MTHFR and acute lymphoblastic leukemia: Nevertheless, coexistence of DHFR 19bp ins/del (rs70991108) in the promoter/first intron of the gene, MTHFR 677 C>T (rs1801133) in A223V codon of exon 4, and MTHFR 1298 A>C (rs1801131) in E429A codon of exon 7 of the gene have never been investigated in combination in a cohort of mother-child dyads of pediatric ALL.