Reciprocal chromosome translocations involving short arm of chromosome 9 as a risk factor of unfavorable pregnancy outcomes after meiotic malsegregation 2:2.

PURPOSE: Genetic counseling of carriers with individual chromosome translocation requires information on how balanced reciprocal chromosome translocations (RCT) will segregate, what possible form of unbalanced embryo/fetus/child can occur, and the survival rates that have been observed in the particular families. We collected new empirical data and evaluated pedigrees of RCT carriers involving 9p in order to improve risk figures.
MATERIAL AND METHODS: Empirical data on 241 pregnancies of 70 carriers were collected from 32 pedigrees of carriers of RCT at risk for a single 9p segment imbalance (RCT9p) from the literature and unpublished data. The probability rates of particular types of pathology have been calculated according to the method of Stengel-Rutkowski and Stene. Cytogenetic interpretation was based on GTG, RBG and FISH techniques.
RESULTS: The probability rate for unbalanced offspring at birth for the whole group of pedigrees was calculated as 17.8+/-3% (33/185) (high risk). Considering the size of the imbalanced segment of 9p, the probability rates for RCT carriers with a breakpoint position at 9p22 at 9p13 and at 9p11.2 were estimated separately, and were found as 21.2+/-4.4% (18/85), 25+/-8.8% (6/24) and 11.8+/-3.7% (9/76), respectively. For unbalanced fetuses at 2nd prenatal diagnosis, we found the risk value as 57.9+/-11.3 % (11/19). The risk value for unkaryotyped stillbirths/early deaths of newborns and miscarriages were 5.4+/-1.7% (10/185) (medium risk) and 13+/-2.8% (rate 24/185) (high risk) respectively.
CONCLUSIONS: Our results showed that the recurrence probability rates are different for particular categories of unfavorable pregnancy outcomes. How much they are dependent on the size of 9p chromosome segments taking part in the imbalance needs further studies based on a larger number of observations.