To analyze the association between prenatal TSE and childhood asthma for the GSTM1 null and positive genotypes and in different gender backgrounds, we categorized all of the children into four groups (males with positive GSTM1 genotype, males with GSTM1 null genotype, females with positive GSTM1 genotype, and females with GSTM1 null genotype). Here, GSTM1 is linked to asthma.