Test Detail

A form of canine degenerative myelopathy (DM) associated with a Bernese Mountain Dog-specific variant in exon 1 of the SOD1 gene, distinct from the classic 'all breeds' variant (c.118G>A, exon 2). The variant produces a superoxide dismutase 1 with a tendency to aggregate and degeneration of the long spinal cord tracts, with progressive paralysis in adults. The Bernese Mountain Dog can carry both the exon 1 and the exon 2 variant, so combined testing for both is recommended in the breed.

The SOD1:c.52T allele was detected only in the Bernese Mountain Dog in a screening of 33,747 dogs from 222 breeds. In 408 Bernese Mountain Dogs: c.118G>A heterozygous 46.1% and homozygous 6.6%; c.52A>T heterozygous 15.9% and homozygous 0.5%; 5.4% were compound heterozygotes.

- Test Bernese Mountain Dog breeding animals with BOTH SOD1 variants (exon 1 and exon 2) before mating
- Do not mate two carriers of the same variant: 25% risk of homozygotes in each litter
- Assess the risk of compound heterozygosity when mating a carrier of the exon 1 variant with a carrier of the exon 2 variant
- A carrier of one variant can be mated with a dog clear for both; offspring intended for breeding must be tested
- Consider that a homozygote will not necessarily develop DM (incomplete penetrance)
- Communicate the combined status to the buyer and record the result in the pedigree

Differential diagnosis with the same causes of chronic myelopathy in adults (spinal compression, disc herniation, tumours, discospondylitis, ischaemic myelopathy). In the Bernese Mountain Dog combined testing of both SOD1 variants is essential. Bear in mind the limit of penetrance: the genotype does not deterministically predict clinical onset. Take into account the possible allele dropout due to the intron 2 insertion when interpreting genotypes. Supportive management (physiotherapy, mobilisation); there is no curative treatment.

1. Awano T, Johnson GS, Wade CM, et al. Genome-wide association analysis reveals a SOD1 mutation in canine degenerative myelopathy that resembles amyotrophic lateral sclerosis. Proc Natl Acad Sci U S A. 2009;106(8):2794-2799. PMID: 19188595
2. Wininger FA, Zeng R, Johnson GS, et al. Degenerative myelopathy in a Bernese Mountain Dog with a novel SOD1 missense mutation. J Vet Intern Med. 2011;25(5):1166-1170. PMID: 21848967
3. Zeng R, Coates JR, Johnson GC, et al. Breed distribution of SOD1 alleles previously associated with canine degenerative myelopathy. J Vet Intern Med. 2014;28(2):515-521. PMID: 24524809
4. Pfahler S, Bachmann N, Fechler C, et al. Degenerative myelopathy in a SOD1 compound heterozygous Bernese mountain dog. Anim Genet. 2014;45(2):309-310. PMID: 24450472
5. Coates JR, Wininger FA. Canine degenerative myelopathy. Vet Clin North Am Small Anim Pract. 2010;40(5):929-950. PMID: 20732599