Rare disease clinical trials: Power in numbers

The limb-girdle muscular dystrophies (LGMDs) encompass a collection of genetic muscle diseases with proximal-predominant weakness of the limbs. Thirty-two of these disorders are named via the common nomenclature, including 8 autosomal-dominant (LGMD1A-H) and 24 autosomal-recessive (LGMD2A-X) disorders.(1) In addition, numerous other genetic muscle diseases, including Bethlem myopathy, dystrophinopathies, ryanodine receptor–associated myopathies, and many more, may clinically present with similar proximal-predominant weakness.(2) Therefore, current genetic testing panels targeting neuromuscular weakness frequently encompass >75 genes. These disorders are quite rare, each with minimum prevalence estimates of 0.01–0.60 cases per 100,000 persons.(3) LGMD2A (attributable to mutations in the gene for calpain-3) and LGMD2B (attributable to mutations in the gene for dysferlin) consistently are the 2 most prevalent LGMD subtypes in a variety of ethnic cohorts.