Characterization of ETFDH and PHGDH Mutations in a Patient with Mild Glutaric Aciduria Type II and Serine Deficiency

Glutaric aciduria type II (GA-II) is a rare autosomal recessive disease caused by defects in electron transfer flavoprotein (ETF), ultimately causing insufficiencies in multiple acyl-CoA dehydrogenase (MAD). 3-phosphoglycerate dehydrogenase (3-PHGDH) deficiency, is another rare autosomal disorder that appears due to a defect in the synthesis of L-serine amino acid. Several mutations of ETFDH and PHGDH genes have been associated with different forms of GA-II and serine deficiency, respectively. In this study, we report a unique case of GA-II with serine deficiency using biochemical, genetic, and in silico approaches. The proband of Syrian descent had positive newborn screening (NBS) for GA-II. At two years of age, the patient presented with developmental regression, ataxia, and intractable seizures. Results of amino acid profiling demonstrated extremely low levels of serine. Confirmatory tests for GA-II and whole exome sequencing (WES) were performed to determine the etiology of intractable seizure. Sequencing results indicated a previously reported homozygous missense mutation, c.679 C>A (p.Pro227Thr) in the ETFDH gene and a novel missense homozygous mutation c.1219 T>C (p.Ser407Pro) in the PHGDH gene. In silico tools predicted these mutations as deleterious. Here, the clinical and biochemical investigations indicate that ETFDH:p.Pro227Thr and PHGDH:p.Ser407Pro variants likely underlie the pathogenesis of GA-II and serine deficiency, respectively. This study indicates that two rare autosomal recessive disorders should be considered in consanguineous families, more specifically in those with atypical presentation

Analysis of tricarboxylic acid cycle intermediates in dried blood spots by ultraperformance liquid chromatography-tandem mass spectrometry

Background: We developed a novel method for measuring the concentrations of tricarboxylic acid (TCA) cycle intermediates in dried blood spots (DBS) using liquid chromatography-tandem mass spectrometry (LC-MS/ MS). Analytes were derivatized before analysis using 4-[2-(N,N-dimethylamino) ethylaminosulfonyl]-7-(2-aminoethylamino)-2,1,3-benzoxa-diazole (DAABD-AE), a reagent that imparts powerful chromatographic and mass spectrometric properties onto carboxyl group-containing analytes. Methodology: Extraction and derivatization of TCA cycle intermediates were achieved in a single step by incubating a 3.2 mm circle of the DBS samples with DAABD-AE for 1 hour at 65 C. From the resultant mixture, 1.0 µl was injected into the LC-MS/MS. Results: Total analytical run time to separate target analytes from other interfering components in the sample was 8 minutes. The peaks corresponding to malic, fumaric, citric, succinic, and 2-ketoglutaric acid appeared at 3.55, 3.62, 3.64, 3.67, and 3.68 minutes, respectively. The method was adequately reproducible with a coefficient of variation for intraday (n = 15) and inter-day (n = 13) studies of 5.2%-18.4%. Reference intervals in DBS from controls (n = 125) were as follow (µmol/l): citric (36.6-126.4), 2-ketoglutaric (9.1-42.1), succinic (1.2-2.4), fumaric (2.4-9.0), and malic acid (15.9-39.3). Compared to controls, the levels of citric, succinic, and malic acids were statistically different in patients (n = 7) with a p-value of< 0.05. No statistically significant difference was detected in concentrations of 2-ketoglutaric and fumaric acids. Conclusion: We describe a simple, quick, and sensitive method to measure TCA cycle intermediates in DBS samples. That TCA cycle plays a central role in cellular metabolism; this method should be useful in studying these metabolites in health and disease. [JBCGenetics 2019; 2(2.000): 93-98

Clinical, Biochemical, and Genetic Heterogeneity in Glutaric Aciduria Type II Patients

The variants of electron transfer flavoprotein (ETFA, ETFB) and ETF dehydrogenase (ETFDH) are the leading cause of glutaric aciduria type II (GA-II). In this study, we identified 13 patients harboring six variants of two genes associated with GA-II. Out of the six variants, four were missense, and two were frameshift mutations. A missense variant (ETFDH:p.Gln269His) was observed in a homozygous state in nine patients. Among nine patients, three had experienced metabolic crises with recurrent vomiting, abdominal pain, and nausea. In one patient with persistent metabolic acidosis, hypoglycemia, and a high anion gap, the ETFDH:p.Gly472Arg, and ETFB:p.Pro94Thrfs*8 variants were identified in a homozygous, and heterozygous state, respectively. A missense variant ETFDH:p.Ser442Leu was detected in a homozygous state in one patient with metabolic acidosis, hypoglycemia, hyperammonemia and liver dysfunction. The ETFDH:p.Arg41Leu, and ETFB:p.Ile346Phefs*19 variants were observed in a homozygous state in one patient each. Both these variants have not been reported so far. In silico approaches were used to evaluate the pathogenicity and structural changes linked with these six variants. Overall, the results indicate the importance of a newborn screening program and genetic investigations for patients with GA-II. Moreover, careful interpretation and correlation of variants of uncertain significance with clinical and biochemical findings are needed to confirm the pathogenicity of such variants