Duchenne muscular dystrophy is a progressive myopathy caused by the absence of dystrophin due to variants in the DMD gene. At least two causal variants have been described in the Cavalier King Charles Spaniel and it presents with weakness, muscle atrophy and marked elevation of creatine kinase. It is inherited in a recessive X-linked manner.

Described in the Cavalier King Charles Spaniel. Duchenne muscular dystrophy is also described in other breeds (Golden Retriever, Rottweiler, Cocker Spaniel, Labrador Retriever, etc.), each with its own DMD variant; they should not be extrapolated between breeds.

- Progressive muscle weakness\n- Abnormal gait and difficulty opening the jaw\n- Muscle atrophy\n- Marked elevation of serum creatine kinase\n- Signs starting in the first weeks of life

Walmsley et al. (2010) described in the Cavalier King Charles Spaniel a variant in the splice donor site of exon 50 of DMD (c.7294+5G>T) that causes skipping of exon 50 and truncation of dystrophin. Nghiem et al. (2017) identified in the same breed a second variant, a 7-bp deletion in exon 42 (c.6051-6057delTCTCAAT, mRNA).

- Test females related to affected animals to identify carriers\n- Do not breed affected dogs or carrier females\n- Affected males must not be used for breeding\n- In the case of a male puppy with weakness and elevated CK, consider DMD testing\n- Molecular confirmation should look for the two variants described in the breed

The clinical picture and the absence of dystrophin on muscle biopsy guide the diagnosis; molecular confirmation requires identifying the specific variant, which is breed-specific. Two different DMD variants have been described in the Cavalier, so a test that detects only one of them may give false negatives.

1. Walmsley GL et al. 2010. A duchenne muscular dystrophy gene hot spot mutation in dystrophin-deficient cavalier king charles spaniels is amenable to exon 51 skipping. PLOS One. PMID: 20072625
2. Nghiem PP et al. 2017. Whole genome sequencing reveals a 7 base-pair deletion in DMD exon 42 in a dog with muscular dystrophy. Mammalian Genome. PMID: 28028563
3. OMIA:001081-9615. Muscular dystrophy, Duchenne type. Online Mendelian Inheritance in Animals.