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

Abstract

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.

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

“…Canine brachycephalic conformation typically includes foreshortening of the facial skeleton (muzzle) and not necessarily incudes the cranium . The results of discriminant analysis gave 75.8% correctly classified grouping with SM‐S highest separation of 92.5%, together with the predictive statistics of ML, consolidate the concept that a deep stop is a risk factor for SM‐S and CM‐P.…”

Dogs attending primary‐care practice in England with clinical signs suggestive of Chiari‐like malformation/syringomyelia

“…However, Griffon Bruxellois was under-represented in the current study despite having high CM/SM incidence in other studies (Rusbridge and others 2009, Marino and others 2012). Two of the three crossbreds in the study were partly CKCS, indicating that despite introduction of new genetic material from crossing, causative factors of CM/SM are likely to be inherited (Rusbridge and Knowler 2003, Knowler and others 2016). This information helps veterinary practitioners to consider CM/SM as a differential diagnosis in these breeds when normally it would not have been considered as a possible cause of the clinical signs observed.…”

MRI-gebaseerde morfometrische analyse gerelateerd aan chiari-achtige malformatie bij brachycefale hondenrassen

“…However, not all dogs with CLM develop SM suggesting that there may be factors that predispose to the development of SM in the presence of CLM. Recent research has discovered a number of other imaging features associated with the CLM-SM complex including increased cerebellar pulsation (Driver et al, 2013), dorsally compressive atlantoaxial bands and obex position (Cerda-Gonzalez et al, 2015), and a shortened distance across the craniocervical junction (Knowler et al, 2016). Further research could consider the inclusion of these additional imaging features in the diagnostic criteria for further accuracy.…”