[Chromosomal microarray analysis of 17 patients with unbalanced reciprocal translocations]

To retrospectively analyze the results of chromosomal microarray analysis (CMA) and parental origins of unbalanced translocations among 17 patients, so as to provide reference for their genetic counseling.

The results of CMA for 7 001 samples tested in Chengdu Women and Children's Central Hospital from January 2019 to January 2022 were retrospectively reviewed. Unbalanced reciprocal translocation was defined as two non-homologous chromosomes with lost and gained segments respectively or both with gained segments, and their parental origins were identified by parental chromosomal karyotyping and/or fluorescence in situ hybridization (FISH).

In total 17 unbalanced translocations were identified. In three cases, two non-homologous chromosomes both had gained segments, which constituted a derivative chromosome, with the total number of chromosomes being 47. In the remaining 14 cases, there was a terminal deletion on one chromosome and a terminal duplication on the other, 10 of which were confirmed by karyotyping, with the total number of chromosomes being 46. In the derivative chromosome, the lost segment was replaced by a gained segment from another chromosome. Among 15 cases undergoing parental origin analysis, 12 had paternal or maternal chromosomal abnormalities, including 11 balanced translocations and 1 unbalanced translocation. The unbalanced gametes therefore may form through meiosis. In 3 cases, the parental chromosomes were normal, indicating a de novo origin.

Discovery of terminal duplication and deletion or gained segments on two non-homologous chromosomes by CMA is suggestive of parental balanced translocation, which can facilitate genetic counseling and assessment the recurrence risk for subsequent pregnancies.