engleski

Risk estimates for offspring of sturctural chromosomal aberrations carriers in comparison with outcome of pregnancies

The risk of having an unbalanced offspring for structural chromosome aberration carriers vary considerably, depending on the type of aberration, sex and age of a carrier. We present the analysis of 80 families (40 reciprocal translocations - rcp, 29 Robertsonian translocations - RT, 10 pericentric inversions - per inv, and 2 paracentric inverskions - para inv). For rcp and per inv empirical method of risk assessment of Stengel-Rutkowski et al (1989) was applied, while for RT segregation analyses of pedigrees and prenatal diagnostics data were performed. Among carriers of rcp no significant difference between sexes was observed, 17 carriers being males and 23 females. The overall risk at second trimester prenatal diagnosis was 14%. The individual risks for and unbalanced offspring at birth ranged from 0-20%. Carriers of 21 translocations had a risk for single-segment imbalances and 19 carriers had a risk for double-segment imbalances. The average risk in the first group of carriers was 3.5 times greater than the risk in the second group. Most (22/40-555) of the rcp were of low risk (0-5%). Without risk and medium risk (5-10%) translocations were equally represented and not so frequent (7/40 - 17.5%), while high-risk translocations (>10%) were quite rare (4/40%). The pedigrees of our families were in good agreement with risk assessment. In translocations ascertained through spontaneous abortions the risk was mostly small or non-existent (82% - 14/17), while in translocations discovered through unbalanced offspring different risk groups with exception of no risk group were found. Because of the fact that unbalanced offspring were observed in different risk groups families, even if the empirical risk of an unbalance offspring in a given rcp was estimated to be very low, prenatal diagnosis in future pregnancies was advised. Only in no risk translocations we could predict with certainty that no unbalanced fetus will be carried out to term. In 9 analysed families with per inv no unbalanced progeny was observed. In five families the estimated risk was low (<1%), while four families where without empirical risk. The overall risk in per inv was about ten times lower than the risk for rcp. The overall risk for RT carriers obtained by the analysis of prenatal segregation data was 15%, and by segregation analysis of family trees 11.9%. Only RT that included 21 chromosome were at risk. The risk was inversely proportionate to the length of the other chromosome included, and absolute in the homologue 21/21 translocation. The risk for para inv were particularly difficult to estimate, but were considered to be very small. Our experience emphasizes the need for accurate individual risk counselling for carriers of structural chromosomal aberration regarding their future pregnancies.

risk; structural chromosomal aberrations; carrier; pregnancy; outcome

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