Definition - One of nine types of muscular dystrophy, a group of genetic, degenerative diseases primarily affecting voluntary muscles.

Cause - A faulty gene for poly(A)-binding protein nuclear 1 (PABPN1), which is suspected to lead to production of extra chemical material that causes formation of clumps in the muscle cells.

Onset - Usually not until the 40s or 50s.

Symptoms - OPMD first causes weakness of the muscles of the eyelids and throat; weakness of facial and limb muscles often occurs later. Swallowing problems and difficulty keeping the eyes open are common problems.

Progression - Slow.

Inheritance - May be autosomal dominant, meaning OPMD is inherited from one parent; or autosomal recessive, occurring when a faulty gene is inherited from each parent.

Facts About Rare Muscular Dystrophies