ARTICLE Mutations in the N-terminal Actin-Binding Domain of Filamin C Cause a Distal Myopathy Rachael M. Duff, 1,2 Valerie Tay, 3 Peter Hackman, 4 Gianina Ravenscroft, 1 Catriona McLean, 5 Paul Kennedy, 5 Alina Steinbach, 6 Wiebke Scho ¨ffler, 6 Peter F.M. van der Ven, 6 Dieter O. Fu ¨rst, 6 Jaeguen Song, 7 Kristina Djinovi c-Carugo, 7,13 Sini Penttila ¨, 8 Olayinka Raheem, 8 Katrina Reardon, 3 Alessandro Malandrini, 9 Simona Gambelli, 9 Marcello Villanova, 10 Kristen J. Nowak, 1 David R. Williams, 11 John E. Landers, 12 Robert H. Brown, Jr., 12 Bjarne Udd, 4,8,14 and Nigel G. Laing 1, * Linkage analysis of the dominant distal myopathy we previously identified in a large Australian family demonstrated one significant linkage region located on chromosome 7 and encompassing 18.6 Mbp and 151 genes. The strongest candidate gene was FLNC because filamin C, the encoded protein, is muscle-specific and associated with myofibrillar myopathy. Sequencing of FLNC cDNA identified a c.752T>C (p.Met251Thr) mutation in the N-terminal actin-binding domain (ABD); this mutation segregated with the disease and was absent in 200 controls. We identified an Italian family with the same phenotype and found a c.577G>A (p.Ala193Thr) filamin C ABD mutation that segregated with the disease. Filamin C ABD mutations have not been described, although filamin A and filamin B ABD mutations cause multiple musculoskeletal disorders. The distal myopathy phenotype and muscle pathology in the two families differ from myofibrillar myopathies caused by filamin C rod and dimerization domain mutations because of the distinct involvement of hand muscles and lack of pathological protein aggregation. Thus, like the position of FLNA and B mutations, the position of the FLNC mutation determines disease phenotype. The two filamin C ABD mutations increase actin-binding affinity in a manner similar to filamin A and filamin B ABD mutations. Cell-culture expression of the c.752T>C (p.Met251)Thr mutant filamin C ABD demonstrated reduced nuclear localization as did mutant filamin A and filamin B ABDs. Expression of both filamin C ABD mutants as full-length proteins induced increased aggregation of filamin. We conclude filamin C ABD mutations cause a recognizable distal myopathy, most likely through increased actin affinity, similar to the pathological mechanism of filamin A and filamin B ABD mutations. Introduction The distal myopathies are a group of genetic muscle- wasting disorders characterized by muscle weakness predominantly originating in distal muscle groups of the upper or lower limbs. 1,2 Currently, the many types of distal myopathy are differentiated by the phenotypic variations within the disease spectrum. These include age at onset, affected muscle groups, severity, presence of cardiomyop- athy, and mode of inheritance. The distal myopathies show either dominant or recessive inheritance, and the genetic basis for several of the distal myopathies has been determined. The known proteins affected in distal myopathies encompass a range of different types but include a significant number of sarcomeric proteins 1 (Table 1). 3–12 In addition, patients with diseases described by other terms, such as myofibrillar myopathy, also often have a distal myopathy phenotype. 2 The genetic basis of other distal myopathies, including Welander distal myop- athy (WDM [MIM 604454]), one of the first distal myopa- thies described, 13 remains unknown. 2 In 2005 we described in a large family from Victoria, Australia, 14 a distal myopathy sometimes termed Distal ABD-filaminopathy or William’s myopathy 15 . The distal myopathy in the family did not link to any of the then known distal myopathy loci, which reinforced the novel clinical phenotype. 14 Here we have reanalyzed the clinical phenotype, reclassified the members in the family, and performed a whole-genome linkage analysis. Significant linkage for the disease in the family (multipoint LOD score 3.3) was obtained on chromosome 7. We subsequently identified a second family from Italy with the same pheno- type and showed that the disease in this second family was compatible with linkage to the same region of chromo- some 7. We found two different missense mutations in the N-terminal ABD of FLNC (MIM 102565), and both mutations segregate with the disease in the two families. Actin-binding studies of the two mutant filamin C ABDs 1 Centre for Medical Research, University of Western Australia and Western Australian Institute for Medical Research, Perth, Western Australia 6009, Australia; 2 Centre for Neuromuscular and Neurological Disorders, University of Western Australia, Perth, Western Australia 6009, Australia; 3 Centre for Clinical Neurosciences and Neurological Research, St. Vincent’s Hospital, Melbourne, Victoria 3065, Australia; 4 Folkha ¨lsan Institute of Genetics, Depart- ment of Medical Genetics, Haartman Institute, University of Helsinki, 00014 Helsinki, Finland; 5 State Neuropathology Service, Department of Pathology, University of Melbourne, Melbourne, Victoria 3010, Australia; 6 Institute for Cell Biology, Department of Molecular Cell Biology, University of Bonn, 53121 Bonn, Germany; 7 Department for Structural and Computational Biology, Max F. Perutz Laboratories, University of Vienna, 1030 Vienna, Austria; 8 Neuro- muscular Research Unit, University of Tampere, Department of Neurology Tampere University Hospital, 33520 Tampere, Finland; 9 Department Neurolog- ical, Neurosurgical and Behavioural Sciences, Unit of Neurometabolic Diseases, University of Siena, 53100 Siena, Italy; 10 Casa di Cura Nigrisoli, 40125 Bologna, Italy; 11 Van Cleef Roet Centre for Nervous Disease, Monash University, Melbourne, Victoria 3800, Australia; 12 Department of Neurology, Univer- sity of Massachusetts Medical School, Worcester, MA 01605, USA; 13 Department of Biochemistry, Faculty of Chemistry and Chemical Technology, Univer- sity of Ljubljana, Ljubljana 1000, Slovenia; 14 Department of Neurology, Vasa Central Hospital, 65130 Vasa, Finland *Correspondence: nlaing@cyllene.uwa.edu.au DOI 10.1016/j.ajhg.2011.04.021. Ó2011 by The American Society of Human Genetics. All rights reserved. The American Journal of Human Genetics 88, 729–740, June 10, 2011 729