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What is Duchenne muscular dystrophy?

The Muscular Dystrophies are a group of inherited diseases that cause weakening and wasting of the muscles. There are approximately 30 types of muscular dystrophy disease, each with a separate cause.  Some are obvious at birth, others develop during childhood and some only become apparent in adults. The most common muscular dystrophy is Duchenne which typically affects young boys and is an important and ongoing research focus at the MCRI.

What is Duchenne muscular dystrophy?
Duchenne muscular dystrophy or DMD is a genetic muscle disease that mostly effects boys. Around one in 3500-6000 boys are born with DMD worldwide each year (Bushby et al., 2010).

DMD is caused by errors (mutations) in a key muscle building block (protein) called dystrophin, which provides the structural support needed for muscle to function. 

The process of disease caused by DMD is well understood, with the loss of dystrophin resulting in an increased chance of the muscles being damaged and breaking down. 

This increase in muscle damage causes inflammation and over time, muscles are replaced by fat and scar tissue which makes the muscles weaker. 

What are the symptoms of DMD?
DMD is typically diagnosed in early childhood, with muscle weakness affecting the legs, and upper limbs first, with most boys requiring a wheel chair by 14 years-of-age. The weakness then spreads to the breathing (respiratory) and heart (cardiac) muscles which can ultimately results in premature death. 

How is DMD currently treated?
There is currently no cure for DMD and the only approved treatments are a class of steroids known as glucocorticoids, which have been used for over 30 years to slow disease progression by blocking the inflammation caused by repeated muscle damage and breakdown over time. However, prolonged steroid use can result in unwanted side effects including weight gain and a shorter stature. 

What research into DMD are Murdoch Children’s Research Institute conducting? 
The Muscle Disease group at the MCRI uses both animal models (mice) and induced pluripotent stem cells (iPSCs) collected from patients with muscle diseases (including DMD) to study muscle disease. 

Some of our current research focuses on developing alternative approaches to the use of steroids to reduce the impacts of the immune response seen in patients with DMD. This research has been performed with the Melbourne based pharmaceutical company, Antisense Therapeutics and uses a more targeted drug to specifically reduce the inflammation seen in boys with DMD. 

These early studies have shown promising results with improved muscle function and performance in both mouse models and a phase II clinical trial performed in patients with DMD at the Royal Children’s Hospital (RCH).

We also use skeletal muscle grown from induced pluripotent stem cells (iPSCs) to model disease and test new drug targets. iPSCs are cells which can be collected from patients’ blood and grown in the laboratory into various tissues including muscle. These muscle tissues can be used to study the patient’s disease in a dish, without the need for an invasive muscle biopsy. Through the MCRI’s Stem cell medicine and Disease Modelling Facilities the same muscle cells can be used to identify new drug targets and potential treatments.

What are we trying to make possible for children with DMD?  
Through this ongoing research at the MCRI and RCH we aim to improve the quality of life of children with muscle disease by developing a better understanding of a patient’s disease and establishing new therapies that will hopefully provide better treatments for patients with muscle diseases like DMD in the future.

Helpful contacts:
Muscular Dystrophy Australia 
Stem Cells Australia 
Save our Sons

Reference
Katharine Bushby et al, for the DMD Care Considerations Working Group (2010) Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and pharmacological and psychosocial management. Lancet Neurology; 9: 77–93

Author 
Dr Peter Houweling is a Team Leader within the Muscle Disease research group at MCRI. Peter’s key research interests focus on understanding how our muscles adapt to change; including during chronic diseases like DMD and after muscle injury, with the goal to develop better treatments for children with muscle disease.