title: A Spontaneous Missense Mutation in Branched Chain Keto Acid Dehydrogenase Kinase in the Rat Affects Both the Central and Peripheral Nervous Systems.
abstract: A novel mutation, causing a phenotype we named frogleg because its most obvious characteristic is a severe splaying of the hind limbs, arose spontaneously in a colony of Sprague-Dawley rats. Frogleg is a complex phenotype that includes abnormalities in hind limb function, reduced brain weight with dilated ventricles and infertility. Using micro-satellite markers spanning the entire rat genome, the mutation was mapped to a region of rat chromosome 1 between D1Rat131 and D1Rat287. Analysis of whole genome sequencing data within the linkage interval, identified a missense mutation in the branched-chain alpha-keto dehydrogenase kinase (Bckdk) gene. The protein encoded by Bckdk is an integral part of an enzyme complex located in the mitochondrial matrix of many tissues which regulates the levels of the branched-chain amino acids (BCAAs), leucine, isoleucine and valine. BCAAs are essential amino acids (not synthesized by the body), and circulating levels must be tightly regulated; levels that are too high or too low are both deleterious. BCKDK phosphorylates Ser293 of the E1α subunit of the BCKDH protein, which catalyzes the rate-limiting step in the catabolism of the BCAAs, inhibiting BCKDH and thereby, limiting breakdown of the BCAAs. In contrast, when Ser293 is not phosphorylated, BCKDH activity is unchecked and the levels of the BCAAs will decrease dramatically. The mutation is located within the kinase domain of Bckdk and is predicted to be damaging. Consistent with this, we show that in rats homozygous for the mutation, phosphorylation of BCKDH in the brain is markedly decreased relative to wild type or heterozygous littermates. Further, circulating levels of the BCAAs are reduced by 70-80% in animals homozygous for the mutation. The frogleg phenotype shares important characteristics with a previously described Bckdk knockout mouse and with human subjects with Bckdk mutations. In addition, we report novel data regarding peripheral neuropathy of the hind limbs.
authors.affiliation: Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: J Samuel
authors.initials: JS
authors.lastname: Zigler
authors.affiliation: National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Rockville, MD, United States of America.
authors.forename: Colin A
authors.initials: CA
authors.lastname: Hodgkinson
authors.affiliation: Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Megan
authors.initials: M
authors.lastname: Wright
authors.affiliation: Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Andrew
authors.initials: A
authors.lastname: Klise
authors.affiliation: Department of Biomedical Sciences, Texas Tech University Health Science Center, El Paso, TX, United States of America.
authors.forename: Olof
authors.identifier: http://orcid.org/0000-0001-8125-2653
authors.initials: O
authors.lastname: Sundin
authors.affiliation: Department of Biostatistics & Informatics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States of America.
authors.forename: Karl W
authors.initials: KW
authors.lastname: Broman
authors.affiliation: National Eye Institute, National Institutes of Health, Bethesda, MD, United States of America.
authors.forename: Fielding
authors.identifier: http://orcid.org/0000-0002-4788-0362
authors.initials: F
authors.lastname: Hejtmancik
authors.affiliation: Department of Radiology, Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America.
authors.forename: Hao
authors.initials: H
authors.lastname: Huang
authors.affiliation: Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Bonnie
authors.initials: B
authors.lastname: Patek
authors.affiliation: National Eye Institute, National Institutes of Health, Bethesda, MD, United States of America.
authors.forename: Yuri
authors.initials: Y
authors.lastname: Sergeev
authors.affiliation: Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Stacey
authors.initials: S
authors.lastname: Hose
authors.affiliation: Department of Molecular and Comparative Pathobiology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Cory
authors.identifier: http://orcid.org/0000-0002-6666-6548
authors.initials: C
authors.lastname: Brayton
authors.affiliation: National Eye Institute, National Institutes of Health, Bethesda, MD, United States of America.
authors.forename: Jiao
authors.initials: J
authors.lastname: Xaiodong
authors.affiliation: Department of Neurosurgery, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: David
authors.initials: D
authors.lastname: Vasquez
authors.affiliation: Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Nicholas
authors.initials: N
authors.lastname: Maragakis
authors.affiliation: Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Susumu
authors.initials: S
authors.lastname: Mori
authors.affiliation: National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Rockville, MD, United States of America.
authors.forename: David
authors.initials: D
authors.lastname: Goldman
authors.affiliation: Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Ahmet
authors.identifier: http://orcid.org/0000-0003-1215-3373
authors.initials: A
authors.lastname: Hoke
authors.affiliation: Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
authors.forename: Debasish
authors.initials: D
authors.lastname: Sinha
mesh_terms: D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide) / Q000235:genetics*; D000818:Animals; D002490:Central Nervous System / Q000201:enzymology*; D020125:Mutation, Missense; D017933:Peripheral Nervous System / Q000201:enzymology*; D051381:Rats
chemical_list: D042942:3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)