A duchenne muscular dystrophy gene hot spot mutation in dystrophin-deficient cavalier king charles spaniels is amenable to exon 51 skipping.
BACKGROUND
Duchenne muscular dystrophy (DMD), which afflicts 1 in 3500 boys, is one of the most common genetic disorders of children. This fatal degenerative condition is caused by an absence or deficiency of dystrophin in striated muscle. Most affected patients have inherited or spontaneous deletions in the dystrophin gene that disrupt the reading frame resulting in unstable truncated products. For these patients, restoration of the reading frame via antisense oligonucleotide-mediated exon skipping is a promising therapeutic approach. The major DMD deletion "hot spot" is found between exons 45 and 53, and skipping exon 51 in particular is predicted to ameliorate the dystrophic phenotype in the greatest number of patients. Currently the mdx mouse is the most widely used animal model of DMD, although its mild phenotype limits its suitability in clinical trials. The Golden Retriever muscular dystrophy (GRMD) model has a severe phenotype, but due to its large size, is expensive to use. Both these models have mutations in regions of the dystrophin gene distant from the commonly mutated DMD "hot spot".


RESULTS
Here we describe the severe phenotype, histopathological findings, and molecular analysis of Cavalier King Charles Spaniels with dystrophin-deficient muscular dystrophy (CKCS-MD). The dogs harbour a missense mutation in the 5' donor splice site of exon 50 that results in deletion of exon 50 in mRNA transcripts and a predicted premature truncation of the translated protein. Antisense oligonucleotide-mediated skipping of exon 51 in cultured myoblasts from an affected dog restored the reading frame and protein expression.


CONCLUSIONS
Given the small size of the breed, the amiable temperament and the nature of the mutation, we propose that CKCS-MD is a valuable new model for clinical trials of antisense oligonucleotide-induced exon skipping and other therapeutic approaches for DMD.
Walmsley
Gemma L
GL
Department of Veterinary Clinical Sciences, Royal Veterinary College, London, United Kingdom.
Arechavala-Gomeza
Virginia
V
Fernandez-Fuente
Marta
M
Burke
Margaret M
MM
Nagel
Nicole
N
Holder
Angela
A
Stanley
Rachael
R
Chandler
Kate
K
Marks
Stanley L
SL
Muntoni
Francesco
F
Shelton
G Diane
GD
Piercy
Richard J
RJ
D000818:Animals; D001483:Base Sequence; D004195:Disease Models, Animal; D004285:Dogs; D016189:Dystrophin / Q000235:genetics*; D005091:Exons; D007150:Immunohistochemistry; D008297:Male; D020388:Muscular Dystrophy, Duchenne / Q000235:genetics* / Q000473:pathology; D009154:Mutation; D010641:Phenotype; D012150:Polymorphism, Restriction Fragment Length; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction
D016189:Dystrophin; D012333:RNA, Messenger