Degenerative Myelopathy Testing
A DNA Test for
DM
Understanding the DNA Test for Degenerative Myelopathy
"We have discovered a mutation in a gene which is associated with development of degenerative myelopathy (DM).
In that gene, the DNA occurs in two possible forms (or alleles). The “G” allele is the predominant form in dogs that seldom or never develop DM; you can think of it as the “Good” allele. The “A” allele is more frequent in dogs exhibiting clinical signs of DM; you can think of it as the “Affected” allele.
Summary: “A” allele is associated with DM; “G” allele is not associated with DM.
Since an individual dog inherits two alleles (one from the sire and one from the dam) there are three possible test results: two “A” alleles; one “A” and one “G” allele; and, two “G” alleles.
Summary: Test results can be A/A (affected/at risk), A/G (carrier), or G/G (normal) .
Microscopic examination of a section of spinal cord (following euthanasia) is the "gold standard" for diagnosing and confirming DM. We do not have the opportunity to examine cord samples from all the dogs that have died or been euthanized due to DM, but for those cords submitted for evaluation, and where the cellular changes have been consistent with a diagnosis of DM, the dogs have had a DNA test result of A/A in all but 2 individuals. There is additional work being done to better understand these 2 exceptions, but it is clear that the vast majority of real DM cases do have the A/A test result.
Summary: Dogs that test A/G or G/G are very unlikely to develop DM. Dogs that test A/A are likely to develop clinical signs of DM at some point as they age.
Additional research now in progress is focused on understanding why some A/A dogs show clincal signs of DM at 7 or 8 years of age while others only begin to show clinical signs at 14 or 15yrs or older, or may die from some other cause without developing recognized clinical signs of DM.
The “A” allele is very common in some breeds. In these breeds, an overly aggressive breeding program to eliminate the dogs testing A/A or A/G might be destructive to the breed as a whole because it would eliminate a large fraction of the high quality dogs that would otherwise contribute desirable qualities to the breed. Nonetheless, DM should be taken seriously. It is a fatal disease with devastating consequences for the dogs and a very unpleasant experience for the owners who care for them. Thus, a realistic approach when considering which dogs to select for breeding would be to consider dogs with the A/A or A/G test result to have a fault, just as a poor top-line or imperfect gait would be considered faults. Dogs that test A/A should be considered to have a worse fault than those that test A/G. Dog breeders could then continue to do what conscientious breeders have always done: make their selections for breeding stock in light of all of the dogs’ good points and all of the dogs’ faults. Using this approach over many generations should substantially reduce the prevalence of DM while continuing to maintain or improve those qualities that have contributed to the various dog breeds.
Summary: We recommend that dog breeders take into consideration the DM test results as they plan their breeding programs; however, they should not over-emphasize this test result. Instead, the test result is one factor among many in a balanced breeding program."
Questo testo l'ho copiato direttamente da Wolfdog/english scritto da Mikael.
Io capisco bene ciò che vi è scritto, ma lascerei la traduzione a qualcun'altro più bravo di me.
Detto questo, la mia considerazione è sempre coerente con quanto già espresso. La dm è una patologia multifattoriale, in cui ci sono altri fattori che intervengono nella manifestazione della malattia specialmente in soggetti affetti. Per questo motivo è utile selezionare per ridurre l'incremento ma non per questo esagerare o fare terrorismo informativo. Si evince che oltre al fattore eredetitario (DM/DM) interviene la concominante presenza dell allele A/A per determinare la manifestazione della sintomatoliga. Mentre l'allele A/G o G/G in un sogetto DM/DM sembra non presentare la sintomatoligia pur essendo geneticamente affetto.
Ora mi chiedo, se con esame del Dna si ottiene il risultato portatore, affetto, esente...perchè non riescono a individuare nello stesso campione anche la presenza o meno dell'Allele A/A? Il genoma è codificato, motivo per cui si hanno i risultati, ma come mai manca questo tassello?
Questa osservazione è principalmente cerso chi ha il cane affetto, in questo modo si avrebbe la sicurezza o meno che sviluppi la malattia. Un altro nodo alla questione, ma allora questi test genetici sono incompleti?