However, there is an adverse viewpoint from Lopez et al. with a research population of 115 ALL children, who claimed that MTHFR (C677T and A1298C), TYMS (28 bp and 6 bp-del), SHMT1 (C1420T), ABCB1 (C3435T), ABCG2 (C421A), RFC1 (G80A), and SLCO1B1 (rs4149081) were not available to show relationships with MTX toxicity in childhood ALL (Lopez-Lopez et al., 2011). Here, ABCG2 is linked to acute lymphoblastic leukemia.