Canine inherited deafness is thought to be caused by either an autosomal dominant (occurs when an abnormal gene from one parent causes a disease) or an autosomal recessive gene (where the gene must be obtained from both parents to be expressed in the offspring). It is also theorized that there may even be multiple genes involved in inherited deafness.
There has been a direct correlation found between deafness and white coated breeds, especially those with piebald (spotted or patched areas especially in black and white) and merle (reddish or bluish gray coat streaked or speckled with black) pigmentation patterns. A dog can be unilaterally (one-sided) or bilaterally (both sides) affected. Dogs with normal hearing can produce puppies that are bilaterally or unilaterally deaf and vice versa but deaf dogs are more likely to produce deaf puppies. Dogs with inherited deafness should never be bred.
When a puppy is born, the ear canals are closed and remain that way for the first few weeks of life. In congenital deafness, the blood supply to the cochlea (the small spiral shaped bone in the inner ear) will deteriorate and the nerve cells of the cochlea die causing sensorineural or profound deafness. There are over 80 different dog breeds where inherited deafness has been reported and the Maltese is included in this group. However, the percentage of Maltese having inherited deafness is low compared to other breeds such as Dalmatians where it is particularly common.
Signs that a puppy is completely deaf may include aggressive play with his littermates since the deaf puppy cannot hear his siblings cry out in pain. Also sound sleeping in a loud environment or having to jostle the puppy awake are tell-tale signs. If the pup is deaf in only one ear the owner may be unaware of any problem since the puppy can compensate quite well with partial hearing.
A hearing test called Brainstem Auditory-Evoked Response or BAER is available. This test determines if there is electrical activity being transmitted from the cochlea to the brain and will be able to tell the owner if the dog is deaf in one or both ears. The test can be performed on any puppy over 6 weeks of age that is suspected of having a hearing impairment. For a list of BAER testing sites see: http://www.lsu.edu/deafness/baersite.htm
While deafness can be genetic it can also be acquired. The causes of acquired deafness can be due to trauma, intense noise, infections, old age, general anesthesia or Aminoglycoside antibiotics that can cause ototoxicity (a toxin or a toxic level of a therapeutic drug causing damage to the ear). Partial to complete recovery from acquired deafness due to trauma, noise or infections is possible but recovery due to drug ototoxicity is rare.
Deaf dogs can make wonderful companions with proper training of both the dog and the owner. Hearing impaired dogs can learn commands by hand signals or sign language. They must be closely supervised at all times since they are unable to hear in dangerous situations.