DARS2 mutations in mitochondrial leucoencephalopathy and multiple sclerosis
- P Isohanni1,2,
- T Linnankivi2,
- J Buzkova1,
- T Lönnqvist2,
- H Pihko2,
- L Valanne3,
- P J Tienari1,4,
- I Elovaara5,
- T Pirttilä6,
- M Reunanen7,
- K Koivisto8,
- S Marjavaara1,
- A Suomalainen1,4
- 1Research Programme of Molecular Neurology, Biomedicum-Helsinki, University of Helsinki, Helsinki, Finland
- 2Department of Child Neurology, Helsinki University Central Hospital, Helsinki, Finland
- 3Helsinki Medical Imaging Center, University of Helsinki, Helsinki, Finland
- 4Department of Neurology, Helsinki University Central Hospital, Helsinki, Finland
- 5Department of Neurology, University of Tampere and Tampere University Hospital, Tampere, Finland
- 6Department of Neurology and Neuroscience, University of Kuopio and Kuopio University Hospital, Kuopio, Finland
- 7Department Neurology, University of Oulu and Oulu University Hospital, Oulu, Finland
- 8Central Hospital of Seinäjoki, Seinäjoki, Finland
- Correspondence to Dr P Isohanni, Department of Child Neurology, Hospital for Children and Adolescents, Helsinki University Central Hospital, PO Box 280 (Lastenlinnantie 2), FIN-00029 HUS, Finland;
- Received 27 March 2009
- Revised 28 June 2009
- Accepted 29 June 2009
- Published Online First 9 July 2009
Background Leucoencephalopathy with brain stem and spinal cord involvement and high brain lactate (LBSL) was first defined by characteristic magnetic resonance imaging and spectroscopic findings. The clinical features include childhood or juvenile onset slowly progressive ataxia, spasticity, and dorsal column dysfunction, occasionally accompanied by learning difficulties. Mutations in DARS2, encoding mitochondrial aspartyl-tRNA synthetase, were recently shown to cause LBSL. The signs and symptoms show some overlap with the most common leucoencephalopathy of young adults, multiple sclerosis (MS).
Objective To clarify the molecular background of LBSL patients in Finland, and to look for DARS2 mutations in a group of MS patients.
Methods Clinical evaluation of LBSL patients, DARS2 sequencing and haplotype analysis, and carrier frequency determination in Finland.
Results All eight LBSL patients were compound heterozygotes for DARS2 mutations: all carried R76SfsX5 change, seven had M134_K165del, and one had C152F change. Axonal neuropathy was found in five of the eight patients. The carrier frequencies of the R76SfsX5 and M134_K165del mutations were 1:95 and 1:380, respectively. All patients shared common European haplotypes, suggestive of common European LBSL ancestors. No enrichment of the two common DARS2 mutations was found in 321 MS patients.
Conclusion All LBSL patients were compound heterozygotes, which suggests that DARS2 mutation homozygosity may be lethal or manifest as a different phenotype. The authors show here that despite identical mutations the clinical picture was quite variable in the patients. Axonal neuropathy was an important feature of LBSL. DARS2 mutations cause childhood-to-adolescence onset leucoencephalopathy, but they do not seem to be associated with MS.
Additional table is published online only at http://jmg.bmj.com/content/vol47/issue1
Funding We thank the following organizations for financial support: Academy of Finland (for AS, PJT and SKM), Helsinki University (for AS), Sigrid Juselius Foundation (for AS, PJT and HP), Foundation for Paediatric Research and Helsinki University Central Hospital EVO grant (for HP, TLi, PJT and PI).
Competing interests None.
Patient consent Obtained.
Provenance and Peer review Not commissioned; externally peer reviewed.