title: Syringomyelia: determining risk and protective factors in the conformation of the Cavalier King Charles Spaniel dog.
abstract: BACKGROUND
  Syringomyelia (SM) is a painful neurological condition, prevalent in brachycephalic toy breeds including the Cavalier King Charles Spaniel (CKCS). In these breeds, SM is typically secondary to Chiari-like Malformation (CM). There has been much debate in the scientific and veterinary communities to what extent head shape is indicative of either pathology, especially as certain craniosynostosis syndromes in humans (highly associated with CM) have characteristic facial and cranial morphologies. Elucidating a risk morphology would allow for selection away from these traits and proffer further breeding guidelines for the condition. Dogs were measured in multiple countries by means of a standardised bony landmark measuring protocol and photo analysis by blinded, trained researchers.
  
  
  RESULTS
  The results found two significant risk factors in the conformation of the CKCS: extent of brachycephaly and distribution of cranium. The study identified a greater amount of cranium distributed caudally (relative to the amount distributed rostrally) to be significantly protective against syrinx development at the levels of three years of age, five years of age and when comparing a sample of SM clear individuals over the age of five to those affected younger than three years of age. A decreased cephalic index (decreasing brachycephaly) was significantly protective at the latter level. Cephalic index and caudal cranium distribution exhibited a negative, linear relationship. Cephalic index demonstrated a positive linear relationship with the amount of doming of the head.
  
  
  CONCLUSIONS
  This study proposes a risk phenotype of brachycephaly with resulting rostrocaudal doming that is more rostrally distributed and hence sloping caudally. The results of this study may allow for selection against risk aspects of conformation in the CKCS in combination with the British Veterinary Association/Kennel Club CM/SM scheme to enable reduction in CM/SM incidence. Further research comparing this external risk phenotype to the internal presentation upon MRI would determine how these features are indicative of syrinx development. Utilising breeds in which CM free individuals are more available may allow for validation of this risk phenotype for CM or determine alternatives.
authors.affiliation: School of Clinical Veterinary Science, University of Bristol, Langford, Bristol BS40 5DU UK.
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Mitchell
authors.affiliation: School of Veterinary Medicine, Faculty of Health & Medical Sciences, University of Surrey, Duke of Kent Building, Guildford, Surrey GU2 7TE UK.
authors.forename: Susan P
authors.initials: SP
authors.lastname: Knowler
authors.affiliation: Fitzpatrick Referrals, Halfway Lane, Eashing, Godalming, Surrey GU7 2QQ UK.
authors.forename: Henny
authors.initials: H
authors.lastname: van den Berg
authors.affiliation: Lawson Imaging, Lawson Health Research Institute, 268 Grosvenor Street, London, Ontario N6A 4V2 Canada.
authors.forename: Jane
authors.initials: J
authors.lastname: Sykes
authors.affiliation: School of Veterinary Medicine, Faculty of Health & Medical Sciences, University of Surrey, Duke of Kent Building, Guildford, Surrey GU2 7TE UK ; Fitzpatrick Referrals, Halfway Lane, Eashing, Godalming, Surrey GU7 2QQ UK.
authors.forename: Clare
authors.initials: C
authors.lastname: Rusbridge
keywords: Canine skull morphology; Cavalier King Charles spaniel; Chiari malformation; Chiari-like malformation; Conformation; Occipital hypoplasia; Pedigree dog health; Syringomyelia; Toy breed dogs