Chronic muscle disease of the Dutch Shepherd with non-suppurative muscle inflammation (polymyositis with mononuclear infiltrate and MHC-I expression), progressive muscle weakness and atrophy with exercise intolerance. It is associated with a homozygous variant of SLC25A12 (mitochondrial aspartate/glutamate transporter), which generates a more oxidising intramitochondrial environment (Shelton et al. 2019). It is distinct from the SLC25A12 variant of the Nova Scotia Duck Tolling Retriever (cerebellar degeneration-myositis complex).

Affected breed: Dutch Shepherd. The disease is described in specific lines of the breed; no reliable figures on incidence or carrier frequency have been published. Consider the low population frequency of the breed when interpreting the available series.

- Progressive muscle weakness and exercise intolerance\n- Muscle atrophy, especially of the proximal musculature\n- Stiff gait and difficulty rising\n- Possible dysphagia or megaoesophagus in forms with pharyngeal/oesophageal involvement\n- Chronic course, with no manifest muscle pain in many cases

Inflammatory myopathy of the Dutch Shepherd was described as a chronic muscle condition of presumed immune basis. Shelton et al. (2019) identified by sequencing a single homozygous variant in SLC25A12 (c.1046T>C; p.L349P) associated with the disease, with functional demonstration of intramitochondrial oxidative stress. Christen et al. (2022) described a DIFFERENT variant of the same gene (c.1337C>T; p.P446L) in the Tolling Retriever with cerebellar degeneration-myositis complex: each test is valid only for its breed and variant.

- With a confirmed case in a line, do not repeat the parental mating\n- Avoid breeding from affected animals or those with a close family history of IM\n- Document the pedigree of cases to support research into the inheritance\n- No molecular test is available: selection is based on clinical history and muscle biopsy\n- Communicate the history to the buyer of offspring from affected lines

Differential diagnosis with myasthenia gravis (which can also cause dysphagia/megaoesophagus and weakness), hereditary muscular dystrophies (e.g., of the Golden Retriever or the Corgi), myopathy due to acid maltase deficiency (type II glycogenosis) and infectious myositis (protozoa, leptospira). Muscle biopsy with histology, MHC-I immunohistochemistry and, depending on the case, electron microscopy are decisive. Immunomodulatory treatment (glucocorticoids and others) according to neurological criteria, with variable response. The absence of a molecular marker makes clinical follow-up essential.

1. Shelton GD et al. 2019, mutación del transportador mitocondrial aspartato/glutamato y miopatía inflamatoria en Pastor holandés (PMID 31594244)
2. Christen JL et al. 2022, variante SLC25A12 distinta en Tolling Retriever con complejo degeneración cerebelosa-miositis (PMID 35886006)
3. OMIA:002294 Complejo degeneración cerebelosa-miositis (SLC25A12)