Publications by authors named "Susan P Knowler"

13 Publications

  • Page 1 of 1

Facial changes related to brachycephaly in Cavalier King Charles Spaniels with Chiari-like malformation associated pain and secondary syringomyelia.

J Vet Intern Med 2020 Jan 5;34(1):237-246. Epub 2019 Nov 5.

School of Veterinary Medicine, Faculty of Health & Medical Sciences, Daphne Jackson Road, Guildford, Surrey, GU7 Q22, United Kingdom.

Background: Recent studies including an innovative machine learning technique indicated Chiari-like malformation (CM) is influenced by brachycephalic features.

Objectives: Morphometric analysis of facial anatomy and dysmorphia in CM-associated pain (CM-P) and syringomyelia (SM) in the Cavalier King Charles Spaniel (CKCS).

Animals: Sixty-six client-owned CKCS.

Methods: Retrospective study of anonymized T2W sagittal magnetic resonance imaging of 3 clinical groups: (1) 11 without central canal dilation (ccd) or SM (CM-N), (2) 15 with CM-P with no SM or <2 mm ccd (CM-P), and (3) 40 with syrinx width ≥4 mm (SM-S). Morphometric analysis assessed rostral skull flattening and position of the hard and soft palate relative to the cranial base in each clinical group and compared CKCS with and without SM-S.

Results: Sixteen of 28 measured variables were associated to SM-S compared to CM-N and CM-P. Of these 6 were common to both groups. Predictive variables determined by discriminant analysis were (1) the ratio of cranial height with cranial length (P < .001 between SM-S and CM-N) and (2) the distance between the cerebrum and the frontal bone (P < .001 between SM-S and CM-P). CM-P had the lowest mean height of the maxillary area.

Conclusions And Clinical Importance: CKCS with CM-P and SM-S have cranial brachycephaly with osseous insufficiency in the skull with rostral flattening and increased proximity of the hard and soft palate to the cranial base. Changes are greatest with CM-P. These findings have relevance for understanding disease pathogenesis and for selection of head conformation for breeding purposes.
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http://dx.doi.org/10.1111/jvim.15632DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6979263PMC
January 2020

Using machine learning to understand neuromorphological change and image-based biomarker identification in Cavalier King Charles Spaniels with Chiari-like malformation-associated pain and syringomyelia.

J Vet Intern Med 2019 Nov 24;33(6):2665-2674. Epub 2019 Sep 24.

CVSSP, Centre for Vision, Speech and Signal Processing, University of Surrey, Guildford, United Kingdom.

Background: Chiari-like malformation (CM) is a complex malformation of the skull and cranial cervical vertebrae that potentially results in pain and secondary syringomyelia (SM). Chiari-like malformation-associated pain (CM-P) can be challenging to diagnose. We propose a machine learning approach to characterize morphological changes in dogs that may or may not be apparent to human observers. This data-driven approach can remove potential bias (or blindness) that may be produced by a hypothesis-driven expert observer approach.

Hypothesis/objectives: To understand neuromorphological change and to identify image-based biomarkers in dogs with CM-P and symptomatic SM (SM-S) using a novel machine learning approach, with the aim of increasing the understanding of these disorders.

Animals: Thirty-two client-owned Cavalier King Charles Spaniels (CKCSs; 11 controls, 10 CM-P, 11 SM-S).

Methods: Retrospective study using T2-weighted midsagittal Digital Imaging and Communications in Medicine (DICOM) anonymized images, which then were mapped to images of an average clinically normal CKCS reference using Demons image registration. Key deformation features were automatically selected from the resulting deformation maps. A kernelized support vector machine was used for classifying characteristic localized changes in morphology.

Results: Candidate biomarkers were identified with receiver operating characteristic curves with area under the curve (AUC) of 0.78 (sensitivity 82%; specificity 69%) for the CM-P biomarkers collectively and an AUC of 0.82 (sensitivity, 93%; specificity, 67%) for the SM-S biomarkers, collectively.

Conclusions And Clinical Importance: Machine learning techniques can assist CM/SM diagnosis and facilitate understanding of abnormal morphology location with the potential to be applied to a variety of breeds and conformational diseases.
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http://dx.doi.org/10.1111/jvim.15621DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6872629PMC
November 2019

Clinical Application of Diagnostic Imaging of Chiari-Like Malformation and Syringomyelia.

Front Vet Sci 2018 28;5:280. Epub 2018 Nov 28.

School of Veterinary Medicine, Faculty of Health & Medical Sciences, University of Surrey, Guildford, United Kingdom.

Chiari-like malformation (CM) and syringomyelia (SM) is a frequent diagnosis in predisposed brachycephalic toy breeds since increased availability of MRI. However, the relevance of that MRI diagnosis has been questioned as CM, defined as identification of a cerebellar herniation, is ubiquitous in some breeds and SM can be asymptomatic. This article reviews the current knowledge of neuroanatomical changes in symptomatic CM and SM and diagnostic imaging modalities used for the clinical diagnosis of CM-pain or myelopathy related to SM. Although often compared to Chiari type I malformation in humans, canine CM-pain and SM is more comparable to complex craniosynostosis syndromes (i.e., premature fusion of multiple skull sutures) characterized by a short skull (cranial) base, rostrotentorial crowding with rostral forebrain flattening, small, and ventrally orientated olfactory bulbs, displacement of the neural tissue to give increased height of the cranium and further reduction of the functional caudotentorial space with hindbrain herniation. MRI may further reveal changes suggesting raised intracranial pressure such as loss of sulci definition in conjunction with ventriculomegaly. In addition to these brachycephalic changes, dogs with SM are more likely to have craniocervical junction abnormalities including rostral displacement of the axis and atlas with increased odontoid angulation causing craniospinal junction deformation and medulla oblongata elevation. Symptomatic SM is diagnosed on the basis of signs of myelopathy and presence of a large syrinx that is consistent with the neuro-localization. The imaging protocol should establish the longitudinal and transverse extent of the spinal cord involvement by the syrinx. Phantom scratching and cervicotorticollis are associated with large mid-cervical syringes that extend to the superficial dorsal horn. If the cause of CSF channel disruption and syringomyelia is not revealed by anatomical MRI then other imaging modalities may be appropriate with radiography or CT for any associated vertebral abnormalities.
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http://dx.doi.org/10.3389/fvets.2018.00280DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6279941PMC
November 2018

Morphogenesis of Canine Chiari Malformation and Secondary Syringomyelia: Disorders of Cerebrospinal Fluid Circulation.

Front Vet Sci 2018 27;5:171. Epub 2018 Jul 27.

Department of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.

Chiari-like Malformation (CM) and secondary syringomyelia (SM), as well as their analogous human conditions, is a complex developmental condition associated with pain and accompanying welfare concerns. CM/SM is diagnosed ever more frequently, thanks in part to the increased availability of magnetic resonance imaging in veterinary medicine. Research over the last two decades has focused primarily on its pathophysiology relating to overcrowding of the cranial caudal fossa. More recent characterizations of CM/SM include brachycephaly with osseous reduction and neural parenchymal displacement involving the entire brain and craniocervical junction to include rostral flattening, olfactory bulb rotation, increased height of the cranium, reduced cranial base with spheno-occipital synchondrosis angulation, reduced supraoccipital and interparietal crest and rostral displacement of the axis and atlas with increased odontoid angulation. The most shared manifestation of CM is the development of fluid-filled pockets (syrinx, syringes) in the spinal cord that can be readily quantified. Dogs with symptomatic CM without SM have a reduced basioccipital bone, compensatory increased cranial fossa height with displaced parenchyma whereby the cerebellum is invaginated beneath the occipital lobes but without compromising cerebrospinal fluid channels enough to cause SM. Thus, broadly defined, CM might be described as any distortion of the skull and craniocervical junction which compromises the neural parenchyma and cerebrospinal fluid circulation causing pain and/or SM. The etiology of CM is multifactorial, potentially including genetically-influenced, breed-specific abnormalities in both skeletal and neural components. Since causation between specific morphologic changes and SM or clinical signs is unproven, CM might be more appropriately considered as a brachycephalic obstructive CSF channel syndrome (BOCCS) rather than a single malformation. Understanding the normal development of the brain, skull and craniocervical junction is fundamental to identifying deviations which predispose to CM/SM. Here we review its anatomical, embryological, bio-mechanical, and genetic underpinnings to update the profession's understanding of this condition and meaningfully inform future research to diminish its welfare impact.
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http://dx.doi.org/10.3389/fvets.2018.00171DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6074093PMC
July 2018

A genome-wide association study identifies candidate loci associated to syringomyelia secondary to Chiari-like malformation in Cavalier King Charles Spaniels.

BMC Genet 2018 03 22;19(1):16. Epub 2018 Mar 22.

Department of Neurosciences, CHU Sainte Justine Research Center, University of Montréal, 3175 Cote-Sainte-Catherine, Room 3.17.006, Montreal, QC, H3T 1C5, Canada.

Background: Syringomyelia (SM) is a common condition affecting brachycephalic toy breed dogs and is characterized by the development of fluid-filled cavities within the spinal cord. It is often concurrent with a complex developmental malformation of the skull and craniocervical vertebrae called Chiari-like malformation (CM) characterized by a conformational change and overcrowding of the brain and cervical spinal cord particularly at the craniocervical junction. CM and SM have a polygenic mode of inheritance with variable penetrance.

Results: We identified six cranial T1-weighted sagittal MRI measurements that were associated to maximum transverse diameter of the syrinx cavity. Increased syrinx transverse diameter has been correlated previously with increased likelihood of behavioral signs of pain. We next conducted a whole genome association study of these traits in 65 Cavalier King Charles Spaniel (CKCS) dogs (33 controls, 32 with extreme phenotypes). Two loci on CFA22 and CFA26 were found to be significantly associated to two traits associated with a reduced volume and altered orientation of the caudal cranial fossa. Their reconstructed haplotypes defined two associated regions that harbor only two genes: PCDH17 on CFA22 and ZWINT on CFA26. PCDH17 codes for a cell adhesion molecule expressed specifically in the brain and spinal cord. ZWINT plays a role in chromosome segregation and its expression is increased with the onset of neuropathic pain. Targeted genomic sequencing of these regions identified respectively 37 and 339 SNPs with significantly associated P values. Genotyping of tagSNPs selected from these 2 candidate loci in an extended cohort of 461 CKCS (187 unaffected, 274 SM affected) identified 2 SNPs on CFA22 that were significantly associated to SM strengthening the candidacy of this locus in SM development.

Conclusions: We identified 2 loci on CFA22 and CFA26 that contained only 2 genes, PCDH17 and ZWINT, significantly associated to two traits associated with syrinx transverse diameter. The locus on CFA22 was significantly associated to SM secondary to CM in the CKCS dog breed strengthening its candidacy for this disease. This study will provide an entry point for identification of the genetic factors predisposing to this condition and its underlying pathogenic mechanisms.
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http://dx.doi.org/10.1186/s12863-018-0605-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865342PMC
March 2018

Use of Morphometric Mapping to Characterise Symptomatic Chiari-Like Malformation, Secondary Syringomyelia and Associated Brachycephaly in the Cavalier King Charles Spaniel.

PLoS One 2017 25;12(1):e0170315. Epub 2017 Jan 25.

School of Veterinary Medicine, Faculty of Health & Medical Sciences, University of Surrey, Guildford, Surrey, United Kingdom.

Objectives: To characterise the symptomatic phenotype of Chiari-like malformation (CM), secondary syringomyelia (SM) and brachycephaly in the Cavalier King Charles Spaniel using morphometric measurements on mid-sagittal Magnetic Resonance images (MRI) of the brain and craniocervical junction.

Methods: This retrospective study, based on a previous quantitative analysis in the Griffon Bruxellois (GB), used 24 measurements taken on 130 T1-weighted MRI of hindbrain and cervical region. Associated brachycephaly was estimated using 26 measurements, including rostral forebrain flattening and olfactory lobe rotation, on 72 T2-weighted MRI of the whole brain. Both study cohorts were divided into three groups; Control, CM pain and SM and their morphometries compared with each other.

Results: Fourteen significant traits were identified in the hindbrain study and nine traits in the whole brain study, six of which were similar to the GB and suggest a common aetiology. The Control cohort had the most elliptical brain (p = 0.010), least olfactory bulb rotation (p = 0.003) and a protective angle (p = 0.004) compared to the other groups. The CM pain cohort had the greatest rostral forebrain flattening (p = 0.007), shortest basioccipital (p = 0.019), but a greater distance between the atlas and basioccipital (p = 0.002) which was protective for SM. The SM cohort had two conformation anomalies depending on the severity of craniocervical junction incongruities; i) the proximity of the dens (p <0.001) ii) increased airorhynchy with a smaller, more ventrally rotated olfactory bulb (p <0.001). Both generated 'concertina' flexures of the brain and craniocervical junction.

Conclusion: Morphometric mapping provides a diagnostic tool for quantifying symptomatic CM, secondary SM and their relationship with brachycephaly. It is hypothesized that CM pain is associated with increased brachycephaly and SM can result from different combinations of abnormalities of the forebrain, caudal fossa and craniocervical junction which compromise the neural parenchyma and impede cerebrospinal fluid flow.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0170315PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5266281PMC
August 2017

Craniometric Analysis of the Hindbrain and Craniocervical Junction of Chihuahua, Affenpinscher and Cavalier King Charles Spaniel Dogs With and Without Syringomyelia Secondary to Chiari-Like Malformation.

PLoS One 2017 25;12(1):e0169898. Epub 2017 Jan 25.

School of Veterinary Medicine, Faculty of Health & Medical Sciences, University of Surrey, Guildford, Surrey, United Kingdom.

Objectives: To characterize and compare the phenotypic variables of the hindbrain and craniocervical junction associated with syringomyelia (SM) in the Chihuahua, Affenpinscher and Cavalier King Charles Spaniel (CKCS).

Method: Analysis of 273 T1-weighted mid-sagittal DICOM sequences of the hindbrain and craniocervical junction from 99 Chihuahuas, 42 Affenpinschers and 132 CKCSs. The study compared 22 morphometric features (11 lines, eight angles and three ratios) of dogs with and without SM using refined techniques based on previous studies of the Griffon Bruxellois (GB) using Discriminant Function Analysis and ANOVA with post-hoc corrections.

Results: The analysis identified 14/22 significant traits for SM in the three dog breeds, five of which were identical to those reported for the GB and suggest inclusion of a common aetiology. One ratio, caudal fossa height to the length of the skull base extended to an imaginary point of alignment between the atlas and supraoccipital bones, was common to all three breeds (p values 0.029 to <0.001). Associated with SM were a reduced occipital crest and two acute changes in angulation i) 'sphenoid flexure' at the spheno-occipital synchondrosis ii) 'cervical flexure' at the foramen magnum allied with medulla oblongata elevation. Comparing dogs with and without SM, each breed had a unique trait: Chihuahua had a smaller angle between the dens, atlas and basioccipital bone (p value < 0.001); Affenpinschers had a smaller distance from atlas to dens (p value 0.009); CKCS had a shorter distance between the spheno-occipital synchondrosis and atlas (p value 0.007).

Conclusion: The selected morphometries successfully characterised conformational changes in the brain and craniocervical junction that might form the basis of a diagnostic tool for all breeds. The severity of SM involved a spectrum of abnormalities, incurred by changes in both angulation and size that could alter neural parenchyma compliance and/or impede cerebrospinal fluid channels.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0169898PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5266279PMC
August 2017

Inheritance of Chiari-Like Malformation: Can a Mixed Breeding Reduce the Risk of Syringomyelia?

PLoS One 2016 23;11(3):e0151280. Epub 2016 Mar 23.

School of Veterinary Medicine, Faculty of Health & Medical Sciences, University of Surrey, Guildford, Surrey, United Kingdom.

Canine Chiari-like malformation (CM) is a complex abnormality of the skull and craniocervical junction associated with miniaturization and brachycephaly which can result in the spinal cord disease syringomyelia (SM). This study investigated the inheritance of CM in a Griffon Bruxellois (GB) family and feasibility of crossbreeding a brachycephalic CM affected GB with a mesaticephalic normal Australian terrier and then backcrossing to produce individuals free of the malformation and regain GB breed characteristics. The study family cohort (n = 27) included five founder dogs from a previous baseline study of 155 GB which defined CM as a global malformation of the cranium and craniocervical junction with a shortened skull base and increased proximity of the cervical vertebrae to the skull. T1-weighted sagittal DICOM images of the brain and craniocervical junction were analysed for five significant traits (two angles, three lines) identified from the previous study and subsequent Qualitative Trait Loci analysis. Mean measurements for mixed breed, pure-breed and baseline study groups were compared. Results indicated that mixed breed traits posed less risk for CM and SM and were useful to distinguish the phenotype. Moreover on the MR images, the filial relationships displayed by the traits exhibited segregation and those presenting the greatest risk for CM appeared additive towards the severity of the condition. The external phenotypes revealed that by outcrossing breed types and with careful selection of appropriate conformation characteristics in the first generation, it is possible to regain the GB breed standard and reduce the degree of CM. The four GB affected with SM in the study all exhibited reduced caudal skull development compared to their relatives. The craniocervical traits may be useful for quantifying CM and assessing the possibility of SM thus assisting breeders with mate selection. However, such a system requires validation to ensure appropriateness for all breeds at risk.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0151280PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4805231PMC
August 2016

Clinical features of idiopathic inflammatory polymyopathy in the Hungarian Vizsla.

BMC Vet Res 2015 Apr 21;11:97. Epub 2015 Apr 21.

Fitzpatrick Referrals, Halfway Lane, Eashing, Godalming, GU7 2QQ, Surrey, UK.

Background: A retrospective study of the clinicopathological features of presumed and confirmed cases of idiopathic inflammatory polymyopathy in the Hungarian Vizsla dog and guidelines for breeding.

Results: 369 medical records were reviewed (1992-2013) and 77 Hungarian Vizslas were identified with a case history consistent with idiopathic inflammatory polymyopathy. Inclusion criteria were: group 1 (confirmed diagnosis); histopathology and clinical findings compatible with an inflammatory polymyopathy and group 2 (probable diagnosis); clinical findings compatible with a polymyopathy including dysphagia, sialorrhea, temporal muscle atrophy, elevated serum creatine kinase (CK) activity, and sufficient clinical history to suggest that other neuromuscular disorders could be ruled out. Some group 2 dogs had muscle biopsy, which suggested muscle disease but did not reveal an inflammatory process. The mean age of onset was 2.4 years; male dogs were slightly overrepresented. Common presenting signs were dysphagia, sialorrhea, masticatory muscle atrophy, and regurgitation. Common muscle histopathological findings included degenerative and regenerative changes, with multifocal mononuclear cell infiltration with lymphoplasmacytic myositis of variable severity. A positive response to immunosuppressive treatment supported an immune-mediated aetiology. The mean age at death and survival time were 6.4 and 3.9 years, respectively. Recurrence of clinical signs and aspiration pneumonia were common reasons for euthanasia.

Conclusions: Diagnosis of Vizsla idiopathic inflammatory polymyopathy can be challenging due to lack of specific tests, however the presence of dysphagia, regurgitation and masticatory muscle atrophy in this breed with negative serological tests for masticatory muscle myositis and myasthenia gravis, along with muscle biopsies suggesting an inflammatory process, support the diagnosis. However, there is an urgent need for a more specific diagnostic test. The average of inbreeding coefficient (CoI) of 16.3% suggests an increased expression of a Dog Leukocyte Antigen Class II haplotype, leading to an increased disease risk. The prognosis remains guarded, as treatment can only manage the disease. Recurrence of clinical signs and perceived poor quality of life are the most common reasons for humane euthanasia.
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http://dx.doi.org/10.1186/s12917-015-0408-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4414416PMC
April 2015

Quantitative trait loci (QTL) study identifies novel genomic regions associated to Chiari-like malformation in Griffon Bruxellois dogs.

PLoS One 2014 16;9(4):e89816. Epub 2014 Apr 16.

CHU Sainte Justine Research Center, Université de Montréal, Montreal, Quebec, Canada.

Chiari-like malformation (CM) is a developmental abnormality of the craniocervical junction that is common in the Griffon Bruxellois (GB) breed with an estimated prevalence of 65%. This disease is characterized by overcrowding of the neural parenchyma at the craniocervical junction and disturbance of cerebrospinal fluid (CSF) flow. The most common clinical sign is pain either as a direct consequence of CM or neuropathic pain as a consequence of secondary syringomyelia. The etiology of CM remains unknown but genetic factors play an important role. To investigate the genetic complexity of the disease, a quantitative trait locus (QTL) approach was adopted. A total of 14 quantitative skull and atlas measurements were taken and were tested for association to CM. Six traits were found to be associated to CM and were subjected to a whole-genome association study using the Illumina canine high density bead chip in 74 GB dogs (50 affected and 24 controls). Linear and mixed regression analyses identified associated single nucleotide polymorphisms (SNPs) on 5 Canis Familiaris Autosomes (CFAs): CFA2, CFA9, CFA12, CFA14 and CFA24. A reconstructed haplotype of 0.53 Mb on CFA2 strongly associated to the height of the cranial fossa (diameter F) and an haplotype of 2.5 Mb on CFA14 associated to both the height of the rostral part of the caudal cranial fossa (AE) and the height of the brain (FG) were significantly associated to CM after 10 000 permutations strengthening their candidacy for this disease (P = 0.0421, P = 0.0094 respectively). The CFA2 QTL harbours the Sall-1 gene which is an excellent candidate since its orthologue in humans is mutated in Townes-Brocks syndrome which has previously been associated to Chiari malformation I. Our study demonstrates the implication of multiple traits in the etiology of CM and has successfully identified two new QTL associated to CM and a potential candidate gene.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0089816PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3989173PMC
January 2015

Quantitative analysis of Chiari-like malformation and syringomyelia in the Griffon Bruxellois dog.

PLoS One 2014 12;9(2):e88120. Epub 2014 Feb 12.

Neurology Department, Fitzpatrick Referrals, Godalming, Surrey, United Kingdom ; School of Veterinary Medicine, Faculty of Health & Medical Sciences, University of Surrey, Guildford, United Kingdom.

This study aimed to develop a system of quantitative analysis of canine Chiari-like malformation and syringomyelia on variable quality MRI. We made a series of measurements from magnetic resonance DICOM images from Griffon Bruxellois dogs with and without Chiari-like malformation and syringomyelia and identified several significant variables. We found that in the Griffon Bruxellois dog, Chiari-like malformation is characterized by an apparent shortening of the entire cranial base and possibly by increased proximity of the atlas to the occiput. As a compensatory change, there appears to be an increased height of the rostral cranial cavity with lengthening of the dorsal cranial vault and considerable reorganization of the brain parenchyma including ventral deviation of the olfactory bulbs and rostral invagination of the cerebellum under the occipital lobes.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0088120PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3922758PMC
January 2015

Syringomyelia: determining risk and protective factors in the conformation of the Cavalier King Charles Spaniel dog.

Canine Genet Epidemiol 2014 29;1. Epub 2014 Jul 29.

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.

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.
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http://dx.doi.org/10.1186/2052-6687-1-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4579371PMC
September 2015

Inheritance of occipital bone hypoplasia (Chiari type I malformation) in Cavalier King Charles Spaniels.

J Vet Intern Med 2004 Sep-Oct;18(5):673-8

Stone Lion Veterinary Centre, Wimbledon, London, UK.

Occipital bone hypoplasia with foramen magnum obstruction and secondary syringomyelia (SM) is a common condition in the Cavalier King Charles Spaniel (CKCS) that is similar to human Chiari type I malformation. A worldwide family tree of more than 5,500 CKCSs spanning a maximum of 24 generations was established by obtaining pedigree information from 120 dogs diagnosed with SM secondary to occipital bone hypoplasia. The ongoing study showed 6 of 8 great grandparents of all affected dogs could be traced back to 2 female ancestors so that all 8 were descended from one or the other or both. The disease appears to be more severe and have an earlier onset with increased inbreeding, especially when breeding from affected dogs. The family tree of idiopathic epilepsy (IE) appears to be a different subset of the CKCS population, although some overlap was observed. Idiopathic epilepsy is more frequent in lines originating from whole-color dogs. Selection for coat color is believed to have influenced the development of both occipital hypoplasia with secondary SM and IE. In addition, breeding guidelines to reduce the incidence of mitral valve disease have placed further pressures on the gene pool.
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http://dx.doi.org/10.1892/0891-6640(2004)18<673:ioobhc>2.0.co;2DOI Listing
December 2004
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