If both parents are carriers (N/A) each puppy has a 25% chance of being clear (N/N), 50% chance of being a carrier (N/A), and 25% chance of being affected and carrier (A/A)
If one parent is clear (N/N) and one parent is affected (A/A) then all puppies will be carriers (N/A)
If one parent is a carrier (N/A) and one is at risk (A/A) each puppy has a 50% chance of being a carrier(N/A) and 50% chance of being affected and carrier (A/A)
If both parents are at risk (A/A) then all puppies will be affected and carrier (A/A)

Symptoms
Degenerative myelopathy initially affects the back legs and causes muscle weakness and loss, and lack of coordination. These cause a staggering affect that may appear to be arthritis. The dog may drag one or both rear paws when it walks. This dragging can cause the nails of one foot to be worn down. The condition may lead to extensive paralysis of the back legs. As the disease progresses, the animal may display symptoms such as incontinence and has considerable difficulties with both balance and walking. If allowed to progress, the animal will show front limb involvement and extensive muscle atrophy and paralysis. Eventually cranial nerve or respiratory muscle involvement necessitates euthanasia or long term palliative care.Progression of the disease is generally slow but highly variable. The animal could be crippled within a few months, or may survive as long as three years or more. Causes
The etiology of this disease is unknown.
Margaret Sullavan, American stage and film actress, suffered from the congenital hearing defect otosclerosis that worsened as she aged, making her more and more hard of hearing. Howard Hughes the pioneering American aviator, engineer, industrialist, and film producer also suffered from otosclerosis. Frankie Valli, lead singer of The Four Seasons, suffered from it in the late 1960s and early 1970s, forcing him to "sing from memory" in the latter part of the 70s (surgery restored most of his hearing by 1980). Pittsburgh Penguins forward Steve Downie suffers from otosclerosis. The British queen Alexandra of Denmark suffered from it, leading to her social isolation; Queen Alexandras biographer, Georgina Battiscombe, was able to have "some understanding of Alexandras predicament" because she too had otosclerosis. Adam Savage, co-host of MythBusters, uses a hearing aid due to otosclerosis. Sir John Cornforth, Australian-British Nobel Prize in Chemistry laureate

References
External links
NIH/Medline