© 1987 by The Society for Integrative and Comparative Biology
Developmental Biology and Human Concerns1
Division of Basic Medical Sciences, Mercer University, School of Medicine Macon, Georgia 31207
There is a large natural loss of human embryos in early gestation. Most conceptual losses occur before pregnancy has been diagnosed in the woman. It is now acknowledged that chromosomal aberrations are the major etiologic agents responsible for spontaneous abortions. Fully 50 percent of naturally aborted embryos in the first trimester have an abnormal karyotype. Most of the chromosomal errors that have been identified in abortuses are only rarely seen in livebirths. Natural in utero selection is relentless in eliminating 99 percent of the chromosomally abnormal conceptuses through spontaneous abortion. The birth of affected offspring that escape nature's screening mechanism can be averted by the option of prenatal diagnosis. The thrust of prenatal diagnosis is to prevent the tragic impact of debilitating genetic disorders. But notall at-risk parents wish to avail themselves of prenatal diagnosis because they are unwilling to accept the choice of therapeutic abortion. Prevention of a genetic disorder before implantation would obviate the necessity of an abortion at a later stage of pregnancy. With this perspective, the correction of the basic genetic flaw by replacing the faulty gene with a functioning allele is an attractive alternative. Notwithstanding the imprecise technology that presently serves to caution against immediate application, gene therapy is a reasonable and natural extension of efforts to ameliorate the effects of severe inherited disorders.