RESUMEN
The Portuguese Neonatal Screening Program (PNSP) conducts nationwide screening for rare diseases, covering nearly 100% of neonates and screening for 28 disorders, including 24 inborn errors of metabolism (IEMs). The study's purpose is to assess the epidemiology of the screened metabolic diseases and to evaluate the impact of second-tier testing (2TT) within the PNSP. From 2004 to 2022, 1,764,830 neonates underwent screening using tandem mass spectrometry (MS/MS) to analyze amino acids and acylcarnitines in dried blood spot samples. 2TT was applied when necessary. Neonates with profiles indicating an IEM were reported to a reference treatment center, and subsequent biochemical and molecular studies were conducted for diagnostic confirmation. Among the screened neonates, 677 patients of IEM were identified, yielding an estimated birth prevalence of 1:2607 neonates. The introduction of 2TT significantly reduced false positives for various disorders, and 59 maternal cases were also detected. This study underscores the transformative role of MS/MS in neonatal screening, emphasizing the positive impact of 2TT in enhancing sensitivity, specificity, and positive predictive value. Our data highlight the efficiency and robustness of neonatal screening for IEM in Portugal, contributing to early and life-changing diagnoses.
RESUMEN
INTRODUCTION: The Portuguese Neonatal Screening Programme (PNSP) identifies patients with rare diseases through nationwide screening. Currently, 27 diseases are diagnosed, amongst which are 24 Inborn Errors of Metabolism (IEM), covering approximately 100% of neonates (1). In 2004, the national laboratory implemented a new screening method, tandem mass spectrometry (MS/MS) to test for amino acids and acylcarnitines. This new protocol revolutionized the PNSP and allowed for the analysis of an increased number of IEM, with clear improvements in treatment timings and clinical outcomes (2). METHODS: From 2004 to 2022, 1 764 830 neonates were screened with MS/MS technology. Those who displayed biochemical profiles indicating an IEM were subjected to molecular characterization via genomic DNA extraction, PCR amplification, and direct Sanger sequencing method of dried blood spot samples. RESULTS/CASE REPORT: A cohort of 681 newborns were diagnosed with an IEM. MCAD deficiency is the most frequent, with 233 confirmed diagnoses, showing predominantly c.985A>G (p.K329E) mutation of the ACADM gene in homozygosity. Approximately 1/3 of the 33 confirmed cases of Glutaric Aciduria type I present homozygous for the c.1204C>T (p.Arg402Trp) mutation in GCDH. Around 60% of cases of MAT II/III deficiency display the dominant mutation of the MAT1A gene, c.791G>A (p.Arg264His). These genetic profiles and others were determined as diagnostic confirmation for 24 of the IEM screened. CONCLUSION: This data shows the molecular epidemiology of patients with confirmed IEM diagnosis identified by neonatal screening. Some diseases out of the scope of the PNSP were also detected as a differential diagnosis after biochemical suspicion in the dried blood spot sample. The retrospective analysis of the PNSP allows for an overview of 18 years of achievements accomplished by the national screening for IEM since MS/MS was implemented. For some pathologies with low incidence, it's difficult to trace a discernible pattern. However, presenting de novo mutations for these diseases might provide insights on how to approach different phenotypes. The aim of this work is to establish the molecular epidemiology of metabolic diseases screened.
