Short snout

The short muzzle trait has been linked to a variant in the BMP3 gene that results in a shortened skull shape, accompanied by a muzzle of decreased length.

Definition

Skull shapes in dogs exhibit a wide variability, although they have been primarily categorized into two types: brachycephaly and dolichocephaly. Brachycephaly is used to describe skulls with a reduced or shortened appearance, while dolichocephaly refers to skulls that give the impression of being more prolonged or elongated. These terms have been adopted because of their similarity to those used in disorders affecting humans. A variant in the BMP3 gene associated with brachycephaly has been identified. Although this gene is related to bone growth, its specific role in cranioskeletal development is still under study.

Genetic basis

It is necessary to carry two copies of the variant to manifest the trait. If the dog carries only one copy of the variant, it is more likely to have a medium to long muzzle; however, there is a 50% chance that the mutation can be inherited by its offspring. Variants have been identified in different genes such as SMOC2, and it is estimated that there are other genetic variants not yet identified that could be linked to the variability of this trait. Consequently, the presence or absence of other variants could alter the expected phenotype.

Other relevant information

It is important to note that certain breeds, due to their brachycephalic condition, show an increased predisposition to suffer from skin, eye and dental conditions, such as dermatitis, corneal ulcers and dental problems due to overcrowding. In addition, brachycephaly in dogs has also been associated with disorders of the upper respiratory system. Breeds commonly exhibiting this trait include the Bulldog, Pug, Boxer, Pekingese, Boston Terrier, Shih Tzu, Brussels Griffon and Chihuahua.

Bibliography

Schoenebeck JJ, Hutchinson SA, Byers A, et al. Variation of BMP3 contributes to dog breed skull diversity. PLoS Genet. 2012;8(8):e1002849.