Genetic factors and radiation effects in early embryos

Most animal experiments have suggested that irradiation during the preimplantation period may only result in the death of the embryo or its survival without anomaly. Irradiation during the period of organogenesis may lead to congenital anomalies, while irradiation during the foetal period can induce tissue anomalies and growth retardation. Exposure of the human conceptus during the last period may also lead to a diminution of the QI and microcephaly. Recent experiments in the mouse have, however, suggested that ionizing radiation could also induce congenital anomalies as well as a genomic instability, when administered during the preimplantation period. Mutations in genes concerned with cell cycle regulation, apoptosis or DNA repair could increase the radiation sensitivity of the embryo. When present at the homozygous state, such mutations revealed most often lethal per se. Research on the incidence of heterozygous mutations on the radiation sensitivity of the early embryo is still scarce but results have suggested that mutations in the p53 gene could increase the sensitivity of early postimplantation embryos to radiation-induction of congenital anomalies. Altogether, these results underline the need for additional research on genetic factors that could modify the embryonic radiosensitivity during the preimplantation and very early postimplantation stages.