What are the genetic changes related to oculopharyngeal muscular dystrophy ?
Mutations in the PABPN1 gene cause oculopharyngeal muscular dystrophy. The PABPN1 gene provides instructions for making a protein that is active (expressed) throughout the body. In cells, the PABPN1 protein plays an important role in processing molecules called messenger RNAs (mRNAs), which serve as genetic blueprints for making proteins. The protein alters a region at the end of the mRNA molecule that protects the mRNA from being broken down and allows it to move within the cell.  The PABPN1 protein contains an area where the protein building block (amino acid) alanine is repeated 10 times. This stretch of alanines is known as a polyalanine tract. The role of the polyalanine tract in normal PABPN1 protein function is unknown.  Mutations in the PABPN1 gene that cause oculopharyngeal muscular dystrophy result in a PABPN1 protein that has an extended polyalanine tract. The extra alanines cause the PABPN1 protein to form clumps within muscle cells that accumulate because they cannot be broken down. These clumps (called intranuclear inclusions) are thought to impair the normal functioning of muscle cells and eventually cause cell death. The progressive loss of muscle cells most likely causes the muscle weakness seen in people with oculopharyngeal muscular dystrophy. It is not known why dysfunctional PABPN1 proteins seem to affect only certain muscle cells.