GSTM1 and asthma: Similar to a previous study showing that the GSTM1 null genotype increases the risk of childhood asthma only in children with a history of intrauterine smoke exposure [33], this study found that the GSTM1 null genotype is associated with a higher incidence of asthma than the positive GSTM1 genotype is in boys and girls with prenatal TSE, with a nonsignificant difference (35.3% versus 30.3%, P = 0.643, OR: 1.243, 95% CI: 0.495–3.121 for boys, 30.0% versus 23.3%, P = 0.535, OR: 1.408, 95% CI: 0.477–4.159 for girls).