Oculopharyngeal muscular dystrophy (OPMD) is a genetic disease that is characterized by muscle wasting. As its name implies, muscles that control the eyelids (oculo) and throat (pharyngeal) are typically the first affected in OPMD patients.
Symptoms of OPMD
Symptoms typically first appear when patients reach middle age (around 40 to 60 years old). The initial symptoms are droopy eyelids and difficulty swallowing caused by the weakening of muscles around the eyes and throat. Eye muscle degeneration can progress and lead to difficulty moving the eyes and, sometimes, to double vision.
Patients may eventually experience weakening of the muscles near the torso, such as the upper legs and shoulders, as well as muscles in the pelvic area. As the disease progresses this weakness and degeneration can extend outward to affect muscles of the lower limbs.
OPMD is a genetic disease, caused by a defect or mutation in the PABPN1 gene. The mutation causes the protein that the gene encodes for to acquire an abnormal form. This abnormal protein clumps inside muscle cells and hampers their function. Eventually, these clumps can kill a muscle cell. Scientists do not yet know why this only seems to occur in certain muscle cells, like those around the eyes and throat, and not in all muscle cells.
OPMD exhibits two different patterns of inheritance. In some cases, a single copy of the mutated PABPN1 gene, inherited from just one parent, is sufficient to cause the disease. This is an autosomal dominant inheritance pattern. In other cases, two copies of the mutated PABPN1 gene (one inherited from each parent) must be present for the disease to develop. This is called an autosomal recessive inheritance pattern.
The different inheritance patterns are linked to different mutations in the PABPN1 gene.