, Melissa Yssel, MB ChB, FC Path(SA) Chem 139, and Wendy M. Zakowicz, BS 79 Purpose: To achieve clinical validation of cutoff values for newborn screening by tandem mass spectrometry through a worldwide collaborative effort. Methods: Cumulative percentiles of amino acids and acylcarnitines in dried blood spots of approximately 25-30 million normal newborns and 10,742 deidentified true positive cases are compared to assign clinical significance, which is achieved when the median of a disorder range is, and usually markedly outside, either the 99th or the 1st percentile of the normal population. The cutoff target ranges of analytes and ratios are then defined as the interval between selected percentiles of the two populations. When overlaps occur, adjustments are made to maximize sensitivity and specificity taking all available factors into consideration.

A novel autosomal recessive developmental disorder associated with pathogenic homozygous or compound heterozygous variants in the KPTN gene (MIM 615620) has recently been described as a dis

Mitochondrial fatty acid b-oxidation disorders (FAOD) are main targets for newborn screening (NBS) programs, which are excellent data sources for accurate estimations of disease birth prevalence. Epidemiological data is of key importance for the understanding of the natural history of the disorders as well as to define more effective public health strategies. In order to estimate FAOD birth prevalence in Iberia, the authors collected data from six NBS programs from Portugal and Spain, encompassing the screening of more than 1.6 million newborns by tandem mass spectrometry (MS/MS), and compared it with available data from other populations. The participating NBS programs are responsible for the screening of about 46% of all Iberian newborns. Data reveals that Iberia has one of the highest FAOD prevalence in Europe (1:7,914) and that Portugal has the highest birth prevalence of FAOD reported so far (1:6,351), strongly influenced by the high prevalence of medium-chain acyl-CoA dehydrogenase deficiency (MCADD; 1:8,380), one of the highest ever reported. This is justified by the fact that more than 90% of Portuguese MCADD patients are of Gypsy origin, a community characterized by a high degree of consanguinity. From the comparative analysis of various populations with comparable data other differences emerge, which points to the existence of significant variations in FAOD prevalences among different populations, but without any clear European variation pattern. Considering that FAOD are one of the justifications for MS/MS NBS, the now estimated birth prevalences stress the need to screen all Iberian newborns for this group of inherited metabolic disorders.

Newborn screening markers (C3, C3/C2, and C3/C16) present an inverse correlation with maternal vitamin B12 status in the first trimester of pregnancy. Regarding factors that may influence maternal serum vitamin B12 levels during the first trimester, smoking seems to have a negative effect, and meat consumption a positive effect.

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