Lapis ISSN 2398-2969

Brachycephalic syndrome

Synonym(s): Brachycephaly

Contributor(s): Kristina Hunter, Livia Benato


  • Cause: congenital shortening of skull bones with widening of the maxilla.
  • Signs: short and broad facial structure, dental malocclusion, nasolacrimal duct disease, respiratory infections, ear infections.
  • Diagnosis: predisposed breed, clinical signs, oral endoscopy, radiography, computed tomography, ultrasonography.
  • Treatment: dietary modification, ear cleaning, dental surgery, nasolacrimal duct cannulation.
  • Prognosis: good for mild cases with early intervention – poor if advanced disease or severe malformations.
Print off the Owner Factsheet on Brachycephalic syndrome to give to your clients.


Predisposing factors



  • The dwarf allele has been shown to be responsible for the craniofacial changes noted in dwarf breeds:
    • 25% heritability estimate.
    • Simple autosomal recessive inheritance with incomplete penetration.
    • Associated with a deletion mutation in the coding sequence.
    • Homozygous dw/dw is lethal:
      • ‘Peanut’ deformity with tiny ears, swollen head and markedly reduced birth weights to littermates.
      • Death inevitable within a few days following birth due to neurological and gastrointestinal dysfunction.
    • Heterozygous Dw/dw:
      • Reach 2/3 size of ‘wild-type’ litter mates at birth.
      • Typically <1 kg in adulthood but given incomplete penetrance can be larger.
      • More compact, rounded body shape with shortened facial structure and wider, broader skull that is disproportionately large.
    • Homozygous wild-type rabbits are DW/DW:
      • Some dwarf rabbits have this genotype but retain the brachycephalic phenotype.
      • Other gene loci are likely to produce dwarf phenotypes alone or in combination with this gene, eg mutations in the HMGA2 transcription regulator gene has also been associated with brachycephalic traits.


  • Inherited gene mutation (one or more) → altered transcription of genes encoding development of cranium → maxilla develops abnormally → maxillary brachygnathism rather than true mandibular prognathism → dental arcades in abnormal alignment (malocclusion) leading to:
    • Insufficient attrition of occlusal surface → spur formation and root elongation with oral soft tissue trauma → progressive worsening of malocclusion → loss of apical bone as roots continue to elongate → secondary tooth root abscessation → jaw osteomyelitis, tooth resorption and tooth loss → Ptyalism → moist dermatitis of mandible and neck.
    • Compression of nasolacrimal ducts by elongating tooth roots → obstructed tear drainage → epiphora → infection of duct causes dacryocystitis → moist dermatitis of face.
    • Extension of tooth root abscesses into nasal cavity → rhinitis → extension into sinuses →rhinosinusitis with nasal turbinate destruction.


  • Progressive and lifelong


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Further Reading


Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Johnson J C & Burn C C (2019) Lop-eared rabbits have more aural and dental problems than erect-eared rabbits: a rescue population study. Vet Rec 185 (24), 758 PubMed.
  • O’Neill D G, Craven H C, Brodbelt D C et al (2019) Morbidity and mortality of domestic rabbits (Oryctolagus cuniculus) under primary veterinary care in England. Vet Rec. 1-8 PubMed.
  • Harvey N D, Oxley J A, Miguel-Pacheco G et al (2019) What makes a rabbit cute? Preference for rabbit faces differs according to skull morphology and demographic factors. Animals 9 (10), 728 PubMed.
  • Carneiro M, Hu D, Archer J et al (2017) Dwarfism and altered craniofacial development in rabbits is caused by a 12.1 kb deletion at the HMGA2 locus. Genetics 205 (2), 955-965 PubMed.
  • de Matos R, Ruby J, Van Hatten R A & Thompson M (2015) Computed tomographic features of clinical and subclinical middle ear disease in domestic rabbits (Oryctolagus cuniculus): 88 cases (2007-2014). JAVMA 246 (3), 336-43 PubMed.

Other sources of information

  • McInnes E F (2011) Background Lesions. In: Laboratory Animals E-Book: A Color Atlas. 1st edn. Elsevier Inc, USA. pp 87-92.
  • Vennen K M & Mitchell M (2008) Rabbits. In: Manual of Exotic Pet Practice. 1st edn. Elsevier Inc, USA. pp 375-405.