When the gene for desmin is knocked out it is no longer able to function properly. Mice with the desmin knockout gene develop normally and are fertile, however soon after birth they begin to show defects in skeletal, smooth and cardiac muscle; in particular the diaphragm and heart are affected. The mice without desmin are weaker and fatigue more easily than wild type mice and the muscle fibers are more likely to be damaged during contraction, presumably because the desmin is responsible for keeping the muscle fibers aligned. Mice without desmin also have impaired mitochondrial function.