"There is always a double mutation in the SOD1 gene in canine DM cases.”

Awano et al. (2009) “Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis” PNAS vol. 106 no. 8, p.2794-2799.

Methodology:

38 DM cases and 17 non-DM cases were compared via genome-wide sequencing to see where mutations tended to cluster.

Some Conclusions:

Researchers discovered a mutation in both genetic copies of SOD1 in all DM-affected dogs, but noticed that non-affected dogs could have 2, 1, or no mutated copies of SOD1.

Researchers saw that nerves in the DM-affected dogs had clusters of mutated SOD1 in clumps throughout the cell.

In Context:

We now know that having 2 copies of the SOD1 mutation ("At Risk” DM test result) means that there is a low chance of developing late-onset DM (typically after age 8) - around 1.5%.

Approximately 60%+ of the Pembroke Welsh Corgi population at the time of the study (2009) was categorized as “DM At Risk”.

There also appear to be other genes responsible for the development of DM in Pembroke Welsh Corgis which have not yet been discovered.