KLHL41, a BTB-Kelch protein, is critical for skeletal muscle function

G. Ravenscroft,¹ E.J. Todd,¹ V.A. Gupta,² R. Shaheen,³ L.C. Swanson,² C. Hsu,² N.F. Clarke,⁴ M. Farrar,⁵ N.D. Manton,⁶ E.M. Thompson,^6,7 S.A. Sandaradura,⁴ K.N. North,⁸ C. Wallgren-Pettersson,⁹ N. Matsumoto,¹⁰ A.H. Beggs² and N.G. Laing,¹ ¹Western Australian Institute for Medical Research, Centre for Medical Research, University of Western Australia, Nedlands, WA, 6009, Australia, ²Genomics Program and Division of Genetics, The Manton Center for Orphan Disease Research, Boston Children's Hospital, Harvard Medical School, Boston, MA, 02115, United States of America, ³Developmental Genetics Unit, King Faisal Specialist Hospital, Riyadh, 11211, Saudi Arabia, ⁴Institute for Neuroscience and Muscle Research, Children’s Hospital at Westmead and Discipline of Pediatrics and Child Health, University of Sydney, NSW, 2145, Australia, ⁵Department of Neurology, Sydney Children’s Hospital, School of Women’s and Children Health, University of South Wales, NSW, 2052, Australia, ⁶Department of Surgical Pathology, SA Pathology at the Women’s and Children’s Hospital, North Adelaide, SA, 5006, Australia, ⁷Department of Pediatrics, University of Adelaide, Adelaide, SA, 5000 Australia, ⁸Murdoch Children’s Research Institute, The Royal Children’s Hospital, Parkville, VIC, 3052, Australia, ⁹The Folkhälsan Institute of Genetics, Samfundet Folkhälsan, Biomedicum Helsinki, and Department of Medical Genetics, Haartman Institute, University of Helsinki, Helsinki, 00014, Finland and ¹⁰Department of Human Genetics, Yokohama City University Graduate School of Medicine, Kanazawa-ku, Yokohama, 236-0004, Japan.

Nemaline myopathy (NEM) is a rare congenital muscle disease that in severe cases results in neonatal death due to respiratory insufficiency. NEM is characterized clinically by skeletal muscle dysfunction (most frequently hypotonia and weakness) and the presence of electron-dense nemaline bodies (rods) on muscle biopsy (Romero et al., 2013). Mutations in eight known genes have previously been found to cause NEM, with six of these encoding thin filament or thin filament-associated proteins (skeletal muscle α-actin, cofilin-2, nebulin, α- and β-tropomyosins, and troponin T1) (Romero et al., 2013). Most recently, causative mutations in genes encoding BTB-Kelch proteins have been identified in myopathies associated with nemaline bodies (KBTBD13 in autosomal dominant core-rod disease (Sambuughin et al., 2010) and KLHL40 in autosomal recessive NEM (Ravenscroft et al., 2013). We performed whole exome sequencing of genetically unresolved severe NEM patients and identified recessive small deletions and missense changes in a third gene encoding a skeletal muscle specific BTB-Kelch protein (Kelch-like family member 41; KLHL41) in four individuals from unrelated NEM families. Subsequent Sanger sequencing identified compound heterozygous changes in KLHL41 in a fifth NEM family. Functional studies in zebrafish showed that loss of klhl41 results in diminished motor function and myofibrillar disorganisation. KLHL40 (also known as sarcosin, Krp1 and KBTBD10) has previously been implicated in myofibril assembly (Greenberg et al., 2008; Paxton et al., 2011; du Puy et al., 2012). Studies of BTB-Kelch proteins, have indicated that members of this protein family (there are over 50 in humans) act as substrate adaptors for E3 ubiquitin ligases (Prag & Adams, 2003; Sambuughin et al., 2012). Despite these studies, the roles of BTB-Kelch proteins in skeletal muscle remain largely unknown. In conclusion, these studies expand the genetic heterogeneity of NEM, and further implicate a critical role of BTB-Kelch family members in maintenance of sarcomeric integrity.

du Puy L, Beqqali A, van Tol HT, Monshouwer-Kloots J, Passier R, Haagsman HP, Roelen BA. (2012) International Journal of Developmental Biology 56, 301-09.

Greenberg CC, Connelly PS, Daniels MP, Horowits R. (2008) Experimental Cell Research 314, 1177-91.

Paxton CW, Cosgrove RA, Drozd AC, Wiggins EL, Woodhouse S, Watson RA, Spence HJ, Ozanne BW, Pell JM. (2011) American Journal of Physiology (Cell Physiology) 300, C1345-55.

Prag S & Adams JC. (2003) BMC Bioinformatics 4, 42, Epub September 17 2003; doi: 0.1186/1471-2105-4-42

Ravenscroft G, Miyatake S, Lehtokari VL, Todd EJ, Vornanen P. et al. (2013). American Journal of Human Genetics 93, 6-18.

Romero NB, Sandaradura SA & Clarke NF. (2013) Current Opinion in Neurology 26, 519-26.

Sambuughin N, Swietnicki W, Techtmann S, Matrosova V, Wallace T, Goldfarb L, Maynard E. (2012) Biochemical and Biophysical Research Communications 421, 743-49.

Sambuughin N, Yau KS, Olivé M, Duff RM, Bayarsaikhan M. et al. (2010) American Journal of Human Genetics 87, 842-47.