title: Homozygous mutations in MFN2 cause multiple symmetric lipomatosis associated with neuropathy.
abstract: Multiple symmetric lipomatosis (MSL) is a mitochondrial disorder with impaired brown fat metabolism that has been associated with MERRF mutations in some, but not all, patients. We studied a sibling pair and an unrelated indiviadual who presented with MSL and neuropathy to determine the genetic etiology of this disorder in patients who did not carry the MSL-associated MERRF mutation. Whole-exome sequencing was performed on the siblings, and a rare, shared homozygous mutation in MFN2 (c.2119C>T: p.R707W) was identified. The mutation was not present in their healthy siblings. In silico programs predict it to be pathogenic, and heterozygous carriers of the MFN2 p.R707W substitution are known to have Charcot-Marie-Tooth (CMT) disease. A third, unrelated patient with multiple symmetrical lipomatosis and neuropathy also harbored the same homozygous mutation and had been previously diagnosed with CMT. Functional studies in patient fibroblasts demonstrate that the p.R707W substitution impairs homotypic (MFN2-MFN2) protein interactions required for normal activity and renders mitochondria prone to perinuclear aggregation. These findings show that homozygous mutations at p.R707W in MFN2 are a novel cause of multiple symmetrical lipomatosis.
authors.affiliation: Department of Genetics, Children's Hospital of Eastern Ontario and Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada, ssawyer@cheo.on.ca.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Sawyer
authors.affiliation: Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Andy
authors.initials: A
authors.lastname: Cheuk-Him Ng
authors.affiliation: Department of Medical Genetics and Alberta Children's Hospital Research Institute for Child and Maternal Health, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors.forename: A Micheil
authors.initials: AM
authors.lastname: Innes
authors.affiliation: Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Justin D
authors.initials: JD
authors.lastname: Wagner
authors.affiliation: Department of Genetics, Children's Hospital of Eastern Ontario and Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: David A
authors.initials: DA
authors.lastname: Dyment
authors.affiliation: Department of Human Genetics and Quebec Innovation Centre, McGill University and Genome, Montréal, Quebec, Canada and.
authors.forename: Martine
authors.initials: M
authors.lastname: Tetreault
authors.affiliation: Department of Human Genetics and Quebec Innovation Centre, McGill University and Genome, Montréal, Quebec, Canada and.
authors.forename: Jacek
authors.initials: J
authors.lastname: Majewski
authors.affiliation: Department of Genetics, Children's Hospital of Eastern Ontario and Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Kym M
authors.initials: KM
authors.lastname: Boycott
authors.affiliation: Children's Hospital of Eastern Ontario Research Institute, University of Ottawa, Ottawa, Ontario, Canada.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Screaton
authors.affiliation: ANZAC Research Institute, University of Sydney, Concord Hospital, New South Wales, Australia.
authors.forename: Garth
authors.initials: G
authors.lastname: Nicholson
mesh_terms: D000328:Adult; D059472:Exome; D020558:GTP Phosphohydrolases / Q000235:genetics*; D056726:Genetic Association Studies; D059014:High-Throughput Nucleotide Sequencing; D006720:Homozygote; D006801:Humans; D008069:Lipomatosis, Multiple Symmetrical / Q000150:complications* / Q000175:diagnosis / Q000235:genetics*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D024101:Mitochondrial Proteins / Q000235:genetics*; D009154:Mutation; D009422:Nervous System Diseases / Q000209:etiology*; D010641:Phenotype; D035781:Siblings; D055815:Young Adult
chemical_list: D024101:Mitochondrial Proteins; D020558:GTP Phosphohydrolases; C470018:MFN2 protein, human