Genetic risks for familial reciprocal translocations with special emphasis on those leading to 9p, 10p and 12p trisomies

Abstract

An analysis of genetic risks for reciprocal translocations is given. Data from translocation families, ascertained through unbalanced offspring with trisomy 9p, 10p and 12p, were taken from the literature. The translocations were specified according to (1) the type of trisomy, (2) the degree of resulting chromosomal imbalance (partial short arm trisomies, complete short arm trisomies, complete short arm trisomies including long arm segments) and (3) the type of disjunction (2:2 or 3:1) and segregation (adjacent-1, adjacent-2; tertiary trisomy, interchange trisomy). The risks for unbalanced liveborn offspring were high for translocations leading to partial short arm trisomies through 2:2 disjunction and adjacent-1 segregation (25-29%). They were lower for translocations leading to complete short arm trisomies through the same disjunction/segregation mechanism (5-17%). Low risks were obtained for translocations, leading through 3:1 disjunction to unbalanced offspring (about 2%). For 2:2 disjunction and adjacent-2 segregation and for 3:1 disjunction the risk is significantly lower for male than for female carriers.--The frequency of balanced karyotypes compared with normal karyotypes deviated among the phenotypically normal offspring of parental carriers from the theoretical 1:1 ratio, both for translocations ascertained through trisomy 12p and trisomy 10p.--It was demonstrated that the genetic risk for reciprocal translocations depends exclusively on (1) the degree of possibly resulting genetic imbalance and (2) the probability of the disjunction/segregation mechanism leading to this type of imbalance. Both factors can be predicted from the position of breakpoints.--The precision of breakpoint localizations and its impact on the risk estimation are also considered.--Finally, general rules for genetic counselling of families with reciprocal translocations are indicated.

Chromosomal abnormalities as a cause of recurrent abortions in Egypt

“…[3] This result from the production of gametes and embryos with unbalanced chromosome sets. [45] The clinical consequences of such abnormal gametes include sterility, repeated abortions, and giving birth to malformed children. [67] The majority of chromosome rearrangements are balanced reciprocal and Robertsonian translocations.…”

Cytogenetic Study in Cases with Recurrent Abortion in Saudi Arabia

“…[4][5][6][7][8] This results from the production of gametes and embryos with unbalanced chromosome sets. 9,10 The clinical consequences of such abnormal gametes include sterility, repeated abortions, and giving birth to malformed children. 11,12 Several studies have been done in various countries to determine the contribution of chromosome abnormalities in parents with fetal wastage.…”

A 5p;22q reciprocal translocation with a high risk for segregation of unbalanced offspring

“…Both modes of unbalance are represented in the present pedigree. The reason for this difference is uncertain, but may in part be related to the fact that the breakpoint in chromosome I 1 in the 11;22 translocation is more proximal than in chromosome 5 in the present case, resulting in a larger chromosomal unbalance in the former (Stene & Stengel-Rutkowski 1982). A further difference between the 11 ;22 translocation and the present 5;22 translocation is the relative low risk for unbalanced offspring of carriers of the 1 1 ; 22 translocation compared to the observed high risk in the present case.…”

“…It has been shown that the risk depends on the nature of the involved chromosomes and the position of the breakpoints, which determines the degree of unbalance (Stene & Stengel-Rutkowski 1982). It has been shown that the risk depends on the nature of the involved chromosomes and the position of the breakpoints, which determines the degree of unbalance (Stene & Stengel-Rutkowski 1982).…”