Exon skipping

Oligoribonucleotides (AONs) vary in length between 16 and 22 nucleotides and are chemically modified to be resistant to intracellular nucleases. They are suggested to bind to specific sequences in the pre-mRNA, and thus disturb exon inclusion signals like splice sites, intronic branch point sequences, or exonic splicing enhancer elements. This leads to the removal of the targeted exon (Figure 1).

introductie techniek
Figure 1. Example of exon skipping therapy

The generally applied procedure for the analysis of therapeutic exon skipping in cultured muscle cells is as followed. Muscle cells derived from DMD patients are proliferated in culture and allowed to differentiate into multinucleated myotubes through serum-deprivation. These myotube cultures are transfected with a sequence-specific, exon-internal AON with which the skipping of a specific exon can be induced. Previous years we used the cationic polymer polyethylenimine (PEI) for transfectiom, now use Lipofectamin. Lipofectamin is very efficient in delivering AONs into myotubes: up to 95% transfection efficiencies (Figure 2).

introductie techniek figuur 1
Figure 2. PEI transfection of myotubes using a fluorescent labeled AON

After 24 to 72 hours, RNA is isolated from the treated cultures and analysed by RT-PCR (Figure 3). Correct exon skipping in the smaller transcript fragment is confirmed by sequencing. Immunohistochemical analyses with different dystrophin antibodies is performed to detect dystrophin expression at the membrane. In addition, total protein samples are isolated to detect dystrophin by western blot analysis  (Figure 4).

Figure 3. RT-PCR analysis to detect specific (exon 46) exon skipping in RNA samples
Figuur 11 OAN treated mdx_versie 3
Figure 4. Westernblot analysis to detect dystrophin in protein samples

Exon skipping for point mutations

Small mutations can directly lead to premature stop codons (nonsense mutation) or disrupt the reading frame (intra exonic deletion or duplication of a number of nucleotides that is not divisible by 3). Either way, if the mutation is present in an in-frame exon, such as exon 49 that contains 102 nucleotides (divisible by 3), the mutation can be bypassed by skipping said exon (Figure 1). This has been confirmed in cultured cells from a patient with a nonsense mutation in exon 49.

application exonskip single point mutation_figuur 5
Figure 1. Single exon skipping for point mutations

If the small mutation is present in an exon that contains a number of nucleotides not divisible by 3 (e.g. exon 43 contains 173 nucleotides), skipping of the mutated exon will bypass mutation, but cause a disruption of the reading frame at the same time (i.e. exon 42 and exon 44 do not fit). However, a deletion of exon 43 and exon 44 is in-frame (321 nucleotides, divisible by 3). Thus by inducing the combined skipping of both exon 43 and exon 44 the mutation can be bypassed, while the reading frame is maintained (Figure 2). Treating cultured cells from a patient with the deletion of a single nucleotide in exon 43 with AONs targeting exon 43 and AONs targeting exon 44 indeed resulted in the generation of dystrophin.

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Figure 2. Double exon skipping for point mutations

Exon skipping for duplications

For patients with a duplication of a single exon e.g. exon 45 (176 nucleotides), skipping either the original or the duplicated exon will restore the wild type transcript, resulting in normal dystrophin (Figure 1). This has indeed been achieved in cultured cells from a patient with a duplication of exon 45.

application exonskip single deletion_figuur 3
Figure 1. Single exon skipping for duplications

Unfortunately, skipping one of the duplicated exons appeared less straightforward for a duplication of exon 44, where skipping was so efficient that both exons 44 were deleted. This resulted in a deletion of exon 44, which contains 148 nucleotides – not divisible by 3 – and thus disrupts the open reading frame. However, using a combination of AONs targeting exon 43 and AONs targeting exon 44, multiexon skipping of exon 43-44-44 could be achieved, thus restoring the open reading frame (Figure 2).

application exonskip triple deletion_figuur 4
Figure 2. Triple exon skipping for duplications

For patients with larger duplications, the situation is more complex as the AON will target both the original exons (the skipping of which is detrimental for the reading frame even when the duplicated exons are skipped) and the duplicated exons (the skipping of which is beneficial for the reading frame). So far, we attempted to restore the reading frame for only a single patient with a large, atypical duplication (exon 52-62 duplicated between original exons 63 and 64). This was unsuccessful, but it is possible that reading frame restoration is feasible for less complex multiple exon duplications.

Exon skipping for deletions

Most patients carry a mutation of one or more exons, e.g. exon 45 (Figure 1). As exon 45 contains 176 nucleotides (not divisible by 3) the deletion disrupts the open reading frame, resulting in the incorporation of aberrant amino acids and a premature truncation codon in exon 46. Since a deletion of both exons 45 and 46 covers 324 nucleotides (divisible by 3), this deletion maintains the open reading frame. To restore the open reading frame for patients with a deletion of exon 45, exon 46 is therefore hidden from the splicing machinery by a specific AON. This leads to the skipping of the targeted exon and an mRNA transcript for which the reading frame is restored. In addition to an exon 45 deletion (exon 46 skip), we have confirmed the therapeutic applicability of single exon skipping in cultured cells from patients with a deletion of exon 45-50 (exon 51 skip), exon 45-54 (exon 44 skip), exon 48-50 (exon 51 skip), exon 49-50 (exon 51 skip), exon 50 (exon 51 skip), exon 51-55 (exon 50 skip) and exon 52 (exon 51 or exon 53 skip).

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Figure 1. Single exon skipping for deletions

For a small number of deletions, skipping a single exon is not sufficient to restore the open reading frame, e.g. a deletion of exon 46-50 (Figure 2). The total number of deleted nucleotides is 695 (not divisible by 3) and neither a deletion of 45-50 (871 nucleotides) or a deletion of 46-51 (928 nucleotides) is divisible by 3 and thus exon 45 skipping or exon 51 skipping will not restore the open reading frame.
However, a deletion of exon 45-51 involves 1106 nucleotides, which is divisible by 3. Therefore, to restore the open reading frame for this patient both exon 45 and exon 51 have to be skipped. This can be achieved by using a combination of AONs targeting exon 45 and AONs targeting exon 51. We have indeed confirmed the applicability of double exon skipping in cultured cells from a patient with a deletion of exon 46-50.

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Figure 2. Double exon skipping for deletions


Welcome to the website of the DMD Genetic Therapy Group

For Parents of Duchenne Muscular Dystrophy patients we have created a special website, written in a non-scientific language. This website can be found under INFORMATION FOR PARENTS (available in Dutch and English).

The DMD Genetic Therapy Group

We hope you find all the information you are looking for on our website. If not please do not hesitate to contact us.

A video has been created to show a “bit more behind the scene footage” of our work in Leiden and tells a bit more about exon skipping and the DMD disease.

Please have a look!

What’s hot in the research field?

Information on new developments in the genetic therapy field

Technology & development

Background information about exon skipping and biomarkers  

Applicability of exon skipping

Exon skipping for deletions, duplications or point mutations

Do you have a question about DMD or do you want to get in contact with Prof. dr. Annemieke Aartsma-Rus? Please leave a comment on the contact page.

Blog on CRISPR technology

What you need to know about the CRISPR technology as a potential therapy for DMD

  • CRISPR technology (or genome editing) is a technique that can change DNA at specific locations
  • For Duchenne, genome editing can in theory bring about permanent exon skipping; so far this has been shown possible in cell models and a subset of muscle fibers of mdx mice
  • Genome editing will only have a therapeutic effect if a large number of muscle cell nuclei are corrected in patients – at the moment this cannot be achieved in humans
  • The tools for genome editing need to be delivered to the body with viral vectors (similar to gene therapy); it is not yet possible to treat all the muscles in the human body with viral vectors
  • Genome editing is a new technique and more optimization is needed. The current tools are not 100% specific, thus risking the introduction of mutations in other genes
  • Genome editing is not a cure for Duchenne: muscle tissue and function that is lost will not return
  • Genome editing will most likely not be in clinical trials for DMD in the near future!
    • Delivery of genome editing tools (gene therapy) needs to be optimized (something the gene therapy has worked on for decades, so far with only limited success)
    • The safety aspects of genome editing need to be charted

If you want to read the complete explanation of how CRISPR works and what the challenges are exactly, please continue reading.

Why you should not go along with the CRISPR cure hype

You’ve heard about CRISPR and genome editing and it is amazing potential and how it may be a cure for Duchenne in as little as 3 year. While I would love for this to happen, I do not think this is a realistic picture. And while I do not want to dash your hopes, I do believe there are some things you need to be aware off so you can have more realistic expectations.

How does genome editing CRISPR work and why is it so hyped?

Let’s start out with some background on how genome editing works and how CRISPR comes into play in this. Our genes consist of DNA and contain the genetic code for proteins. When there are mistakes (mutations) in genes, this will often result in the absence of functional proteins or the production of toxic proteins and lead to disease (Figure 1). Genome editing aims to modify the DNA, to correct the mistake and allow the production of a missing protein or a reduction of toxic protein production.

Figure 1. Genes encode proteins. When genes are mutated, this results in disease due to lack of proteins or the formation of toxic proteins.

You need tools to modify DNA. Genome editing makes use of the systems in the cell that repair DNA when it is damaged. These systems are activated when the DNA is damaged (e.g. UV light can generate breaks in the DNA of your skin cells). When breaks occur in the DNA, the DNA repair systems are immediately activated, because DNA will quickly ‘unravel’ when it is broken and the cell does not want to lose genetic information.

In order to utilize the repair system for genome editing, one needs to activate the repair system by generating a break in the DNA at the location of the mutation. This is where CRISPR comes in – CRISPR is a tool that recognizes specific locations in the DNA and guides an enzyme that can cut the DNA (Cas9) to this location. The beauty of the CRISPR is that one can design the DNA recognizing component (“guide”) to recognize specific parts of the DNA. While there are some rules that have to be adhered to, it is possible to design these components to specifically target most regions in the genome. Thus it now becomes possible to cut at or close to mutations.

There are two repair pathways that can be activated, called non-homologous end-joining (NHEJ) and homologous recombination (HR). NHEJ glues the two ends together – however, because DNA often unravels a little bit before the break is repaired, often some of the DNA is lost in this process. HR uses a template and exchanges this for the part that is broken (Figure 2). So here there is no loss of DNA. With this system, you can correct mutations: when you introduce a break close to the mutation and provide a template with the correct DNA this template will be used to repair the break and the mutation is corrected. Unfortunately, the HR system is very inefficient and does not occur at all in non-dividing cells like muscle. So for muscle diseases only the NHEJ system can be used for now.

Figure 2. CRISPR Cas9 can cut at a target region in the DNA (close to the mutation). This will activate DNA repair mechanisms. Non homologous end joining (NHEJ) will ligate the two ends of the break – often this will lead to loss of some of DNA subunits, since DNA will quickly unravel and breakdown due to the break. How much DNA subunits are lost will very for each targeted cells, and sometimes this will lead to a deletion of the mutation. Homologous recombination makes use of a provided template, containing the correct genetic information and swaps the region with the break (and the mutation) for the template (without the mutation). This will correct the DNA. However, homologous recombination is a very inefficient process and does appear to occur in non-dividing cells.

How does CRISPR work for Duchenne?

As explained, in muscle tissue only the NHEJ process is active. The NHEJ process results in minor mutations in the repaired DNA. This is generally not something that is desired. However, for DMD this loss of DNA can be exploited to restore the genetic code of the dystrophin gene. As you are probably aware, DMD is caused by mutations in the dystrophin gene that disrupt the genetic code. For most genes, including dystrophin, the genetic code lies dispersed over the gene in so called exons. Most DMD patients miss one or more exons, causing the genetic code to be disrupted (Figure 3). When patients miss exons without disrupting the genetic code, a partially functional dystrophin can be produced. These patients have a less severe disease called Becker muscular dystrophy.

Figure 3. Duchenne muscular dystrophy is most frequently caused by deletions of one or more exons (exon 51 in this example), resulting in a disruption of the genetic code (illustrated by the fact that exon 50 does not fit to exon 52). When the genetic code is disrupted, no functional dystrophin protein can be produced, resulting in Duchenne muscular dystrophy. Becker muscular dystrophy is also most frequently caused by deletions of one or more exons (exon 50 and 51 in this example). However, these deletions maintain the genetic code (exon 50 fits to exon 53) and therefore a partially functional dystrophin protein can be produced. 

The exon skipping approach aims to restore the genetic code by deleting an extra exon on transcript level. The disadvantage of this system is that transcripts are temporary gene copies with a high turnover, and therefore patients need to be treated with the exon skipping compounds regularly (weekly in current clinical trials). If it would be possible to delete an extra exon on DNA level, this would result in a permanent effect: all transcripts produced from the DNA would have a readable genetic code.

The CRISPR technology has been exploited in several ways to delete an exon – the two most commonly used are explained in Figure 4. The first system uses two guides to target a break at each side of the exon. When the repair system repairs this break it will sometimes join the two outer ends, so the whole exon is deleted. This restores the genetic code on DNA level.

Another option is to use only one guide and generate a single break close to the border of the exon. This is where exon recognition signals are located. When the break is repaired, some DNA subunits will be lost in the process, and consequently the exon recognition signals will be lost. So while the exon is still present in the DNA, it is no longer recognized by the cellular machinery and will not be included on transcript level. Now the genetic code is restored on transcript level.

Figure 4. The two most commonly used CRISPR strategies to correct the genetic code for dystrophin mutations. In the top panel the deletion is made larger. For this, two guides are needed that will cut at both ends of the exon that needs to be deleted (in this example exon 52, because exon 50 and exon 53 fit together). When the double cuts are repaired, sometimes the outer ends will be joined and the exon will be deleted. In the bottom panel, the exon is made unrecognizable. When transcripts are generated, each exon is recognized by the cell machinery because it contains special recognition signals. A break is generated just before the exon. Because the repair system is not perfect, the recognition signals will be lost after repair of the break. Consequently, the exon will no longer be recognized and the resulting transcript will lack it (in this example exon 52) and the genetic code will be restored.  For both methods transcripts are generated that allow the translation of a partially functional Becker-like dystrophin protein.

Permanent exon skipping! That sounds amazing. So what is the catch?

The catch is that you need tools to introduce the breaks: the Cas9 enzyme that generates the DNA breaks and the CRISPR guide(s) to lead the Cas9 enzyme to the proper location in the DNA. It is not enough to have these tools in one nucleus of one muscle fiber – the tools need to be delivered to a significant number of nuclei in muscle fibers of each of the more than 750 different muscles of the human body – because almost all of these are affected by Duchenne. How can we do this? Antisense oligonucleotides (AONs) that are used for exon skipping are small and will be distributed throughout the body and take up by muscle fibers to some extent. However, when you inject the Cas9 enzyme, it will not be taken up by muscle fibers. The trick that is currently used is to generate a viral vector containing the genetic information for the Cas9 enzyme and another one containing the genetic code for the guides. The adeno-associated virus (AAV) can used to deliver these genes to muscle (AAV can infect muscle with reasonable efficiency). AAV vectors have been used to deliver Cas9 and guides to muscle of Duchenne mouse models.

Indeed! There are three papers in Science showing that CRISPR works in DMD mouse models. So the proof has been provided and we should start planning a clinical trial!

Unfortunately, things are not that simple. Gene therapy been shown to work in DMD mouse models for decades (viral vectors delivering a custom made gene encoding a mini-version of dystrophin). However, it has not yet been possible to treat all the muscles of a human with viral vectors. Gene therapy for muscle diseases faces multiple challenges and most of these challenges are also faced by the CRISPR system:

  • We have a lot of muscle (~30-40% of our body is muscle), this means that a lot of viral vector particles are needed to treat a good amount of muscle fibers in each of the 750 muscles
  • Muscle tissues does not take up viruses that well. It is possible to increase the uptake of viruses for an arm or a leg using high pressure (hydrodynamic limb perfusion) – if humans respond the same way as dogs, this is anticipated to lead to good uptake of the viruses in one arm or leg and some uptake in the rest of the body
  • Treatment with viral vectors will illicit an immune response (the immune system does not know that these virus has good intentions)
  • The AAV virus does not integrate into the DNA. In healthy muscle it will be stable for ~10 years. However, in dystrophic muscle the turnover is higher. Work in a Duchenne dog model has shown that the virus and the transgene are lost after ~5 years. For the CRISPR system this is less of an issue than when AAV is used to deliver a mini-dystrophin gene, because once the mutation has been corrected, the CRISPR system is no longer needed. However, on the other hand, the CRISPR system is a two-tiered system: the Cas9 tools AND the guides need to be delivered to the same nucleus in order to work. Then they also have to do their job (the cutting) and the cell will have to do its job (the repairing). These events will not happen in all the targeted cells but only for a subset. So the CRISPR system is expected to be less effective than gene addition therapy where all nuclei that were targeted can produce the mini-dystrophin protein
  • Like all therapeutic approaches, gene therapy relies on muscle quality. Dystrophin prevents muscle damage during exercise. Once muscle has been lost, it will not return. Therapeutic approaches currently in development for Duchenne aim to slow down disease progression, they will not bring back muscle that is lost – they are not cures. Genome edition is no exception to this. When disease progresses in Duchenne patients, muscle tissue is replaced by fat and adipose tissue. Fibrotic and adipose tissues do not produce dystrophin, so repairing the dystrophin gene in these tissues will not have an impact – only repairing the dystrophin gene in muscle tissue will.

Are there risks involved?

As with most therapies, there are risks and potential side effects. Genome editing however has an added risk in that it targets DNA, so the effects are permanent and will not go away when treatment is stopped. The genome editing system is not fool-proof, CRISPR has been known to direct Cas9 also to other locations than the target, leading to cuts in the DNA at the wrong location. There are multiple ways in which this can leads to problems, for example this can lead to cells being unable to produce proteins that prevent tumor formation. As said, the effects in the DNA are permanent and cannot be undone. There is no undo button with genome editing.

So what needs to be done?

I am not saying this is the end of all hope for genome editing for Duchenne. I am pointing out that we need to be cautious. We should not expect too much from this approach (it is not a cure, it slows down disease progression) and we should not expect things too soon. Before clinical trials can be started, the delivery of the tools needs to be optimized. This should not be underestimated. The step from a 25 gram mouse with 16 gram muscle to a 30 kg Duchenne boy with 20 kg muscle is huge. Furthermore, more information needs to be obtained on the risks of this technology – not just for Duchenne, but in general: How serious are the risks? Can they be mitigated? Do they outweigh the risk of having Duchenne? This will take time – something I know Duchenne patients do not have. However, I know from personal experience that rushing into clinical trials seldom turns out well and leads to further delays.

Funding for research

Money is needed to do the research we have done and will perform in the (near) future. Happily we can anounce and thank different companies; funding organisations and parent organisations for their funding for the exon skipping group.

Duchenne Parent Project

* Improving the 2’-O-methyl phosphorothioate induced exon skipping for Duchenne through chemical modification and/or a combination with added components: summary of the project (in Dutch)
* Clarifying the role and therapeutic effect of myostatin/ TGF-β receptors: summary of the project (in Dutch)
* Preparing for double exon skipping therapy
* Validating a mouse model to test human specific antisense oligonucleotides
* In-depth characterisation of brain pathology in mice lacking one or multiple brain dystrophin isoforms

Prinses Beatrix Spierfonds

* Improving exon skipping therapy for Duchenne
* mRNA as key to improve possible Duchenne therapies
* Double therapy for Duchenne muscular dystrophy: research ended


* Biomarkers in DMD: from the discovery to the development toward clinical application and translation in other NMDs (ENMC WS 204)
* Antisense therapy for several major rare diseases


* Cross-sectional study to assess detailed natural disease history of limb girdle muscular dystrophy mouse models

What’s hot in the Duchenne research field?

Eteplirsen approved by FDA (Sept 2016)

The Food and Drug administration has granted accellerated approval to eteplirsen (an exon 51 skipping compound) for Duchenne muscular dystrophy in the US. FDA based the approval on increased levels of dystrophin in biopsies from patients treated with eteplirsen in clinical trials. They have requested Sarepta to conduct additional clinical trials to test whether eteplirsen leads to a slower disease progression. It is anticipated that eteplirsen will become available in the US in 3-6 months.

BioMarin stops clinical development of exon skipping compounds (May 2016)

BioMarin has indicated to stop the clinical development of drisapersen (exon 51 skipping compound) and their compounds for exon 44, 45 and 53 skipping. They have made this decision based on discussions with the Food and Drug Administration (which ruled in January that they did not consider drisapersen ready for approval) and the European Medicines Agency (from which they have now withdrawn their application). BioMarin will focus on the development of the next generation of exon skipping compounds.

Medicine approved for Duchenne! (June 2014)

For the first time the Committee for Human Medicinal Products (CHMP) of the European Medicines Agency (EMA) gave a positive advise for a Conditional Market Authorisation for the medicine Translarna (ataluren) for the European Market to be used in ambulant patients over 5 years of age. This is a first time a medicine for Duchenne has received market authorization. Translarna only works for patients with a nonsense mutation. This is a small mutation where the code for an amino acid (protein subunit) is replaced by the code for a stop signal (indicating that the protein translation is complete). About 13% of the Duchenne patients have this type of mutation.

Conditional Market Authorisation can be granted to a medicine for patients with disabilities or life threatening affections for which no treatment is available. Conditional Market Authorisation is granted when the risk/ benefit balance is positive, but under the condition that additional data is collected in the future to confirm the positive benefit/risk balance. The Market Authorization will be re-evaluated on a yearly basis. Once sufficient data have been collected the conditional approval can be converted into full Market Authorization. However, if the company fails to fulfil the conditions of the conditional approval, or if the post-approval data reveal a negative benefit/risk ratio, the drug can be taken off the market.
Read the complete article about the advise.

Mutation-specific compounds tested in clinical trials

Two therapies for Duchenne patients are currently being tested in clinical trials, which are applicable only to patients with specific mutations: Translarna (treats only stop mutations) and exon skipping (restores the genetic code for certain deletions).

News from the DMD Genetic Therapy group Leiden



Congratulations to prof. dr. Annemieke Aartsma-Rus for receiving the Outstanding Achievement Award from the Netherlands Society of Gene and Cell Therapy (NVGCT)!

The Netherlands Society of Gene and Cell Therapy (NVGCT) established the Outstanding Achievement Award in 2019. The award honors an individual who has achieved a specific high impact contribution or a lifetime of significant contributions to the field of gene and cell therapy. Prof. dr. Annemieke Aartsma-Rus received this award for her pioneering work in exon skipping therapy development during the award lecture at the annual NVGCT conference in Lunteren.

The information and picture is adapted from the website of the Netherlands Society of Gene & Cell Therapy


After the ceremony was postponed twice due to the pandemic, on September 14th prof. dr. Annemieke Aartsma-Rus received her Ammodo Science Award in an official ceremony at the Muziekgebouw in Amsterdam. The award was handed out by president of Ammodo Steven Perrick and president of the KNAW Ineke Sluiter. The beautiful award consists of 9 pieces of bronze that together make a cube, weighing 2540 grams including the box.

For each laureate Ammodo made a short movie about their work, accomplishments and the motivation of the jury to give the award to that person. The short movie of prof. dr. Annemieke Aartsma-Rus, which is completely filmed in our lab and in her office, can be found here.

The information and picture is adapted from the website of the Ammodo Science Award

On the 7th of september 2021 it was the annual World Duchenne Awareness Day (WDAD). This year the theme of WDAD was Adult Life & Duchenne. Over the last years the life expectancy of individuals affected by Duchenne has increased significantly. An adult life with Duchenne comes with new challenges and opportunities, but also with new medical issues. On WDAD, experts shared their experiences with Duchenne in adult life to inspire and empower Duchenne adults to think about their future.

The World Duchenne Organization hosted a livestream where experts shared their knowledge on DMD/BMD ain adult life. The livestream is recorded and available on their website.

The information and picture is adapted from the World Duchenne Organization.


Congratulations to prof. dr. Annemieke Aartsma-Rus for receiving the Ammodo Science Award!

The Ammodo Science Award for fundamental research is intended to reward and support outstanding internationally recognized mid-career scientists working in the Netherlands, who were awarded their PhD no longer than fifteen years ago. Divided over four scientific domains (Biomedical Sciences, Humanities, Natural Sciences and Social Sciences), every two years, eight laureates are awarded a cash prize of 300,000 euros each. This amount can be spent on a fundamental scientific research project at the discretion of the laureate.

The information and picture is adapted from the website of the Ammodo Science Award


Prof. dr. Annemieke Aartsma-Rus and dr. Willeke van Roon-Mom (Neuro-D group), together with other scientists and clinicians from the Leiden University Medical Center (LUMC) and Radboud University Medical Center (Radboudumc), launched the Dutch Center for RNA Therapeutics (DCRT) in February last year.

On the 28th of February, Rare Disease Day 2021, the DCRT existed one year and celebrated this by the launch of their website. The website of the DCRT can be accessed via this link.


The DMD Genetic Therapy group Leiden wishes all its readers all the best for 2021. We look forward to another year of scientific research, interesting results and publications. Let’s hope that 2021 will also bring an end to lockdowns and the global pandemic.

The Netherlands began vaccinating people against COVID-19 in the first week of January. Starting with care workers, people over the age of 60 and people who already have specific serious health conditions, Duchenne patients are vaccinated against COVID-19 since March. Eventually, the vaccine will be offered to everyone aged 18 and over.



With great sadness we learned that prof. dr. Gert-Jan van Ommen, the former head of the Department of Human Genetics of the Leiden University Medical Center (LUMC), passed away on the 7th of November.

Prof. dr. Gert-Jan van Ommen was head of the LUMC Department of Human Genetics for 20 years (1992-2012) and played a key role in the field of human genetics as chair and board member of multiple national, European and international professional organizations and societies. He was an inspiring and involved mentor for a generation of scientists. From the early days Van Ommen was involved in the elucidation of the human genome. First at a gene by gene basis, but later at a broader scale embracing the opportunities next generation sequencing offered. He founded one of the first LUMC research facilities, the Leiden Genome Technology Center, to give LUMC researchers the opportunity to use the latest genomic technologies.

His scientific interests were primarily on Duchenne muscular dystrophy and Huntington Disease. His contribution went beyond discovering the genes involved. As such, he can be considered a translational scientist avant la letre. Under his guidance the exon skipping therapy for genetic diseases Duchenne muscular dystrophin and Huntington flourished. He received multiple internation-al awards for his work. In 2010 van Ommen was knighted in the order of the Dutch Lion (Ridder in de Orde van de Nederlandse Leeuw).

After he became a professor emeritus in 2012, van Ommen was actively involved in the human genetics research and shifted his focus to biobanking. He remained editor of the European Journal of Human Genetics until the end.

We will remember his critical yet creative scientific mind and his endless supply of amusing anecdotes.

The information and picture is adapted from the intranet of the LUMC


Congratulations to dr. Maaike van Putten!

She has been awarded a Vidi grant by the Dutch Research Council (NWO). Vidi is aimed at experienced researchers who have carried out successful research for a number of years after obtaining their PhDs. The grant enables them to develop their own innovative line of research and set up their own research group in the coming five years. Dr. Maaike van Putten will study, in cultured human brain cells, how lack of dystrophin results in abnormalities and to which extent deficits can be remedied by a therapy aimed to restore dystrophin synthesis.

Congratulations again to dr. Maaike van Putten: she is officially appointed as assistant professor.


On the 7th of september 2020 it was the 7th annual World Duchenne Awareness Day (WDAD). This year the theme was Duchenne and the brain. The dystrophin protein that is missing in muscle causing muscle breakdown, is also missing in the brain. This is causing problems such as learning difficulties or behavioural issues such as ADD, ADHD, OCD and autism. For many families in day to day life, this is causing more stress and worries than the physical problems.

The World Duchenne Organization hosted a livestream where experts shared their knowledge on DMD/BMD and the brain. The livestream is recorded and available on their website.

The information and picture is adapted from the World Duchenne Organization.


Congratulations to dr. Pietro Spitali for publishing an article in the research journal PNAS!

Proceedings of the National Academy of Sciences (PNAS) is one of the most prestigious and highly cited multidisciplinary research journals. In this article dr. Spitali describes that the DMD-gene is barely transcribed in Duchenne patients, leading to less dystrophin mRNA present in muscle cells. This finding may have consequences for the development of therapies that focus on the (pre-)mRNA.

More information about the article can be read here.


Every year Duchenne Parent Project Netherlands organises the Duchenne Congress, special for parents, (para)medici and other people interested in Duchenne. During this congress the audience learns more about ongoing research, care and the future. Parents also have time to talk to each other and to exchange ideas. There is a special program for the Duchenne patients and their brothers and sisters.

Unfortunately, due to the COVID-19 pandemic it was not possible to organise the yearly Duchenne Congress this year. Instead the Duchenne Parent Projects Netherlands organised an online Duchenne Festival. In 8 days all participants received Duchenne related information during short online sessions. On the last day of the festival there was a live closing event, including a presentation about neuropsychology from Jos Hendriksen and a talk about the future for Duchenne patients with members from Duchenne Centre NL: Annemieke Aartsma-Rus, Jan Verschuuren, Jos Hendriksen and Imelda de Groot.

The information and picture is adapted from Duchenne Parent Project the Netherlands.


In the Netherlands, the government implemented an ‘intelligent lockdown’ in March. Everyone was urged to work from home and stay at home as much as possible. We were allowed to go outside for urgent matters such as grocery shopping, as long as we kept a distance of 1.5 meters to others.

From that moments onwards, all our group members were forced to work from home. We were not allowed to come to the LUMC anymore, only crucial, long term experiments (e.g. cell culturing) had to be finished as soon as possible.

Since we all love to work in the lab it was quite hard to work from home for some of our group members. With children and/or partners at home, the concentration was sometimes hard to find. But during this period we also finally had time to finish unfinished projects, to write interesting papers and reviews, to analyse data we generated in the past, and so on. We even welcomed a new member in our group!

From May 8th we were (finally) allowed to slowly start up lab work, but with some strict measures. There is a maximum of people per lab, depending on the size of the lab. Meetings and congresses still have to be done online, and if we show any symptoms of COVID-19, we have to get tested directly.

And of course, also in the LUMC we have to keep the distance of 1.5 meters, so we are pleased that our labs are big enough for all of us.


Prof. dr. Annemieke Aartsma-Rus and dr. Willeke van Roon-Mom (Neuro-D group), together with other scientists and clinicians from the Leiden University Medical Center (LUMC) and Radboud University Medical Center (Radboudumc), launched the Dutch Center for RNA Therapeutics (DCRT). The aim of this new, virtual center is to develop customised RNA-therapies for patients with rare genomic conditions.

The DCRT will focus on RNA therapy for patients for whom local treatment of the affected tissue is possible. The treatment targets progressive eye, muscle or brain diseases. The focus is on genetic diseases and mutations, which are so rare that pharmaceutical companies have no interest to invest in developing treatments.

In September dr. Dianne Baunbaek will start as Senior Project Manager for the DCRT. More news about the DCRT and a link to the website will follow.



Congratulations to prof. dr. Annemieke Aartsma-Rus for receiving the EURORDIS Black Pearl Scientific Award!

The Scientific Award recognises Professor Aartsma-Rus’ exceptional achievements and dedication in the field of Duchenne Muscular Dystrophy (DMD). She is widely recognised as a world leader in the field of DMD research, as a pioneer who led the path of antisense for others to follow, and as a prolific author of academic publications. By sharing her expertise on numerous EU-funded projects, Professor Aartsma-Rus has demonstrated her total commitment to the rare disease community and to scientific collaboration at a European level.

The information and pictures are adapted from the website of EURORDIS.



On the 7th of september 2019 it was the 6th annual World Duchenne Awareness Day (WDAD). This year the theme was Nutrition; to raise awareness on nutrition and the risk of supplement use in Duchenne. Together with Duchenne Centre in the Netherlands we join forces for optimal care for Duchenne. Another short movie was made to raise awareness for Duchenne and challenges regarding ‘nutrition in Duchenne’.

Please have a look!



On Thursday 7th of September 2017 it was World Duchenne Awareness Day (WDAD). Traditionally on this day, worldwide WDAD balloons were released. Our group, together with colleagues from the LUMC who are also involved in Duchenne, released 79 balloons: the amount of exons in the dystrophin gene.

Duchenne Centrum Nederland made a short movie to show that we (researchers, health care workers, patients, patient organisations) stand together for Duchenne in the Netherlands. In this movie a balloon is passed to one another. In this way, the balloon virtually passed people involved in Duchenne around the Netherlands.

Please have a look!



7th of September 2015 it was Duchenne Awareness Day. A Day everybody linked to Duchenne Muscular Dystrophy (Patients; Parents; Hospitals and reasearchers like ourselfs) tries to raise awareness for the disease boys are suffering from. Worldwide people released red (Biodegradable) balloons with wishes or notes attached to it.

Here in Leiden we also released balloons and attached the beautiful blogposts from several boys to the balloons. We hope people find the balloons and read the story of that specific boy and note life is not as easy as we might think sometimes…


Annemieke Aartsma-Rus has been nominated in the category “Knappe Koppen” (brainiacs) by the Dutch magazine VIVA. They list 400 inspiring women who achieved something remarkable last year: the VIVA-400 list. The public can then vote for their favourite, leading to winners in each category. The nominees are however asked to ask our colleagues and fans to vote for them.

Annemieke Aartsma-Rus was a guest at the Dutch radio show “Een Vandaag” in the item “Wetenschap Op Woensdag”. The interview can be listened here (in Dutch). Annemieke also gave a talk on another Dutch radio show about Duchenne muscular dystrophy and blood transfusions.

The first drug for Duchenne patients will be on the market! Info about this drug can be found here.


When Annemieke Aartsma-Rus visited Germany for a meeting she was interviewed by Günter Scheuerbrandt. More information about Günter Scheuerbrandt and the overviews he has written about DMD (in a language parents and patients can understand) can be found on his website.

Dwi Kemaladewi participated in the “Dance your PhD” contest of the journal Science. The dance is titled “Antisense oligonucleotide mediated exon skipping for Duchenne muscular dystrophy” and has been selected as one of the four finalists in the category biology. Click here to see the dance!

The exon skip work has recieved a “pearl award” from the Netherlands Organization of Scientific Research (ZonMw) – one of the founders of the exon skip work. The award was handed out to Gert-Jan van Ommen on Sept 23.


When Annemieke Aartsma-Rus visited the Nationwide Children’s Hospital Center for Gene Therapy she was interviewed by Kevin Flanigan about exon skipping approaches for neuromuscular disorders.
The interview is available as a podcast and can be found here.

Omroep Rijnland (Dutch local television station) has made a movie about a Duchenne patient. The movie also features our exon skipping work. You can find the movie here (in Dutch).