Intolerance research needs

Some populations of freshwater isopods are tolerant to lead. Inasmuch as intolerant isopods from an unpolluted site can be made tolerant by exposure to low levels, it is suggested that naturally occurring tolerance may be achieved by acclimatization. Research is needed on lead transformation mechanisms, on toxic forms of lead and interaction effects with other compounds, and on effects of lead-contaminated sediments on benthos. 

MAD deficiencies were detected (patient 2,4). Among 12 patients with these complaints, one showed decreased NH formation during ischaemic exercise. MAD subsequently was found decreased in muscle biopsy (patient 3). MAD deficiency so could be found in these patients in a frequency of about 10%. In consecutive biopsy series from literature, a frequency of about 1,8% can be estimated. Half of the cases in these series display exercise intolerance. However, it is very probable that much less than half of the biopsies in these series come from patients with exercise intolerance. Therefore the available evidence from our study and from literature suggests that myoadenylate deaminase is possibly a rather frequent cause of exercise intolerance. Further research is needed to decide if the occurrence of MAD deficiency together with other often well defined neuromuscular diseases is determined by chance, or if there exists a rather varying clinical expression of the deficiency. 

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