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 The explanation of this is obvious. Deafness in dogs can be either congenital or hereditary. Congenital deafness can be described as acquired - caused by infections, drugs like gentamicin, liver disorders, or other toxic exposures before or soon after birth.
Inherited deafness is caused by a gene defect that can be autosomal dominant, recessive, sex-linked, mitochondrial, or may involve multiple genes. Congenital deafness in Bull Terriers is most often associated with the piebald gene, which is the gene responsible for carrying pigmentation to cells. This does not mean that only white dogs are affected though. In fact, recent statistics posted at the University of Guelph indicate that there is only a slight difference in the number of instances of deafness between white Bull Terriers and Coloured Bull Terriers. It is not due to a lack of pigment per se but rather the body's ability to transport pigmentation cells to various parts of the body and specifically to the stria. It is known that one function of these cells is to maintain high potassium concentrations in the fluid (endolymph) surrounding the hair cells of the cochlea; these pigment cells are critical for survival of the stria. If it is absent or inadequate, the result is deafness.
The deafness associated with congenital diseases develops in the first few weeks after birth while the ear canal is still closed. The nerve cells of the cochlea subsequently die and permanent deafness results. If the puppy is deaf it is permanently deaf - there is no cure. If on the other hand, the puppy hears at the time of BAER certification, it has no greater chance of becoming deaf in later years than any other breed of dog. Deafness can be either unilaterally (one-sided) in which the dog is able to hear in one ear, or bilateral (both ears affected) in which the dog cannot hear at all. However, both unilateral and bilateral deafness are equally telling for producing affected offspring so only bilaterally hearing dogs should be used for breeding.
The best test to determine a puppy's hearing is called BAER or brain stem auditory evoked response. It is a simple and painless procedure available at a limited number of animal hospitals.
 The issue of heart disease in Bull Terriers is primarily seen in the form of congenital heart disease. The two forms commonly seen are Mitral Valve Dysplasia and Sub-aortic Stenosis.
Mitral valve dysplasia can be described as a "leaking" valve between the two chambers of the heart, the left atrium and left ventricle. Usually the mitral valve does not shut completely which causes the blood that should be pumped entirely into the aorta to supply the body with oxygenated blood from the left ventricle; to leak back into the left atrium. The result is a murmur. It is called Mitral Regurgitation. When the mitral valve is narrowed, it is difficult for the blood to leave the left atrium. This is called Mitral Stenosis. Dogs with this condition can affected mildly or severely. Most dogs can live active normal lives, but with age the condition can worsen and they can die of heart failure.
Sub-aortic Stenosis is the narrowing of the aorta, the major artery carrying the blood supply away from the heart. The condition leads to pulmonary edema which results in left-sided heart failure. There are several tests your veterinarian can perform to screen for these conditions, x-ray series of the chest, ECG or electrocardiography to measure the heart's electrical activity, and a cardiac ultrasound or echocardiography. Many reputable breeders test their dogs with cardiac color doppler ultrasound for very accurate diagnosis.
Kidney disease in Bull Terriers is divided into three forms. The first is renal dysplasia, which, results in kidney failure. The disease causes the kidney's cells to develop improperly, resulting in a non-functioning kidney.
The second form is Hereditary nephritis. This is also fatal, but with a slower progression. Research has not been able to determine a specific age to test for because it can range in age from as early as 2 years up to 8 years. The best prevention (until DNA testing becomes available) is testing breeding dogs every year for Urine-Protein/ Urine-Creatinine Ratio.
The most recently discovered kidney disease is Polycystic Kidney Disease. You may also hear it as PCKD. It is very common to be seen in dogs with heart valve problems. Currently, the most reliable diagnose is made from an ultrasound of the kidneys.
In simplest terms, this is when the kneecap slips out of place. The range can be mild to severe and depends on how shallow the groove is. Adult breeding dogs can be checked for luxating patellas when they are two years old by an orthopedic veterinarian however, the dog cannot be registered clear until 12 months of age. It is always wise to limit a puppy/ adolescence bull terrier's strenuous activity to help not cause undue strain on young joints. Just ask your breeder if the parents were checked for luxating patellas.
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