There is such exciting news lately about the gains made in treatments for DMD. I attended the conference hosted by Action Duchenne in London a few weeks ago and heard representatives speak from AVI, Biomarin and Prosenza. What I find a little puzzling is why two trials are both testing deletion of exon 51. Is that deletion the most prevanlent form of mutation causing DMD? It seems they are going on next to a trial to treat patients with a deletion of exon 50. How do they make these decisions on which exon deletion to test next? Does anyone have any idea?

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We've also been contacted. Sam has a deletion of 50.

jenn said:
our two boys have deletion of 52, although clinically they couldnt be more different, max is almost 8, he runs, jumps and plays, he seems to get "better"... austin is almost 11, and has used a scooter for 4 years, he just got his first power chair. we have been contacted by nationwide childrens in columbus, for pre enrollment data for the avi trial of exon51 skipping that will possibly begin in march.has anyone else shown interest in that trial? we hope that both boys will get in, we will take any improvement we can get for austin.
Rhiannon - how do you know you're out of frame at the MRNA level?

My son has an in-frame deletion and is progressing as DMD also.

Can they test the MRNA somehow?
Yes, it can be tested using a muscle biopsy or even a skin biopsy. I am not sure who ca do it using the skin biopsy though. I did talk to Steve Wilton 2 years ago and he said that he could look at our son's mRNA (or test if exon skipping works on his cells) if our doctor would send the skin biopsy to him. Since Robert is so young, we decided not to do it at this point.

In my opinion, a muscle biopsy would be the best way to go for the in-frame mutations progressing like DMD, it can provide complete information. Also, muscle biopsy is used for enrollment to trials.

Keith Van Houten said:
Rhiannon - how do you know you're out of frame at the MRNA level?

My son has an in-frame deletion and is progressing as DMD also.

Can they test the MRNA somehow?
I guess I don't understand how you get the mRNA from a biopsy. I thought a biopsy tells you if you have dystrophin present. Maybe I don't understand what mRNA is properly. I understood it to be a copy of the DNA that is made and used for creation of the protein.

Can you explain it in simple terms? Send me a private message if you want to continue this off thread.

Thanks, Keith
Hi Kieth,

A biopsy is just a chunk of tissue taken for diagnostic assessment. This can be the chunk within the core of a largish needle ..needle biopsy, or a larger chunk taken by open biopsy. The tissue is often treated in someway to preserve it, which can vary depending on the diagnostic test to be performed. It can be frozen or fixed in preservative or some other options. Many of these options preserve much of the integrity of each DNA, RNA and protein in the cells within the biopsy, though certain techniques are better for easy evaluation of one or another of these. RNA is the most fragile as it can be easily degraded by RNAses and so treatment and storage of the tissue will be important for this RNA extraction to work. Generally muscle biopsies for DMD are used to assess dystrophin protein expression in the muscle tissue; both location and abundance. For this, the muscle tissue is sliced into thin sections (from a block of frozen or embedded biopsy tissue) and stained with tagged antibodies specific for the dystrophin protein to enable dystrophin detection...just as you referred to. This same tissue block, or some of the slices, can theoretically be used to extract either DNA or RNA for assessment of dystrophin gene (DNA) or message (RNA) composition. Generally blood is used for DNA since the genome is the same in all cell of the body (except germ cells) and so blood is the most accessible. I dont know the details of the various preservation techniques used in different clinical labs or in standard DMD biopsy tissues, so I can adress the specifics of the likelihood of a given biopsy yielding sufficient useful mRNA. I hope this is understandable. Feel free to ask or email privately if not.

Best,
Carrie

Keith Van Houten said:
I guess I don't understand how you get the mRNA from a biopsy. I thought a biopsy tells you if you have dystrophin present. Maybe I don't understand what mRNA is properly. I understood it to be a copy of the DNA that is made and used for creation of the protein.

Can you explain it in simple terms? Send me a private message if you want to continue this off thread.

Thanks, Keith
Awesome, Carrie. Thanks. I'll digest that a bit before I start with any followup questions.

Please accept my friend request.
Keith you are correct, RNA is the messenger protein used as a template for protein production.

It can be analysed using a northern blot and dystrophin probe, which gives an indication of the size of the RNA transcript. The size of the mRNA is relative to the location and type of deletion. Whilst every cell has the DNA for dystrophin, the best source of mRNA will always be tissues that are actively expressing the gene (skeletal muscles for the long isoform). It is possible to test for mRNA in other tissues, due to some isoforms being ubiquitously expressed, however there are a lot of factors that then need to be considered when interpreting the results.

I don't know if that was what you were after, but if you need anymore information please feel free to contact me :)

Keith Van Houten said:
I guess I don't understand how you get the mRNA from a biopsy. I thought a biopsy tells you if you have dystrophin present. Maybe I don't understand what mRNA is properly. I understood it to be a copy of the DNA that is made and used for creation of the protein.

Can you explain it in simple terms? Send me a private message if you want to continue this off thread.

Thanks, Keith

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