An unusual mutation in the dystrophin gene sheds new light on Duchenne muscular dystrophy, according to the latest paper written by researchers from the JU Faculty of Biochemistry, Biophysics and Biotechnology. Their findings were published in the prestigious journal Circulation: Genomic and Precision Medicine, published by the American Heart Association, one of the world’s leading scientific societies devoted to cardiovascular disease.

Duchenne muscular dystrophy (DMD) affects approximately 1 in 5,000 boys and is caused by mutations in the DMD gene, which encodes dystrophin, a protein essential for the proper skeletal and cardiac muscle function. Mutations in the DMD gene most often result in a lack of dystrophin, which leads to progressive muscle weakness and wasting, loss of the ability to walk, and the development of cardiomyopathy and respiratory failure.

Research into the mechanisms of DMD has for many years been one of the main areas of work of Prof. Józef Dulak and the team at the Department of Medical Biotechnology of the Jagiellonian University. The team’s latest publication is also an example of collaboration with clinicians, in this case with the team at the Department of Neurology of the Medical University of Warsaw (Prof. Anna Kostera-Pruszczyk and Prof. Anna Potulska-Chromik).

The paper 'Gene-Corrected Human iPSC–Derived Cardiomyocytes and Skeletal Muscles Reveal Partial Dystrophin Dp427 Preservation and Cardiac Dp116 Expression in Duchenne Muscular Dystrophy Patient With a Splice-Site Mutation in Intron 68 (c.9975-1G>T)', written by Marta Białobrzeska and her colleagues from Prof. Dulak's team, is concerned with the case of a boy diagnosed with Duchenne muscular dystrophy in whom a previously undescribed mutation in the DMD gene had been identified. Based on existing knowledge, this mutation was predicted to completely prevent dystrophin production. The results, however, proved far more complex.

The physician collected blood cells from the patient and researchers from the Department of Medical Biotechnology reprogrammed them into induced pluripotent stem cells (iPSCs). Then, using CRISPR/Cas9 genome-editing technology, they created a corresponding cell line in which they corrected the mutation. This allowed them to directly compare diseased and 'corrected' cells with an identical genetic background. Because iPSCs can differentiate into many cell types, the researchers then derived skeletal muscle cells and cardiomyocytes, i.e. heart muscle cells, from the iPSCs.

The most important finding of the paper was that the studied mutation does not cause a complete loss of dystrophin. Instead, it results in the loss of only two amino acids in the protein. Moreover, dystrophin levels in heart cells remained surprisingly high, whereas they were markedly reduced in skeletal muscle cells. These results showed that the same mutation can have different effects in different tissues.

Although DMD is recognised primarily as a disease of skeletal muscle, heart damage is one of the main causes of premature death in patients. This is why the results concerning cardiomyocytes were of particular interest. The researchers showed that despite preserved dystrophin (Dp427) production, the heart cells did not function entirely normally. Changes were observed in their response to adrenergic stimulation, i.e., the signaling that drives the heart during stress or physical exertion. These changes, revealed through collaboration with Dr Paweł Ferdek from the JU Department of Cell Biology, suggest that even minor dystrophin damage may cause subtle disturbances in heart function that, over time, may contribute to the development of cardiomyopathy.

What was equally interesting was the discovery of Dp116, a shorter dystrophin isoform, in human cardiomyocytes. The authors emphasise that this is the first direct evidence of this protein in iPSC-derived heart cells.

The study is another example of the use of modern cellular models and CRISPR/Cas9 technology in research on rare diseases. The team’s work shows that DNA analysis alone cannot predict the effects of mutations in the DMD gene. Even mutations that should theoretically lead to a complete absence of dystrophin can produce a more complex biological picture. The discovery may also help explain why in some patients the disease follows a milder course or deviates from the classic presentation of Duchenne muscular dystrophy.