GSTO1 and Myalgia: The GSTM1 null genotype was associated with a more than two-fold increased risk of developing brain fog (OR 2.29, 95% CI 0.79–6.58), while carriers of at least one Val allele of GSTP1 AB (OR 0.43, 95% CI 0.21–0.87) and those with the GSTO1 AspAsp genotype (OR 0.51, 95% CI 0.25–1.02) had a reduced risk of developing myalgia.