In 2009 a DNA mutation was found that explained the observed DM cases ([2]). A cheek swab DNA test is available for this simple recessive mutation - meaning that a dog has to have two copies of the DM-allele - one from each parent - to be consider DM-affected (at high-risk for developing DM).
A March 2014 paper in the Journal of Veterinary Internal Medicine ([3]) has reported that this DM-allele has been found in 124 breeds so far.
1. One of the breeds where the DM-allele was found is Norwich terriers. The paper reports that 74 Norwich terriers were tested and 16 were found to be DM-carriers (no DM-affecteds).
2. NTCA member Denise Faulkner has made the DM-carrier status of a Norwich that she owns ([4]) public on the OFA web site (www.offa.org).
3. The Norwich Breed Club Health Survey on the OFA web site ([5]) lists one Norwich terrier with DM - although we do not know who the dog is or how the diagnosis was made.
I conclude from this that the DM allele is in the Norwich gene pool, and that I can use the DM DNA test to reduce the chances that I will breed a DM Norwich. All I have to do is never breed a DM-carrier to a DM-carrier. Of course, the only way to know the status of a dog is by testing.
In my opinion, DM DNA testing joins PLL (primary lens luxation) DNA testing as something done by responsible Norwich breeders.
Blair Kelly
20140815
[1] http://www.offa.org/dnatesting/dm.html
[2] Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis, Awano et.al., Proceedings of the National Academy of Sciences of the United States of America, Feb 2009.
[3] Breed Distribution of SOD1 Alleles Previously Associated with Canine Degenerative Myelopathy, Zeng et.al., Journal of Veterinary Internal Medicine, March 2014.
[4] Denwich The Lion Hearted (Leo), RN16047102.