major strides have been taken in the regulation of lead intoxication in the general population , but studies using genetic markers of susceptibility to environmental toxicants raise the question of whether genes can make certain individuals more vulnerable to environmental toxins such as lead . 
 at least three polymorphic genes have been identified that potentially can influence the bioaccumulation and toxicokinetics of lead in humans . 
 the first gene to be discussed in this review is the gene coding for delta - aminolevulinic acid dehydratase ( alad ) , an enzyme of heme biosynthesis , that exists in two polymorphic forms . 
 the resulting isozymes have been shown to affect the blood and bone lead levels in human populations . 
 the effects of alad in lead intoxication have also been studied in laboratory mice that differ in the genetic dose for this enzyme . 
 the second gene reviewed here is the vitamin d receptor ( vdr ) gene . 
 the vdr is involved in calcium absorption through the gut and into calcium - rich tissues such as bone . 
 recent findings suggest that vdr polymorphism may influence the accumulation of lead in bone . finally , the third gene to be discussed here that may influence the absorption of lead is the hemochromatosis gene coding for the hfe protein . 
 the presence of mutations in the hfe gene leads to hemochromatosis in homozygotic individuals . 
 because of the associations between iron and lead transport , it is possible that polymorphisms in the hfe gene may also influence the absorption of lead , but this has not yet been studied . 
 more studies will be needed to define the role of these genes in lead intoxication.imagesfigure 2figure 4