Case reportBecker muscular dystrophy due to an intronic splicing mutation inducing a dual dystrophin transcript

•A novel mutation in the intron 10 acceptor splice site of the DMD gene was found.•This splicing mutation induces an out of frame transcript skipping exon 11.•However, it permits production of a low abundant full length transcript.•Patient presents with a mild Becker phenotype.•A reduced amount of full length dystrophin is enough to avoid the Duchenne phenotype.

We describe a 29-year-old patient who complained of left thigh muscle weakness since he was 23 and of moderate proximal weakness of both lower limbs with difficulty in climbing stairs and running since he was 27. Mild weakness of iliopsoas and quadriceps muscles and muscle atrophy of both the distal forearm and thigh were observed upon clinical examination. He harboured a novel c.1150-3C>G substitution in the DMD gene, affecting the intron 10 acceptor splice site and causing exon 11 skipping and an out-of-frame transcript. However, protein of normal molecular weight but in reduced amounts was observed on Western Blot analysis. Reverse transcription analysis on muscle RNA showed production, via alternative splicing, of a transcript missing exon 11 as well as a low abundant full-length transcript which is enough to avoid the severe Duchenne phenotype. Our study showed that a reduced amount of full length dystrophin leads to a mild form of Becker muscular dystrophy. These results confirm earlier findings that low amounts of dystrophin can be associated with a milder phenotype, which is promising for therapies aiming at dystrophin restoration.