Muscular Dystrophies and Myopathies

Myopathies are a general class of diseases where muscle cells have impaired function, resulting in clinical weakness. There are many types of myopathies caused by many different disease conditions, and many of these myopathies may be positively impacted by an agent known to increase muscle mass.

Myopathies can be acute due to infection, medication or injury, or chronic, such as congenital myopathies, mitochondrial myopathies, glycogen storage diseases or muscular dystrophies. Muscular dystrophies are generally inherited diseases characterized by progressive weakness of voluntary muscles. They are particularly attractive as a target for drugs that will cause muscle cell growth.

GTx’s SARMs have been shown to increase muscle mass in other settings, such as cachexia. Although there are more than 30 defined dystrophic conditions, diseases which have the best rationale to benefit from treatment with a SARM include:

  • Duchenne Muscular Dystrophy (DMD), a rare, genetic disorder characterized by progressive muscle degeneration and weakness. It is caused by an absence of dystrophin, a protein that helps keep muscle cells intact. Symptom onset is in early childhood, usually between the ages of 3 and 5, and the disease primarily affects boys. Until recently, boys with DMD did not survive much beyond their teen years, but with advances in cardiac and respiratory care, survival into the early thirties is becoming more common. DMD remains an unmet medical need and the U.S. Food and Drug Administration (FDA) issued guidance in 2015 affirming FDA’s interest in finding new treatment options for this disease.
  • Becker Muscular Dystrophy (BMD), a potentially less severe variant of DMD. It shares the same reduction and impairment in normal dystrophin as patients with DMD; however some of their protein may be functional. BMD’s onset is usually in late childhood or adolescence, and the course is slower and less predictable than that of DMD. Generalized weakness first affects muscles of the hips, pelvic area, thighs and shoulders.