Alternative dystrophin gene transcripts in golden retriever muscular dystrophy

Golden retriever muscular dystrophy (GRMD), the canine model of Duchenne muscular dystrophy (DMD), is caused by a splice site mutation in the dystrophin gene. This mutation predicts a premature termination codon in exon 8 and a peptide that is 5% the size of normal dystrophin. Western blot analysis of skeletal muscle from GRMD dogs reveals a slightly truncated 390-kD protein that is approximately 91% the size of normal dystrophin. This 390-kD dystrophin suggests that GRMD dogs, like some DMD patients, employ a mechanism to overcome their predicted frameshift. Reverse-transcriptase polymerase chain reaction on GRMD muscle has revealed two in-frame dystrophin transcripts which lack either exons 3-9 or exons 5-12. Both transcripts could be translated into a dystrophin protein of approximately 390 kD. An understanding of how truncated dystrophin is produced in GRMD may allow this mechanism to be manipulated toward a potential therapy for DMD.