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SOME GENETIC ASPECTS OF THERAPEUTIC ABORTION* JAMES V. NEEL, M.D., PA.D.f My rolein thisprogram is to discuss the geneticindications for interruption ofpregnancy. To those ofyou expecting simple, clear-cut formulas, I must apologize. From my vantage point, with respect to the issue ofpregnancy interruption, your specialtyhas onepieceofan increasinglycomplex problem, a problem which raises some of the more difficult biomedical issues toward whose solution our society is groping. We most assuredly will not settle your piece ofthe problem in the course ofthis panel discussion , but perhaps together we can put it in a light which will suggest certain courses of action. For some twenty-six years now the University of Michigan has maintained a Heredity Clinic. The Hmitations on staff, time, and space being what they are, we have not attempted to see all the potential problems in genetic counseling referred to the University Hospital but rather, both for service and training purposes, to consult each year with a hmited number ofpeople with representative questions requiring such counseling. One of the issues arising from time to time has been whether a given probability of congenital abnormality in a child is an indication for interrupting a pregnancy. Each time this question has fallen to me, I have been troubled by the near total absence ofguidelines. For present purposes, we will define a possible "genetic indication" for terminating a pregnancy as an appreciable probability that the unborn child will, either at birth or subsequently, be found to have a major abnormality in whose etiology genetic factors are of established importance. The most common situation involves serious congenital defect. In passing, let us recognize that the etiology ofcongenital defect is extremely com- * Paper delivered April, 1967, in a panel discussion, "The Place ofTherapeutic Abortion in Modern Obstetric Practice," at the annual meeting ofthe American College ofObstetrics and Gynecology in Washington, D.C. Published with the permission ofObstetrics and Gynecology. f Department ofHuman Genetics, University ofMichigan Medical School, Ann Arbor. 129 plex, with both environmental and genetic factors of various types involved , but we will not go further into this subject now. Begging for the moment the legality ofabortion on genetic grounds—a subject we come to shortly—let me at thisjuncture point out the wide range ofrecurrence risks with which one may be confronted in genetic counseling. Five examples , any one ofwhich might prompt the question ofthe propriety of terminating a pregnancy, will suffice: 1.First child with anencephaly; no other instance ofcongenital defect known in family ; mother again pregnant. Here the recurrence risk for this or other severe defect ofthe central nervous system is about 4 per cent [1]. 2.Two children with severe central nervous system defect; immediate family history otherwise negative for congenital defect; mother again pregnant. Now the recurrence risk is 10 per cent [2]. 3.Parents second cousins; first child normal; second child developed infantile amauroticidiocyatsixmonths . Onthewell-justifiedassumptionofsimplerecessiveinheritance, the recurrence risk is 25 per cent. 4.For the fourth example, we turn to a problem seen fourteen years ago. The first child of normal-appearing parents had died of a complex cardiac malformation; the second had beenfoundto have cysticfibrosis ofthepancreas. Moreover, arising anti-Rh titer was encountered during that second pregnancy, although there was no clinical erythroblastosis; the mother was Rh-negative and the father was found very probably to be R1R2, so that all subsequent children would be Rh-incompatible. Our calculation ofthe probability ofa normal outcome, should the mother again become pregnant, was 36 per cent, computed as the product of three probabilities: normality for congenital heart disease (95 per cent), normality for cystic fibrosis (75 per cent), and non-occurrence ofRh disease (50 per cent). This illustration was chosen not only to bring out the complexity sometimes encountered in counseling but also the rapid evolution ofknowledge. Successive developments in the anticipation and treatment oferythroblastosis would now lessen greatly the likelihood ofsevere disease on this score, while the prophylactic use of an anti-D serum during the pregnancies ofpredisposed women has the possibility ofpreventing the disease altogether [3, 4]. 5.The final example concerns pregnancy in a woman with the dominantly inherited disorder termed Huntington's chorea. The child will have a 50 per...

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