pathologically confirmed DM affected dogs. A genetic test for the sodi mutation is available from several dog DNA testing laboratories including the University of Missouri (OFA testing). As DM is a complexly inherited disease, dogs must have a mutation in another (yet unidentified) gene or genes in addition to being homozygous for the sodi mutation to become clinically affected. Based on the lack of confirmed cases in the French Bulldog breed it is probable that the breed lacks other causative genes necessary to produce clinical DM.
The sodi mutation is an ancient mutation in the dog genome and is the most frequent mutation identified in the genetic screening of mixed-breed and purebred dogs. Mars/Genoscoper testing finds that the sodi mutation frequency is 7.77% in all mixed-breed dogs tested, and 5.41% in all purebred dogs tested. In several breeds the frequency of the sodi mutation is over 90%, but no members of the breed have ever been diagnosed with clinical DM.
In worldwide testing of French Bulldogs, 2-5% test homozygous "at risk" for the sodi mutation, and 18-33% test as heterozygous carriers. However, the presence of the sodi mutation is of no consequence to any French Bulldog as DM is not a clinical disease in the breed.
Due to misdiagnoses, misconception and misinterpretation of sodi testing, several national French Bulldog parent clubs call for pre-breeding sodi testing. This erroneous call places an enormous pressure to restrict the breeding of healthy, quality French Bulldogs. It severely restricts the genetic diversity of the breed by selecting against up to one-third of all dogs for breeding. In addition, a sodi homozygous "at risk" test result places a significant and unnecessary emotional burden on owners who believe that their family member will develop DM and die from the disease. Unless and until DM is proven to be a significant clinical disease in the French Bulldog breed, no French Bulldog should be tested for the sodi mutation and no breeding decisions should be made based on the results of sodi testing. French Bulldog breeders should concentrate on selecting for quality breeding dogs that are free of validated breed-specific disease liability genes and genetic disorders.
Pertinent References
Mayousse et. al. Prevalence of neurological disorders in French bulldog: a retrospective study of 343 cases (2002-
2016). BMC Vet Res. 2017;13:212.
O'Neill et al. Demography and disorders of the French Bulldog population under primary veterinary care in the UK in 2013. Canine Genet Epidem. 2018;5:3
Ryan et. al. Prevalence of thoracic vertebral malformations in French bulldogs, pugs and English bulldogs with and without associated neurological deficits. Vet 1. 2017;221:25-9.
Inglez de Souza et. al. Evaluation of the influence of kyphosis and scoliosis on intervertebral disc extrusion in French bulldogs. BMC Vet Res. 2018;14(1):5.
Donner et. al. Frequency and distribution of 152 genetic disease variants in over 100,000 mixed breed and purebred dogs. PLos Genet. 2018;15(1):1007938.
Zeng et. al. Breed Distribution of SOD1 Alleles
Previously Associated with Canine Degenerative Myelopathy. J Vet Intern Med. 2014;28:515-521.
This article can be reproduced with the permission of the author; jerold.bell@tufts.edu
