Laryngeal paralysis is an inherited disease affecting Bull Terriers and characterised by difficulties in breathing, especially during physical activity, and may cause death by suffocation in severe cases. Larynx paralysis may require surgery to relieve the difficulties in breathing. Clinical signs include decreasing exercise tolerance, progressive laryngeal stridor, voice impairment, episodes of breathing difficulties and collapsing. In the Bull Terrier and Miniature Bull Terrier, a genetic variant has been identified as a major genetic risk factor for an early onset form of laryngeal paralysis. Dogs which are homozygous for the variant are at 23 fold increased risk of developing the disease, and therefore, dogs carrying the varian should be bred with clear dogs to avoid producing puppies with two copies of the variant.