A key biomarker of lead exposure is the blockade of the enzyme ALAD (delta-aminolevulinic acid dehydratase). When ALAD is blocked, its substrate ALA (aminolevulinic acid) builds up, and causes the reduction of GABA (gamma-aminobutyric acid) in the central nervous system.
Lead also inhibits the formation of vitamin D, which plays a key role in calcium metabolism. Thus, calcium homeostasis is significantly altered by lead. This interferes with calcium-dependent signal transduction processes and may alter the most basic nervous system functions.