Molecular test for upper airway syndrome (Upper Airway Syndrome, UAS) of the Norwich terrier, a hereditary respiratory condition with elongated soft palate, additional dorsal pharyngeal tissue and variable laryngeal collapse that causes dyspnoea and stridor. It affects the upper respiratory system and compromises exercise and quality of life. The test reports clear/carrier/affected status for the known risk variant.

Applicable breed: Norwich terrier. In the genomic analysis of 401 Norwich terriers the risk allele frequency was 0.57 (Marchant et al. 2019, PMID 31095560); the allele is also enriched in English and French Bulldogs. No systematic clinical frequencies are published (limited data).

- Inspiratory stridor and dyspnoea, especially on exertion
- Elongated soft palate and additional dorsal pharyngeal tissue
- Variable laryngeal collapse (everted saccules, keyhole larynx)
- Exercise intolerance and respiratory noises
- Worsening with heat and excitement

Upper airway syndrome of the Norwich terrier was described as a respiratory condition with a genetic basis reminiscent of brachycephalic syndrome but in a breed that is not strictly brachycephalic. Molecular characterisation identified a missense variant in ADAMTS3 associated with the disease (Marchant et al. 2019, PMID 31095560).

- Genotype breeding dogs before mating
- While the mode of inheritance is being confirmed, treat the molecular status with caution: avoid mating two animals with the variant or with a clinical respiratory history
- A clinically affected animal must not be bred; assess the respiratory phenotype of breeding dogs (rhinoscopy/laryngoscopy if appropriate)
- After a confirmed clinical case, do not repeat the parental mating and inform the buyer of the status

Differential diagnosis with classic brachycephalic syndrome, tracheal collapse, laryngeal paralysis and nasal obstructive processes (foreign bodies, neoplasia). Rhinoscopy/laryngoscopy and assessment under sedation guide the diagnosis. Medical management (weight control, avoiding heat/excitement) and surgical management (rhinoplasty, palatoplasty, arytenoidopexy depending on grade).

1. Marchant TW, Dietschi E, Rytz U, et al. (2019) An ADAMTS3 missense variant is associated with Norwich Terrier upper airway syndrome. PLoS Genet 15:e1008102. PMID: 31095560