[Genetic analysis of a fetus with de novo 46,X,der(X)t(X;Y)(q26;q11)].

OBJECTIVE: To carry out prenatal genetic testing for a fetus with de novo 46,X,der(X)t(X;Y)(q26;q11).

METHODS: A pregnant woman who had visited the Birth Health Clinic of Lianyungang Maternal and Child Health Care Hospital on May 22, 2021 was selected as the study subject. Clinical data of the woman was collected. Peripheral blood samples of the woman and her husband and umbilical cord blood of the fetus were collected and subjected to conventional G-banded chromosomal karyotyping analysis. Fetal DNA was also extracted from amniotic fluid sample and subjected to chromosomal microarray analysis (CMA).

RESULTS: For the pregnant women, ultrasonography at 25th gestational week had revealed permanent left superior vena cava and mild mitral and tricuspid regurgitation. G-banded karyotyping analysis showed that the pter-q11 segment of the fetal Y chromosome was connected to the Xq26 of the X chromosome, suggesting a Xq-Yq reciprocal translocation. No obvious chromosomal abnormality was found in the pregnant woman and her husband. The CMA results showed that there was approximately 21 Mb loss of heterozygosity at the end of the long arm of the fetal X chromosome [arr [hg19] Xq26.3q28(133912218_154941869)×1], and 42 Mb duplication at the end of the long arm of the Y chromosome [arr [hg19] Yq11.221qter(17405918_59032809)×1]. Combined with the search results of DGV, OMIM, DECIPHER, ClinGen and PubMed databases, and based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), the deletion of arr[hg19] Xq26.3q28(133912218_154941869)×1 region was rated as pathogenic, and the duplication of arr[hg19] Yq11.221qter(17405918_59032809)×1 region was rated as variant of uncertain significance.

CONCLUSION: The Xq-Yq reciprocal translocation probably underlay the ultrasonographic anomalies in this fetus, and may lead to premature ovarian insufficiency and developmental delay after birth. Combined G-banded karyotyping analysis and CMA can determine the type and origin of fetal chromosomal structural abnormalities as well as distinguish balanced and unbalanced translocations, which has important reference value for the ongoing pregnancy.