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#apaperaday: A Proof of Principle Proteomic Study Detects Dystrophin in Human Plasma: Implications in DMD Diagnosis and Clinical Monitoring

In today’s #apaperaday, Prof. Aartsma-Rus reads and comments on the paper titled: A Proof of Principle Proteomic Study Detects Dystrophin in Human Plasma: Implications in DMD Diagnosis and Clinical Monitoring

Today’s pick is from the international journal of molecular sciences by Rossi et al on detecting dystrophin fragments in human plasma. Spoiler: still a long way to go… Doi 10.3390/ijms24065215.

Duchenne is caused by lack of dystrophin, while Becker is caused by internally deleted but partially functional dystrophins. Authors outline that there is a delay in diagnosis for Duchenne with an average age of diagnosis at 5 and variability between countries.

Biomarkers for diagnosis and treatment monitoring would be useful. Creatine kinase in blood is a marker for muscle damage but it is general and not specific for Duchenne. A biopsy with dystrophin analysis is specific but very invasive.

Urine analysis is not at all invasive but dystrophin is expressed at such low levels that urine analysis is non informative. Authors here aim to see if detecting dystrophin peptides in blood us a low invasive alternative that is more specific than creatine kinase.

Note authors aberrantly mention that EMA has accepted dystrophin as a pharmacodynamic biomarker (citing one of my papers to substantiate the claim). Regulators suggest using dystrophin restoration analysis as a market but accepting them as validated markers involves much more.

Back to the paper: authors first use a suspension bead array with antibodies to detect two different regions dystrophin. It is clear there is a lot of variation for antibody 1 (left). Duchenne patients have lower levels but within range of what is found in controls.

So you cannot use this to diagnose Duchenne. Antibody 2 shows no difference at all. Note that this is an antibody targeting the end of dystrophin. Blood cells make a smaller dystrophin containing only the end. Most Duchenne patients can make this protein.

So it is not surprising that there is no difference. Authors also tried mass spectrometry for specific dystrophin peptides but they only got this to work for control serum and not patient serum. More work needed.

Not discussed by the authors is the relation between mutation and detection. Even Duchenne patients will make dystrophin: the smaller isoforms and the beginning part (not stable so degraded but the peptides will be there maybe?)

However patients cannot make the part that is deleted. Which part is deleted varies for different patients so using a few peptides or antibodies may not be enough. And ideally patients not making a peptide recognized by the antibody is used to confirm specificity.

Authors outline they wanted to provide proof of concept and that more work is needed. However I doubt this analysis will be able to replace dystrophin analysis in biopsies as it does not tell the size of dystrophin, the location, the distribution. As such for pharmacodynamic analysis I’m afraid a combination of immunofluorescence and western blotting will be required.