[Genetic counseling in cases of chromosome insertions]

The principles of the estimation of the risk of repeated birth of malformed child and spontaneous abortion in families of balanced carriers of insertions are presented. A risk for a carrier is formed from two parts: a risk for a carrier of reciprocal translocation and a risk for a carrier of insertion of the came length as inseried segment. The first component of the risk is a constant, the latter one is a variable. It depends on the length of the inserted segment, the type of its inclusion (direct or inverted) and sites of break points. An estimation of the risk in hypothetical insertion 46, XX, inv ins (4; 2) (q24; q22q34) is described as a model. The same method of counselling may be used for the families with triple translocations t(a-, b-, c+) with "insertion" of fragment of chromosome "a" between the parts of "b" and "c" chromosomes. A tentative empirical mean value of repeated birth of malformed child and spontaneous abortion in families with insertions is 29% and 45% for the female carrier, and about 37% and 25% for the male carrier.