A dynamic trinucleotide repeat (TNR) expansion in the DMD gene.

Dystrophinopathies are allelic X-linked myopathies caused by large deletions/duplications or small lesions along the DMD gene. An unexpected dynamic trinucleotide (GAA) expansion, ranging from ∼59 to 82 pure GAA repeats, within the DMD intron 62, was revealed to segregate through three family generations. From the pedigree, two female patients were referred for DMD investigation due to chronic myopathy and a muscle biopsy compatible with dystrophinopathy.