Characterization of Bullmastiff Head Morphology and Identification of RUNX2 Allelic Variation within the Breed

We are interested in phenotypic variation of the canine skull both within a particular breed, the Bullmastiff, and between the Bullmastiff and other domestic breeds.  Bullmastiffs’ are an interesting breed as they are often cited for head shape, specifically snout length.  In order to gain a better understanding of the genetic contribution to head variation among Bullmastiffs’ and between breeds we collected head measurements.  For the collection of head measurements, pre-determined anatomic points on the dog skull were chosen to ensure a reproducible system for measuring.  Skull length was measured from inion to prosthion, skull width was determined as the widest interzygomatic distance, facial length was nasion to prosthion, cranial length inion to nasion and muzzle diameter.  Fondon and Garner (2004) established that variations in the number of repeats in the coding region of the gene RUNX2 correlated with significant differences in skull morphology.  We chose to determine the extent of RUNX2 repeat alleles within Bullmastiffs with an overall hypothesis that a gene having functional allelic variation associated with head morphology might be of value in developing genetically informed breeding programs for Bullmastiffs given that dystocia and cesarean section are common within the breed. We identified a number of RUNX2 repeat alleles within Bullmastiffs and other breeds and present the analysis of head measurements in the context of these alleles.