CKM and Duchenne muscular dystrophy: Repeat specimens were not available from newborns with DMD for comparison; however, given the sustained CK-MM elevation in older children, and previously reported cases of repeat testing in newborns with neuromuscular conditions [10,14,21], repeat CK-MM testing is expected to distinguish DMD cases from unaffected newborns and significantly improve the positive predictive value of NBS.