The incidence of SOS is reported at 16% (range: 0%–34%), with risk factors including combining busulfan with cyclophosphamide, GSTA1 genotypes, age, weight <9 kg, weight-based dosing, and the use of once-daily IV busulfan (Lawson et al., 2021). The gene discussed is GSTA1; the disease is spondylo-ocular syndrome.