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.
Causes
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.
Inheritance
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 PABPN1Â 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.
Diagnosis
A physician may suspect a patient has OPMD based on the characteristic patterns of muscle weakness and on family history. Doctors will often conduct tests to determine whether the muscle dysfunction is due to problems with the muscles themselves or with the nerves controlling them. They may also do blood tests to look for an enzyme called creatinine kinase that is released into the blood when muscles are damaged.
Finally, they may request a muscle biopsy, so that a sample of muscle cells can be examined under a microscope to determine the specific kind of damage they’ve sustained.
Because there are multiple other diseases with symptoms similar to those of OPMD, a diagnosis must be confirmed via a genetic test. This can be done using a blood sample, and it detects the presence or absence of a mutation in the PABPN1 gene.
Prognosis
OPMD is a progressive disease, meaning that its symptoms worsen over time. Although the progression is typically slow, the speed of progression and specific symptoms vary greatly from patient to patient. OPMD is not thought to significantly affect life expectancy.
Treatment
Most OPMD treatments focus on addressing specific disease symptoms. However, researchers are working on new approaches that directly target the PABPN1 gene, as well as on approaches that address muscle dysfunction more directly.
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