 5% of the mothers were vegetarian or had poor eating while 15% were diagnosed of pernicious anemia. Newborns and their mothers received treatment with B12 with different posology, normalizing their levels and the secondary alterations disappeared.

CONCLUSIONS

Elevated C3 are a frequent cause for abnormal result in newborn screening with a high rate of false positive cases. Presymptomatic diagnosis of most of PA and some MMA/MMAHC is difficult. Vitamin B12 deficiency secondary to maternal deprivation is frequent with an heterogenous clinical and biochemical spectrum.

A narrative review of metabolomics in the era of "-omics": integration into clinical practice for inborn errors of metabolism

BACKGROUND AND OBJECTIVE

Traditional targeted metabolomic investigations identify a pre-defined list of analytes in samples and have been widely used for decades in the diagnosis and monitoring of inborn errors of metabolism (IEMs). Recent technological advances have resulted in the development and maturation of untargeted metabolomics: a holistic, unbiased, analytical approach to detecting metabolic disturbances in human disease. We aim to provide a summary of untargeted metabolomics [focusing on tandem mass spectrometry (MS-MS)] and its application in the field of IEMs.

METHODS

Data for this review was identified through a literature search using PubMed, Google Scholar, and personal repositories of articles collected by the authors. Findings are presented within several sections describing the metabolome, the current use of targeted metabolomics in the diagnostic pathway of patients with IEMs, the more recent integration of untargeted metabolomics into clinical care, and the limitations of this newly employed analytical technique.

KEY CONTENT AND FINDINGS

Untargeted metabolomic investigations are increasingly utilized in screening for rare disorders, improving understanding of cellular and subcellular physiology, discovering novel biomarkers, monitoring therapy, and functionally validating genomic variants. Although the untargeted metabolomic approach has some limitations, this "next generation metabolic screening" platform is becoming increasingly affordable and accessible.

CONCLUSIONS

When used in conjunction with genomics and the other promising "-omic" technologies, untargeted metabolomics has the potential to revolutionize the diagnostics of IEMs (and other rare disorders), improving both clinical and health economic outcomes.

Very long-term outcomes in 23 patients with cblA type methylmalonic acidemia

OBJECTIVES

To present the very long-term follow up of patients with cobalamin A (cblA) deficiency.

METHODS

A retrospective case series of adult (>16 years) patients with molecular or enzymatic diagnosis of cblA deficiency.

RESULTS

We included 23 patients (mean age: 27 ± 7.6 years; mean follow-up: 24.9 ± 7.6 years). Disease onset was mostly pediatric (78% < 1 year, median = 4 months) with acute neurologic deterioration (65%). Eight patients presented with chronic symptoms, and one had an adult-onset mild cblA deficiency. Most of the patients (61%) were initially classified as vitamin B12-unresponsive methylmalonic aciduria (MMA); in vitro B12 responsiveness was subsequently found in all the tested patients (n = 13). Initial management consisted of protein restriction (57%), B12 (17%), or both (26%). The main long-term problems were intellectual disability (39%) and renal failure (30%). However, 56.5% of the patients were living independently. Intellectual disability was equally distributed among the initial treatment groups, while renal failure (moderate and beginning at the age of 38 years) was present in only one out of seven patients initially treated with B12.

CONCLUSIONS

We provide a detailed picture of the long-term outcome of a series of adult cblA patients, mostly diagnosed before the enzymatic and molecular era. We confirm that about 35% of the patients do not present acutely, underlining the importance of measuring MMA in any case of unexplained chronic renal failure, intellectual disability, or growth delay. In addition, we describe a patient with a milder adult-onset form. Early B12 supplementation seems to protect from severe renal insufficiency.

Review of neuropsychological outcomes in isolated methylmalonic acidemia: recommendations for assessing impact of treatments

Methylmalonic acidemia (MMA) due to methylmalonyl-CoA mutase deficiency (OMIM #251,000) is an autosomal recessive disorder of organic acid metabolism associated with life-threatening acute metabolic decompensations and significant neuropsychological deficits. "Isolated" MMA refers to the presence of excess methylmalonic acid without homocysteine elevation. Belonging to this class of disorders are those that involve complete deficiency (mut⁰) and partial deficiency (mut^-) of the methylmalonyl-CoA mutase enzyme and other disorders causing excess methylmalonic acid excretion. These other disorders include enzymatic subtypes related to cobalamin A defect (cblA) (OMIM #25,110), cobalamin B defect (cblB) (OMIM #251,110) and related conditions. Neuropsychological attributes associated with isolated MMA have become more relevant as survival rates increased following improved diagnostic and treatment strategies. Children with this disorder still are at risk for developmental delay, cognitive difficulties and progressive declines in functioning. Mean IQ for all types apart from cblA defect enzymatic subtype is rarely above 85 and much lower for mut⁰ enzymatic subtype. Identifying psychological domains responsive to improvements in biochemical status is important. This review suggests that processing speed, working memory, language, attention, and quality of life may be sensitive to fluctuations in metabolite levels while IQ and motor skills may be less amenable to change. Due to slower developmental trajectories, Growth Scale Values, Projected Retained Ability Scores and other indices of change need to be incorporated into clinical trial study protocols. Neuropsychologists are uniquely qualified to provide a differentiated picture of cognitive, behavioral and emotional consequences of MMA and analyze benefits or shortcomings of novel treatments.

Analysis of the relationship between phenotypes and genotypes in 60 Chinese patients with propionic acidemia: a fourteen-year experience at a tertiary hospital

Background

Propionic acidemia is a severe inherited metabolic disorder, caused by the deficiency of propionyl-CoA carboxylase which encoded by the PCCA and PCCB genes. The aim of the study was to investigate the clinical features and outcomes, molecular epidemiology and phenotype-genotype relationship in Chinese population.

Methods

We conducted a retrospective study of 60 Chinese patients diagnosed at Peking University First Hospital from 2007 to 2020. Their clinical and laboratory data were reviewed. The next-generation sequencing was conducted on blood samples from 58 patients.

Results

Only 5 (8.3%) patients were identified by newborn screening. In the rest 55 patients, 25 had early-onset (≤ 3 months) disease and 30 had late-onset (> 3 months) disease. Neurological abnormalities were the most frequent complications. Five cases detected by newborn screening had basically normal development. Nine (15%) cases died in our cohort. 24 patients (41.4%) harbored PCCA variants, and 34 (58.6%) harbored PCCB variants. 30 (11 reported and 19 novel) variants in PCCA and 28 (18 reported and 10 novel) variants in PCCB mere identified. c.2002G>A and c.937C>T in PCCA, and c.838dupC in PCCB were the most common variants in this cohort, with the frequency of 13.9% (6/44 alleles), 13.9% (6/44 alleles) and 12.5% (8/64 alleles), respectively. There was no difference in clinical features and outcomes between patients with PCCA and PCCB variants. Certain variants with high frequencies and homozygotes may be associated with early-onset or late-onset propionic acidemia.

Conclusions

Although the genotype–phenotype correlation is still unclear, certain variants seemed to be related to early-onset or late-onset propionic acidemia. Our study further delineated the complex clinical manifestations of propionic acidemia and expanded the spectrum of gene variants associated with propionic acidemia.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02271-3.

The Follow-Up of Chinese Patients in cblC Type Methylmalonic Acidemia Identified Through Expanded Newborn Screening

Objective: The cblC type of combined methylmalonic acidemia and homocystinuria, an inherited disorder with variable phenotypes, is included in newborn screening (NBS) programs at multiple newborn screening centers in China. The present study aimed to investigate the long-term clinical benefits of screening individual.

Methods: A national, retrospective multi-center study of infants with confirmed cblC defect identified by NBS between 2004 and 2020 was conducted. We collected a large cohort of 538 patients and investigated their clinical data in detail, including disease onset, biochemical metabolites, and gene variation, and explored different factors on the prognosis.

Results: The long-term outcomes of all patients were evaluated, representing 44.6% for poor outcomes. In our comparison of patients with already occurring clinical signs before treatment to asymptomatic ones, the incidence of intellectual impairment, movement disorders, ocular complications, hydrocephalus, and death were significantly different (p < 0.01). The presence of disease onset [Odd ratio (OR) 12.39, 95% CI 5.15–29.81; p = 0.000], variants of c.609G>A (OR 2.55, 95% CI 1.49–4.35; p = 0.001), and c.567dupT (OR 2.28, 95% CI 1.03–5.05; p = 0.042) were independently associated with poor outcomes, especially for neurodevelopmental deterioration.

Conclusion: NBS, avoiding major disease-related events and allowing an earlier treatment initiation, appeared to have protective effects on the prognosis of infants with cblC defect.

Rare Disease Registries Are Key to Evidence-Based Personalized Medicine: Highlighting the European Experience

Rare diseases, such as inherited metabolic diseases, have been identified as a health priority within the European Union more than 20 years ago and have become an integral part of EU health programs and European Reference Networks. Having the potential to pool data, to achieve sufficient sample size, to overcome the knowledge gap on rare diseases and to foster epidemiological and clinical research, patient registries are recognized as key instruments to evidence-based medicine for individuals with rare diseases. Patient registries can be used for multiple purposes, such as (1) describing the natural history and phenotypic diversity of rare diseases, (2) improving case definition and indication to treat, (3) identifying strategies for risk stratification and early prediction of disease severity (4), evaluating the impact of preventive, diagnostic, and therapeutic strategies on individual health, health economics, and the society, and (5) informing guideline development and policy makers. In contrast to clinical trials, patient registries aim to gather real-world evidence and to achieve generalizable results based on patient cohorts with a broad phenotypic spectrum. In order to develop a consistent and sustained framework for rare disease registries, uniform core principles have been formulated and have been formalized through the European Rare Disease Registration Infrastructure. Adherence to these core principles and compliance with the European general data protection regulations ensures that data collected and stored in patient registries can be exchanged and pooled in a protected environment. To illustrate the benefits and limitations of patient registries on rare disease research this review focuses on inherited metabolic diseases.

Different mutations in the MMUT gene are associated with the effect of vitamin B12 in a cohort of 266 Chinese patients with mut-type methylmalonic acidemia: A retrospective study

BACKGROUND

To summarize the relationship between different MMUT gene mutations and the response to vitamin B12 in MMA.

METHODS

This was a retrospective study of patients diagnosed with mut-type MMA. All patients with mut-type MMA were tested for responsiveness to vitamin B12.

RESULTS

There were 81, 27, and 158 patients in the completely responsive, partially responsive, and nonresponsive groups, respectively, and the proportions of symptom occurrence were 30/81 (37.0%), 21/27 (77.8%), and 131/158 (82.9%), respectively (p < .001). The median levels of posttreatment propionyl carnitine (C3), C3/acetyl carnitine (C2) ratio in the blood, and methylmalonic acid in the urine were all lower than pretreatment, and the median level of C3/C2 ratio in the completely responsive group was within the normal range. In 266 patients, 144 different mutations in the MMUT gene were identified. Patients with the mutations of c.1663G>A, c.2080C>T, c.1880A>G, c.1208G>A, etc. were completely responsive and with the mutations of c.1741C>T, c.1630_1631GG>TA, c.599T>C, etc. were partially responsive. The proportions of healthy/developmental delay outcomes in the three groups were 63.0%/23.5%, 33.3%/40.7%, and 13.3%/60.1%, respectively (p < .001).

CONCLUSION

Different mutations in the MMUT gene are associated with the effect of vitamin B12 treatment.

Newborn screening and disease variants predict neurological outcome in isovaleric aciduria

Isovaleric aciduria (IVA), a metabolic disease with severe (classic IVA) or attenuated phenotype (mild IVA), is included in newborn screening (NBS) programs worldwide. The long-term clinical benefit of screened individuals, however, is still rarely investigated. A national, prospective, observational, multi-center study of individuals with confirmed IVA identified by NBS between 1998 and 2018 was conducted. Long-term clinical outcomes of 94 individuals with IVA were evaluated, representing 73.4% (for classic IVA: 92.3%) of the German NBS cohort. In classic IVA (N = 24), NBS prevented untimely death except in one individual with lethal neonatal sepsis (3.8%) but did not completely prevent single (N = 10) or recurrent (N = 7) metabolic decompensations, 13 of them occurring already neonatally. IQ (mean ± SD, 90.7 ± 10.1) was mostly normal but below the reference population (P = .0022) and was even lower in individuals with severe neonatal decompensations (IQ 78.8 ± 7.1) compared to those without crises (IQ 94.7 ± 7.5; P = .01). Similar results were obtained for school placement. In contrast, individuals with mild IVA had excellent neurocognitive outcomes (IQ 105.5 ± 15.8; normal school placement) and a benign disease course (no metabolic decompensation, normal hospitalization rate), which did not appear to be impacted by metabolic maintenance therapy. In conclusion, NBS reduces mortality in classic IVA, but does not reliably protect against severe neonatal metabolic decompensations, crucial for favorable neurocognitive outcome. In contrast, individuals with mild IVA had excellent clinical outcomes regardless of metabolic maintenance therapy, questioning their benefit from NBS. Harmonized stratified therapeutic concepts are urgently needed.

Current Perspectives on Neonatal Screening for Propionic Acidemia in Japan: An Unexpectedly High Incidence of Patients with Mild Disease Caused by a Common PCCB Variant

Propionic acidemia (PA) is a disorder of organic acid metabolism which typically presents with acute encephalopathy-like symptoms associated with metabolic acidosis and hyperammonemia during the neonatal period. The estimated incidence of symptomatic PA in Japan is 1/400,000. The introduction of neonatal screening using tandem mass spectrometry has revealed a far higher disease frequency of approximately 1/45,000 live births due to a prevalent variant of c.1304T>C (p.Y435C) in PCCB, which codes β-subunit of propionyl-CoA carboxylase. Our questionnaire-based follow-up study reveals that most of these patients remain asymptomatic. However, reports on symptomatic patients exhibiting cardiac complications such as cardiomyopathy and QT prolongation have been increasing. Moreover, there were even cases in which these cardiac complications were the only symptoms related to PA. A currently ongoing study is investigating the risk of cardiac complications in patients with neonatal screening-detected PA caused by this common variant.

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

Isolated methylmalonic acidaemia (MMA) and propionic acidaemia (PA) are rare inherited metabolic diseases. Six years ago, a detailed evaluation of the available evidence on diagnosis and management of these disorders has been published for the first time. The article received considerable attention, illustrating the importance of an expert panel to evaluate and compile recommendations to guide rare disease patient care. Since that time, a growing body of evidence on transplant outcomes in MMA and PA patients and use of precursor free amino acid mixtures allows for updates of the guidelines. In this article, we aim to incorporate this newly published knowledge and provide a revised version of the guidelines. The analysis was performed by a panel of multidisciplinary health care experts, who followed an updated guideline development methodology (GRADE). Hence, the full body of evidence up until autumn 2019 was re-evaluated, analysed and graded. As a result, 21 updated recommendations were compiled in a more concise paper with a focus on the existing evidence to enable well-informed decisions in the context of MMA and PA patient care.

Liver and/or kidney transplantation in amino and organic acid-related inborn errors of metabolism: An overview on European data

BACKGROUND

This study provides a general overview on liver and/or kidney transplantation in patients with an amino and organic acid-related disorder (AOA) with the aim to investigate patient characteristics and global outcome in Europe. This study was an initiative of the E-IMD and the AOA subnetwork of MetabERN.

METHODS

A questionnaire was sent to all clinically active European Society for the Study of Inborn Errors of Metabolism (SSIEM) members. The questionnaire focused on transplanted individuals with methylmalonic acidemia (MMA), propionic acidemia (PA), maple syrup urine disease (MSUD), and urea-cycle disorders (UCDs).

RESULTS

We identified 280 transplanted AOA patients (liver transplantation in 20 MMA, 37 PA, 47 MSUD, and 111 UCD patients, kidney or combined liver and kidney transplantation in 57 MMA patients and undefined transplantation type in 8 MMA patients), followed by 51 metabolic centers. At a median follow-up of 3.5 years, posttransplant survival ranged between 78% and 100%, being the lowest in PA patients. Overall, the risk of mortality was highest within 14 days posttransplantation. Neurological complications were mainly reported in Mut⁰ type MMA (n = 8). Nonneurological complications occurred in MMA (n = 28), PA (n = 7), and UCD (n = 14) patients, while it was virtually absent in MSUD patients. Only 116/280 patients were psychologically tested. In all, except MSUD patients, the intelligence quotient (IQ) remained unchanged in the majority (76/94, 81%). Forty-one percentage (9/22) of MSUD patient showed improved IQ.

CONCLUSION

The survival in AOA individuals receiving liver and/or kidney transplantation seems satisfactory. Evidence-based guidelines, systematic data collection, and improved cooperation between transplantation centers and European Reference Networks are indispensable to improve patient care and outcomes.

U-IMD: the first Unified European registry for inherited metabolic diseases

Background

Following the broad application of new analytical methods, more and more pathophysiological processes in previously unknown diseases have been elucidated. The spectrum of clinical presentation of rare inherited metabolic diseases (IMDs) is broad and ranges from single organ involvement to multisystemic diseases. With the aim of overcoming the limited knowledge about the natural course, current diagnostic and therapeutic approaches, the project has established the first unified patient registry for IMDs that fully meets the requirements of the European Infrastructure for Rare Diseases (ERDRI).

Results

In collaboration with the European Reference Network for Rare Hereditary Metabolic Disorders (MetabERN), the Unified European registry for Inherited Metabolic Diseases (U-IMD) was established to collect patient data as an observational, non-interventional natural history study. Following the recommendations of the ERDRI the U-IMD registry uses common data elements to define the IMDs, report the clinical phenotype, describe the biochemical markers and to capture the drug treatment. Until today, more than 1100 IMD patients have been registered.

Conclusion

The U-IMD registry is the first observational, non-interventional patient registry that encompasses all known IMDs. Full semantic interoperability for other registries has been achieved, as demonstrated by the use of a minimum common core data set for equivalent description of metabolic patients in U-IMD and in the patient registry of the European Rare Kidney Disease Reference Network (ERKNet). In conclusion, the U-IMD registry will contribute to a better understanding of the long-term course of IMDs and improved patients care by understanding the natural disease course and by enabling an optimization of diagnostic and therapeutic strategies.

Delineating the clinical spectrum of isolated methylmalonic acidurias: cblA and mut

INTRODUCTION

Long-term outcome is postulated to be different in isolated methylmalonic aciduria caused by mutations in the MMAA gene (cblA type) compared with methylmalonyl-CoA mutase deficiency (mut), but case definition was previously difficult.

METHOD

Cross-sectional analysis of data from the European Registry and Network for Intoxication type Metabolic Diseases (Chafea no. December 1, 2010).

RESULTS

Data from 28 cblA and 95 mut patients in most cases confirmed by mutation analysis (including 4 new mutations for cblA and 19 new mutations for mut). Metabolic crisis is the predominant symptom leading to diagnosis in both groups. Biochemical disturbances during the first crisis were similar in both groups, as well as the age at diagnosis. Z scores of body height and body weight were similar in both groups at birth, but were significantly lower in the mut group at the time of last visit. Glomerular filtration rate was significantly higher in cblA; and as a consequence, chronic renal failure and related complications were significantly less frequent and renal function could be preserved even in older patients. Neurological complications were predominantly found in the mut subgroup. Methylmalonic acidemia (MMA) levels in urine and plasma were significantly lower in cblA. 27/28 cblA patients were reported to be responsive to cobalamin, only 86% of cblA patients were treated with i.m. hydroxocobalamin. In total, 73% of cblA and 98% of mut patients followed a calculated diet with amino acid supplements in 27% (cblA) and 69% (mut). During the study interval, six patients from the mut group died, while all cblA patients survived.

CONCLUSION

Although similar at first, cblA patients respond to hydroxocobalamin treatment, subsequently show significantly lower levels of MMA and a milder course than mut patients.

The Cost-Effectiveness of Expanding the UK Newborn Bloodspot Screening Programme to Include Five Additional Inborn Errors of Metabolism

Glutaric aciduria type 1, homocystinuria, isovaleric acidaemia, long-chain hydroxyacyl CoA dehydrogenase deficiency and maple syrup urine disease are all inborn errors of metabolism that can be detected through newborn bloodspot screening. This evaluation was undertaken in 2013 to provide evidence to the UK National Screening Committee for the cost-effectiveness of including these five conditions in the UK Newborn Bloodspot Screening Programme. A decision-tree model with lifetable estimates of outcomes was built with the model structure and parameterisation informed by a systematic review and expert clinical judgment. A National Health Service/Personal Social Services perspective was used, and lifetime costs and quality-adjusted life years (QALYs) were discounted at 1.5%. Uncertainty in the results was explored using expected value of perfect information analysis methods together with a sensitivity analysis using the screened incidence rate in the UK from 2014 to 2018. The model estimates that screening for all the conditions is more effective and cost saving when compared to not screening for each of the conditions, and the results were robust to the updated incidence rates. The key uncertainties included the sensitivity and specificity of the screening test and the estimated costs and QALYs.

Glutaric acidemia type 1: Treatment and outcome of 168 patients over three decades

Glutaric acidemia type 1 (GA1) is a disorder of cerebral organic acid metabolism resulting from biallelic mutations of GCDH. Without treatment, GA1 causes striatal degeneration in >80% of affected children before two years of age. We analyzed clinical, biochemical, and developmental outcomes for 168 genotypically diverse GA1 patients managed at a single center over 31 years, here separated into three treatment cohorts: children in Cohort I (n = 60; DOB 2006-2019) were identified by newborn screening (NBS) and treated prospectively using a standardized protocol that included a lysine-free, arginine-enriched metabolic formula, enteral l-carnitine (100 mg/kg•day), and emergency intravenous (IV) infusions of dextrose, saline, and l-carnitine during illnesses; children in Cohort II (n = 57; DOB 1989-2018) were identified by NBS and treated with natural protein restriction (1.0-1.3 g/kg•day) and emergency IV infusions; children in Cohort III (n = 51; DOB 1973-2016) did not receive NBS or special diet. The incidence of striatal degeneration in Cohorts I, II, and III was 7%, 47%, and 90%, respectively (p < .0001). No neurologic injuries occurred after 19 months of age. Among uninjured children followed prospectively from birth (Cohort I), measures of growth, nutritional sufficiency, motor development, and cognitive function were normal. Adherence to metabolic formula and l-carnitine supplementation in Cohort I declined to 12% and 32%, respectively, by age 7 years. Cessation of strict dietary therapy altered plasma amino acid and carnitine concentrations but resulted in no serious adverse outcomes. In conclusion, neonatal diagnosis of GA1 coupled to management with lysine-free, arginine-enriched metabolic formula and emergency IV infusions during the first two years of life is safe and effective, preventing more than 90% of striatal injuries while supporting normal growth and psychomotor development. The need for dietary interventions and emergency IV therapies beyond early childhood is uncertain.

Long-term Outcomes of Individuals With Metabolic Diseases Identified Through Newborn Screening

BACKGROUND

Although extended newborn screening (NBS) programs have been introduced more than 20 years ago, their impact on the long-term clinical outcome of individuals with inherited metabolic diseases (IMDs) is still rarely investigated.

METHODS

We studied the clinical outcomes of individuals with IMDs identified by NBS between 1999 and 2016 in a prospective multicenter observational study.

RESULTS

In total, 306 screened individuals with IMDs (115 with phenylketonuria and 191 with other IMDs with a lifelong risk for metabolic decompensation) were followed for a median time of 6.2 years. Although the risk for metabolic decompensation was disease-specific and NBS could not prevent decompensations in every individual at risk (n = 49), the majority did not develop permanent disease-specific signs (75.9%), showed normal development (95.6%) and normal cognitive outcome (87.7%; mean IQ: 100.4), and mostly attended regular kindergarten (95.2%) and primary school (95.2%). This demonstrates that not only individuals with phenylketonuria, serving as a benchmark, but also those with lifelong risk for metabolic decompensation had a favorable long-term outcome. High NBS process quality is the prerequisite of this favorable outcome. This is supported by 28 individuals presenting with first symptoms at a median age of 3.5 days before NBS results were available, by the absence of neonatal decompensations after the report of NBS results, and by the challenge of keeping relevant process parameters at a constantly high level.

CONCLUSIONS

NBS for IMDs, although not completely preventing clinical presentations in all individuals, can be considered a highly successful program of secondary prevention.

Orthopaedic manifestations of glutaric acidemia Type 1

PURPOSE

Glutaric acidemia type 1 (GA1), a rare hereditary metabolic disease caused by biallelic mutations of GCDH, can result in acute or insidious striatal degeneration within the first few years of life. We reviewed the orthopaedic sequelae and management of 114 neurologically injured patients with a confirmed molecular diagnosis of GA1.

METHODS

We performed a retrospective chart review spanning 28 years identifying 114 GA1 patients, most from the Old Order Amish population of Lancaster County, Pennsylvania, who were homozygous for a pathogenic founder variant of GCDH (c.1262C>T). We collected demographics, medical comorbidities, muscle tone patterns, Gross Motor Function Classification System level, gastrostomy tube status, seizure history, inpatient events, orthopaedic diagnoses and operative characteristics.

RESULTS

Over an average follow-up of 4.7 ± 3.4 years, 24 (21%) of 114 patients had musculoskeletal problems requiring orthopaedic consultation. Scoliosis (n = 14), hip dislocation (n = 8/15 hips), hip subluxation (n = 2/three hips), and windswept hip deformity (n = 2) in the spine and hip joint were most common. In total, 35 orthopaedic surgeries were performed in 17 (71%) patients. The most common primary operations were one-stage procedures with proximal femoral varus derotation osteotomy and/or pelvic osteotomy (n = 8/14 hips) for subluxation or dislocation. In all, 11 patients had posterior spinal fusion for severe scoliosis. With the recommended metabolic management, there were no disease-specific complications in this cohort.

CONCLUSIONS

Children with GA1 who have static striatal lesions are at risk for musculoskeletal complications, especially scoliosis and hip dislocation, and appropriate operative management requires consultation with a metabolic specialist with specific considerations for fluid management and nutrition.

LEVEL OF EVIDENCE

IV.

Long Term Follow-Up of Polish Patients with Isovaleric Aciduria. Clinical and Molecular Delineation of Isovaleric Aciduria

Isovaleric acidemia (IVA) is an autosomal recessive leucine inborn error of metabolism caused by isovaleryl-CoA dehydrogenase deficiency. The disease has various courses, from severe ones manifesting in newborns to the intermittent form with first manifestation in children and adults. The aim of this study was to analyze clinical and neurological outcomes in Polish patients with IVA. Ten patients diagnosed and treated in The Children's Memorial Health Institute were included in the study. The diagnosis was based on tandem MS (increased level of C5 acylcarnitine) and urine GCMS (increased isovalerylglycine, and 3-hydroxyisovaleric acid). Molecular analysis was performed in seven patients (70%) leading to the detection of pathogenic variants in the IVD gene in all of them. A retrospective analysis of patients' medical records included: demographics, symptoms at diagnosis, medical management, and biochemical and clinical outcomes following therapy. The median follow-up time (median; Q1-Q2) was 2.5 years (1.5-9.0) for newborn screening (NBS) and family screening (FS) children, and 17 years (5.0-20) for symptomatic patients. Five patients were in a good clinical state, four children presented mild neurological symptoms, and one-severely delayed child. In the IVD gene, five known and two novel variants (p.466C>G, c.1132G>A) were identified. Molecular analysis was performed in seven patients leading to identification of biallelic pathogenic variants in the IVD gene in all of them. We can conclude that long-term clinical and neurological outcomes of patients with IVA were satisfactory as a result of an early diagnosis and proper management. Although early treatment did not prevent decompensations, they were milder in these patients.

Clinical Course and Nutritional Management of Propionic and Methylmalonic Acidemias

Propionic and methylmalonic acidemias result in multiple health problems including increased risk for neurological and intellectual disabilities. Knowledge regarding factors that correlate to poor prognosis and long-term outcomes is still limited. In this study, we aim to provide insight concerning clinical course and long-term complications by identifying possible correlating factors to complications. Results. This is a retrospective review of 20 Egyptian patients diagnosed with PA (n = 10) and MMA (n = 10) in the years 2014–2018. PA patients had lower DQ/IQ and were more liable to hypotonia and developmental delay. The DQ/IQ had a strong negative correlation with length of hospital stay, frequency of PICU admissions, time delay until diagnosis, and the mode ammonia level. However, DQ/IQ did not correlate with age of onset of symptoms or the peak ammonia level at presentation. Both the growth percentiles and albumin levels had a positive correlation with natural protein intake and did not correlate with the total protein intake. Additionally, patients on higher amounts of medical formula did not necessarily show an improvement in the frequency of decompensation episodes. Conclusion. Our findings indicate that implementation of NBS, vigilant and proactive management of decompensation episodes, and pursuing normal ammonia levels during monitoring can help patients achieve a better neurological prognosis. Furthermore, patients can have a better outcome on mainly natural protein; medical formula should only be used in cases where patients do not meet 100–120% of their DRI from natural protein.

Performance of Expanded Newborn Screening in Norway Supported by Post-Analytical Bioinformatics Tools and Rapid Second-Tier DNA Analyses

In 2012, the Norwegian newborn screening program (NBS) was expanded (eNBS) from screening for two diseases to that for 23 diseases (20 inborn errors of metabolism, IEMs) and again in 2018, to include a total of 25 conditions (21 IEMs). Between 1 March 2012 and 29 February 2020, 461,369 newborns were screened for 20 IEMs in addition to phenylketonuria (PKU). Excluding PKU, there were 75 true-positive (TP) (1:6151) and 107 (1:4311) false-positive IEM cases. Twenty-one percent of the TP cases were symptomatic at the time of the NBS results, but in two-thirds, the screening result directed the exact diagnosis. Eighty-two percent of the TP cases had good health outcomes, evaluated in 2020. The yearly positive predictive value was increased from 26% to 54% by the use of the Region 4 Stork post-analytical interpretive tool (R4S)/Collaborative Laboratory Integrated Reports 2.0 (CLIR), second-tier biochemical testing and genetic confirmation using DNA extracted from the original dried blood spots. The incidence of IEMs increased by 46% after eNBS was introduced, predominantly due to the finding of attenuated phenotypes. The next step is defining which newborns would truly benefit from screening at the milder end of the disease spectrum. This will require coordinated international collaboration, including proper case definitions and outcome studies.

Retrospective evaluation of the Dutch pre-newborn screening cohort for propionic acidemia and isolated methylmalonic acidemia: What to aim, expect, and evaluate from newborn screening?

Evidence for effectiveness of newborn screening (NBS) for propionic acidemia (PA) and isolated methylmalonic acidemia (MMA) is scarce. Prior to implementation in the Netherlands, we aim to estimate the expected health gain of NBS for PA and MMA. In this national retrospective cohort study, the clinical course of 76/83 Dutch PA and MMA patients, diagnosed between January 1979 and July 2019, was evaluated. Five clinical outcome parameters were defined: adverse outcome of the first symptomatic phase, frequency of acute metabolic decompensations (AMD), cognitive function, mitochondrial complications, and treatment-related complications. Outcomes of patients identified by family testing were compared with the outcomes of their index siblings. An adverse outcome due to the first symptomatic phase was recorded in 46% of the clinically diagnosed patients. Outcome of the first symptomatic phase was similar in 5/9 sibling pairs and better in 4/9 pairs. Based on the day of diagnosis of the clinically diagnosed patients and sibling pair analysis, a preliminary estimated reduction of adverse outcome due to the first symptomatic phase from 46% to 36%-38% was calculated. Among the sibling pairs, AMD frequency, cognitive function, mitochondrial, and treatment-related complications were comparable. These results suggest that the health gain of NBS for PA and MMA in overall outcome may be limited, as only a modest decrease of adverse outcomes due to the first symptomatic phase is expected. With current clinical practice, no reduced AMD frequency, improved cognitive function, or reduced frequency of mitochondrial or treatment-related complications can be expected.

What are the information needs of parents caring for a child with Glutaric aciduria type 1?

Background

Newborn screening has enabled the early diagnosis of Glutaric aciduria type 1, with the possibility of improving neurological outcomes in affected children. Achieving those outcomes requires parents to effectively manage their child’s condition by adherence to a strict dietary regime and responding to situations that may trigger decompensation. The specific information and support needs of this group of parents are unknown.

Methods

A focus group with five parents was conducted to gain insights into the information that parents needed and the ways in which they accessed and used information to manage their child’s condition. A topic guide was used to direct the discussion which was recorded and fully transcribed. All participants gave informed consent. Data were analysed using thematic analysis, a structured approach that contributes to transparency and validity of results while allowing the integration of predetermined and emerging themes. To ensure rigour, two researchers were involved in initial coding of data and key analytic decisions.

Results

Two main themes were identified. ‘Understanding the condition’ explored parent’s needs to understand the scientific complexity of the condition and to be aware of the worst case scenario associated with loss of metabolic control. ‘Managing the condition’ explained how parents co-ordinated and controlled the involvement of other carers and parents’ need to be active partners in medical management to feel in control of the situation.

Conclusions

The study highlights the importance of addressing parents’ initial and ongoing informational needs so they can fulfil their role and protect their child from metabolic harm.

Pathophysiology of propionic and methylmalonic acidemias. Part 1: Complications

Over the last decades, advances in clinical care for patients suffering from propionic acidemia (PA) and isolated methylmalonic acidemia (MMA) have resulted in improved survival. These advances were possible thanks to new pathophysiological insights. However, patients may still suffer from devastating complications which largely determine the unsatisfying overall outcome. To optimize our treatment strategies, better insight in the pathophysiology of complications is needed. Here, we perform a systematic data-analysis of cohort studies and case-reports on PA and MMA. For each of the prevalent and rare complications, we summarize the current hypotheses and evidence for the underlying pathophysiology of that complication. A common hypothesis on pathophysiology of many of these complications is that mitochondrial impairment plays a major role. Assuming that complications in which mitochondrial impairment may play a role are overrepresented in monogenic mitochondrial diseases and, conversely, that complications in which mitochondrial impairment does not play a role are underrepresented in mitochondrial disease, we studied the occurrence of the complications in PA and MMA in mitochondrial and other monogenic diseases, using data provided by the Human Phenotype Ontology. Lastly, we combined this with evidence from literature to draw conclusions on the possible role of mitochondrial impairment in each complication. Altogether, this review provides a comprehensive overview on what we, to date, do and do not understand about pathophysiology of complications occurring in PA and MMA and about the role of mitochondrial impairment herein.

Systematic literature review and meta-analysis on the epidemiology of methylmalonic acidemia (MMA) with a focus on MMA caused by methylmalonyl-CoA mutase (mut) deficiency

Methylmalonic acidemia/aciduria (MMA) is a genetically heterogeneous group of inherited metabolic disorders biochemically characterized by the accumulation of methylmalonic acid. Isolated MMA is primarily caused by the deficiency of methylmalonyl-CoA mutase (MMA mut; EC 5.4.99.2). A systematic literature review and a meta-analysis were undertaken to assess and compile published epidemiological data on MMA with a focus on the MMA mut subtype (OMIM #251000). Of the 1114 identified records, 227 papers were assessed for eligibility in full text, 48 articles reported on disease epidemiology, and 39 articles were included into the quantitative synthesis. Implementation of newborn screening in various countries has allowed for the estimation of birth prevalence of MMA and its isolated form. Meta-analysis pooled point estimates of MMA (all types) detection rates were 0.79, 1.12, 1.22 and 6.04 per 100,000 newborns in Asia-Pacific, Europe, North America and the Middle East and North Africa (MENA) regions, respectively. The detection rate of isolated MMA was < 1 per 100,000 newborns in all regions with the exception of MENA where it approached 6 per 100,000 newborns. Few studies published data on the epidemiology of MMA mut, therefore no meta-analysis could have been performed on this subtype. Most of the identified papers reported birth prevalence estimates below 1 per 100,000 newborns for MMA mut. The systematic literature review clearly demonstrates that MMA and its subtypes are ultra-rare disorders.

Systematic literature review and meta-analysis on the epidemiology of propionic acidemia

Propionic acidemia (PA, OMIM #606054) is a serious, life-threatening, inherited, metabolic disorder caused by the deficiency of the mitochondrial enzyme propionyl-coenzyme A (CoA) carboxylase (EC 6.4.1.3). The primary objective of this study was to conduct a systematic literature review and meta-analysis on the epidemiology of PA. The literature search was performed covering Medline, Embase, Cochrane Database of Systematic Reviews, CRD Database, Academic Search Complete, CINAHL and PROSPERO databases. Websites of rare disease organizations were also searched for eligible studies. Of the 2338 identified records, 188 articles were assessed for eligibility in full text, 43 articles reported on disease epidemiology, and 31 studies were included into the quantitative synthesis. Due to the rarity of PA, broadly targeted population-based prevalence studies are not available. Nonetheless, implementation of newborn screening programs has allowed the estimation of the birth prevalence data of PA across multiple geographic regions. The pooled point estimates indicated detection rates of 0.29; 0.33; 0.33 and 4.24 in the Asia-Pacific, Europe, North America and the Middle East and North Africa (MENA) regions, respectively. Our systematic literature review and meta-analysis confirm that PA is an ultra-rare disorder, with similar detection rates across all regions with the exception of the MENA region where the disease, similar to other inherited metabolic disorders, is more frequent.

Transatlantic combined and comparative data analysis of 1095 patients with urea cycle disorders-A successful strategy for clinical research of rare diseases

BACKGROUND

To improve our understanding of urea cycle disorders (UCDs) prospectively followed by two North American (NA) and European (EU) patient cohorts.

AIMS

Description of the NA and EU patient samples and investigation of the prospects of combined and comparative analyses for individuals with UCDs.

METHODS

Retrieval and comparison of the data from 1095 individuals (NA: 620, EU: 475) from two electronic databases.

RESULTS

The proportion of females with ornithine transcarbamylase deficiency (fOTC-D), particularly those being asymptomatic (asfOTC-D), was higher in the NA than in the EU sample. Exclusion of asfOTC-D resulted in similar distributions in both samples. The mean age at first symptoms was higher in NA than in EU patients with late onset (LO), but similar for those with early (≤ 28 days) onset (EO) of symptoms. Also, the mean age at diagnosis and diagnostic delay for EO and LO patients were similar in the NA and EU cohorts. In most patients (including fOTC-D), diagnosis was made after the onset of symptoms (59.9%) or by high-risk family screening (24.7%), and less often by newborn screening (8.9%) and prenatal testing (3.7%). Analysis of clinical phenotypes revealed that EO patients presented with more symptoms than LO individuals, but that numbers of symptoms correlated with plasma ammonium concentrations in EO patients only. Liver transplantation was reported for 90 NA and 25 EU patients.

CONCLUSIONS

Combined analysis of databases drawn from distinct populations opens the possibility to increase sample sizes for natural history questions, while comparative analysis utilizing differences in approach to treatment can evaluate therapeutic options and enhance long-term outcome studies.

Hyperammonaemia in classic organic acidaemias: a review of the literature and two case histories

Background

The ‘classic’ organic acidaemias (OAs) (propionic, methylmalonic and isovaleric) typically present in neonates or infants as acute metabolic decompensation with encephalopathy. This is frequently accompanied by severe hyperammonaemia and constitutes a metabolic emergency, as increased ammonia levels and accumulating toxic metabolites are associated with life-threatening neurological complications. Repeated and frequent episodes of hyperammonaemia (alongside metabolic decompensations) can result in impaired growth and intellectual disability, the severity of which increase with longer duration of hyperammonaemia. Due to the urgency required, diagnostic evaluation and initial management of patients with suspected OAs should proceed simultaneously. Paediatricians, who do not have specialist knowledge of metabolic disorders, have the challenging task of facilitating a timely diagnosis and treatment. This article outlines how the underlying pathophysiology and biochemistry of the organic acidaemias are closely linked to their clinical presentation and management, and provides practical advice for decision-making during early, acute hyperammonaemia and metabolic decompensation in neonates and infants with organic acidaemias.

Clinical management

The acute management of hyperammonaemia in organic acidaemias requires administration of intravenous calories as glucose and lipids to promote anabolism, carnitine to promote urinary excretion of urinary organic acid esters, and correction of metabolic acidosis with the substitution of bicarbonate for chloride in intravenous fluids. It may also include the administration of ammonia scavengers such as sodium benzoate or sodium phenylbutyrate. Treatment with N-carbamyl-L-glutamate can rapidly normalise ammonia levels by stimulating the first step of the urea cycle.

Conclusions

Our understanding of optimal treatment strategies for organic acidaemias is still evolving. Timely diagnosis is essential and best achieved by the early identification of hyperammonaemia and metabolic acidosis. Correcting metabolic imbalance and hyperammonaemia are critical to prevent brain damage in affected patients.

Organic acidurias in adults: late complications and management

Organic acidurias (synonym, organic acid disorders, OADs) are a heterogenous group of inherited metabolic diseases delineated with the implementation of gas chromatography/mass spectrometry in metabolic laboratories starting in the 1960s and 1970s. Biochemically, OADs are characterized by accumulation of mono-, di- and/or tricarboxylic acids ("organic acids") and corresponding coenzyme A, carnitine and/or glycine esters, some of which are considered toxic at high concentrations. Clinically, disease onset is variable, however, affected individuals may already present during the newborn period with life-threatening acute metabolic crises and acute multi-organ failure. Tandem mass spectrometry-based newborn screening programmes, in particular for isovaleric aciduria and glutaric aciduria type 1, have significantly reduced diagnostic delay. Dietary treatment with low protein intake or reduced intake of the precursor amino acid(s), carnitine supplementation, cofactor treatment (in responsive patients) and nonadsorbable antibiotics is commonly used for maintenance treatment. Emergency treatment options with high carbohydrate/glucose intake, pharmacological and extracorporeal detoxification of accumulating toxic metabolites for intensified therapy during threatening episodes exist. Diagnostic and therapeutic measures have improved survival and overall outcome in individuals with OADs. However, it has become increasingly evident that the manifestation of late disease complications cannot be reliably predicted and prevented. Conventional metabolic treatment often fails to prevent irreversible organ dysfunction with increasing age, even if patients are considered to be "metabolically stable". This has challenged our understanding of OADs and has elicited the discussion on optimized therapy, including (early) organ transplantation, and long-term care.

Liver involvement in kidney disease and vice versa

The liver and kidneys are often similarly affected by a single disease. This is the case in metabolic, immunological, toxic, and infectious diseases, and in the different congenital malformation syndromes. Also, an enzymatic defect in an otherwise healthy liver or the consequences of advanced liver disease by itself can cause kidney disease as a secondary phenomenon. In this review, we describe numerous pathogenic mechanisms leading to dysfunction or malformations of the liver and kidneys in children. We encourage multidisciplinary management for optimal care. A combined liver-kidney transplantation is sometimes needed.

Incidence of maple syrup urine disease, propionic acidemia, and methylmalonic aciduria from newborn screening data

Incidence for the branched-chain intoxication-type disorders, maple syrup urine disease, propionic acidemia and methlymalonic aciduria is dependent on the population screened. Here newborn screening results from three world regions, state screening laboratories in the United States, a region in Germany and Kuwait provides new incidence numbers. Maple syrup urine disease incidence in the United States was calculated to be 1: 220219, in South-West Germany 1: 119573 (Germany nationwide 1:177978), and in Kuwait 1: 59426. Incidence of propionic acidemia alone is calculated to be 1: 242741 in the United States, 1: 284450 in South-West Germany (Germany nationwide 1:202617) and 1:59426 in Kuwait. Incidence of isolated methylmalonic aciduria alone is 1:69354 in the United States, 1:568901 in South-West Germany (Germany nationwide 1:159199) and 1: 19809 in Kuwait. In the United States several newborn screening laboratories combine their results for propionic acidemia and methylmalonic aciduria, and also include combined remethylation disorders in the respective category, resulting in an incidence of 1:50709. Combined evaluation of methylmalonic aciduria, propionic aciduria and combined remethylation disorders results in a similar incidence for Germany of 1:67539. This evaluation of newborn screening incidences reflects some population differences for three intoxication-type metabolic disorders. However, different sample sizes of the populations screened over different time periods, and differences in case definitions for methylmalonic acidurias have to be considered when interpreting these data.

Impact of pregnancy on inborn errors of metabolism

Once based mainly in paediatrics, inborn errors of metabolism (IEM), or inherited metabolic disorders (IMD) represent a growing adult medicine specialty. Individually rare these conditions have currently, a collective estimated prevalence of >1:800. Diagnosis has improved through expanded newborn screening programs, identification of potentially affected family members and greater awareness of symptomatic presentations in adolescence and in adulthood. Better survival and reduced mortality from previously lethal and debilitating conditions means greater numbers transition to adulthood. Pregnancy, once contraindicated for many, may represent a challenging but successful outcome. Successful pregnancies are now reported in a wide range of IEM. Significant challenges remain, given the biological stresses of pregnancy, parturition and the puerperium. Known diagnoses allow preventive and pre-emptive management. Unrecognized metabolic disorders especially, remain a preventable cause of maternal and neonatal mortality and morbidity. Increased awareness of these conditions amongst all clinicians is essential to expedite diagnosis and manage appropriately. This review aims to describe normal adaptations to pregnancy and discuss how various types of IEM may be affected. Relevant translational research and clinical experience will be reviewed with practical management aspects cited. Based on current literature, the impact of maternal IEM on mother and/or foetus, as well as how foetal IEM may affect the mother, will be considered. Insights gained from these rare disorders to more common conditions will be explored. Gaps in the literature, unanswered questions and steps to enhance further knowledge and systematically capture experience, such as establishment of an IEM-pregnancy registry, will be summarized.

Aspects of Newborn Screening in Isovaleric Acidemia

Isovaleric acidemia (IVA), an inborn error of leucine catabolism, is caused by mutations in the isovaleryl-CoA dehydrogenase (IVD) gene, resulting in the accumulation of derivatives of isovaleryl-CoA including isovaleryl (C5)-carnitine, the marker metabolite used for newborn screening (NBS). The inclusion of IVA in NBS programs in many countries has broadened knowledge of the variability of the condition, whereas prior to NBS, two distinct clinical phenotypes were known, an "acute neonatal" and a "chronic intermittent" form. An additional biochemically mild and potentially asymptomatic form of IVA and its association with a common missense mutation, c.932C>T (p.A282V), was discovered in subjects identified through NBS. Deficiency of short/branched chain specific acyl-CoA dehydrogenase (2-methylbutyryl-CoA dehydrogenase), a defect of isoleucine degradation whose clinical significance remains unclear, also results in elevated C5-carnitine, and may therefore be detected by NBS for IVA. Treatment strategies for the long-term management of symptomatic IVA comprise the prevention of catabolism, dietary restriction of natural protein or leucine intake, and supplementation with l-carnitine and/or l-glycine. Recommendations on how to counsel and manage individuals with the mild phenotype detected by NBS are required.