An Inherited Balanced Translocation Between Chromosomes 4 and 6 in Recurrent Pregnancy Loss: A Case Report

Recurrent pregnancy loss is an important reproductive issue with a heterogeneous etiology where two or more consecutive abortions occur before 20 weeks of gestation. Approximately 15% of all clinically recognized pregnancies result in miscarriage with an incidence of 1 in 300 cases. Couples, who experience repeated pregnancy loss before three months of gestation, mostly have fetuses with chromosomal aneuploids. A non-consanguineous couple with a married life of 4 years was referred to the Institute with a clinical history of three first trimester abortions. Karyotype analysis revealed a balanced autosomal translocation between chromosomes 4 and 6 with 46, XX, t (4;6)(q35; q22) karyotype in the female and normal 46, XY in the male partner. Therefore, the siblings and the couple were suggested for extended genetic counseling. Interestingly, similar translocation was seen in her father and three sisters, whereas her mother and elder sister showed a normal chromosomal constitution, indicating the paternal inheritance.

Sex Chromosome Translocations

The sex chromosomes (gonosomes) are different, and sex chromosome translocations need to be considered separately from translocations between autosomes. A sex chromosome can engage in translocation with an autosome, with the other sex chromosome, or even with its homolog. The qualities of the sex chromosomes have unique implications in terms of the genetic functioning of gonosome-autosome translocations. This chapter acknowledges the specific peculiarities that the sex chromosomes imply: the X being subject to transcriptional silencing; and the very small Y gene complement being confined largely to sex-determining loci. It reviews translocations between sex chromosomes and autosomes; between X and Y chromosomes; and even the very rare circumstance of between X chromosomes and between Y chromosomes. The differences in assessing risk, according to chromosome form, in comparison with the autosomal translocation, are reviewed, and the biology behind these differences is discussed.