Question

1. Outline a workflow for the diagnosis of Duchenne Muscular Dystrophy. Include what patient details and material may be assessed and what would be detected/observed at each point of the workflow.

Answer 1

TESTING

The currently used primary biomarker test for Duchenne muscular dystrophy looks for the presence of creatine kinase (CK) enzyme activity in serum by fluorescence measurement of enzyme activity in blood, followed by confirmation by muscle biopsy or genetic testing to identify dystrophin mutations, e.g. by multiplex PCR, multiplex ligation –dependent probe amplification, single-condition amplification /internal primer or multiplex amplifiable probe hybridization. Recently, next-generation sequencing (NGS)-based targeted gene analysis has become clinically available for detection of point mutations and other sequence variants (small insertions, deletions, and indels). CK is a protein found in muscle but when the muscles are damaged, owing to disease or injury, it leaks into the bloodstream. The same assay concept has been converted for use with dried blood spot (DBS) samples in the pilots or early screening programs.

Creatine kinase is an isoenzyme and several different forms exist. CK-MM is the predominant isoform present in skeletal muscle and is elevated in patients with muscular dystrophies. The CK is a nonspecific marker for DMD since other conditions such as muscle trauma during birth cause transient elevated levels of CK-MM in blood. In addition, CK can be elevated in other rarer forms of muscular dystrophy.