[Genetic analysis of a fetus with mosaicism Y chromosome aberration].

Objective: To carry out prenatal diagnosis for a fetus with mosaicism Yq deletion.

Methods: A fetus with high risk of sex chromosomes indicated by non-invasive prenatal testing (NIPT) at Tianjin Medical University General Hospital in July 2021 was selected as the study subject. Prenatal diagnosis of the fetus was performed with combined G-banded chromosomal karyotyping, fluorescence in situ hybridization (FISH), copy number variation sequencing (CNV-seq), real-time fluorescence PCR (QF-PCR), and ultrasound examination.

Results: Analysis of the amniocytes at 23 gestational weeks had yielded a 45,X karyotype. However, FISH had shown signals of Y chromosome. Re-examination by cordocentesis had shown a mosaicism of 46,X,+mar[33]/45,X[17]. FISH showed that 69% of the cells had contained Y chromosome signals. The result of CNV-seq was seq[19]del(Y)(q11.1q12)(mos) chrY: g.13200001_ 28820000del (mosaicism rate = 64%), which suggested mosaicism for a Yq deletion, which encompassed the azoospermia factor (AZF) region. Deletion of the AZF region was verified by QF-PCR. The fetal karyotype was ultimately determined as mos46,X,del(Y)(q11.1)[33]/45,X[17]. Although ultrasound examination had shown no abnormality in the fetus, the couple had opted to terminate the pregnancy, and the induced fetus had a normal male appearance.

Conclusion: The combined use of multiple techniques is beneficial for accurate and rapid prenatal diagnosis. For fetuses with mosaicism chromosomal abnormalities, it may be difficult to accurately predict the postnatal phenotype. It is therefore necessary to further explore their genotype-phenotype correlation in order to provide better guidance upon genetic counseling.