After the recent publication of Degenerative Myelopathy - Diagnosis and Inheritance, we received an excellent query from an experience breeder of French Bulldogs, who was concerned that her middle-aged dog was showing "classic" signs of Degenerative Myelopathy (DM).

The dog had a clear genetic test for the SOD 1 mutation, but was experiencing clinical signs associated with DM: awkward and uncoordinated hind gait, loss of balance and falling when turning and also when stressed. The breeder had also observed French Bulldogs over the years in dog showing with uncoordinated hindlegs, dragging feet, and other mobility challenges that they questioned, could this be DM?

There have been concerns raised by researchers in DM diagnosis, and usage of testing for SOD 1 in the French Bulldog. French Bulldogs are currently not included as a breed associated with DM. French Bulldogs have been the subject of research investigating neurological disorders in the breed identifying other myelopathies of concern, but not DM (Mayousse, 2017). The current best available information is that SOD 1 mutation testing is unlikely to be relevant for the breed.

Unfortunately, clinical signs of DM across many breeds of dog can mimic or appear very similar to other more common breed-associated spinal or neurological issues, it can be very difficult to confirm a diagnosis of DM without a post-mortem. This may explain why the breeder's dog appears to have clinical signs, but has tested clear for SOD 1. Some more common conditions in the French Bulldog include degenerating hemivertebrae, or missing hemivertebrae, both of which could have similar clinical signs. 

One of the main concerns raised by vets and researchers regarding DM is the potential for misdiagnosis for more common and in some cases treatable or more manageable conditions.

French Bulldogs are currently listed as "orange" for SOD 1 breed relevance rating (BRR), which means that the evidence reviewed is either inconclusive for relevance, or the disease has never been observed in the breed. There are some breeds listed as green (some evidence) or yellow (no research available), for SOD 1 testing. However, given the very low predictability of risk for even "green" breeds, it is a genetic test that should be approached with caution. Even for the breeds where the risk prediction value is better, it appears that the SOD 1 test is best for eliminating DM as the likely condition rather than use for breed-wide management. 

The breeder's dog almost certainly does not have DM, but there are a number of other conditions that have similar clinical symptoms, including those that respond to treatment and management. Even for breeds where DM testing may be relevant, as described in the articles around using SOD1 (and SOD2) genetic tests for DM, the usefulness is mostly in eliminating DM as a diagnosis. 

Resources:

Infographic of SOD 1 testing for DM
Summary of new research
Original research, including diagnosis definition, which may be especially interesting to vets

Ref:

Mayousse, V., Desquilbet, L., Jeandel, A. et al. Prevalence of neurological disorders in French bulldog: a retrospective study of 343 cases (2002–2016). BMC Vet Res 13, 212 (2017). https://doi.org/10.1186/s12917-017-1132-2

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