In this article, the latest clinical trials and studies in: limb-girdle muscular dystrophy, McArdle's disease, and Pompe's disease
Study suggests LGMD carriers have weakness
Several members of a German family with a sarcoglycan-deficient form of limb-girdle muscular dystrophy (LGMD) have been found to have muscle weakness themselves, even though carriers of this type of MD haven't until now been thought to show disease symptoms.
In this family, seven out of 12 carriers of a mutation in the gene for alpha-sarcoglycan, a protein in the muscle cell membrane, whose absence leads to LGMD, showed signs of upper-body weakness with a winglike appearance of the shoulder blades.
Carriers of recessively inherited diseases like sarcoglycan-deficient LGMD, for which the gene isn't on the X chromosome, have previously been considered "exempt" from disease symptoms. However, this report, published in the November issue of Annals of Neurology, suggests disease manifestations can occur in these carriers after all.
About 20 percent of carriers of Duchenne muscular dystrophy, for which the gene is on the X chromosome, show some muscle-related symptoms.
The investigators say there may be another gene in this LGMD family thats modifying the effects of the single alpha-sarcoglycan mutation in the carriers cells.
Ingesting a sugar-containing drink 30 to 40 minutes before exercising appears to boost endurance and prevent muscle damage in people with phosphorylase deficiency (McArdle's disease), according to a study published in the Dec. 25 issue of the New England Journal of Medicine, in which MDA research grantee Ronald Haller was a co-investigator.
People with McArdle's disease can't break apart large glycogen molecules, a process necessary to manufacture the kind of energy needed for exercise.
Earlier research has shown that intravenous infusions of glucose boost exercise tolerance in the disease, presumably by compensating for the block in glycogen metabolism.
Haller's study shows that oral ingestion of sugar (in this case, sucrose) also works.
Haller, who directs the Neuromuscular Center at the University of Texas Southwestern Medical Center in Dallas, along with John Vissing of the Copenhagen Muscle Research Center in Denmark, studied 12 people with McArdle's disease. Each participant had a lifelong history of exercise intolerance, with repeated episodes of cramps and myoglobin (a muscle protein) in their urine when they engaged in sudden, vigorous exercise.
Participants drank 660 milliliters (22 ounces) of a caffeine-free soft drink that contained either 75 grams (about 2.6 ounces) of sugar or a taste-equivalent amount of an artificial sweetener. Some 30 to 40 minutes later, they were asked to ride a stationary bicycle for 15 minutes.
The sugar drink resulted in marked improvement in exercise tolerance, lowered participants' perceived levels of exertion, and reduced their heart rates considerably compared with the artificially sweetened drink.
Haller noted that his findings conflict with earlier recommendations that patients with McArdle's restrict carbohydrates (presumably to improve their ability to use alternate fuel sources, such as fatty acids).
"The results of this study support our view that glucose has a critical role in muscle oxidative metabolism and that the diet of affected patients should contain an adequate amount of carbohydrates," he said. "However, we stress that patients should not consume more calories than they expend."
Genzyme to study later-onset Pompe
The biotechnology company Genzyme of Cambridge, Mass., which is conducting two trials to test a laboratory-engineered enzyme in infants and young children with acid maltase deficiency (Pompe disease), will perform an observational study of people with the late-onset form of the disease.
The investigators are interested in observing and testing approximately 60 people with mild to intermediate, late-onset Pompe disease. Participants must be able to walk, with or without assistive devices, and can't require ventilatory support while awake.
Final selection will probably admit U.S. participants who are 8 years old or older, while European participants must be at least 18.
The study will involve pulmonary and muscle function testing so the researchers can better understand disease progression in preparation for a clinical trial.
Later this year, some participants in the observational study may be selected for a clinical trial of a therapeutic agent. Participation in the treatment trial is neither required nor guaranteed for those in the observational study.