GSTM1 and asthma: In GSTM1-null children of school age, in utero exposure to smoking is associated with an increased prevalence of early-onset asthma, asthma with current symptoms, persistent asthma, lifetime history of wheezing, wheezing with exercise, wheezing requiring medication, and number of emergency department visits in the past year in comparison to children with the GSTM1+ genotype [61, 87, 88].