title: Leigh-Like Syndrome Due to Homoplasmic m.8993T>G Variant with Hypocitrullinemia and Unusual Biochemical Features Suggestive of Multiple Carboxylase Deficiency (MCD).
abstract: Leigh syndrome (LS), or subacute necrotizing encephalomyelopathy, is a genetically heterogeneous, relentlessly progressive, devastating neurodegenerative disorder that usually presents in infancy or early childhood. A diagnosis of Leigh-like syndrome may be considered in individuals who do not fulfil the stringent diagnostic criteria but have features resembling Leigh syndrome.We describe a unique presentation of Leigh-like syndrome in a 3-year-old boy with elevated 3-hydroxyisovalerylcarnitine (C5-OH) on newborn screening (NBS). Subsequent persistent plasma elevations of C5-OH and propionylcarnitine (C3) as well as fluctuating urinary markers were suggestive of multiple carboxylase deficiency (MCD). Normal enzymology and mutational analysis of genes encoding holocarboxylase synthetase (HLCS) and biotinidase (BTD) excluded MCD. Biotin uptake studies were normal excluding biotin transporter deficiency. His clinical features at 13 months of age comprised psychomotor delay, central hypotonia, myopathy, failure to thrive, hypocitrullinemia, recurrent episodes of decompensation with metabolic keto-lactic acidosis and an episode of hyperammonemia. Biotin treatment from 13 months of age was associated with increased patient activity, alertness, and attainment of new developmental milestones, despite lack of biochemical improvements. Whole exome sequencing (WES) analysis failed to identify any other variants which could likely contribute to the observed phenotype, apart from the homoplasmic (100%) m.8993T>G variant initially detected by mitochondrial DNA (mtDNA) sequencing.Hypocitrullinemia has been reported in patients with the m.8993T>G variant and other mitochondrial disorders. However, persistent plasma elevations of C3 and C5-OH have previously only been reported in one other patient with this homoplasmic mutation. We suggest considering the m.8993T>G variant early in the diagnostic evaluation of MCD-like biochemical disturbances, particularly when associated with hypocitrullinemia on NBS and subsequent confirmatory tests. An oral biotin trial is also warranted.
authors.affiliation: Metabolic Unit, Department of Rheumatology and Metabolic Medicine, Princess Margaret Hospital, Perth, WA, Australia. saras329@hotmail.com.|School of Paediatrics and Child Health, University of Western Australia, Perth, WA, Australia. saras329@hotmail.com.|Western Sydney Genetics Program, Children's Hospital at Westmead, Westmead, NSW, Australia. saras329@hotmail.com.
authors.forename: Shanti
authors.initials: S
authors.lastname: Balasubramaniam
authors.affiliation: PathWest Laboratories WA, Princess Margaret Hospital, Perth, WA, Australia.
authors.forename: B
authors.initials: B
authors.lastname: Lewis
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Mock
authors.affiliation: Department of Medicine, University of California School of Medicine Irvine, Irvine, CA, USA.
authors.forename: H M
authors.initials: HM
authors.lastname: Said
authors.affiliation: Centre for Molecular Medicine, Department of Medical Genetics, Child and Family Research Institute, University of British Columbia, Vancouver, BC, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Tarailo-Graovac
authors.affiliation: Adult Metabolic Diseases Clinic, Division of Endocrinology and Metabolism, Vancouver General Hospital, UBC, Vancouver, BC, Canada.
authors.forename: A
authors.initials: A
authors.lastname: Mattman
authors.affiliation: Centre for Molecular Medicine, Department of Pediatrics, Child and Family Research Institute, University of British Columbia, Vancouver, BC, Canada.
authors.forename: C D
authors.initials: CD
authors.lastname: van Karnebeek
authors.affiliation: Murdoch Childrens Research Institute and Victorian Clinical Genetics Services, Royal Children's Hospital, Melbourne, VIC, Australia.|Department of Paediatrics, The University of Melbourne, Melbourne, VIC, Australia.
authors.forename: D R
authors.initials: DR
authors.lastname: Thorburn
authors.affiliation: Radboud Center for Mitochondrial Medicine, Radboud University Medical Centre, Nijmegen, The Netherlands.
authors.forename: R J
authors.initials: RJ
authors.lastname: Rodenburg
authors.affiliation: Murdoch Childrens Research Institute and Victorian Clinical Genetics Services, Royal Children's Hospital, Melbourne, VIC, Australia.|Department of Paediatrics, The University of Melbourne, Melbourne, VIC, Australia.
authors.forename: J
authors.initials: J
authors.lastname: Christodoulou
keywords: Acylcarnitines; Citrulline; Leigh syndrome; Newborn screening (NBS); mtDNA mutation