RESUMO
INTRODUCTION: Carriership of reciprocal chromosomal translocation (RCT) may be the reason the occurrence of congenital malformations in the offspring, early neonatal death, stillbirth, and recurrent miscarriages due to unbalanced karyotype of gametes. The probability rate for individual categories of unfavorable outcomes depends on the kind of chromosome involved and is individually variable. OBJECTIVES: The aim of study was to estimate the probability rates for unbalanced offspring and to evaluate the risk for different categories of unfavorable pregnancy outcomes, depending on the size of chromosomal segment with differentiation between maternal/paternal origin of the reciprocal chromosomal translocations involving chromosome 7p (RCT-7p) and 7q (RCT-7q). In addition, the use of the obtained results has been illustrated by the example of a family with unique RCT t(7;9)(p21.3,p23). MATERIAL AND METHODS: Empirical and cytogenetic data on 341 pregnancies and offspring of 133 carriers were collected from 69 pedigrees of carriers of RCT-7p and RCT-7q at risk for a single 7 segment imbalance. The probability rates of particular form of pregnancy pathology have been calculated according to the method of Stengel-Rutkowski and Stene, including all forms of meiotic segregation and their survival rates after fertilization to term childbirth. RESULTS: The probability rates for unbalanced offspring for carriers of RCT-7p after 2:2 disjunction and adjacent-1 segregation were calculated as 5.5% +/- 2.2% (6/108); for maternal (MAT) and paternal (PAT) carriers were about < 1% (0/56) and 13.6 +/- 5.2% (6/44) (p = 0.04) respectively. Considering different segment lengths of 7p, the following values for shorter and longer segments were obtained: 23.0 +/- 11.7% (3/13) for 7p21-->pter; 3.3 +/- 3.3% (1/30) for 7p 14-->pter and 3.1 +/- 2.1% (2/65) for 7p 1-->pter The risk figures for stillbirth/earl neonatal death were estimated at 2.8 +/- 1.6% (3/108), but for miscarriage were calculated at 25.9 +/- 4.2% (28/108) for carriers RCT-7p. The probability rates for unbalanced offspring at birth for carriers of RCT-7q were calculated as 2.7 +/- 1.5% (3/111); for MAT and PAT carriers were 3.5 +/- 2.0% (3/86) and < 2.6% (0/19) respectively. Considering different segment lengths of 7q, the following values for shorter and longer segments were obtained: 6.2 +/- 6.1% (1/16) for 7q33-->qter; 5.3 +/- 3.6% (2/38) for 7q32-->qter and < 0.82% (0/57) for 7q11-->qter. The risk figures for stillbirth/early neonatal death were estimated at 9.9 +/- 2.8% (11/111), but for miscarriage were calculated at 34.2 +/-4.5% (38/111) for carriers RCT-7q. The probability estimated values for unbalanced fetuses, evaluated prenatally in the second trimester of pregnancy for carriers of RCT-7p and RCT-7q were similar i.e. 41.7 +/- 14.2% (5/12) and 46.7 +/-12.9% (7/15), respectively. CONCLUSIONS: 1. The probability rates for unbalanced offspring and the risk values for individual categories of unfavorable outcomes for carriers of RCT-7 are different and depend on the size of chromosome 7 segment involved in RCT 2. The probability rate for unbalanced offspring for paternal carriers of RCT-7p is higher than for maternal carriers (p = 0.04). 3. It is suggested that the probability rate for unbalanced offspring for maternal carriers of RCT-7q may be higher than for paternal carriers.