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PLoS One. 2016 Jul 29;11(7):e0160447. doi: 10.1371/journal.pone.0160447. eCollection 2016.

A Spontaneous Missense Mutation in Branched Chain Keto Acid Dehydrogenase Kinase in the Rat Affects Both the Central and Peripheral Nervous Systems.

Author information

1
Department of Ophthalmology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
2
National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Rockville, MD, United States of America.
3
Department of Neurology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
4
Department of Biomedical Sciences, Texas Tech University Health Science Center, El Paso, TX, United States of America.
5
Department of Biostatistics & Informatics, University of Wisconsin School of Medicine and Public Health, Madison, WI, United States of America.
6
National Eye Institute, National Institutes of Health, Bethesda, MD, United States of America.
7
Department of Radiology, Children's Hospital of Philadelphia, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States of America.
8
Department of Molecular and Comparative Pathobiology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
9
Department of Neurosurgery, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.
10
Department of Radiology, The Johns Hopkins University School of Medicine, Baltimore, MD, United States of America.

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.

PMID:
27472223
PMCID:
PMC4966912
DOI:
10.1371/journal.pone.0160447
[Indexed for MEDLINE]
Free PMC Article

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