Segregation analysis and genetic counseling when both parents carry balanced chromosomal translocations

Objective: To assess the risk of chromosomally abnormal offspring and discuss counseling approach when both parents carry balanced translocations. Design: Theoretical segregation analysis is performed and use of empiric data is used in genetic counseling. Setting: Patients are referred to Division of Reproductive Genetics at the University of Tennessee, Memphis. Patients, Participants: The mother, heterozygous for reciprocal translocation 46,XX,rcp(7;13)(p21;q22) and father, heterozygous for Robertsonian translocation 45,XY,rob(13q;14q) were referred for genetic counseling concerning risks of chromosomally abnormal offspring. Interventions: Segregation analysis, genetic counseling, and chorionic villus sampling. Main Outcome Measure(s): A cumulative risk was derived to use for counseling purposes. Cytogenetics using GTG-banding was performed on cultured chorionic villus cells. Results: Theoretical risk of this couple having chromosomally abnormal offspring was 40.5%. On the basis of empirical data and risk factors inherent in the specific translocations, the maternal contribution at midtrimester was 3.5%; the paternal contribution was 1% to 2%. The sum of these risks was used in counseling. Conclusions: The fetus was found to be 46,XY,rcp(7;13)(p21;q22).