Oculopharyngeal muscular dystrophy (OPMD) is a rare genetic muscle disorder with usual symptom onset between 40 and 60 years of age. It was first reported in a French-Canadian family in 1915 and has now been reported in at least 33 countries, with the largest cluster in the French-Canadian population, where the estimated prevalence is 1:1000. Symptoms usually start insidiously and follow a slow progressive course. It is considered a primary muscle disorder and selectively affects the muscles of the eyelids and pharynx, resulting in drooping of the eyelids (ptosis) and difficulty swallowing (dysphagia). Other muscle involvement may appear later, with weakness involving the upper arms and legs, the tongue and facial muscles.

Ptosis is usually the first symptom to appear, and will affect both eyes, although involvement is often asymmetric. Eye movements may become impaired at later stages, although complete weakness is rare. Dysphagia is first noticed for solid foods but may progress to include liquids as well. Difficulty speaking with a hoarse, weak voice may be noticed. Other muscle involvement may appear later, with weakness involving the upper arms and legs, the tongue and facial muscles.

Lower limb weakness affecting muscles around the hip (hip girdle muscles) is usually more pronounced than upper limb weakness, and a number of patients will require mobility devices and some eventually a wheelchair. In addition to muscle weakness, some patients will experience progressive fatigue. Cognitive function is generally unaffected, although neuropsychological tests have shown impaired executive functions in some patients.

OPMD is inherited in an autosomal dominant pattern. In individuals, there are two sets of genes, each inherited from one parent. An autosomal dominant trait means that the presence of only one abnormal gene out of two gene copies from parents is sufficient to result in disease manifestation. OPMD is caused by changes in a gene named PABPN1. Abnormal expansion of this gene has been correlated with causing OPMD. There is a readily available free blood test that evaluates this genetic mutation. The penetrance of the disease increases with age. OPMD is 100% penetrant after the age of 70, meaning that 100% of patients having the abnormal gene will become symptomatic by this age.