Vockley, Jerry

ABSTRACT 3‐hydroxy acylcarnitines (3‐OH‐ACs) are key biomarkers for screening of long‐chain 3‐hydroxyacyl‐CoA dehydrogenase and trifunctional protein deficiencies (LCHADD/TFPD). The utility of this biomarker for disease monitoring in identified patients remains debated, and recent suggestions have highlighted the potential use of lipidomics for diagnosis, monitoring, prognosis, and/or identification of new biomarkers. We evaluated the use of omics in LCHADD/TFPD patients by analyzing plasma acylcarnitine profiles, metabolomics, and lipidomics, combined with genotype, visual assessments, and dietary records. Fasting plasma from 39 participants with LCHADD/TFPD and 32 control subjects were analyzed through untargeted metabolomic and lipidomic analyses. In LCHADD/TFPD participants, acylcarnitine profiling, visual and retinal function assessments were performed, and 3‐day diet records were collected. Relationships between acylcarnitines, metabolomics, lipidomics, along with visual outcomes and dietary intake were investigated. Plasma of LCHADD/TFPD participants exhibited elevated 3‐OH‐ACs, which correlated with genotype and visual outcomes. Metabolomics successfully distinguished LCHADD/TFPD from controls, and the biggest divergence was observed in lipid pathways. Metabolomic profiles tightly correlated with 3‐OH‐ACs, genotype, and visual outcomes. Lower concentrations of total lipids and some individual lipid species such as phosphoethanolamines (PE) were detected in LCHADD/TFPD, except for elevations in several certain triglycerides. LCHADD/TFPD participants followed a diet low in long‐chain fat (LCFA) as recommended. LCFA intake did not correlate with either plasma 3‐OH‐ACs or metabolomics. 3‐OH‐ACs are strong consistent biomarkers of LCHADD/TFPD that are associated with clinical parameters of vision and genotype. We did not observe a relationship between dietary LCFA intake and 3‐OH‐ACs.

AbstractBackground: A38-year-old man presented with a history of fish odor (since age 5) and unusual muscle fatigue with increased serum creatine kinase. Our aim was to identify the metabolic error in this new condition.Methods: We used 1H NMR spectroscopy to study serum and urine from the patient.Results: The concentration of N,N-dimethylglycine (DMG) was increased ∼100-fold in the serum and ∼20-fold in the urine. The presence of DMG as a storage product was confirmed by use of 13C NMR spectroscopy and gas chromatography–mass spectrometry. The high concentration of DMG was caused by a deficiency of the enzyme dimethylglycine dehydrogenase (DMGDH). A homozygous missense mutation was found in the DMGDH gene of the patient.Conclusions: DMGDH deficiency must be added to the differential diagnosis of patients complaining of a fish odor. This deficiency is the first inborn error of metabolism discovered by use of in vitro 1H NMR spectroscopy of body fluids.

AbstractBackgroundObservational reports suggest that supplementation that increases citric acid cycle intermediates via anaplerosis may have therapeutic advantages over traditional medium‐chain triglyceride (MCT) treatment of long‐chain fatty acid oxidation disorders (LC‐FAODs) but controlled trials have not been reported. The goal of our study was to compare the effects of triheptanoin (C7), an anaplerotic seven‐carbon fatty acid triglyceride, to trioctanoin (C8), an eight‐carbon fatty acid triglyceride, in patients with LC‐FAODs.MethodsA double blinded, randomized controlled trial of 32 subjects with LC‐FAODs (carnitine palmitoyltransferase‐2, very long‐chain acylCoA dehydrogenase, trifunctional protein or long‐chain 3‐hydroxy acylCoA dehydrogenase deficiencies) who were randomly assigned a diet containing 20% of their total daily energy from either C7 or C8 for 4 months was conducted. Primary outcomes included changes in total energy expenditure (TEE), cardiac function by echocardiogram, exercise tolerance, and phosphocreatine recovery following acute exercise. Secondary outcomes included body composition, blood biomarkers, and adverse events, including incidence of rhabdomyolysis.ResultsPatients in the C7 group increased left ventricular (LV) ejection fraction by 7.4% (p = 0.046) while experiencing a 20% (p = 0.041) decrease in LV wall mass on their resting echocardiogram. They also required a lower heart rate for the same amount of work during a moderate‐intensity exercise stress test when compared to patients taking C8. There was no difference in TEE, phosphocreatine recovery, body composition, incidence of rhabdomyolysis, or any secondary outcome measures between the groups.ConclusionsC7 improved LV ejection fraction and reduced LV mass at rest, as well as lowering heart rate during exercise among patients with LC‐FAODs.Clinical Trial Registration: Clinicaltrials.gov NCT01379625.

AbstractBlood and urine acylcarnitine profiles are commonly used to diagnose long‐chain fatty acid oxidation disorders (FAOD: i.e., long‐chain hydroxy‐acyl‐CoA dehydrogenase [LCHAD] and carnitine palmitoyltransferase 2 [CPT2] deficiency), but the global metabolic impact of long‐chain FAOD has not been reported. We utilized untargeted metabolomics to characterize plasma metabolites in 12 overnight‐fasted individuals with FAOD (10 LCHAD, two CPT2) and 11 healthy age‐, sex‐, and body mass index (BMI)‐matched controls, with the caveat that individuals with FAOD consume a low‐fat diet supplemented with medium‐chain triglycerides (MCT) while matched controls consume a typical American diet. In plasma 832 metabolites were identified, and partial least squared‐discriminant analysis (PLS‐DA) identified 114 non‐acylcarnitine variables that discriminated FAOD subjects and controls. FAOD individuals had significantly higher triglycerides and lower specific phosphatidylethanolamines, ceramides, and sphingomyelins. Differences in phosphatidylcholines were also found but the directionality differed by metabolite species. Further, there were few differences in non‐lipid metabolites, indicating the metabolic impact of FAOD specifically on lipid pathways. This analysis provides evidence that LCHAD/CPT2 deficiency significantly alters complex lipid pathway flux. This metabolic signature may provide new clinical tools capable of confirming or diagnosing FAOD, even in subjects with a mild phenotype, and may provide clues regarding the biochemical and metabolic impact of FAOD that is relevant to the etiology of FAOD symptoms.

Background —Genetic defects are being increasingly recognized in the etiology of primary cardiomyopathy (CM). Very-long-chain acyl-CoA dehydrogenase (VLCAD) catalyzes the first step in the β-oxidation spiral of fatty acid metabolism, the crucial pathway for cardiac energy production. Methods and Results —We studied 37 patients with CM, nonketotic hypoglycemia and hepatic dysfunction, skeletal myopathy, or sudden death in infancy with hepatic steatosis, features suggestive of fatty acid oxidation disorders. Single-stranded conformational variance was used to screen genomic DNA. DNA sequencing and mutational analysis revealed 21 different mutations on the VLCAD gene in 18 patients. Of the mutations, 80% were associated with CM. Severe CM in infancy was recognized in most patients (67%) at presentation. Hepatic dysfunction was common (33%). RNA blot analysis and VLCAD enzyme assays showed a severe reduction in VLCAD mRNA in patients with frame-shift or splice-site mutations and absent or severe reduction in enzyme activity in all. Conclusions —Infantile CM is the most common clinical phenotype of VLCAD deficiency. Mutations in the human VLCAD gene are heterogeneous. Although mortality at presentation is high, both the metabolic disorder and cardiomyopathy are reversible.

SummaryWe report a 16‐month‐old asymptomatic male with enzyme confirmed isovaleric acidaemia (IVA; isovaleryl‐CoA dehydrogenase deficiency; OMIM 243500) who, upon routine nutritional follow‐up, presented evidence of peroxisomal dysfunction. The newborn screen (2 days of life) revealed elevated C5‐carnitine (2.95 μmol/L; cutoff <0.09 μmol/L) and IVA was subsequently confirmed by metabolic profiling and in vitro enzymology. Plasma essential fatty acid (EFA) analysis, assessed to evaluate nutritional status during protein restriction and l‐carnitine supplementation, revealed elevated C26:0 (5.0 μmol/L; normal <1.3). Subsequently, metabolic profiling and molecular genetic analysis confirmed X‐linked adrenoleukodystrophy (XALD). Identification of co‐inherited XALD with IVA in this currently asymptomatic patient holds significant treatment ramifications for the proband prior to the onset of neurological sequelae, and critically important counselling implications for this family.

We report 2 patients with isolated 3-methylcrotonyl-coenzyme A carboxylase deficiency whose urine was devoid of, or contained only trace, 3-methylcrotonylglycine, the pathognomonic marker for this disorder. The first patient, a girl with trisomy 21, was detected through newborn screening with an elevated 5 carbon hydroxycarnitine species level, and the second patient came to clinical attention at the age of 5 months because of failure to thrive and developmental delay. Investigation of urinary organic acids revealed an elevated 3-hydroxyisovaleric acid level but no demonstrable 3-methylcrotonylglycine in both patients. Enzyme studies in cultured fibroblasts confirmed isolated 3-methylcrotonyl-coenzyme A carboxylase deficiency with residual activities of 5% to 7% and 12% of the median control value, respectively. Incorporation of 14C-isovaleric acid into intact fibroblasts was essentially normal, showing that the overall pathway was at least partially functional and potentially explaining the absence of 3-methylcrotonylglycine in urine. Mutation analysis of the MCCA and MCCB genes revealed that both patients were compound heterozygous for a missense mutation, MCCB-c.1015G→A (p.V339M), and a second mutation that leads to undetectable MCCB messenger (poly A+) RNA. Absent or trace 3-methylcrotonylglycine levels in urine raises the potential for misdiagnosis in the clinical biochemical genetics laboratory based solely on urine organic acid analysis using combined gas chromatography-mass spectrometry.