Organic acidurias are inherited metabolic diseases due to the deficiency of an enzyme or a transport protein involved in one of the several cellular metabolic pathways devoted to the catabolism of amino acids, carbohydrates or lipids. These deficiencies result in abnormal accumulation of organic acids in the body and their abnormal excretion in urine. More than 65 organic acidurias have been described; the incidence varies, individually, from 1 out of 10,000 to >1 out of 1000,000 live births. Collectively, their incidence approximates 1 out of 3000 live births. Among these disorders, methyl malonic aciduria, propionic aciduria, maple syrup urine disease and isovaleric aciduria are sometimes referred to as classical organic acidurias. In this review, we focused on the basic GC-MS-based methodologies employed in the diagnosis of classical organic acidurias and provided updated reference values for the most common involved organic acids. We also attempted to provide the most recent updates on the pathogenetic bases of these diseases.

Purpose: To improve quality of newborn screening by tandem mass spectrometry with a novel approach made possible by the collaboration of 154 laboratories in 49 countries. Methods: A database of 767,464 results from 12,721 cases affected with 60 conditions was used to build multivariate pattern recognition software that generates tools integrating multiple clinically significant results into a single score. This score is determined by the overlap between normal and disease ranges, penetration within the disease range, differences between conditions, and weighted correction factors. Results: Ninety tools target either a single condition or the differential diagnosis between multiple conditions. Scores are expressed as the percentile rank among all cases with the same condition and are compared to interpretation guidelines. Retrospective evaluation of past cases suggests that these tools could have avoided at least half of 279 false-positive outcomes caused by carrier status for fatty-acid oxidation disorders and could have prevented 88% of known false-negative events. Conclusions: Application of this computational approach to raw data is independent from single analyte cutoff values. In Minnesota, the tools have been a major contributing factor to the sustained achievement of a false-positive rate below 0.1% and a positive predictive value above 60%

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Inborn errors of metabolism are genetic disorders due to impaired activity of enzymes, transporters, or cofactors resulting in accumulation of abnormal metabolites proximal to the metabolic block, lack of essential products or accumulation of by-products. Many of these disorders have serious clinical consequences for affected neonates, and an early diagnosis allows presymptomatic treatment which can prevent severe permanent sequelae and in some cases death. Expanded newborn screening for these diseases is a promising field of targeted metabolomics. Here we report the application, between 2007 and 2014, of this approach to the identification of newborns in southern Italy at risk of developing a potentially fatal disease. The analysis of amino acids and acylcarnitines in dried blood spots by tandem mass spectrometry revealed 24 affected newborns among 45,466 infants evaluated between 48 and 72 hours of life (overall incidence: 1 : 1894). Diagnoses of newborns with elevated metabolites were confirmed by gas chromatography-mass spectrometry, biochemical studies, and genetic analysis. Five infants were diagnosed with medium-chain acyl CoA dehydrogenase deficiency, 1 with methylmalonic acidemia with homocystinuria type CblC, 2 with isolated methylmalonic acidemia, 1 with propionic acidemia, 1 with isovaleric academia, 1 with isobutyryl-CoA dehydrogenase deficiency, 1 with beta ketothiolase deficiency, 1 with short branched chain amino acid deficiency, 1 with 3-methlycrotonyl-CoA carboxylase deficiency, 1 with formimino-transferase cyclodeaminase deficiency, and 1 with cystathionine-beta-synthase deficiency. Seven cases of maternal vitamin B12 deficiency and 1 case of maternal carnitine uptake deficiency were detected. This study supports the widespread application of metabolomic-based newborn screening for these genetic diseases.