Ravenscroft G., Colley S., Walker K., Clement S., Bringans S.D., Lipscombe R.J., Fabian V., Laing N., and Nowak K.J. (2008) Neuromuscular Disorders,18:953-958.
As with many skeletal muscle diseases, the extraocular muscles (EOMs) are spared in skeletal muscle a-actin diseases, with no ophthalmoplegia even in severely affected patients. We hypothesised that the extraocular muscles sparing in these patients was due to significant expression of cardiac a-actin, the a-actin isoform expressed in heart and foetal skeletal muscle. We have shown by immunochemistry, Western blotting and a novel MRM-mass spectrometry technique, comparable levels of cardiac a-actin in the extraocular muscles of human, pig and sheep to those in the heart. The sparing of extraocular muscles in skeletal muscle a-actin disease is thus probably due to greater levels of cardiac a-actin, than the negligible amounts in skeletal muscles, diluting out the effects of the mutant skeletal muscle a-actin.