Studying the role of dystrophin-associated proteins in influencing Becker muscular dystrophy disease severity

• We studied factors involved in Becker disease severity in 24 patients.
• Severity was assessed by quantitative muscle testing and age at disease milestones.
• Dystrophin-associated proteins and utrophin expression were investigated.
• An inverse relation between disease severity and utrophin expression existed.
• No relation between the other proteins, including nNOS, and disease severity existed.

Becker muscular dystrophy is characterized by a variable disease course. Many factors have been implicated to contribute to this diversity, among which the expression of several components of the dystrophin associated glycoprotein complex. Together with dystrophin, most of these proteins anchor the muscle fiber cytoskeleton to the extracellular matrix, thus protecting the muscle from contraction induced injury, while nNOS is primarily involved in inducing vasodilation during muscle contraction, enabling adequate muscle oxygenation. In the current study, we investigated the role of three components of the dystrophin associated glycoprotein complex (beta-dystroglycan, gamma-sarcoglycan and nNOS) and the dystrophin homologue utrophin on disease severity in Becker patients. Strength measurements, data about disease course and fresh muscle biopsies of the anterior tibial muscle were obtained from 24 Becker patients aged 19 to 66. The designation of Becker muscular dystrophy in this study was based on the mutation and not on the clinical severity. Contrary to previous studies, we were unable to find a relationship between expression of nNOS, beta-dystroglycan and gamma-sarcoglycan at the sarcolemma and disease severity, as measured by muscle strength in five muscle groups and age at reaching several disease milestones. Unexpectedly, we found an inverse correlation between utrophin expression at the sarcolemma and age at reaching disease milestones.