FAMILIAL AUTOSOMAL RECIPROCAL TRANSLOCATI ONS

Reciprocal translocations are one of the most frequently observed stru ctural chromosome abnormalities. They are defined by a segment exchang e between two non-homologous chromosomes. A great number of different translocations exist since any chromosome can be involved in the trans location and the position of the breakpoint can vary. Though generally silent these translocations can be expressed in the form of reproduct ion failure or, more seriously, as offspring showing mental retardatio n/malformation syndromes. Since the risk of malformation varies from o ne translocation to the next, genetic counselling and prenatal diagnos is strategies should be adopted to suit the particular malformation ri sks of each individual translocation, This is currently not the case. Different prediction methods (for the most probable mode of unbalance at birth, the risk of unbalance at term) are presented, A computer sys tem, called Reci-Conseil brings these different functionalities togeth er to create a new aid for genetic counselling. The data base on which it is founded (approx 2000 families) offers interesting perspectives for genomic mapping of partial trisomies and monosomies.