Some outstanding problems in the detection of trace element deficiency diseases.

Knowledge of the functional roles of many essential trace elements has grown rapidly. Despite this, it is rarely possible to relate this information to observed pathological consequences of deficiency. Few studies of the effect of deficiency upon enzyme activity have attempted to determine whether such changes influence substrate-product relations and thus may have pathological significance. Evidence that the differing susceptibility of tissues to deficiency may reflect metabolic activity or the lifespan of cells and their organelles is considered. The need is growing for more effective biochemical diagnostic techniques for the early detection of covert pathological changes in trace element deficient subjects. Progress towards satisfying this need will reflect the future availability of information from which to predict the nature of rate-limiting metabolic defects in sensitive populations of cells.