Mitochondrial DNA content affects the fertilizability of human oocytes

Mitochondrial DNA content varies considerably in oocytes, even when collect ed from the same patient. In the present study, real-time quantitative poly merase chain reaction analysis of 113 unfertilized oocytes obtained from 43 patients revealed an average of 193 000 (range: 20 000 to 598 000) mitocho ndrial genomes per cell, We compared several groups of oocytes to investiga te the relationship between mitochondrial DNA content and fertilizability, The average mitochondrial DNA copy number was significantly lower in cohort s suffering from fertilization failure compared to cohorts with a normal ra te of fertilization. In addition, the mitochondrial copy number of oocytes from patients with fertilization failure due to unknown causes was signific antly lower than that of oocytes from patients in which IVF failure was due mainly to a severe sperm defect. The lower mtDNA copy number could be due to defective cytoplasmic maturation of oocytes. We conclude that low mitoch ondrial DNA content, due to inadequate mitochondrial biogenesis or cytoplas mic maturation, may adversely affect oocyte fertilizability.