The SELENON gene (also called SEPN1) provides instructions for making a protein called selenoprotein N. This protein is part of a family of selenoproteins, which have several critical functions within the body. Selenoproteins are primarily involved in chemical reactions called oxidation-reduction reactions, which are essential for protecting cells from damage caused by unstable oxygen-containing molecules. Although the exact function of selenoprotein N is unknown, it is likely involved in protecting cells against oxidative stress. Oxidative stress occurs when unstable molecules called free radicals accumulate to levels that damage or kill cells.~Selenoprotein N is highly active in many tissues before birth and may be involved in the formation of muscle tissue (myogenesis). The protein may also be important for normal muscle function after birth, although it is active at much lower levels in adult tissues. This protein is thought to play a role in maintaining an appropriate balance of calcium (calcium homeostasis) in cells. Calcium plays an important role in muscle movement.