Study Evaluates Diagnostic Tests For Muscular Dystrophy

Researchers at the University of Iowa Roy J. and Lucille A. Carver College of Medicine will compare two protein-based tests used to diagnose certain types of muscular dystrophy. The two-year study is funded by a $122,000 grant from the National Institute of Neurological Disorders and Stroke.

Steve Moore, M.D., Ph.D., UI professor of pathology, and his colleagues will compare the current standard test that examines protein levels in biopsied muscle samples with a newer test that measures the same proteins in a blood sample. Identifying which proteins are absent or deficient can help identify which genes are most likely to harbor the disease-causing mutation. “Discovering which gene mutations are causing a patient’s disease is important because that helps us provide accurate genetic counseling, predict the clinical course and eventually treat patients,” said Moore, who also is the co-director of the Sen. Paul D. Wellstone Muscular Dystrophy Cooperative Research Centre (MDCRC) at the UI.The study will focus on diagnostic tests for limb-girdle muscular dystrophy Type 2B (LGMD2B) and Miyoshi myopathy, two types of muscular dystrophy caused by mutations in the dysferlin gene.Limb-girdle muscular dystrophies cause weakness of the muscles that control movements at the shoulders and hips. To date, 13 different genes, including dysferlin, have been discovered that cause LGMD. Miyoshi myopathy causes weakness of distal muscles, especially muscles of the lower leg.The current standard diagnostic test for these conditions evaluates protein expression in a muscle biopsy. The discovery that dysferlin protein is expressed in peripheral blood cells as well as in muscle has led to a second diagnostic test that measures the amount of dysferlin in a blood sample. For patients with a muscle-wasting disease, giving a blood sample is typically preferable to giving a muscle sample, and the new diagnostic test has become popular.However, while a total absence of dysferlin protein expression in muscle is a very specific predictor of dysferlin mutations, the relationship between the amount of dysferlin protein in blood and the presence of dysferlin gene mutations has not been well validated.One major aim of the UI study will be to directly compare dysferlin expression in muscle biopsies and peripheral blood samples from the same patients. The team also will perform mutational analysis of the dysferlin gene to determine which patients truly have LGMD2B or Miyoshi myopathy. “Knowledge of whether or not patients have dysferlin mutations will allow us to determine the specificity of muscle biopsy and peripheral blood dysferlin testing,” Moore said. “It is our hope that this study will clarify the role of protein-based testing modalities in arriving at a genetic diagnosis in patients with Limb-Girdle Muscular Dystrophy Type 2B and Miyoshi Myopathy.”(Source: University of Iowa: September 2006).