The results of an international clinical trial, led in part by a UC Davis School of Medicine expert, have shown that a drug therapy for a severe type of muscular dystrophy holds promise for a subgroup of patients.
In a paper just published online in the journal The Lancet, Craig McDonald and colleagues at 53 study sites in 18 countries describe the clinical benefit of using the drug ataluren for a certain group of patients carrying a specific “nonsense mutation” for Duchenne muscular dystrophy.
Duchenne muscular dystrophy is a rare but fatal genetic disorder characterized by progressive muscle degeneration and weakness, which is caused by an absence of dystrophin, a protein that helps keep muscle cells intact. The so-called nonsense mutation, a genetic mutation in the DNA sequence that results in a shorter, non-functional protein, is present in about 13 percent of Duchenne patients and makes the disease more severe.
McDonald and his co-authors say treatments focusing on dystrophin restoration, such as ataluren, are important because they can preserve existing muscle function, which otherwise progressively deteriorates.
“What’s very encouraging about these findings is that a treatment using ataluren for certain individuals with Duchenne muscular dystrophy may prompt a slowing or stabilizing of the disease progression and motor function that can be very meaningful to patients and provide them with invaluable, quality-of-life benefits,” said McDonald, who was the lead author on the study and serves as professor and chair of the UC Davis Department of Physical Medicine and Rehabilitation.
The study, a randomized, double-blind Phase 3 clinical trial, was sponsored by the New Jersey-based company that developed ataluren, PTC Therapeutics. It included 230 patients, half of whom received the drug therapy over a course of 48 weeks, and the other half who received a placebo.
To assess patient muscle function and mobility as well as drug efficacy, researchers used a six-minute walk test, which was developed by McDonald and his team at UC Davis. Duchenne study participants with the nonsense mutation who had a baseline six-minute walk of between 300 meters and under 400 meters were the subgroup of patients who were the most likely to see the clinical benefits of ataluren.
“While not all of the ataluren-treated participants reached statistical significance, this subgroup seems to represent a stage in the progression of disease where dystrophin restoration therapy, as measured by the six-minute walk test, does have value,” added McDonald, who has been a consultant to drug manufacturing companies working on therapies for Duchenne, including PTC Therapeutics. “Our findings certainly merit additional study because the patients and families I see in clinic every week are desperate for help.”
Duchenne muscular dystrophy primarily affects males. The lack of functional dystrophin protein affects the structural stability of skeletal, diaphragm and heart muscles. Patients with the disease lose the ability to walk as early as age 10 and experience life-threatening lung and heart complications in their late teens and twenties.
Of the approximately 250,000 people with the disorder worldwide, the nonsense mutation in Duchenne accounts for about 13 percent of cases, which represents approximately 2,000 patients in the U.S.