Intact erythrocyte membranes from patients with myotonic muscular dystrophy (MMD) have been shown by spin labelling to have greater membrane surface fluidity than normal. The authors have now evaluated the specificity of this phenomenon. They used erythrocytes from patients with MMD, and also from patients with Duchenne muscular dystrophy (DMD), as a model of dystrophy with no myotonia, and from patients with congenital myotonia (CM) as a model of myotonia without dystrophy. The data reported indicate similarly high erythrocyte fluidity near the membrane surface in CM, whereas erythrocytes from DMD and other non myotonic muscular dystrophic patients have normal membrane fluidity as assessed using 5 nitroxide methyl stearate (5 NMS). These results suggest a correlation of increased membrane fluidity with the presence of myotonia.
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