PbB and ALAD in mentally retarded and normal children

Summary

Blood lead (PbB) and erythrocyte delta-aminolevulinic acid dehydratase (ALAD) were measured in a group (A) of 50 mentally retarded children of unknown etiology (24 boys and 26 girls; average age 13.38 years, range 10–17 years) from an institution for handicapped children in Zagreb, and in a group (B) of 50 “normal” children (31 boys and 19 girls; average age 13.36 years, range 10–17 years) from a nearby orphanage in the same area (less polluted) of northern Zagreb. The children in group A had spent an average of 4.12 years (0.6–12 years) in the institution, and came from both urban (n=23) and rural (n=27) areas. The children in group B had spent an average of 4.88 years (1–14 years) in the orphanage, and also came from both urban (n=38) and rural (n= 12) areas. The data obtained indicate a very close distribution of PbB levels in both groups, but a considerably different distribution of ALAD levels in favour of a lower activity in mentally retarded children. However, PbB and ALAD in both groups were within the range of currently acceptable “normal” values. The median and range values in groups A and B, respectively, were: 132 μg/l (85–256 μg/l) and 135 μg/l (78–215 μg/1) for PbB; 49.2 European units (27.0–65.0 European units) and 54.6 European units (27.0–69.9 European units) for ALAD. The semi-logarithmic dose-effect relationship between PbB and ALAD was significant within the group of “normal” children (r=−0.3235,P<0.05), but was not significant either within the group of mentally retarded children (r=−0.0876,P > 0.50) or for the pooled data of both groups (r=−0.1693,P> 0.05). The present data indicate no causal association between increased lead exposure and mental retardation. However, the possibility of an increased biologically active lead deposit due to past over-exposure to lead and/or a relative zinc deficiency in mentally retarded children cannot be excluded.