Effects of the δ-aminolevulinic acid dehydratase polymorphism rs1800435 on blood lead levels: a new systematic review and meta-analysis

Exposure to lead has various health effects. Studies have correlated the δ-aminolevulinic acid dehydratase (ALAD) polymorphism rs1800435 (ALAD1 and ALAD2) with blood lead levels, but the results have been inconsistent. This meta-analysis evaluated the associations between the rs1800435 and blood lead levels. Studies reporting the relationships of rs1800435 with blood lead levels were included. The sample size, means, and standard deviations were calculated. Subgroup analysis was performed on the basis of the presence or absence of lead exposure, age, sex, and geographic latitude of the investigated people. Twenty-seven studies with 17,344 individuals were included. There was no significant association between rs1800435 status and blood lead levels, either in the lead-exposed group (p = 0.280), nonlead-exposed group (p = 0.642), or overall analysis (p = 0.165). Among those exposed to lead, for people living at non-low latitudes (latitude > 30°), ALAD2 allele carriers had higher lead levels than ALAD1 homozygotes did (p = 0.001). For non-lead-exposed respondents, blood lead levels in male ALAD2 allele carriers demonstrated a marginally significant decrease compared with those in male ALAD1 homozygotes (p = 0.061). Lead exposure levels and the geographical latitude of long-term residence may modify the ALAD2-associated effects on blood lead concentrations.