Emery-Dreifuss muscular dystrophy (EDMD) is a type of muscular dystrophy characterized by the wasting and weakness of muscles in the shoulders, upper arms, and calves. It can also cause stiff joints in the elbows, neck, and heels. Patients with EDMD commonly have a heart problem called a conduction block that can be very serious.
The EMD gene encodes for a protein called emerin which is made in many types of cells but is particularly important in skeletal and cardiac muscle cells. Emerin is a component of the nuclear envelope, the membrane that sequesters DNA from the rest of the cell. The nuclear envelope has many functions, but one of the most important is determining what molecules can move in and out of the nucleus. By controlling this movement, emerin is involved in regulating gene expression, controlling cell division, and maintaining the structure and stability of the nucleus.
Researchers don’t know how mutations in EMD cause EDMD, but think that these mutations may cause the nuclear envelope to destabilize, causing muscle cell death.
The FHL1 gene provides instructions for making three versions (FHL1A, FHL1B, and FHL1C) of a protein that plays a role in muscles. Not much is known about FHL1B or FHL1C, but FHL1A is thought to play a role in the assembly of sarcomeres (the structures that are necessary for muscle contraction), as well as the maintenance of muscle structure, size, and growth.
It is thought that mutations in FHL1 may cause sarcomeres to fail to form or to destabilize after they have formed, leading to the breakdown of muscle tissue.
The LMNA gene provides instructions to make several slightly different proteins called lamins. The two major proteins, lamin A and lamin C, are made in most cells in the body and are structural proteins called intermediate filaments, which provide stability and strength to cells. As such, lamins A and C support the nuclear envelope by forming a scaffolding.
Although how LMNA mutations cause EDMD is unknown, they are thought to lead to the weakening of the nuclear envelope, causing cell death. Lamins are also thought to play a role in controlling the expression of other genes.
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