RISK ESTIMATES FOR BALANCED RECIPROCAL TRANSLOCATION CARRIERS - PRENATAL-DIAGNOSIS EXPERIENCE

An analysis was performed on 40 families at risk for an unbalanced rea rrangement in the fetus because one of the parents is a reciprocal tra nslocation carrier, The overall risk at second trimester prenatal diag nosis was 14% (8/57). The individual risks for unbalanced offspring at second trimester prenatal diagnoses and at birth were estimated using empirical data by Stengel-Rutkowski et al. (1988). The risks at birth ranged from 0%-21.6%. Most reciprocal translocations (22 or 55%) were at low risk. Without risk (7 or 17.5%), medium risk (6 or 15%) and hi gh risk (5 or 12.5%) translocations were about equally represented and relatively infrequent. The analysis shows that the mode of ascertainm ent as well as the measurement of lengths of observed or probable imba lances cannot serve as a reliable risk predictor in individual counsel ling. In the translocations ascertained through spontaneous abortions the risk is frequently small or nonexistent, but remarkable exceptions to this rule are observed. Translocations discovered through unbalanc ed offspring were found to belong to different risk groups with the ex ception of the no risk group. Individual risk estimates have to be per formed as a basis of genetic counselling before or during pregnancy so that parents with reciprocal translocations can make their choices re garding the available options.