Laminopathy is a term designed for the diseases caused by mutations in a gene encoding nuclear
envelope proteins, lamin A/C (LMNA). Skeletal muscle laminopathy includes autosomal dominant/
recessive Emery-Dreifuss muscular dystrophies (AD/AR-EDMD) and limb-girdle muscular dystrophy
type 1B (LGMD1B), which are clinically characterized by progressive muscular weakness, varying
degree of joint contractures and cardiac involvement. Since lamin A/C is believed to maintain nuclear
integrity by polymerizing into nuclear lamina, the mutations in LMNA might affect nuclear shape and
subsequently alter normal gene expression, especially in skeletal muscles. Our observation using
electron microscope to analyze skeletal muscle nuclei of laminopathy supports this notion. It has been
shown that nuclei are quite altered in their shapes (e.g. nuclear chain formation, sawtooth deformity
and serpentine shape) and chromatin is disorganized in majority of nuclei. Chromatin disorganization
occurred also in nuclei of satellite cells, which are precursors of skeletal muscle cells, suggesting that
muscle regeneration is disturbed in laminopathy. Furthermore, vacuolar formations are frequently
detected nearby nuclei, the consistent finding of which implies that nuclear vacuoles may have a role
in the pathogenesis. Despite of significant changes in nuclei, myofibrils are relatively well arranged.
Thus, it is concluded that nuclear abnormalities and the disturbed muscle regeneration mainly
contribute to the pathogenesis of skeletal muscle laminopathy.

KEYWORDS : Skeletal muscle laminopathy, Lamin A/C, Nucleus, Satellite cell, Vacuole