AbstractThere are large amounts of zinc in muscle and zinc ions can enhance the degree of muscle contraction in response to direct stimulation while at the same time inhibiting neuromuscular transmission. The opposites of these effects would lead to myotonia and muscle weakness. There are many parallels between the non-muscular features of myotonic dystrophy and those of zinc deficiency. The particular patterns of reproductive disturbance in both males and females, the abnormalities of metabolism, the defects in gut funcion, the defects in bone and the congenital abnormalities are very similar in the two conditions. However there are important differences between simply zinc deficiency states and myotonic dystrophy which mean that the latter is unlikely to be due to the former. Instead it is proposed that the fundamental defect in myotonic dystrophy is the presence of an abnormal zinc binding ligand which fails to deliver appropriate amounts of zinc ions to the tissues. The functioning of this ligand may, however, be affected by dietary zinc, perhaps accounting for the apparent variation in the expression of the dominant myotonic dystrophy gene due to some unknown environmental factor. Some of the effects of zinc may be due to lack of the zinc ion directly, while others are probably related to defects in essential fatty acid and prostaglandin metabolism. The hypothesis can be readily tested by the employment of nutritional measures designed to counteract the defects in zinc and essential fatty acid metabolism.
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