Increased blood lead levels in mentally retarded children in Greece.

In 60 children with mental retardation of unknown etiology, the whole blood lead, as well as the activity of the red cell delta-aminolevulinic acid dehydratase (delta-ALAD), was measured. Thirty normal children and 30 with mental retardation of known etiology were used as controls. The lead values were found significantly higher in the study patients compared with both control groups (P less than 0.001). The delta-ALAD activity in the 14 patients with blood lead levels greater than or equal to 40 microgram/dl, was significantly reduced compared with the normal controls (P less than 0.001) and the mentally retarded controls (P less than 0.01). In more than 20% of the patients with mental retardation of unknown etiology, indications of significant exposure to lead were found. There was no difference in blood lead values between children from cities and those from rural areas. The possible role of lead in the etiology of mental retardation is discussed.