Investigations of vitamin D receptor polymorphism affecting workers' susceptibility to lead

Gene polymorphism is an important factor that affects human susceptibility to toxins. For example, previous studies suggested that the ALAD genotype is an important factor affecting workers' susceptibility to lead toxic effects, including hemopoietic and nervous system. But we have had few researches in Taiwan, though there are thousands of workers involved in lead-related industries. On the other hand, although it is well known that lead deposits in the bone mineral component and interacts with calcium, vitamin D receptor may therefore be an important factor in the metabolism of lead. Some studies suggested that different vitamin D receptor genotypes have various kinds of receptor activity. The goal of this study was to investigate the polymorphism affecting workers' susceptibility to lead. Three allelic variants of the VDR gene were defined by means of the polymerase chain reaction (PCR) and three restriction enzymes (ApaI, BsmI, and TaqI). We determined the relationships of different VDR genotypes (AA, Aa, aa, BB, Bb, bb, TT, Tt, and tt) to blood lead and the index of cumulative blood lead levels (ICL). Altogether we analyzed 544 workers' VDR genotypes (BsmI, TaqI, and ApaI) and compared to their blood lead levels and ICL in the VDR genotypes. The results showed that workers had higher blood lead levels and ICL in the Apa I- aa genotypes, but this is not statistically significant when adjusted for potential confounding factors. Other characteristics, such as exposure status, smoking and alcohol drinking, were significantly associated with ICL and time-weighted ICL. Regression analyses suggested that exposure status and personal habits (smoking and alcohol drinking) are still the major effects on blood lead parameters for lead workers rather than genotypes. In conclusion, VDR genotypes did not significantly affect the long term blood lead parameters after adjustment for all factors, but industrial hygiene improvement, including engineering control and health education, are the most important ways to protect workers' health.