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Degenerative Myelopathy (DM)

DM is a disease which affects older dogs, the mode of inheritance is recessive with variable penetrance, two clears will only produce clears,if two carriers were bred, carriers, clears and affected could be produced.

It is a progressive disease of the spinal cord, depicted initially by a loss of coordination in the hind limbs, muscle atrophy will follow and eventually the front limbs will succumb, the dog eventually will be unable to raise itself and will probably become incontinent, the disease is chronic and will ultimately result in paralysis. There is no cure for DM. The progression of the disease can be different for each individual from several months to several years, some dogs will never develop the disease as it may be likely that they would be affected by some other condition first.

Researchers have discovered the two alleles associated with DM, the normal allele G, which is the predominant allele, where the dogs will not go on to develop DM and the affected allele A where dogs are at a higher risk of developing DM but do not necessarily go on to do so.

Puppies inherit two alleles, one from the sire and one from the dam, the table below shows a summary of  how an individual can inherit copies from it's parents.
An individual needs two copies of the affected allele to be at risk from the disease.


There is now a DNA test in the UK for DM.

Table showing the percentage offspring affected between various matings,  even if the hound carries two copies of the affected alleles it does not mean that the hound will go on to develop the disease as it has variable penetrance, it is advisable to only mate carriers to clears so that no affected/at risk progeny are produced.


 OFFSPRING  AFFECTED

SIRE

CLEAR

G/G

CARRIER

G/A

AFFECTED

A/A




DAM

CLEAR

G/G

100% CLEAR

50%CLEAR

100% CARRIER

50%CARRIER


CARRIER

G/A

50%CLEAR

25%CLEAR

50%CARRIER

50%CARRIER

50%CARRIER

50%AFFECTED

 25%AFFECTED

AFFECTED

A/A

100% CARRIER

50%CARRIER

100% AFFECTED

 50%AFFECTED










Clear - G/G -  Homozygous Normal
The dog has two normal copies of the allele.
The dog is very unlikely to develop DM.

Carrier - G/A - Heterozygous
The dog carries one normal allele and one affected allele.
The dog is very unlikely to develop DM.

Affected - A/A - Homozygous Affected/At Risk
The dog carries two affected copies of the affected/at risk allele.
The dog is likely to show signs of DM as it gets older. 
Age of onset is variable and the dog may die from different causes.

Breeders need to take into account the results of the test but there is also a lot of other considerations when making breeding choices. Test results form part of a balanced breeding plan.