GSTA1 and hepatic veno-occlusive disease: Analyses between HSCT-related toxicities and the four GSTA1 diplotype groups revealed a strong association with Sinusoidal Obstruction Syndrome (SOS) (p < 0.0005; Figure 3a), whereby Group IV carriers had seven-fold higher risk of SOS (HR = 7.1; 95% CI: 2.5-20.4) compared to patients with other GSTA1 diplotypes.