Analysis of 2-methylcitric acid, methylmalonic acid, and total homocysteine in dried blood spots by LC-MS/MS for application in the newborn screening laboratory: A dual derivatization approach.

Inborn errors of propionate, cobalamin and methionine metabolism are targets for Newborn Screening (NBS) in most programs world-wide, and are primarily screened by analyzing for propionyl carnitine (C3) and methionine in dried blood spot (DBS) cards using tandem mass spectrometry (MS/MS). Single-tier NBS approaches using C3 and methionine alone lack specificity, which can lead to an increased false-positive rate if conservative cut-offs are applied to minimize the risk of missing cases. Implementation of liquid chromatography tandem mass spectrometry (LC-MS/MS) second-tier testing for 2-methylcitric acid (MCA), methylmalonic acid (MMA), and homocysteine (HCY) from the same DBS card can improve disease screening performance by reducing the false-positive rate and eliminating the need for repeat specimen collection. However, DBS analysis of MCA, MMA, and HCY by LC-MS/MS is challenging due to limited specimen size and analyte characteristics leading to a combination of low MS/MS sensitivity and poor reverse-phase chromatographic retention. Sufficient MS response and analytical performance can be achieved for MCA by amidation using DAABD-AE and by butylation for MMA and HCY. Herein we describe the validation of a second-tier dual derivatization LC-MS/MS approach to detect elevated MCA, MMA, and HCY in DBS cards for NBS. Clinical utility was demonstrated by retrospective analysis of specimens, an interlaboratory method comparison, and assessment of external proficiency samples. Imprecision was <10.8% CV, with analyte recoveries between 90.2 and 109.4%. Workflows and analytical performance characteristics of this second-tier LC-MS/MS approach are amenable to implementation in the NBS laboratory.

Congenital lactic acidosis, cerebral cysts and pulmonary hypertension in an infant with FOXRED1 related complex 1 deficiency.

Mitochondrial complex I is encoded by 38 nuclear-encoded and 7 mitochondrial-encoded genes. FOXRED1 is one of the 13 additional nuclear genes known as assembly factors. So far, four patients have been described with complex I deficiency caused by autosomal recessive mutations in FOXRED1. Here, we report the fifth patient with FOXRED1 related complex 1 deficiency presenting with prenatal onset of bilateral periventricular cysts, congenital lactic acidosis, and persistent life-limiting pulmonary hypertension. Whole exome sequencing identified a compound heterozygosity for a known pathogenic variant (c.612_615dupAGTG; p.A206SfsX15) (paternal) and a likely pathogenic variant (c.874G>A; p.Gly292Arg) (maternal). Deficiency of complex I was demonstrated by the absence of complex I on Blue Native Gel Electrophoresis and by a significantly reduced complex I enzyme activity in the patient's fibroblasts. Compared with the previous known FOXRED1 cases, unique clinical features observed in our patient include bilateral periventricular cysts and severe pulmonary hypertension. Whole exome sequencing was instrumental in recognizing the underlying gene defect in this patient.

Congenital lactic acidosis, cerebral cysts and pulmonary hypertension in an infant with FOXRED1 related complex I deficiency.

Mitochondrial complex I is encoded by 38 nuclear-encoded and 7 mitochondrial-encoded genes. FOXRED1 is one of the 13 additional nuclear genes known as assembly factors. So far, four patients have been described with complex I deficiency caused by autosomal recessive mutations in FOXRED1. Here, we report the fifth patient with FOXRED1 related complex 1 deficiency presenting with prenatal onset of bilateral periventricular cysts, congenital lactic acidosis, and persistent life-limiting pulmonary hypertension. Whole exome sequencing identified a compound heterozygosity for a known pathogenic variant (c.612_615dupAGTG; p.A206SfsX15) (paternal) and a likely pathogenic variant (c.874G > A; p.Gly292Arg) (maternal). Deficiency of complex I was demonstrated by the absence of complex I on Blue Native Gel Electrophoresis and by a significantly reduced complex I enzyme activity in the patient's fibroblasts. Compared with the previous known FOXRED1 cases, unique clinical features observed in our patient include bilateral periventricular cysts and severe pulmonary hypertension. Whole exome sequencing was instrumental in recognizing the underlying gene defect in this patient.

Sialic acid catabolism by N-acetylneuraminate pyruvate lyase is essential for muscle function.

Sialic acids are important components of glycoproteins and glycolipids essential for cellular communication, infection, and metastasis. The importance of sialic acid biosynthesis in human physiology is well illustrated by the severe metabolic disorders in this pathway. However, the biological role of sialic acid catabolism in humans remains unclear. Here, we present evidence that sialic acid catabolism is important for heart and skeletal muscle function and development in humans and zebrafish. In two siblings, presenting with sialuria, exercise intolerance/muscle wasting, and cardiac symptoms in the brother, compound heterozygous mutations [chr1:182775324C>T (c.187C>T; p.Arg63Cys) and chr1:182772897A>G (c.133A>G; p.Asn45Asp)] were found in the N-acetylneuraminate pyruvate lyase gene (NPL). In vitro, NPL activity and sialic acid catabolism were affected, with a cell-type-specific reduction of N-acetyl mannosamine (ManNAc). A knockdown of NPL in zebrafish resulted in severe skeletal myopathy and cardiac edema, mimicking the human phenotype. The phenotype was rescued by expression of wild-type human NPL but not by the p.Arg63Cys or p.Asn45Asp mutants. Importantly, the myopathy phenotype in zebrafish embryos was rescued by treatment with the catabolic products of NPL: N-acetyl glucosamine (GlcNAc) and ManNAc; the latter also rescuing the cardiac phenotype. In conclusion, we provide the first report to our knowledge of a human defect in sialic acid catabolism, which implicates an important role of the sialic acid catabolic pathway in mammalian muscle physiology, and suggests opportunities for monosaccharide replacement therapy in human patients.

Gene Expression Profiling of Endoplasmic Reticulum Stress in Hepatitis C Virus-Containing Cells Treated with an Inhibitor of Protein Disulfide Isomerases.

Protein disulfide isomerases (PDIs) catalyze disulfide bond formation between protein cysteine residues during protein folding in the endoplasmic reticulum (ER) lumen and are essential for maintaining ER homoeostasis. The life cycle of the hepatitis C virus (HCV) is closely associated with the ER. Synthesis and maturation of HCV proteins occur in the ER membrane and are mediated by multiple host cell factors that include also PDI. Here, we present a study investigating the effect of PDI inhibition on Huh7 human hepatoma cells harboring an HCV subgenomic replicon using the abscisic acid-derived PDI inhibitor origamicin. Transcriptional profiling shows that origamicin changed the expression levels of genes involved in the oxidative and ER stress responses and the unfolded protein response, as indicated by the upregulation of antioxidant enzymes and chaperone proteins, the downregulation of cell-cycle proteins, and induction of apoptosis-associated genes. Our data suggest that origamicin negatively impacts HCV replication by causing an imbalance in cellular homoeostasis and induction of stress responses. These insights suggest that inhibition of PDIs by low-molecular-weight inhibitors could be a promising approach to the discovery of novel antiviral compounds.

Consensus recommendations for the diagnosis, treatment and follow-up of inherited methylation disorders.

Inherited methylation disorders are a group of rarely reported, probably largely underdiagnosed disorders affecting transmethylation processes in the metabolic pathway between methionine and homocysteine. These are methionine adenosyltransferase I/III, glycine N-methyltransferase, S-adenosylhomocysteine hydrolase and adenosine kinase deficiencies. This paper provides the first consensus recommendations for the diagnosis and management of methylation disorders. Following search of the literature and evaluation according to the SIGN-methodology of all reported patients with methylation defects, graded recommendations are provided in a structured way comprising diagnosis (clinical presentation, biochemical abnormalities, differential diagnosis, newborn screening, prenatal diagnosis), therapy and follow-up. Methylation disorders predominantly affect the liver, central nervous system and muscles, but clinical presentation can vary considerably between and within disorders. Although isolated hypermethioninemia is the biochemical hallmark of this group of disorders, it is not always present, especially in early infancy. Plasma S-adenosylmethionine and S-adenosylhomocysteine are key metabolites for the biochemical clarification of isolated hypermethioninemia. Mild hyperhomocysteinemia can be present in all methylation disorders. Methylation disorders do not qualify as primary targets of newborn screening. A low-methionine diet can be beneficial in patients with methionine adenosyltransferase I/III deficiency if plasma methionine concentrations exceed 800 µmol/L. There is some evidence that this diet may also be beneficial in patients with S-adenosylhomocysteine hydrolase and adenosine kinase deficiencies. S-adenosylmethionine supplementation may be useful in patients with methionine adenosyltransferase I/III deficiency. Recommendations given in this article are based on general principles and in practice should be adjusted individually according to patient's age, severity of the disease, clinical and laboratory findings.

A small-molecule probe for hepatitis C virus replication that blocks protein folding.

The hepatitis C virus (HCV) is a growing global health problem. Small molecules that interfere with host-viral interactions can serve as powerful tools for elucidating the molecular mechanisms of pathogenesis and defining new strategies for therapeutic development. Using a cell-based screen involving subgenomic HCV replicons, we identified the ability of 18 different abscisic acid (ABA) analogs, originally developed as plant growth regulators, to inhibit HCV replication. Three of these were further studied. One compound, here named origamicin, showed antiviral activity through the inhibition of host proteins involved in protein folding. Origamicin could therefore be an important tool for studying the maturation of both host and viral proteins. Herein we demonstrate an application for molecular scaffolds based on ABA for mammalian cell targets involved in protein folding.

Peroxisome proliferator-activated receptor alpha antagonism inhibits hepatitis C virus replication.

Hepatitis C virus (HCV) is a global health problem and a leading cause of liver disease. Here, we demonstrate that the replication of HCV replicon RNA in Huh-7 cells is inhibited by a peroxisome proliferator-activated receptor (PPAR) antagonist, 2-chloro-5-nitro-N-(pyridyl)benzamide (BA). Downregulation of PPARgamma with RNA interference approaches had no effect on HCV replication in Huh-7 cells, whereas PPARalpha downregulation inhibited HCV replication. Fluorescence and coherent anti-Stokes Raman scattering (CARS) microscopy demonstrate a clear buildup of lipids upon treatment with BA. These observations are consistent with the misregulation of lipid metabolism, phospholipid secretion, cholesterol catabolism, and triglyceride clearance events associated with the inhibition of PPARalpha. The inhibition of HCV replication by BA may result from disrupting lipidation of host proteins associated with the HCV replication complex or, more generally, by disrupting the membranous web where HCV replicates.