Evaluation of parental mitochondrial inheritance in neonates born after intracytoplasmic sperm injection

Intracytoplasmic sperm injection (ICSI) is now used when severe male-factor infertility has been documented. Since defective mitochondrial functions m ay result in male hypofertility, it is of prime importance to evaluate the risk of paternal transmission of an mtDNA defect to neonates. DNA samples f rom the blood of 21 infertile couples and their 27 neonates born after ICSI were studied. The highly polymorphic mtDNA D-loop region was analyzed by f our PCR-based approaches. With denaturing gradient gel electrophoresis (DGG E), which allows 2% of a minor mtDNA species to be detected, the 27 newborn s had a DGGE pattern identical to that of their mother but different from t hat of their father. Heteroplasmy documented in several parents and childre n supported an exclusive maternal inheritance of mtDNA. The parental origin of the children's mtDNA molecules also was studied by more-sensitive assay s: restriction-endonuclease analysis (REA) of alpha[P-32]-radiolabeled PCR products; paternal-specific PCR assay; and depletion of maternal mtDNA, fol lowed by REA. We did not detect paternal mtDNA in nine neonates, with a sen sitivity level of 0.01% in five children, 0.1% in two children, and 1% in t wo children. The estimated ratio of sperm-to-oocyte mtDNA molecules in huma ns is 0.1%-1.5%. Thus, we conclude that, in these families, the ICSI proced ure performed with mature spermatozoa did not alter the uniparental pattern of inheritance of mtDNA.