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?

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.

Retrospective study of propionic acidemia using natural language processing in Mayo Clinic electronic health record data

BACKGROUND

Propionic acidemia (PA) is a rare autosomal recessive organic acidemia that classically presents within the first days of life with a metabolic crisis or via newborn screening and is confirmed with laboratory tests. Limited data exist on the natural history of patients with PA describing presentation, treatments, and clinical outcomes.

OBJECTIVE

To retrospectively describe the natural history of patients with PA in a clinical setting from a real-world database using both structured and unstructured electronic health record (EHR) data using novel data extraction techniques in a unique care setting.

DESIGN/METHODS

This retrospective study used EHR data to identify patients with PA seen at the Mayo Clinic. Unstructured clinical text (medical notes, pathology reports) were analyzed using augmented curation natural language processing models to enhance analysis of data extracted by structured data fields (International Classification of Diseases 9th or 10th revision [ICD-9/-10] codes, Current Procedural Terminology [CPT] codes, and medication orders). De-identified health records were also manually reviewed by clinical scientists to ensure data accuracy and completeness. The index date was defined as the patient's date of PA diagnosis at the Mayo Clinic. Results were reported as aggregate descriptive statistics relative to patients' index dates. Complications, therapeutic interventions, laboratory tests, procedures, and hospitalization encounters related to PA were described at and within 6 months of the patient's index date, and from medical history available before the index date.

RESULTS

In total, 13 patients with PA were identified, with visits occurring from 1998 to 2022. Age at diagnosis ranged from birth to 3 years; age at initial evaluation at the Mayo Clinic ranged from 3 days to 28 years. The mean number of Mayo Clinic outpatient visits was 31 (median duration of care, 2 years). PA-related complications were documented in 85% of patients and included nutritional difficulties (46%), metabolic decompensation events (MDEs; 38%), neurologic abnormalities (38%), and cardiomyopathy (7%). One pair of affected siblings had mild symptoms and no complications or MDEs. All 5 patients with a history of MDEs presented with developmental delays. Among patients with MDEs, the mean frequency of outpatient clinical care visits was 10 per year, and 3 patients required inpatient hospitalization (mean duration, 16 days). The incidence of severe complications was higher among patients with MDEs than those without MDEs. Of the patients with MDEs, 2 experienced crises while receiving treatment at the Mayo Clinic, with 9 total MDEs occurring between the 2 patients. Symptoms at presentation included hyperammonemia (78%), fever and/or decreased nutritional intake (67%), hyperglycemia/hypoglycemia (56%), intercurrent upper respiratory infection and/or lethargy (44%), constipation (33%), altered mental status (33%), and cough (33%).

CONCLUSIONS

This study highlights the range and frequency of clinical outcomes experienced by patients with PA and demonstrates the clinical burden of MDEs.

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.

A Retrospective Analysis of Clinically Focused Exome Sequencing Results of 372 Infants with Suspected Monogenic Disorders in China

Objective

The context was designed to optimize the diagnostic utility of clinically focused exome sequencing (CFES) and shorten the diagnostic odyssey among pediatric patients suspected of monogenic disorders (MDs).

Methods

Here, we retrospectively analyzed the clinical notes of 372 patients from different areas in the Jiangxi province that were referred for a diagnostic CFES and analysis from June 2018 to March 2022 with symptoms suggestive of MDs. In our study, preliminary tests using the proband-only clinical exome sequencing as a cost-effective first-tier diagnostic test for pediatric patients with unidentified MDs, supplemented by family segregation studies for targeted variants when indicated.

Results

Probands with confirmed diagnostic (CD) or likely diagnostic (LD) genetic influences accounted for 12% of all cases, whereas those with an uncertain diagnosis accounted for 48%. We also found that systemic primary carnitine deficiency (CDSP) (SLC22A5 gene) and phenylketonuria (PAH gene) were relatively more prevalent, and these patients with CDSP had the most frequent c.1400C > G variant (p.S467C) and c.51C > G variant (p. F17L) in this study. In addition, statistical analysis revealed that the estimates of diagnostic yields varied across certain phenotypic features of patients, and patients with specific phenotypic traits tended to benefit more from CFES.

Conclusion

The CFES may be a first-line genetic test for diagnosing young children with suspected genetic conditions, as it validates the identification of molecular genetics alterations and facilitates comprehensive medical management. Moreover, we found that infants exhibiting metabolism/homeostasis abnormalities, craniofacial /otolaryngology/ ophthalmologic abnormalities, and/or the integument were significantly more likely to receive a genetic diagnosis via CFES than infants without such features. However, due to the current study's low diagnostic yield and inherent limitations, high-quality clinical studies with larger sample sizes are still needed to provide more likely results and confirm our findings.

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.

Natural history of propionic acidemia in the Amish population

Propionic acidemia (PA) in the Amish is caused by a homozygous pathogenic variant (c.1606A>G; p.Asn536Asp) in the PCCB gene. Amish patients can have borderline or normal newborn screening (NBS) results and symptoms can present at any time from early childhood to mid-adulthood. Early diagnosis and initiation of treatment for PA in the non-Amish population improves patient outcomes. Here, we present data from a retrospective chart review of Amish patients diagnosed with PA from three different medical centers in order to document its natural history in the Amish and determine the influence of treatment on outcomes in this population. A total of 38 patients with average current age 19.9 years (range 4y-45y), 57.9% males, were enrolled in the study. Fourteen patients (36.8%) were diagnosed with a positive newborn screening (NBS) while 24 patients (63.2%) had negative or inconclusive NBS or had no record of NBS in their charts. These 24 patients were diagnosed by screening after a family member was diagnosed with PA (14; 58.3%), following a hospitalization for metabolic acidosis (5; 20.8%), hospitalization for seizures (3; 12.5%) or via cord blood (2; 8.3%). The majority of patients were prescribed a protein restricted diet (32; 84.2%), including metabolic formula (29; 76.3%). Most were treated with carnitine (35; 92.1%), biotin (2; 76.3%) and/or Coenzyme Q10 (16; 42.1%). However, treatment adherence varied widely among patients, with 7 (24.1%) of the patients prescribed metabolic formula reportedly nonadherent. Cardiomyopathy was the most prevalent finding (22; 63.2%), followed by developmental delay/intellectual disability (15; 39.5%), long QT (14; 36.8%), seizures (12; 31.6%), failure to thrive (4; 10.5%), and basal ganglia strokes (3; 7.9%). No difference in outcome was obvious for those diagnosed by NBS and treated early with dietary and supplement management, especially for cardiomyopathy. However, this is a limited retrospective observational study. A prospective study with strict documentation of treatment adherence and universal screening for cardiomyopathy and long QT should be conducted to better study the impact of early detection and treatment. Additional treatment options such as liver transplantation and future therapies such as mRNA or gene therapy should be explored in this population.

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.

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.

Diagnosis of inborn errors of metabolism within the expanded newborn screening in the Madrid region

We present the results of our experience in the diagnosis of inborn errors of metabolism (IEM) since the Expanded Newborn Screening was implemented in our Region. Dried blood samples were collected 48 h after birth. Amino acids and acylcarnitines were quantitated by mass spectrometry (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. In the period 2011 to 2019, 592 822 children were screened: 902 of them were referred for abnormal results. An IEM was confirmed in 222 (1/2670): aminoacidopathies: 89 hyperphenylalaninemia (HPA) (51 benign HPA, 32 phenylketonuria, 4 DNAJC12 defect, and 2 primapterinuria), 6 hypermethioninemia, 3 tyrosinemia type 1 (TYR‐1), 1 TYR‐3, 4 maple syrup urine disease (MSUD), 2 branched‐chain amino acid transferase 2 deficiency, 2 homocystinuria, 1 cystinuria, 2 ornithine transcarbamylase (OTC) deficiency, 2 citrullinemia type I (CTLN1); FAO defects: 43 medium‐chain acyl‐CoA dehydrogenase deficiency (MCADD), 13 very long‐chain acyl‐CoA dehydrogenase deficiency, 2 long‐chain 3‐hydroxyacyl‐CoA dehydrogenase deficiency (LCHADD), 1 multiple acyl‐coA dehydrogenation deficiency, 11 systemic primary carnitine deficiency, 2 carnitine palmitoyltransferase type 2 (CPT‐II) deficiency, 1 CPT‐I deficiency; organic acidurias: 12 glutaric aciduria type 1 (GA‐1), 4 methylmalonic acidemia (MMA), 7 MMA including combined cases with homocystinuria (MMAHC), 6 propionic acidemia (PA), 7 3‐methylcrotonyl‐CoA carboxylase, 1 3‐hydroxy‐3‐methylglutaryl‐CoA lyase deficiency lyase deficiency. Only 19 infants (8.5%) were symptomatic at newborn screening result (1 LCHADD, 5 PA, 1 CPT‐II deficiency, 1 MMA, 3 MMAHC, 2 MSUD, 2 OTC deficiency, 1 CTLN1, 1 MCADD, 2 TYR‐1). No false negative cases were identified. Genetic diagnosis was conclusive in all biochemically confirmed cases, except for two infants with HPA, identifying pathogenic variants in 32 different genes. The conditions with the highest incidence were HPA (1/6661) and MCAD deficiencies (1/13 787).

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.

High protein prescription in methylmalonic and propionic acidemia patients and its negative association with long-term outcome

BACKGROUND AND OBJECTIVE

Methylmalonic acidemia (MMA) and propionic acidemia (PA) are inborn errors of metabolism. While survival of MMA and PA patients has improved in recent decades, long-term outcome is still unsatisfactory. A protein restricted diet is the mainstay for treatment. Additional amino acid mixtures (AAM) can be prescribed if natural protein is insufficient. It is unknown if dietary treatment can have an impact on outcome.

DESIGN

We performed a nationwide retrospective cohort study and evaluated both longitudinal dietary treatment and clinical course of Dutch MMA and PA patients. Protein prescription was compared to the recommended daily allowances (RDA); the safe level of protein intake as provided by the World Health Organization. The association of longitudinal dietary treatment with long-term outcome was evaluated.

RESULTS

The cohort included 76 patients with a median retrospective follow-up period of 15 years (min-max: 0-48 years) and a total of 1063 patient years on a protein restricted diet. Natural protein prescription exceeded the RDA in 37% (470/1287) of all prescriptions and due to AAM prescription, the total protein prescription exceeded RDA in 84% (1070/1277). Higher protein prescriptions were associated with adverse outcomes in severely affected patients. In PA early onset patients a higher natural protein prescription was associated with more frequent AMD. In MMA vitamin B12 unresponsive patients, both a higher total protein prescription and AAM protein prescription were associated with more mitochondrial complications. A higher AAM protein prescription was associated with an increased frequency of cognitive impairment in the entire.

CONCLUSION

Protein intake in excess of recommendations is frequent and is associated with poor outcome.

SARS-CoV-2 infection in a patient with propionic acidemia

We describe a 14-month-old boy, with a previous diagnosis of propionic acidemia (PA) by expanded newborn screening, who, admitted for a suspected metabolic crisis, tested positive for SARS-CoV-2. Since propionic acidemia was diagnosed, the patient has followed the recommended diet for this inborn error of metabolism. Although propionic acidemia patients are at a high risk of suffering metabolic crises, frequently associated with permanent clinical complications, psychomotor development of this patient was normal. The SARS-CoV-2 infection (at about 1 year of age) caused the patient’s first metabolic crisis. However, his clinical course was in keeping with a mild clinical form of COVID-19, and he recovered without experiencing severe clinical consequences. We describe this patient in order to improve the knowledge about follow up of PA patients identified by newborn screening and to increase the limited number of reports of SARS-CoV-2 infection in children with comorbidities, especially inborn errors of metabolism.

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.