title: Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation: clinical and genetic characterization and target for therapy.
abstract: Leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation is a disorder caused by recessive mutations in the gene DARS2, which encodes mitochondrial aspartyl-tRNA synthetase. Recent observations indicate that the phenotypic range of the disease is much wider than initially thought. Currently, no treatment is available. The aims of our study were (i) to explore a possible genotype-phenotype correlation; and (ii) to identify potential therapeutic agents that modulate the splice site mutations in intron 2 of DARS2, present in almost all patients. A cross-sectional observational study was performed in 78 patients with two DARS2 mutations in the Amsterdam and Helsinki databases up to December 2012. Clinical information was collected via questionnaires. An inventory was made of the DARS2 mutations in these patients and those previously published. An assay was developed to assess mitochondrial aspartyl-tRNA synthetase enzyme activity in cells. Using a fluorescence reporter system we screened for drugs that modulate DARS2 splicing. Clinical information of 66 patients was obtained. The clinical severity varied from infantile onset, rapidly fatal disease to adult onset, slow and mild disease. The most common phenotype was characterized by childhood onset and slow neurological deterioration. Full wheelchair dependency was rare and usually began in adulthood. In total, 60 different DARS2 mutations were identified, 13 of which have not been reported before. Except for 4 of 42 cases published by others, all patients were compound heterozygous. Ninety-four per cent of the patients had a splice site mutation in intron 2. The groups of patients sharing the same two mutations were too small for formal assessment of genotype-phenotype correlation. However, some combinations of mutations were consistently associated with a mild phenotype. The mitochondrial aspartyl-tRNA synthetase activity was strongly reduced in patient cells. Among the compounds screened, cantharidin was identified as the most potent modulator of DARS2 splicing. In conclusion, the phenotypic spectrum of leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation is wide, but most often the disease has a relatively slow and mild course. The available evidence suggests that the genotype influences the phenotype, but because of the high number of private mutations, larger numbers of patients are necessary to confirm this. The activity of mitochondrial aspartyl-tRNA synthetase is significantly reduced in patient cells. A compound screen established a 'proof of principle' that the splice site mutation can be influenced. This finding is promising for future therapeutic strategies.
authors.affiliation: 1 Department of Child Neurology, VU University Medical Centre, Neuroscience Campus, Amsterdam, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands.
authors.forename: Laura
authors.initials: L
authors.lastname: van Berge
authors.forename: Eline M
authors.initials: EM
authors.lastname: Hamilton
authors.forename: Tarja
authors.initials: T
authors.lastname: Linnankivi
authors.forename: Graziella
authors.initials: G
authors.lastname: Uziel
authors.forename: Marjan E
authors.initials: ME
authors.lastname: Steenweg
authors.forename: Pirjo
authors.initials: P
authors.lastname: Isohanni
authors.forename: Nicole I
authors.initials: NI
authors.lastname: Wolf
authors.forename: Ingeborg
authors.initials: I
authors.lastname: Krägeloh-Mann
authors.forename: Nils J
authors.initials: NJ
authors.lastname: Brautaset
authors.forename: P Ian
authors.initials: PI
authors.lastname: Andrews
authors.forename: Brigit A
authors.initials: BA
authors.lastname: de Jong
authors.forename: Malak
authors.initials: M
authors.lastname: al Ghamdi
authors.forename: Wessel N
authors.initials: WN
authors.lastname: van Wieringen
authors.forename: Bakhos A
authors.initials: BA
authors.lastname: Tannous
authors.forename: Esther
authors.initials: E
authors.lastname: Hulleman
authors.forename: Thomas
authors.initials: T
authors.lastname: Würdinger
authors.forename: Carola G M
authors.initials: CG
authors.lastname: van Berkel
authors.forename: Emiel
authors.initials: E
authors.lastname: Polder
authors.forename: Truus E M
authors.initials: TE
authors.lastname: Abbink
authors.forename: Eduard A
authors.initials: EA
authors.lastname: Struys
authors.forename: Gert C
authors.initials: GC
authors.lastname: Scheper
authors.forename: Marjo S
authors.initials: MS
authors.lastname: van der Knaap
mesh_terms: D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D017398:Alternative Splicing / Q000187:drug effects*; D001226:Aspartate-tRNA Ligase / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D002193:Cantharidin / Q000494:pharmacology; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D004252:DNA Mutational Analysis; D018450:Disease Progression; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D056726:Genetic Association Studies; D006801:Humans; D007223:Infant; D056784:Leukoencephalopathies / Q000150:complications* / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics*; D008297:Male; D008875:Middle Aged; D028361:Mitochondrial Diseases / Q000150:complications* / Q000188:drug therapy / Q000201:enzymology / Q000235:genetics*; D009154:Mutation; D020133:Reverse Transcriptase Polymerase Chain Reaction; D055815:Young Adult
chemical_list: D004791:Enzyme Inhibitors; D001226:Aspartate-tRNA Ligase; C558608:DARS2 protein, human; D002193:Cantharidin
keywords: DARS2; compound screen; enzyme activity; genotype-phenotype correlation; white matter disorder