[Prenatal diagnosis for two fetuses carrying partial deletion of Y chromosome]

To perform prenatal diagosis for two fetuses carrying partial deletion of Y chromosome.

Routine G- and C-banding were carried out to analyze the chromosomal karyotypes of the fetuses and their fathers. Fetal DNA was also subjected to low-coverage massively parallel copy number variation sequencing (CNV-seq), fluorescence in situ hybridization (FISH), SRY gene and AZF factor testing.

Both fetuses showed a 46, XN, del(Y) (q11.2) karyotype at 320-400 band level by the analysis of amniotic fluid chromosomes. FISH with Y chromosome centromere probe indicated that in both cases the number of Y chromosome was normal. Both fathers had an apparently normal karyotype at 320-400 band level. For fetus 1, CNV-seq test revealed a 12.88 Mb deletion at Yq11.221-q12, which encompassed the whole of AZFb+AZFc regions and may lead to male infertility, sperm deficiency and/or severe oligospermia. In fetus 2, CNV-seq also detected a 14.84 Mb deletion at Yq11.21-q12, which encompassed the whole of the AZF region and may lead to severe spermatogenesis disorder resulting in severe oligoasthenospermia and azoospermia. In both cases, testing of SRY gene was positive. No point mutation of the SRY gene was identified. Analysis of amniotic fluid DNA confirmed partial or total absence of AZF in the two fetuses, respectively.

Combined use of various technologies can enable accurate detection of structural abnormalities of the Y chromosome and facilitate genetic counseling. CNV-seq can help with rapid screening of Y chromosome microdeletions and may be used as a complementary test for chromosomal karyotyping.