Mitochondrial D-loop polymorphisms and mitochondrial DNA content in childhood acute lymphoblastic leukemia

The mitochondrial displacement loop (D-loop) controls mitochondrial expression, with mutations and mitochondrial DNA (mtDNA) content linked to oncogenesis. We investigated D-loop polymorphisms and mtDNA content in childhood acute lymphoblastic leukemia (ALL). The D-loop was sequenced in 251 children: precursor B ALL (n=114), with 76 paired remission/relapse samples; T-ALL (n=24); cord blood controls (n=113). The mtDNA copy number was analyzed using real-time quantitative polymerase chain reaction for 92 controls and 54 ALL patients at diagnosis and remission. Polymorphisms around H-strand replication origin (nucleotides 150 to 199) and conserved sequence block II (nucleotides 299 to 317) were associated with leukemia biology and treatment response. T-ALL patients were more likely to have longer nt303 poly-C tract. T199C polymorphism was associated with increased risk of ALL in Malays; T152C was more frequent in good responders. There was no difference in mtDNA content between diagnostic ALL samples and controls; however, there was significant decrease in mtDNA content after treatment, especially in samples with OH polymorphisms. Somatic mutations were found in 13% (9 of 76) of patients, suggesting a link to leukemogenesis. Our results suggest that polymorphisms impacting transcriptional control could affect mtDNA replication. Decrease in mtDNA content after treatment may confer susceptibility to chemotherapy and be a clue to the good prognosis of childhood ALL.