Risk evaluation of carriers with chromosome reciprocal translocation t(7;13)(q34;q13) and concomitant meiotic segregation analyzed by FISH on ejaculated spermatozoa

Abstract

We performed the segregation analysis of a relatively large pedigree of t(7;13)(q34;q13) carriers together with the sperm karyotype analysis of the one carrier using a tri-color fluorescence in situ hybridization (FISH) method. The risk assessments for unfavorable pregnancy outcomes in a series of 36 pregnancies in eight reciprocal chromosome translocation (RCT) couples of carriers were estimated directly from a pedigree after ascertainment correction. The individual probability rate for unbalanced child was predicted according to Stengel-Rutkowski and co-workers. The unbalanced karyotypes in the form of monosomy 7q34-->qter and trisomy 13q13-->qter were detected among stillborn/early death newborns with holoprosencephaly (HPE), cyclopia and other malformations. Based on clinical description of unkaryotyped stillbirth progeny, it can be assumed that the phenotype distinctions were connected with the unbalanced karyotype from 2:2 segregation (monosomy 7q with trisomy 13q) and 3:1 segregation as interchange trisomy 13 (Patau syndrome). Probability rates for miscarriages, stillbirth/early death were 12.9 +/- 6% (4/31) and 29 +/- 8.2% (9/31), respectively. The results of the meiotic segregation pattern indicated the rate of unbalanced spermatozoa for about 60%, with the unusual high rate (29.4%) of 3:1 segregant (i.e., 13.4% of the tertiary segregation and 16% of the interchange segregation). Adjacent-1 segregation followed with 23.5% and adjacent-2 followed with 7.2% of analyzed spermatozoa. The high rate of unbalanced gametes in comparison to the number of stillborn/early death and miscarriages detected in pedigree suggests a strong selection against unbalanced chromosomal constitutions during fetal development. It corresponds to a very small probability rate (about 0.3%) of viable unbalanced progeny from 3:1 meiotic segregation predicted for maternal carriers. This knowledge can be used in genetic counseling of families with similar RCT ascertained in a different way.