MTHFR and mucositis: The MTHFR 1298A>C genotype was significantly associated with grade 3–4 diarrhoea and/or mucositis (P=0.005), with patients with the A/A genotype having a higher risk of toxicity (OR=4.71; 95% CI=1.63, 13.59) compared to patients with the A/C or C/C genotype (Figure 2A).