Why do healthy female carriers of Duchenne muscular dystrophy have increased serum creatine kinase levels?
Normal muscle stained for dystrophin. Firstly the levels are nowhere near as high as the affected boys. The boys levels may be as high as 30,000 units per litre the carriers are usually below 500 U/l and normal women are usually below 100U/l. The normal DMD gene codes for a protein dystrophin which is related to the muscle cell wall. In this picture a cross section of normal muscle fibres has been stained using a dye attached to anti dystrophin antibodies. The dystophin is seen in region of the muscle fibre walls. All fibres are of even size. DMD muscle stained for dystrophin. In DMD there is no dystrophin made and this leaves holes in the muscle cell wall where the dystrophin would have been attached to other proteins which are also involved in other forms of musclular dystrophy. Creatine kinase is an intracellular enzyme but it can leak out of these holes into the serum. Note that that not only is dystrophin missing but the muscle fibres are of varying sizes and shapes and some muscl
