Six patients with myotonic muscular dystrophy representing 6 separate families were studied. Washed muscle membrane preparations from both control and myotonic tissues were able to incorporate 32P into membrane protein using only γ 32P ATP as substrate. Since the enzymatic activity of protein phosphorylation within the membrane seems so easily affected by environmental changes, it seems more reasonable to ascribe the changes noted with myotonic muscle to an altered membrane rather than to a specific genetically mediated alteration in the protein kinase enzyme. The demonstration of lowered protein phosphorylation in muscle membranes confirms the similar observations made on erythrocyte ghosts. Although the authors were initially concerned that fibrosis, fatty infiltration, dystrophy or denervation might specifically affect the outcome, none of these seem to be particularly pertinent since morphological evaluation of the biopsies employed would suggest that minimal pathology was present in the muscle segments used. Whether the altered protein phosphorylation of muscle membrane and red blood cells or the physical alteration in the red cell membrane is the more pertinent etiological factor is not known at present. Either of these alterations might be associated with an abnormal membrane, and both would lend support to the concept of myotonic muscular dystrophy as a diffuse disorder of membranes.
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