ERCC2 and xeroderma pigmentosum group D: Specific genes including OGG1 (encodes the enzyme 8-oxoguanine DNA glycosylase responsible for the excision of 8-oxoguanine, a mutagenic base byproduct which occurs as a result of exposure to reactive oxygen), APE1(encodes multifunctional protein involved in DNA repair), and XRCC1 (BER pathway), XPD (xeroderma pigmentosum group D (XPD) protein with a function in nucleotide excision repair of DNA damage caused by UV radiation) and POLD1 (NER pathway), and BRCA1 (homologous recombination) show down-regulation following Pb exposure [155].