From Dog

Brachygnathism (Undershot bite) refers to shortening of the upper jaw. In many affected dogs, brachycephalic upper airway obstructive syndrome is a consequential development.

Brachygnathism is often a congenital disease, but can be observed in dogs with:

Although this condition may arise spontaneously in mesocephalic breeds, it is maintained as a breed characteristic in the brachycephalic (bulldog) type, and secondary abnormalities of soft tissues are often associated with this condition.

Due to extreme reduction of the maxillary region, abnormal development of the nasal alae and turbinate bones may occur with subsequent respiratory dyspnoea. Secondary laryngeal collapse has been reported in relation to these conditions[2]. Oversize of the tongue may occur, although the tongue would fit a skull of normal maxillary proportions; this then may be relative oversize of the tongue. The tongue may be protruded continually and has been mistaken for hypoglossal paralysis.

Elongation of the soft palate is a common anomaly in brachyfacial breeds and contributes to respiratory embarrassment, heat stroke, laryngeal collapse, and the reverse sneeze syndrome. This disproportionate size of soft tissue may be absolute oversize[3].

Polygenic disorders causing brachygnathism have been reported in the Australian Shepherd with lumbar scoliosis, short malformed tibias and fibulas, polydactyly, cleft palate and cleft lip[4].


  1. Epub Bud
  2. Leonard, HC (1960) Collapse of larynx and adjacent structures in the dog. JAVMA 137(6):360-363
  3. Fox MW (1963) Developmental Abnormalities of the Canine Skull. Can J Comp Med Vet Sci 27(9):219-222
  4. Senders CW et al (1986) Observations about the normal and abnormal embryogenesis of the canine lip and palate. J Craniofac Genet Dev Biol Suppl 2:241-248