Portuguese Neonatal Screening Programme: A Retrospective Cohort Study of 18 Years of MS/MS.

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.