Approximately 1 in every 3,600 male infants worldwide is affected by Duchenne muscular dystrophy – an inherited condition that causes severe muscle weakness. At present, there is no specific treatment for the disease. But new research published in the journal Neurology suggests that certain drugs usually prescribed for erectile dysfunction may be effective.
Duchenne muscular dystrophy (DMD) is caused by a defective gene for dystrophin – a protein that helps maintain healthy muscles. Low levels or absence of dystrophin means the muscles lack nitric oxide – a chemical that signals blood vessels to dilate during exercise so blood flow can increase.
As a result of the way the gene is inherited, the condition primarily affects boys and young men. Onset of the disease usually occurs before the age of 6 years. As well as muscle degeneration, the condition can cause intellectual disability, congestive heart failure or irregular heart rhythm, back and chest deformities and respiratory disorders.
Many individuals with DMD are treated with corticosteroids. This medication can help to slow muscle degeneration and reduce negative effects on the heart and lung.
But the researchers of this study, including Dr. Ronald G. Victor of the Cedars-Sinai Heart Institute in Los Angeles, CA, note that corticosteroids cause an array of side effects and more than 75% of patients are unable to endure them.
With this in mind, the team set out to determine whether the drugs sildenafil (Viagra) or tadalafil (Cialis) could help treat DMD. Both drugs are commonly used to treat erectile dysfunction and pulmonary arterial hypertension. They work by relaxing blood vessels, therefore increasing blood flow.
Drugs improved blood flow in boys with DMD
For their study, the team assessed 10 boys aged between 8 and 13 years who had DMD. All boys were taking corticosteroids and were able to walk, although some often used a wheelchair or scooter to help with mobility.
The blood flow in the muscles of these participants was measured as they carried out a handgrip exercise and when they were resting.
Their blood flow was compared with 10 similarly aged healthy boys, which confirmed that those with DMD had abnormal blood flow, even when taking corticosteroids.
The boys with DMD were then required to take each drug – sildenafil or tadalafil – 2 weeks apart. Their blood flow was measured again as they rested and carried out a handgrip exercise, and this was compared with the blood flow of the 10 healthy boys.
The researchers found that after taking each drug, the boys with DMD had the same blood flow response as the healthy boys during exercise. The team notes that this result was instantaneous and was more pronounced when the drug was given in higher doses.
Dr. Victor notes that although a lot more research is to be done before either drug can be recommended for individuals with DMD, the team’s findings are encouraging. “This is not a cure, but it is the first stop toward identifying potential treatments,” he adds.
However, the researchers say their study has limitations. For example, they note that it is unknown whether long-term use of either drug can maintain improved blood flow.