title: A novel movement disorder in related male Labrador Retrievers characterized by extreme generalized muscular stiffness.
abstract: OBJECTIVE
  To describe the clinical phenotype of a new motor disorder in Labrador Retrievers.
  
  
  METHODS
  Case series study. Seven young male Labrador Retrievers presented for evaluation of stiff gait.
  
  
  RESULTS
  All affected dogs had generalized muscular stiffness, persistent at rest and resulting in restricted joint movements. They showed a forward flexed posture, festinating gait, and bradykinesia. Signs developed between 2 and 16 months of age and tended to stabilize in adulthood. Needle electromyogram in the conscious state showed continuous motor unit activity in resting epaxial and proximal limb muscles. This activity was abolished by general anesthesia. Muscle and nerve histopathology was normal. In 2 dogs necropsied, astrocytosis was evident throughout the spinal cord gray matter, reticular formation and caudate nuclei. Decreased neuronal counts were selectively found in the spinal cord Rexed's lamina VII, but not in VIII and IX. Pedigree analysis showed that the affected dogs were from 5 related litters.
  
  
  CONCLUSIONS
  This new hypertonicity syndrome in Labrador Retrievers is unique because of the selective distribution of the histological lesions, the lack of progression in adulthood, and its exclusive occurrence in male dogs. Pedigree analysis suggests an X-linked hereditary disease, although other modes of inheritance cannot be ruled out with certainty. We hypothesize that altered output from basal nuclei and reticular formation together with motor neuron disinhibition caused by a decreased number of spinal cord interneurons leads to the muscular stiffness.
authors.affiliation: Department of Veterinary Medicine, The Queen's Veterinary School Hospital, University of Cambridge, Cambridge, UK. av354@cam.ac.uk
authors.forename: A E
authors.initials: AE
authors.lastname: Vanhaesebrouck
authors.forename: G D
authors.initials: GD
authors.lastname: Shelton
authors.forename: L
authors.initials: L
authors.lastname: Garosi
authors.forename: T R
authors.initials: TR
authors.lastname: Harcourt-Brown
authors.forename: J
authors.initials: J
authors.lastname: Couturier
authors.forename: S
authors.initials: S
authors.lastname: Behr
authors.forename: R J
authors.initials: RJ
authors.lastname: Harvey
authors.forename: N D
authors.initials: ND
authors.lastname: Jeffery
authors.forename: K
authors.initials: K
authors.lastname: Matiasek
authors.forename: W F
authors.initials: WF
authors.lastname: Blakemore
authors.forename: N
authors.initials: N
authors.lastname: Granger
mesh_terms: D000818:Animals; D004283:Dog Diseases / Q000175:diagnosis / Q000235:genetics* / Q000503:physiopathology; D004285:Dogs; D004576:Electromyography / Q000662:veterinary; D005684:Gait / Q000502:physiology; D040181:Genetic Diseases, X-Linked / Q000175:diagnosis / Q000235:genetics / Q000503:physiopathology / Q000662:veterinary; D008297:Male; D009069:Movement Disorders / Q000175:diagnosis / Q000235:genetics / Q000503:physiopathology / Q000662:veterinary*; D009127:Muscle Rigidity / Q000175:diagnosis / Q000235:genetics / Q000503:physiopathology / Q000662:veterinary*; D018482:Muscle, Skeletal / Q000473:pathology; D010375:Pedigree