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Original research
MRM2 variants in families with complex dystonic syndromes: evidence for phenotypic heterogeneity
  1. Anum Shafique1,
  2. Beenish Arif1,
  3. Mary Lynn Chu2,3,
  4. Ellen Moran4,
  5. Tooba Hussain1,
  6. Francisca Millan Zamora5,
  7. Elizabeth Wohler6,
  8. Nara Sobreira6,
  9. Christine Klein7,
  10. Katja Lohmann7,
  11. Sadaf Naz1
  1. 1School of Biological Sciences, University of the Punjab Quaid-i-Azam Campus, Lahore, Pakistan
  2. 2Department of Neurology, New York University Grossman School of Medicine, New York, New York, USA
  3. 3Langone Orthopedic Hospital, New York University, New York, New York, USA
  4. 4Clinical Genetics, Center for Children, Hassenfeld Children's Hospital, New York University, New York, New York, USA
  5. 5GeneDx, Gaithersburg, Maryland, USA
  6. 6McKusick-Nathans Department of Genetic Medicine, Johns Hopkins University, Baltimore, Maryland, USA
  7. 7Institute of Neurogenetics, University of Lübeck, Lübeck, Germany
  1. Correspondence to Dr Sadaf Naz, School of Biological Sciences, University of the Punjab Quaid-i-Azam Campus, Lahore, Pakistan;{at}


Background Dystonia involves repetitive movements and muscle contractions leading to abnormal postures. We investigated patients in two families, DYAF11 and M, exhibiting dystonic or involuntary movement disorders.

Methods Clinical investigations were performed for all patients. Genetic analyses included genome-wide linkage analysis and exome sequencing followed by Sanger sequencing validation. MRM2-specific transcripts were analysed from participants’ blood samples in Family DYAF11 after cloning of gene-specific cDNA.

Results Four affected siblings in Family DYAF11 had progressive dystonic features. Two patients in Family M exhibited a neurodevelopmental disorder accompanied by involuntary movements. In Family DYAF11, linkage was detected to the telomere at chromosome 7p22.3, spanning <2 Mb. Exome sequencing identified a donor splice-site variant, c.8+1G>T in MRM2, which segregated with the phenotype, corresponding to the linkage data since all affected individuals were homozygous while the obligate unaffected carriers were heterozygous for the variant. In the MRM2 c.8+1G>T allele, an aberrant alternative acceptor splice-site located within exon 2 was used in a subset of the transcripts, creating a frameshift in the open reading frame. Exome sequencing in Family M revealed a rare missense variant c.242C>T, p.(Ala81Val), which affected a conserved amino acid.

Conclusions Our results expand the clinical and allelic spectrum of MRM2 variants. Previously, these descriptions were based on observations in a single patient, diagnosed with mitochondrial DNA depletion syndrome 17, in whom movement disorder was accompanied by recurrent strokes and epilepsy. We also demonstrate a subset of correctly spliced tt-ag MRM2 transcripts, raising the possibility to develop treatment by understanding the disease mechanism.

  • movement disorders
  • human genetics
  • gene expression profiling
  • germ-line mutation
  • high-throughput nucleotide sequencing

Data availability statement

Data are available on reasonable request.

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  • Contributors SN and KL designed and supervised the study. BA, TH, MLC, EM collected the family samples and arranged clinical testing. AS, BA, SN, EM, FM, EW, NLdeMS analysed the SNP genotyping data, exome data and performed Sanger sequencing. AS performed and analysed RNA and cDNA cloning experiments. CK reviewed clinical data and offered diagnosis. AS, BA, KL and SN drafted the manuscript. All authors contributed to, reviewed and approved the manuscript. Guarantor: SN.

  • Funding This research was funded by the Baylor-Hopkins Center for Mendelian Genomics, USA, the DFG, Germany (LO 1555/8-1, FOR 2488), the Damp Foundation, Germany and Higher Education Commission, Pakistan 2877.

  • Competing interests FM is an employee of GeneDx. CK serves as a medical advisor to Centogene for genetic testing reports in the field of movement disorders, excluding Parkinson’s disease and on the Scientific Advisory Board of Retromer Therapeutics. No conflict of interest for all other authors.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.