Publications by authors named "Johan L K Van Hove"

70 Publications

Enantiomer-specific pharmacokinetics of D,L-3-hydroxybutyrate: Implications for the treatment of multiple acyl-CoA dehydrogenase deficiency.

J Inherit Metab Dis 2021 Feb 5. Epub 2021 Feb 5.

University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Section of Metabolic Diseases, Groningen, The Netherlands.

D,L-3-hydroxybutyrate (D,L-3-HB, a ketone body) treatment has been described in several inborn errors of metabolism, including multiple acyl-CoA dehydrogenase deficiency (MADD; glutaric aciduria type II). We aimed to improve the understanding of enantiomer-specific pharmacokinetics of D,L-3-HB. Using UPLC-MS/MS, we analyzed D-3-HB and L-3-HB concentrations in blood samples from three MADD patients, and blood and tissue samples from healthy rats, upon D,L-3-HB salt administration (patients: 736-1123 mg/kg/day; rats: 1579-6317 mg/kg/day of salt-free D,L-3-HB). D,L-3-HB administration caused substantially higher L-3-HB concentrations than D-3-HB. In MADD patients, both enantiomers peaked at 30 to 60 minutes, and approached baseline after 3 hours. In rats, D,L-3-HB administration significantly increased C and AUC of D-3-HB in a dose-dependent manner (controls vs ascending dose groups for C : 0.10 vs 0.30-0.35-0.50 mmol/L, and AUC: 14 vs 58-71-106 minutes*mmol/L), whereas for L-3-HB the increases were significant compared to controls, but not dose proportional (C : 0.01 vs 1.88-1.92-1.98 mmol/L, and AUC: 1 vs 380-454-479 minutes*mmol/L). L-3-HB concentrations increased extensively in brain, heart, liver, and muscle, whereas the most profound rise in D-3-HB was observed in heart and liver. Our study provides important knowledge on the absorption and distribution upon oral D,L-3-HB. The enantiomer-specific pharmacokinetics implies differential metabolic fates of D-3-HB and L-3-HB.
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http://dx.doi.org/10.1002/jimd.12365DOI Listing
February 2021

In Memoriam.

J Inherit Metab Dis 2021 Jan 22;44(1):286-287. Epub 2020 Dec 22.

Department of Pediatrics, Section of Clinical Genetics and Metabolism, University of Colorado, Anschutz Campus, Aurora, Colorado, USA.

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http://dx.doi.org/10.1002/jimd.12330DOI Listing
January 2021

Successful liver transplantation in hyperornithinemia-hyperammonemia-homocitrullinuria syndrome: Case report.

Pediatr Transplant 2020 Dec 14:e13943. Epub 2020 Dec 14.

Department of Pediatric Gastroenterology, Hepatology and Nutrition, Princess Elisabeth Children's Hospital, Ghent University Hospital, Ghent, Belgium.

Background: HHH syndrome is a rare autosomal recessive disorder of the urea cycle, caused by a deficient mitochondrial ornithine transporter. We report the first successful liver transplantation in HHH syndrome performed in a seven-year-old boy. The patient presented at 4 weeks of age with hyperammonemic coma. The plasma amino acid profile was suggestive of HHH syndrome, and the diagnosis was confirmed when sequencing of the SLC25A15 gene identified two mutations p.R275Q and p.A76D. Although immediate intervention resulted in normalization of plasma ammonia levels within 24 hours, he developed cerebral edema, coma, convulsions, and subsequent neurological sequelae. Metabolic control was difficult requiring severe protein restriction and continued treatment with sodium benzoate and L-arginine. Despite substantial developmental delay, he was referred to our center for liver transplantation because of poor metabolic control. Following cadaveric split liver transplantation, there was complete normalization of his plasma ammonia and plasma amino acid levels under a normal protein-containing diet. This excellent metabolic control was associated with a markedly improved general condition, mood and behavior, and small developmental achievements. Twelve years after liver transplantation, the patient has a stable cognitive impairment without progression of spastic diplegia.

Conclusion: This first case of liver transplantation in HHH syndrome demonstrates that this procedure is a therapeutic option for HHH patients with difficult metabolic control.
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http://dx.doi.org/10.1111/petr.13943DOI Listing
December 2020

A novel acceptor stem variant in mitochondrial tRNA impairs mitochondrial translation and is associated with a severe phenotype.

Mol Genet Metab 2020 12 24;131(4):398-404. Epub 2020 Nov 24.

Section of Clinical Genetics and Metabolism, Department of Pediatrics, University of Colorado, Aurora, CO, USA; Department of Pathology and Laboratory Medicine, Children's Hospital Colorado, 13121 East 16th Avenue, Aurora, CO, USA. Electronic address:

Genetic defects in mitochondrial DNA encoded tRNA genes impair mitochondrial translation with resultant defects in the mitochondrial respiratory chain and oxidative phosphorylation system. The phenotypic spectrum of disease seen in mitochondrial tRNA defects is variable and proving pathogenicity of new variants is challenging. Only three pathogenic variants have been described previously in the mitochondrial tRNA gene MT-TY, with the reported phenotypes consisting largely of adult onset myopathy and ptosis. We report a patient with a novel MT-TY acceptor stem variant m.5889A>G at high heteroplasmy in muscle, low in blood, and absent in the mother's blood. The phenotype consisted of a childhood-onset severe multi-system disorder characterized by a neurodegenerative course including ataxia and seizures, failure-to-thrive, combined myopathy and neuropathy, and hearing and vision loss. Brain imaging showed progressive atrophy and basal ganglia calcifications. Mitochondrial biomarkers lactate and GDF15 were increased. Functional studies showed a deficient activity of the respiratory chain enzyme complexes containing mtDNA-encoded subunits I, III and IV. There were decreased steady state levels of these mitochondrial complex proteins, and presence of incompletely assembled complex V forms in muscle. These changes are typical of a mitochondrial translational defect. These data support the pathogenicity of this novel variant. Careful review of variants in MT-TY additionally identified two other pathogenic variants, one likely pathogenic variant, nine variants of unknown significance, five likely benign and four benign variants.
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http://dx.doi.org/10.1016/j.ymgme.2020.11.006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7749820PMC
December 2020

Consensus guidelines for the diagnosis and management of pyridoxine-dependent epilepsy due to α-aminoadipic semialdehyde dehydrogenase deficiency.

J Inherit Metab Dis 2021 Jan 1;44(1):178-192. Epub 2020 Dec 1.

Department of Pediatrics Emma Children's Hospital, Amsterdam University Medical Centre, Amsterdam, The Netherlands.

Pyridoxine-dependent epilepsy (PDE-ALDH7A1) is an autosomal recessive condition due to a deficiency of α-aminoadipic semialdehyde dehydrogenase, which is a key enzyme in lysine oxidation. PDE-ALDH7A1 is a developmental and epileptic encephalopathy that was historically and empirically treated with pharmacologic doses of pyridoxine. Despite adequate seizure control, most patients with PDE-ALDH7A1 were reported to have developmental delay and intellectual disability. To improve outcome, a lysine-restricted diet and competitive inhibition of lysine transport through the use of pharmacologic doses of arginine have been recommended as an adjunct therapy. These lysine-reduction therapies have resulted in improved biochemical parameters and cognitive development in many but not all patients. The goal of these consensus guidelines is to re-evaluate and update the two previously published recommendations for diagnosis, treatment, and follow-up of patients with PDE-ALDH7A1. Members of the International PDE Consortium initiated evidence and consensus-based process to review previous recommendations, new research findings, and relevant clinical aspects of PDE-ALDH7A1. The guideline development group included pediatric neurologists, biochemical geneticists, clinical geneticists, laboratory scientists, and metabolic dieticians representing 29 institutions from 16 countries. Consensus guidelines for the diagnosis and management of patients with PDE-ALDH7A1 are provided.
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http://dx.doi.org/10.1002/jimd.12332DOI Listing
January 2021

The mitochondrial DNA variant m.9032T > C in MT-ATP6 encoding p.(Leu169Pro) causes a complex mitochondrial neurological syndrome.

Mitochondrion 2020 11 12;55:8-13. Epub 2020 Sep 12.

Section of Clinical Genetics and Metabolism, Department of Pediatrics, University of Colorado, Aurora, CO, USA; Department of Pathology and Laboratory Medicine, Children's Hospital Colorado, 13121 East 16th Avenue, Aurora, CO, USA. Electronic address:

Diagnosing complex V deficiencies caused by new variants in mitochondrial DNA is challenging due to the rarity, phenotypic diversity, and limited functional assessments. We describe a child with the m.9032T > C variant in MT-ATP6 encoding p.(Leu169Pro), with primary presentation of microcephaly, ataxia, hearing loss, and lactic acidosis. Functional studies reveal abnormal fragment F of complex V on blue native gel electrophoresis. Respirometry showed excessively tight coupling through complex V depressing oxygen consumption upon ADP stimulation and an excessive increase following uncoupling, in the presence of upregulation of mitochondrial biogenesis. These data add evidence about pathogenicity and functional impact of this variant.
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http://dx.doi.org/10.1016/j.mito.2020.08.009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7669648PMC
November 2020

The North American mitochondrial disease registry.

J Transl Genet Genom 2020 28;4:81-90. Epub 2020 Apr 28.

Department of Neurology, Columbia University Medical Center, New York, NY 10032, USA.

Aim: The North American Mitochondrial Disease Consortium (NAMDC) comprises a network of 17 clinical centers with a mission to conduct translational research on mitochondrial diseases. NAMDC is a part of the Rare Disease Clinical Research Network (RDCRN) and is funded by the National Institutes of Health. To foster its mission, NAMDC has implemented a comprehensive Mitochondrial Disease Clinical Registry (hereafter NAMDC Registry), collected biosamples deposited into the NAMDC Biorepository, defined phenotypes and genotypes of specific disorders, collected natural history data, identified outcome measures, characterized safety and long-term toxicity and efficacy of promising therapies, and trained young investigators interested in patient-oriented research in mitochondrial disease.

Methods: Research conducted by NAMDC is built on the foundation of the Clinical Registry. Data within the registry are encrypted and maintained in a centralized database at Columbia University Medical Center. In addition to clinical data, NAMDC has established a mitochondrial disease biorepository, collecting DNA, plasma, cell, and tissue samples. Specimens are assigned coded identifiers in compliance with all relevant regulatory entities and with emerging NIH guidelines for biorepositories. NAMDC funds two pilot projects each year. Pilot grants are small grants typically supporting an early stage concept to obtain preliminary data. Pilot grants must enhance and address major issues in mitochondrial medicine and specific areas of need for the field and for the successful outcome of NAMDC. The grant selection process is facilitated by input from multiple stakeholders including patient organizations and the strategic leadership of NAMDC. To train new mitochondrial disease investigators, NAMDC has established a Fellowship Program which offers a unique training opportunity to senior postdoctoral clinical fellows. The fellowship includes a 6-month period of intensive training in clinical trial methodology through the Clinical Research Enhancement through Supplemental Training program and equivalent programs at the other sites, along with rotations up to 3 months each to two additional consortium sites where a rich and varied training experience is provided. Nine core educational sites participate in this training program, each offering a summer grant program in mitochondrial medicine funded by our NAMDC partner the United Mitochondrial Disease Foundation (www.umdf.org). All clinical research in NAMDC depends on the participation of mitochondrial disease patients. Since individual mitochondrial disorders are often extremely rare, major communication and recruitment efforts are required. Therefore, NAMDC has forged a very close partnership with the premier patient advocacy group for mitochondrial diseases in North America, the United Mitochondrial Disease Foundation (UMDF).

Results: The NAMDC Registry has confirmed the clinical and genetical heterogeneity of mitochondrial diseases due to primary mutations in mitochondrial DNA or nuclear DNA. During the 8 years of this NIH-U54 grant, this consortium, acting in close collaboration with a patient advocacy group, the UMDF, has effectively addressed these complex diseases. NAMDC has expanded a powerful patient registry with more than 1600 patients enrolled to date, a website for education and recruitment of patients (www.namdc.org), a NAMDC biorepository housed at the Mayo Clinic in Rochester, MN, and essential diagnostic guidelines for consensus research. In addition, eight clinical studies have been initiated and the NAMDC fellowship program has been actively training the next generation of mitochondrial disease clinical investigators, of which six have completed the program and remain actively involved in mitochondrial disease research.

Conclusion: The NAMDC Patient Registry and Biorepository is actively facilitating mitochondrial disease research, and accelerating progress in the understanding and treatment of mitochondrial diseases.
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http://dx.doi.org/10.20517/jtgg.2020.12DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7323997PMC
April 2020

Improved lactate control with dichloroacetate in a case with severe neonatal lactic acidosis due to MTFMT mitochondrial translation disorder.

Mol Genet Metab Rep 2020 Sep 15;24:100616. Epub 2020 Jun 15.

Department of Medical Genetics and Pediatrics, Alberta Children's Hospital, Research Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.

Mitochondrial methionyl-tRNA formyltransferase () is a nuclear-encoded gene that produces a protein involved in mitochondrial translation. MTFMT formylates a portion of Met-tRNA, which allows for translation initiation of mitochondrial mRNA. Mutations in this gene have been shown to result in decreased mitochondrial translation with reduction function of the electron transport chain complexes I, III, IV, and V, thus affecting cellular energy production. Our patient presented with severe lactic acidosis in the neonatal period, and was found to be homozygous for the pathogenic mutation c.994C > T, p.(Arg332*). Her blood lactate levels normalized and her cardiomyopathy reversed after initiation of dichloroacetate (30 mg/kg/day). After two years of follow-up, she continues to show long-term lactate stability, continues to make developmental gains, and is in overall good general health. This is the first report using dichloroacetate in a patient with MTFMT deficiency, which may be a potential therapeutic option that warrants further study.
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http://dx.doi.org/10.1016/j.ymgmr.2020.100616DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7303673PMC
September 2020

Mitochondrial diseases in North America: An analysis of the NAMDC Registry.

Neurol Genet 2020 Apr 2;6(2):e402. Epub 2020 Mar 2.

Department of Neurology (E.B., V.E., S.D., K.E., X.Q.R., M.H.), Columbia University Medical Center, New York; Department of Biostatistics (Y.L., V.C., J.K., J. Grier, R.B., J.L.P.T.), Mailman School of Public Health, Columbia University, New York; Radboudumc (R.S.), Nijmegen, The Netherlands; Department of Pediatrics (B.H.C.), Northeast Ohio Medical University and Akron Children's Hospital; Genetics Unit (A.K.), Massachusetts General Hospital, Boston; Department of Pediatrics (G.D.V.), State University of New York at Buffalo; Departments of Neurosciences and Pediatrics (R.H.), University of California at San Diego; Department of Pediatrics (J.L.K.V.H., A.L.), University of Colorado School of Medicine, Aurora; Department of Molecular and Human Genetics (F.S.), Baylor College of Medicine, Houston, TX; Texas Children's Hospital (F.S.), Houston; Joint BCM-CUHK Center of Medical Genetics (F.S.), Prince of Wales Hospital, ShaTin, New Territories, Hong Kong; Department of Neurology (S.P.), Cleveland Clinic, OH; Departments of Genetics and Genome Sciences and Pediatrics (J.K.B., S.D.D.), and Center for Human Genetics, University Hospitals Cleveland Medical Center, Case Western Reserve University, OH; Departments of Neurology and Clinical Genomics (R.H.G.), Mayo Clinic, Rochester, MN; Department of Neurology (R.P.S.), University of Washington, Seattle Children's Hospital; Department of Pediatrics (G.M.E.), Stanford University, Palo Alto, CA; Department of Medicine (P.W.S.), University of Florida at Gainesville; Genetics and Genomic Sciences at the Icahn School of Medicine at Mount Sinai (J. Ganesh), New York; Mitochondrial Medicine Frontier Program (Z.Z.-C., M.J.F., A.C.G.), Division of Human Genetics, The Children's Hospital of Philadelphia and University of Pennsylvania Perelman School of Medicine; University of Pennsylvania Perelman School of Medicine (Z.Z.-C.), Philadelphia; Department of Neurology (M.T.), McMasters University, Toronto, Ontario, Canada; Department of Neurology (A.G.), Children's National Health Network, Washington, DC; Office of Dietary Supplements (K.C.), National Institutes of Health, Bethesda, MD; and Eunice Kennedy Shriver National Institute of Child Health and Human Development (D.K.), National Institutes of Health, Bethesda, MD.

Objective: To describe clinical, biochemical, and genetic features of participants with mitochondrial diseases (MtDs) enrolled in the North American Mitochondrial Disease Consortium (NAMDC) Registry.

Methods: This cross-sectional, multicenter, retrospective database analysis evaluates the phenotypic and molecular characteristics of participants enrolled in the NAMDC Registry from September 2011 to December 2018. The NAMDC is a network of 17 centers with expertise in MtDs and includes both adult and pediatric specialists.

Results: One thousand four hundred ten of 1,553 participants had sufficient clinical data for analysis. For this study, we included only participants with molecular genetic diagnoses (n = 666). Age at onset ranged from infancy to adulthood. The most common diagnosis was multisystemic disorder (113 participants), and only a minority of participants were diagnosed with a classical mitochondrial syndrome. The most frequent classical syndromes were Leigh syndrome (97 individuals) and mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (71 individuals). Pathogenic variants in the mitochondrial DNA were more frequently observed (414 participants) than pathogenic nuclear gene variants (252 participants). Pathogenic variants in 65 nuclear genes were identified, with and being the most commonly affected. Pathogenic variants in 38 genes were reported only in single participants.

Conclusions: The NAMDC Registry data confirm the high variability of clinical, biochemical, and genetic features of participants with MtDs. This study serves as an important resource for future enhancement of MtD research and clinical care by providing the first comprehensive description of participant with MtD in North America.
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http://dx.doi.org/10.1212/NXG.0000000000000402DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7164977PMC
April 2020

Treating neutropenia and neutrophil dysfunction in glycogen storage disease type Ib with an SGLT2 inhibitor.

Blood 2020 08;136(9):1033-1043

Groupe de Recherches Metaboliques, de Duve Institute, Université Catholique de Louvain, Brussels, Belgium.

Neutropenia and neutrophil dysfunction cause serious infections and inflammatory bowel disease in glycogen storage disease type Ib (GSD-Ib). Our discovery that accumulating 1,5-anhydroglucitol-6-phosphate (1,5AG6P) caused neutropenia in a glucose-6-phosphatase 3 (G6PC3)-deficient mouse model and in 2 rare diseases (GSD-Ib and G6PC3 deficiency) led us to repurpose the widely used antidiabetic drug empagliflozin, an inhibitor of the renal glucose cotransporter sodium glucose cotransporter 2 (SGLT2). Off-label use of empagliflozin in 4 GSD-Ib patients with incomplete response to granulocyte colony-stimulating factor (GCSF) treatment decreased serum 1,5AG and neutrophil 1,5AG6P levels within 1 month. Clinically, symptoms of frequent infections, mucosal lesions, and inflammatory bowel disease resolved, and no symptomatic hypoglycemia was observed. GCSF could be discontinued in 2 patients and tapered by 57% and 81%, respectively, in the other 2. The fluctuating neutrophil numbers in all patients were increased and stabilized. We further demonstrated improved neutrophil function: normal oxidative burst (in 3 of 3 patients tested), corrected protein glycosylation (2 of 2), and normal neutrophil chemotaxis (1 of 1), and bactericidal activity (1 of 1) under treatment. In summary, the glucose-lowering SGLT2 inhibitor empagliflozin, used for type 2 diabetes, was successfully repurposed for treating neutropenia and neutrophil dysfunction in the rare inherited metabolic disorder GSD-Ib without causing symptomatic hypoglycemia. We ascribe this to an improvement in neutrophil function resulting from the reduction of the intracellular concentration of 1,5AG6P.
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http://dx.doi.org/10.1182/blood.2019004465DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7530374PMC
August 2020

Successful liver transplantation in mitochondrial neurogastrointestinal encephalomyopathy (MNGIE).

Mol Genet Metab 2020 05 6;130(1):58-64. Epub 2020 Mar 6.

Department of Pediatrics, Section of Genetics and Metabolism, University of Colorado School of Medicine, Aurora, CO, USA. Electronic address:

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a fatal disorder characterized by progressive gastrointestinal dysmotility, peripheral neuropathy, leukoencephalopathy, skeletal myopathy, ophthalmoparesis, and ptosis. MNGIE stems from deficient thymidine phosphorylase activity (TP) leading to toxic elevations of plasma thymidine. Hematopoietic stem cell transplant (HSCT) restores TP activity and halts disease progression but has high transplant-related morbidity and mortality. Liver transplant (LT) was reported to restore TP activity in two adult MNGIE patients. We report successful LT in four additional MNGIE patients, including a pediatric patient. Our patients were diagnosed between ages 14 months and 36 years with elevated thymidine levels and biallelic pathogenic variants in TYMP. Two patients presented with progressive gastrointestinal dysmotility, and three demonstrated progressive peripheral neuropathy with two suffering limitations in ambulation. Two patients, including the child, had liver dysfunction and cirrhosis. Following LT, thymidine levels nearly normalized in all four patients and remained low for the duration of follow-up. Disease symptoms stabilized in all patients, with some manifesting improvements, including intestinal function. No patient died, and LT appeared to have a more favorable safety profile than HSCT, especially when liver disease is present. Follow-up studies will need to document the long-term impact of this new approach on disease outcome. Take Home Message: Liver transplantation is effective in stabilizing symptoms and nearly normalizing thymidine levels in patients with mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) and may have an improved safety profile over hematopoietic stem cell transplant.
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http://dx.doi.org/10.1016/j.ymgme.2020.03.001DOI Listing
May 2020

Pathogenic variants in SQOR encoding sulfide:quinone oxidoreductase are a potentially treatable cause of Leigh disease.

J Inherit Metab Dis 2020 09 15;43(5):1024-1036. Epub 2020 Apr 15.

Section of Clinical Genetics and Metabolism, Department of Pediatrics, University of Colorado, Aurora, Colorado.

Hydrogen sulfide, a signaling molecule formed mainly from cysteine, is catabolized by sulfide:quinone oxidoreductase (gene SQOR). Toxic hydrogen sulfide exposure inhibits complex IV. We describe children of two families with pathogenic variants in SQOR. Exome sequencing identified variants; SQOR enzyme activity was measured spectrophotometrically, protein levels evaluated by western blotting, and mitochondrial function was assayed. In family A, following a brief illness, a 4-year-old girl presented comatose with lactic acidosis and multiorgan failure. After stabilization, she remained comatose, hypotonic, had neurostorming episodes, elevated lactate, and Leigh-like lesions on brain imaging. She died shortly after. Her 8-year-old sister presented with a rapidly fatal episode of coma with lactic acidosis, and lesions in the basal ganglia and left cortex. Muscle and liver tissue had isolated decreased complex IV activity, but normal complex IV protein levels and complex formation. Both patients were homozygous for c.637G > A, which we identified as a founder mutation in the Lehrerleut Hutterite with a carrier frequency of 1 in 13. The resulting p.Glu213Lys change disrupts hydrogen bonding with neighboring residues, resulting in severely reduced SQOR protein and enzyme activity, whereas sulfide generating enzyme levels were unchanged. In family B, a boy had episodes of encephalopathy and basal ganglia lesions. He was homozygous for c.446delT and had severely reduced fibroblast SQOR enzyme activity and protein levels. SQOR dysfunction can result in hydrogen sulfide accumulation, which, consistent with its known toxicity, inhibits complex IV resulting in energy failure. In conclusion, SQOR deficiency represents a new, potentially treatable, cause of Leigh disease.
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http://dx.doi.org/10.1002/jimd.12232DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7484123PMC
September 2020

Pathogenic variants in NUBPL result in failure to assemble the matrix arm of complex I and cause a complex leukoencephalopathy with thalamic involvement.

Mol Genet Metab 2020 03 30;129(3):236-242. Epub 2019 Dec 30.

Department of Pediatrics, Section of Clinical Genetics and Metabolism, University of Colorado, RC1-N P18-4404K, 12800 East 19th Avenue, Aurora, CO 80045, USA; Department of Pathology and Laboratory Medicine, Children's Hospital Colorado, 13121 East 16th Avenue, Aurora, CO 80045, USA. Electronic address:

Disorders of the white matter are genetically very heterogeneous including several genes involved in mitochondrial bioenergetics. Diagnosis of the underlying cause is aided by pattern recognition on neuroimaging and by next-generation sequencing. Recently, genetic changes in the complex I assembly factor NUBPL have been characterized by a consistent recognizable pattern of leukoencephalopathy affecting deep white matter including the corpus callosum and cerebellum. Here, we report twin boys with biallelic variants in NUBPL, an unreported c.351 G > A; p.(Met117Ile) and a previously reported pathological variant c. 693 + 1 G > A. Brain magnetic resonance imaging showed abnormal T2 hyperintense signal involving the periventricular white matter, external capsule, corpus callosum, and, prominently, the bilateral thalami. The neuroimaging pattern evolved over 18 months with marked diffuse white matter signal abnormality, volume loss, and new areas of signal abnormality in the cerebellar folia and vermis. Magnetic resonance spectroscopy showed elevated lactate. Functional studies in cultured fibroblasts confirmed pathogenicity of the genetic variants. Complex I activity of the respiratory chain was deficient spectrophotometrically and on blue native gel with in-gel activity staining. There was absent assembly and loss of proteins of the matrix arm of complex I when traced with an antibody to NDUFS2, and incomplete assembly of the membrane arm when traced with an NDUFB6 antibody. There was decreased NUBPL protein on Western blot in patient fibroblasts compared to controls. Compromised NUBPL activity impairs assembly of the matrix arm of complex I and produces a severe, rapidly-progressive leukoencephalopathy with thalamic involvement on MRI, further expanding the neuroimaging phenotype.
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http://dx.doi.org/10.1016/j.ymgme.2019.12.013DOI Listing
March 2020

Efficacy and safety of D,L-3-hydroxybutyrate (D,L-3-HB) treatment in multiple acyl-CoA dehydrogenase deficiency.

Genet Med 2020 05 6;22(5):908-916. Epub 2020 Jan 6.

Section of Metabolic Diseases, University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, Groningen, The Netherlands.

Purpose: Multiple acyl-CoA dehydrogenase deficiency (MADD) is a life-threatening, ultrarare inborn error of metabolism. Case reports described successful D,L-3-hydroxybutyrate (D,L-3-HB) treatment in severely affected MADD patients, but systematic data on efficacy and safety is lacking.

Methods: A systematic literature review and an international, retrospective cohort study on clinical presentation, D,L-3-HB treatment method, and outcome in MADD(-like) patients.

Results: Our study summarizes 23 MADD(-like) patients, including 14 new cases. Median age at clinical onset was two months (interquartile range [IQR]: 8 months). Median age at starting D,L-3-HB was seven months (IQR: 4.5 years). D,L-3-HB doses ranged between 100 and 2600 mg/kg/day. Clinical improvement was reported in 16 patients (70%) for cardiomyopathy, leukodystrophy, liver symptoms, muscle symptoms, and/or respiratory failure. D,L-3-HB appeared not effective for neuropathy. Survival appeared longer upon D,L-3-HB compared with historical controls. Median time until first clinical improvement was one month, and ranged up to six months. Reported side effects included abdominal pain, constipation, dehydration, diarrhea, and vomiting/nausea. Median D,L-3-HB treatment duration was two years (IQR: 6 years). D,L-3-HB treatment was discontinued in 12 patients (52%).

Conclusion: The strength of the current study is the international pooling of data demonstrating that D,L-3-HB treatment can be effective and safe in MADD(-like) patients.
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http://dx.doi.org/10.1038/s41436-019-0739-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7200590PMC
May 2020

Hybrid gel electrophoresis using skin fibroblasts to aid in diagnosing mitochondrial disease.

Neurol Genet 2019 Jun 1;5(3):e336. Epub 2019 May 1.

Department of Medical Genetics (C.N., A.K., D.S.) and Department of Pediatrics (A.K.), Alberta Children's Hospital Research Institute, Cumming School of Medicine, University of Calgary, Canada; Atlanta (J. Shoffner), GA; Departments of Pediatrics (M.W.F., J.L.K.V.H.), Section of Clinical Genetics and Metabolism, University of Colorado; Department of Medical Genetics (S.H.), University of Alberta, Canada; Faculty of Kinesiology (J. Shearer), University of Calgary, Alberta, Canada; and Departments of Laboratory Medicine and Pathology (I.S.), University of Alberta, Edmonton, Canada.

Objective: We developed a novel, hybrid method combining both blue-native (BN-PAGE) and clear-native (CN-PAGE) polyacrylamide gel electrophoresis, termed BCN-PAGE, to perform in-gel activity stains on the mitochondrial electron transport chain (ETC) complexes in skin fibroblasts.

Methods: Four patients aged 46-65 years were seen in the Metabolic Clinic at Alberta Children's Hospital and investigated for mitochondrial disease and had BN-PAGE or CN-PAGE on skeletal muscle that showed incomplete assembly of complex V (CV) in each patient. Long-range PCR performed on muscle-extracted DNA identified 4 unique mitochondrial DNA (mtDNA) deletions spanning the gene of CV. We developed a BCN-PAGE method in skin fibroblasts taken from the patients at the same time and compared the findings with those in skeletal muscle.

Results: In all 4 cases, BCN-PAGE in skin fibroblasts confirmed the abnormal CV activity found from muscle biopsy, suggesting that the mtDNA deletions involving were most likely germline mutations that are associated with a clinical phenotype of mitochondrial disease.

Conclusions: The BCN-PAGE method in skin fibroblasts has a potential to be a less-invasive tool compared with muscle biopsy to screen patients for abnormalities in CV and other mitochondrial ETC complexes.
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http://dx.doi.org/10.1212/NXG.0000000000000336DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6515941PMC
June 2019

Biomarkers of oxidative stress, inflammation, and vascular dysfunction in inherited cystathionine β-synthase deficient homocystinuria and the impact of taurine treatment in a phase 1/2 human clinical trial.

J Inherit Metab Dis 2019 05 11;42(3):424-437. Epub 2019 Apr 11.

Department of Pediatrics, School of Medicine, University of Colorado, Aurora, Colorado.

Study Objective: A phase 1/2 clinical trial was performed in individuals with cystathionine β synthase (CBS) deficient homocystinuria with aims to: (a) assess pharmacokinetics and safety of taurine therapy, (b) evaluate oxidative stress, inflammation, and vascular function in CBS deficiency, and (c) evaluate the impact of short-term taurine treatment.

Methods: Individuals with pyridoxine-nonresponsive CBS deficiency with homocysteine >50 μM, without inflammatory disorder or on antioxidant therapy were enrolled. Biomarkers of oxidative stress and inflammation, endothelial function (brachial artery flow-mediated dilation [FMD]), and disease-related metabolites obtained at baseline were compared to normal values. While maintaining current treatment, patients were treated with 75 mg/kg taurine twice daily, and treatment response assessed after 4 hours and 4 days.

Results: Fourteen patients (8-35 years; 8 males, 6 females) were enrolled with baseline homocysteine levels 161 ± 67 μM. The study found high-dose taurine to be safe when excluding preexisting hypertriglyceridemia. Taurine pharmacokinetics showed a rapid peak level returning to near normal levels at 12 hours, but had slow accumulation and elevated predosing levels after 4 days of treatment. Only a single parameter of oxidative stress, 2,3-dinor-8-isoprostaglandin-F2α, was elevated at baseline, with no elevated inflammatory parameters, and no change in FMD values overall. Taurine had no effect on any of these parameters. However, the effect of taurine was strongly related to pretreatment FMD values; and taurine significantly improved FMD in the subset of individuals with pretreatment FMD values <10% and in individuals with homocysteine levels >125 μM, pertinent to endothelial function.

Conclusion: Taurine improves endothelial function in CBS-deficient homocystinuria in patients with preexisting reduced function.
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http://dx.doi.org/10.1002/jimd.12085DOI Listing
May 2019

Brain imaging in classic nonketotic hyperglycinemia: Quantitative analysis and relation to phenotype.

J Inherit Metab Dis 2019 05 20;42(3):438-450. Epub 2019 Mar 20.

Department of Pediatrics, Section of Clinical Genetics and Metabolism, University of Colorado, Aurora, Colorado.

Patients with severe nonketotic hyperglycinemia (NKH) have absent psychomotor development and intractable epilepsy, whereas attenuated patients have variable psychomotor development and absent or treatable epilepsy; differences in brain magnetic resonance imaging (MRI) between phenotypes have not been reported. In a retrospective cross-sectional study, we reviewed 38 MRI studies from 24 molecularly proven NKH patients, and 2 transient NKH patients. Quantitative analyses included corpus callosum size, apparent diffusion coefficient, automated brain volumetric analysis, and glycine/creatine ratio by spectroscopy. All patients age <3 months had restricted diffusion in the posterior limb of the internal capsule, anterior brainstem, posterior tegmental tracts, and cerebellum, not present in transient NKH. In older infants, the pattern evolved and included generalized diffusion restriction in the supratentorial white matter, which quantitatively peaked between 3 and 12 months. No patient had absent corpus callosum or gyral malformation. The corpus callosum was relatively short in severe compared to attenuated phenotypes, and thin in severe cases only. The corpus callosum growth rate differed by severity; age-matched Z-scores of thickness worsened in severe cases only. Cerebral volume was decreased in the hippocampus, globus pallidus, cerebral cortex, thalamus, and cerebellum. Severe patients had greatest glycine/creatine ratios. In this study, no brain malformations were identified. The growth failure of the corpus callosum is worse in severe NKH, whereas the diffusion restriction pattern, reflecting microspongiosis, does not discriminate by phenotypic severity. NKH is therefore a disorder of brain growth best recognized in the corpus callosum, whereas spongiosis is not prognostic.
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http://dx.doi.org/10.1002/jimd.12072DOI Listing
May 2019

Identification of a novel biomarker for pyridoxine-dependent epilepsy: Implications for newborn screening.

J Inherit Metab Dis 2019 05 11;42(3):565-574. Epub 2019 Mar 11.

Department of Pediatrics, Section of Clinical Genetics and Metabolism, University of Colorado School of Medicine, Aurora, Colorado.

Pyridoxine-dependent epilepsy (PDE) is often characterized as an early onset epileptic encephalopathy with dramatic clinical improvement following pyridoxine supplementation. Unfortunately, not all patients present with classic neonatal seizures or respond to an initial pyridoxine trial, which can result in the under diagnosis of this treatable disorder. Restriction of lysine intake and transport is associated with improved neurologic outcomes, although treatment should be started in the first year of life to be effective. Because of the documented diagnostic delay and benefit of early treatment, we aimed to develop a newborn screening method for PDE. Previous studies have demonstrated the accumulation of Δ -piperideine-6-carboxylate and α-aminoadipic semialdehyde in individuals with PDE, although these metabolites are unstable at room temperature (RT) limiting their utility for newborn screening. As a result, we sought to identify a biomarker that could be applied to current newborn screening paradigms. We identified a novel metabolite, 6-oxo-pipecolate (6-oxo-PIP), which accumulates in substantial amounts in blood, plasma, urine, and cerebral spinal fluid of individuals with PDE. Using a stable isotope-labeled internal standard, we developed a nonderivatized liquid chromatography tandem mass spectrometry-based method to quantify 6-oxo-PIP. This method replicates the analytical techniques used in many laboratories and could be used with few modifications in newborn screening programs. Furthermore, 6-oxo-PIP was measurable in urine for 4 months even when stored at RT. Herein, we report a novel biomarker for PDE that is stable at RT and can be quantified using current newborn screening techniques.
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http://dx.doi.org/10.1002/jimd.12059DOI Listing
May 2019

Pathogenic variants in glutamyl-tRNA amidotransferase subunits cause a lethal mitochondrial cardiomyopathy disorder.

Nat Commun 2018 10 3;9(1):4065. Epub 2018 Oct 3.

Section of Clinical Genetics and Metabolism, Department of Pediatrics, University of Colorado, Aurora, 80045, CO, USA.

Mitochondrial protein synthesis requires charging mt-tRNAs with their cognate amino acids by mitochondrial aminoacyl-tRNA synthetases, with the exception of glutaminyl mt-tRNA (mt-tRNA). mt-tRNA is indirectly charged by a transamidation reaction involving the GatCAB aminoacyl-tRNA amidotransferase complex. Defects involving the mitochondrial protein synthesis machinery cause a broad spectrum of disorders, with often fatal outcome. Here, we describe nine patients from five families with genetic defects in a GatCAB complex subunit, including QRSL1, GATB, and GATC, each showing a lethal metabolic cardiomyopathy syndrome. Functional studies reveal combined respiratory chain enzyme deficiencies and mitochondrial dysfunction. Aminoacylation of mt-tRNA and mitochondrial protein translation are deficient in patients' fibroblasts cultured in the absence of glutamine but restore in high glutamine. Lentiviral rescue experiments and modeling in S. cerevisiae homologs confirm pathogenicity. Our study completes a decade of investigations on mitochondrial aminoacylation disorders, starting with DARS2 and ending with the GatCAB complex.
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http://dx.doi.org/10.1038/s41467-018-06250-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6170436PMC
October 2018

The genotypic spectrum of ALDH7A1 mutations resulting in pyridoxine dependent epilepsy: A common epileptic encephalopathy.

J Inherit Metab Dis 2019 03 22;42(2):353-361. Epub 2019 Feb 22.

Section of Clinical Genetics and Metabolism, Department of Pediatrics, University of Colorado School of Medicine, Aurora, Colorado, USA.

Pyridoxine dependent epilepsy (PDE) is a treatable epileptic encephalopathy characterized by a positive response to pharmacologic doses of pyridoxine. Despite seizure control, at least 75% of individuals have intellectual disability and developmental delay. Current treatment paradigms have resulted in improved cognitive outcomes emphasizing the importance of an early diagnosis. As genetic testing is increasingly accepted as first tier testing for epileptic encephalopathies, we aimed to provide a comprehensive overview of ALDH7A1 mutations that cause PDE. The genotypes, ethnic origin and reported gender was collected from 185 subjects with a diagnosis of PDE. The population frequency for the variants in this report and the existing literature were reviewed in the Genome Aggregation Database (gnomAD). Novel variants identified in population databases were also evaluated through in silico prediction software and select variants were over-expressed in an E.coli-based expression system to measure α-aminoadipic semialdehyde dehydrogenase activity and production of α-aminoadipic acid. This study adds 47 novel variants to the literature resulting in a total of 165 reported pathogenic variants. Based on this report, in silico predictions, and general population data, we estimate an incidence of approximately 1:64,352 live births. This report provides a comprehensive overview of known ALDH7A1 mutations that cause PDE, and suggests that PDE may be more common than initially estimated. Due to the relative high frequency of the disease, the likelihood of under-diagnosis given the wide clinical spectrum and limited awareness among clinicians as well as the cognitive improvement noted with early treatment, newborn screening for PDE may be warranted.
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http://dx.doi.org/10.1002/jimd.12045DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6345606PMC
March 2019

In memoriam.

J Inherit Metab Dis 2018 May 7. Epub 2018 May 7.

University of Colorado and Children's Hospital Colorado, Aurora, CO, USA.

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http://dx.doi.org/10.1007/s10545-018-0191-2DOI Listing
May 2018

COQ2 nephropathy: a treatable cause of nephrotic syndrome in children.

Pediatr Nephrol 2018 07 10;33(7):1257-1261. Epub 2018 Apr 10.

Department of Pediatrics, Division of Genetic Medicine, Seattle Children's Hospital and University of Washington, Seattle, WA, USA.

Background: Nephrotic syndrome can be caused by a subgroup of mitochondrial diseases classified as primary coenzyme Q (CoQ) deficiency. Pathogenic COQ2 variants are a cause of primary CoQ deficiency and present with phenotypes ranging from isolated nephrotic syndrome to fatal multisystem disease.

Case-diagnosis/treatment: We report three pediatric patients with COQ2 variants presenting with nephrotic syndrome. Two of these patients had normal leukocyte CoQ levels prior to treatment. Pathologic findings varied from mesangial sclerosis to focal segmental glomerulosclerosis, with all patients having abnormal appearing mitochondria on kidney biopsy. In two of the three patients treated with CoQ supplementation, the nephrotic syndrome resolved; and at follow-up, both have normal renal function and stable proteinuria.

Conclusions: COQ2 nephropathy should be suspected in patients presenting with nephrotic syndrome, although less common than disease due to mutations in NPHS1, NPHS2, and WT1. The index of suspicion should remain high, and we suggest that providers consider genetic evaluation even in patients with normal leukocyte CoQ levels, as levels may be within normal range even with significant clinical disease. Early molecular diagnosis and specific treatment are essential in the management of this severe yet treatable condition.
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http://dx.doi.org/10.1007/s00467-018-3937-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5990461PMC
July 2018

Mutations in PMPCB Encoding the Catalytic Subunit of the Mitochondrial Presequence Protease Cause Neurodegeneration in Early Childhood.

Am J Hum Genet 2018 04 22;102(4):557-573. Epub 2018 Mar 22.

Department of Neuropediatrics, Christian-Albrechts-University of Kiel, Kiel 24105, Germany; Division of Neurology, The Children's Hospital of Philadelphia, Philadelphia, PA 19104, USA. Electronic address:

Mitochondrial disorders causing neurodegeneration in childhood are genetically heterogeneous, and the underlying genetic etiology remains unknown in many affected individuals. We identified biallelic variants in PMPCB in individuals of four families including one family with two affected siblings with neurodegeneration and cerebellar atrophy. PMPCB encodes the catalytic subunit of the essential mitochondrial processing protease (MPP), which is required for maturation of the majority of mitochondrial precursor proteins. Mitochondria isolated from two fibroblast cell lines and induced pluripotent stem cells derived from one affected individual and differentiated neuroepithelial stem cells showed reduced PMPCB levels and accumulation of the processing intermediate of frataxin, a sensitive substrate for MPP dysfunction. Introduction of the identified PMPCB variants into the homologous S. cerevisiae Mas1 protein resulted in a severe growth and MPP processing defect leading to the accumulation of mitochondrial precursor proteins and early impairment of the biogenesis of iron-sulfur clusters, which are indispensable for a broad range of crucial cellular functions. Analysis of biopsy materials of an affected individual revealed changes and decreased activity in iron-sulfur cluster-containing respiratory chain complexes and dysfunction of mitochondrial and cytosolic Fe-S cluster-dependent enzymes. We conclude that biallelic mutations in PMPCB cause defects in MPP proteolytic activity leading to dysregulation of iron-sulfur cluster biogenesis and triggering a complex neurological phenotype of neurodegeneration in early childhood.
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http://dx.doi.org/10.1016/j.ajhg.2018.02.014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5985287PMC
April 2018

Biallelic Mutations in ATP5F1D, which Encodes a Subunit of ATP Synthase, Cause a Metabolic Disorder.

Am J Hum Genet 2018 03 22;102(3):494-504. Epub 2018 Feb 22.

Center for Undiagnosed Diseases, Stanford University, Stanford, CA 94305, USA; Department of Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA. Electronic address:

ATP synthase, H transporting, mitochondrial F1 complex, δ subunit (ATP5F1D; formerly ATP5D) is a subunit of mitochondrial ATP synthase and plays an important role in coupling proton translocation and ATP production. Here, we describe two individuals, each with homozygous missense variants in ATP5F1D, who presented with episodic lethargy, metabolic acidosis, 3-methylglutaconic aciduria, and hyperammonemia. Subject 1, homozygous for c.245C>T (p.Pro82Leu), presented with recurrent metabolic decompensation starting in the neonatal period, and subject 2, homozygous for c.317T>G (p.Val106Gly), presented with acute encephalopathy in childhood. Cultured skin fibroblasts from these individuals exhibited impaired assembly of FF ATP synthase and subsequent reduced complex V activity. Cells from subject 1 also exhibited a significant decrease in mitochondrial cristae. Knockdown of Drosophila ATPsynδ, the ATP5F1D homolog, in developing eyes and brains caused a near complete loss of the fly head, a phenotype that was fully rescued by wild-type human ATP5F1D. In contrast, expression of the ATP5F1D c.245C>T and c.317T>G variants rescued the head-size phenotype but recapitulated the eye and antennae defects seen in other genetic models of mitochondrial oxidative phosphorylation deficiency. Our data establish c.245C>T (p.Pro82Leu) and c.317T>G (p.Val106Gly) in ATP5F1D as pathogenic variants leading to a Mendelian mitochondrial disease featuring episodic metabolic decompensation.
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http://dx.doi.org/10.1016/j.ajhg.2018.01.020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6117612PMC
March 2018

Correction: The genetic basis of classic nonketotic hyperglycinemia due to mutations in GLDC and AMT.

Genet Med 2018 09;20(9):1098

Section of Genetics, Department of Pediatrics, University of Colorado School of Medicine, Aurora, Colorado, USA.

The original supplementary information included with this article contained several minor errors. Corrected Supplementary Information accompanies this corrigendum.
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http://dx.doi.org/10.1038/gim.2017.232DOI Listing
September 2018

Comment on Late-Onset Nonketotic Hyperglycinemia With a Heterozygous Novel Point Mutation of the GLDC Gene.

Pediatr Neurol 2018 02 28;79:e1. Epub 2017 Sep 28.

Department of Pediatrics, Section of Clinical Genetics and Metabolism, University of Colorado School of Medicine, Aurora, CO 80045, USA.. Electronic address:

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http://dx.doi.org/10.1016/j.pediatrneurol.2017.09.014DOI Listing
February 2018

d-Glyceric aciduria does not cause nonketotic hyperglycinemia: A historic co-occurrence.

Mol Genet Metab 2017 06 20;121(2):80-82. Epub 2017 Apr 20.

Bioanalytics & Biochemistry, Department of Natural Sciences, Bonn-Rhein-Sieg University of Applied Sciences, von-Liebig-Str. 20, 53359 Rheinbach, Germany. Electronic address:

Historically, d-glyceric aciduria was thought to cause an uncharacterized blockage to the glycine cleavage enzyme system (GCS) causing nonketotic hyperglycinemia (NKH) as a secondary phenomenon. This inference was reached based on the clinical and biochemical results from the first d-glyceric aciduria patient reported in 1974. Along with elevated glyceric acid excretion, this patient exhibited severe neurological symptoms of myoclonic epilepsy and absent development, and had elevated glycine levels and decreased glycine cleavage system enzyme activity. Mutations in the GLYCTK gene (encoding d-glycerate kinase) causing glyceric aciduria were previously noted. Since glycine changes were not observed in almost all of the subsequently reported cases of d-glyceric aciduria, this theory of NKH as a secondary syndrome of d-glyceric aciduria was revisited in this work. We showed that this historic patient harbored a homozygous missense mutation in AMT c.350C>T, p.Ser117Leu, and enzymatic assay of the expressed mutation confirmed the pathogeneity of the p.Ser117Leu mutation. We conclude that the original d-glyceric aciduria patient also had classic NKH and that this co-occurrence of two inborn errors of metabolism explains the original presentation. We conclude that no evidence remains that d-glyceric aciduria would cause NKH.
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http://dx.doi.org/10.1016/j.ymgme.2017.04.009DOI Listing
June 2017

X-Linked Cobalamin Disorder (HCFC1) Mimicking Nonketotic Hyperglycinemia With Increased Both Cerebrospinal Fluid Glycine and Methylmalonic Acid.

Pediatr Neurol 2017 Jun 7;71:65-69. Epub 2017 Jan 7.

Department of Pediatrics, University of Colorado, School of Medicine, Aurora, Colorado. Electronic address:

Background: Autosomal recessive or X-linked inborn errors of intracellular cobalamin metabolism can lead to methylmalonic aciduria and homocystinuria. In neonates, both increased cerebrospinal fluid glycine and cerebrospinal fluid/plasma glycine ratio are biochemical features of nonketotic hyperglycinemia.

Methods: We describe a boy presenting in the neonatal period with hypotonia, tonic, clonic, and later myoclonic seizures, subsequently evolving into refractory epilepsy and severe neurocognitive impairment.

Results: Increased cerebrospinal fluid glycine and cerebrospinal fluid to plasma glycine ratio were indicative of nonketotic hyperglycinemia. Early magnetic resonance imaging showed restricted diffusion and decreased apparent diffusion coefficient values in posterior limb of internal capsules and later in entire internal capsules and posterior white matter. Sequencing did not show a mutation in AMT, GLDC, or GCSH. Biochemical analysis identified persistently increased cerebrospinal fluid levels of glycine and methylmalonic acid and increased urinary methylmalonic acid and plasma homocysteine levels, which improved on higher parenteral hydroxocobalamin dose. Exome sequencing identified a known pathogenic sequence variant in X-linked cobalamin (HCFC1), c.344C>T, p. Ala115Val. In addition, a hemizygous mutation was found in the ATRX (c. 2728A>G, p. Lys910Glu). Retrospective review of two other patients with X-linked cobalamin deficiency also identified increased cerebrospinal fluid glycine levels.

Conclusions: This boy had X-linked cobalamin deficiency (HCFC1) with increased cerebrospinal fluid glycine and methylmalonic acid and increased cerebrospinal fluid to plasma glycine ratio suggesting a brain hyperglycinemia. Putative binding sites for HCFC1 and its binding partner THAP11 were identified near genes of the glycine cleavage enzyme, providing a potential mechanistic link between HCFC1 mutations and increased glycine.
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http://dx.doi.org/10.1016/j.pediatrneurol.2016.12.003DOI Listing
June 2017

Nonketotic hyperglycinemia: Functional assessment of missense variants in GLDC to understand phenotypes of the disease.

Hum Mutat 2017 06 20;38(6):678-691. Epub 2017 Mar 20.

Centro de Diagnóstico de Enfermedades Moleculares, Centro de Biología Molecular Severo Ochoa, CBM-CSIC, Departamento de Biología Molecular, Universidad Autónoma Madrid, Centro de Investigación Biomédica en Red de Enfermedades Raras (CIBERER), IDIPAZ, Madrid, Spain.

The rapid analysis of genomic data is providing effective mutational confirmation in patients with clinical and biochemical hallmarks of a specific disease. This is the case for nonketotic hyperglycinemia (NKH), a Mendelian disorder causing seizures in neonates and early-infants, primarily due to mutations in the GLDC gene. However, understanding the impact of missense variants identified in this gene is a major challenge for the application of genomics into clinical practice. Herein, a comprehensive functional and structural analysis of 19 GLDC missense variants identified in a cohort of 26 NKH patients was performed. Mutant cDNA constructs were expressed in COS7 cells followed by enzymatic assays and Western blot analysis of the GCS P-protein to assess the residual activity and mutant protein stability. Structural analysis, based on molecular modeling of the 3D structure of GCS P-protein, was also performed. We identify hypomorphic variants that produce attenuated phenotypes with improved prognosis of the disease. Structural analysis allows us to interpret the effects of mutations on protein stability and catalytic activity, providing molecular evidence for clinical outcome and disease severity. Moreover, we identify an important number of mutants whose loss-of-functionality is associated with instability and, thus, are potential targets for rescue using folding therapeutic approaches.
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http://dx.doi.org/10.1002/humu.23208DOI Listing
June 2017

Activation of a cryptic splice site in the mitochondrial elongation factor GFM1 causes combined OXPHOS deficiency.

Mitochondrion 2017 05 12;34:84-90. Epub 2017 Feb 12.

Division of Metabolic Disorders, CHOC Children's, Orange, CA, USA; Department of Pediatrics, University of California Irvine, Irvine, CA, USA. Electronic address:

We report the clinical, biochemical, and molecular findings in two brothers with encephalopathy and multi-systemic disease. Abnormal transferrin glycoforms were suggestive of a type I congenital disorder of glycosylation (CDG). While exome sequencing was negative for CDG related candidate genes, the testing revealed compound heterozygous mutations in the mitochondrial elongation factor G gene (GFM1). One of the mutations had been reported previously while the second, novel variant was found deep in intron 6, activating a cryptic splice site. Functional studies demonstrated decreased GFM1 protein levels, suggested disrupted assembly of mitochondrial complexes III and V and decreased activities of mitochondrial complexes I and IV, all indicating combined OXPHOS deficiency.
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http://dx.doi.org/10.1016/j.mito.2017.02.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5444868PMC
May 2017