Blood lead levels in normal and mentally deficient children

Abstract

A series of prepubertal children were investigated for evidence of exposure to lead. Comprising the series were 20 children of normal intelligence (Group A), 20 with mental deficiency of known aetiology (Group B), and 20 who were mentally deficient from unknown aetiology (Group C). 9 of these children, 3 in Group A and 6 in Group C were found to have blood lead levels greater than 40 μg./100 g. blood. In these the urinary lead excretion was normal but was increased significantly after an oral dose of 300 mg. penicillamine. This test (the penicillamine-lead excretion test) and the blood lead levels are shown to be the most helpful procedures in the diagnosis of lead exposure in childhood. The presence of a raised erythrocyte protoporphyrin level is suggestive of lead exposure, but in contrast to adult lead poisoning urinary coproporphyrin and Δ-amino laevulic acid estimations are of no value in the detection of this state. All of the 9 children with raised blood lead levels had a history of pica and with one exception lived in old houses. Furthermore, there were no children with raised blood lead levels in Group B which contained children with organic brain damage some of whom were severely immobilized and consequently were more closely supervised than those in the other two groups. This emphasizes the importance of pica and of access to environmental lead in the development of lead intoxication. There is evidence that lead inhibits an important haem enzyme in the brain (ALA dehydrase) and that acute lead intoxication leads in some cases to mental deficiency or aggravates a pre-existent mentally deficient state. The growing brain of young animals is more susceptible to damage by lead than that of adult animals. These considerations add weight to the suggestion that previously undetected lead poisoning may be a factor in the development of some cases of mental deficiency, but the problem requires further investigation.