Clinical Genetic Study of Mosaic Pseudoisodicentric X Chromosome Patient

In the determination of mosaicism in prenatal diagnosis, due to the influence of different methods and the growth advantages of different cells in the process of cell culture, the mosaic rate varied between different methods. This research focused on improving the understanding of the differential diagnosis and clinical features of patients suffering from Turner syndrome with mosaic pseudoisodicentric X chromosome (psu idic(X)).

The amniocytes of a fetus with complex cardiac malformation were examined by karyotyping. Fluorescence in situ hybridization (FISH), chromosome microarray assay (CMA), and Whole Exome Sequencing (WES) were used to verify the results.

We identified the karyotype of the patient as mos 45,X[94]/46,XX,psu idic(X)(p22.3)[6]. FISH detection confirmed three X chromosome centromeres and a single X chromosome centromere in interphase cells. CMA results showed arr[GRCh37]Xp22.33p22.31(168,552_9,057,932)x1, suggesting a pathogenic 8.89 Mb deletion in p22.33p22.31 region of the X chromosome, arr[GRCh37]Xp22.31q28(9,057,932_155,233,098)x1.30, which indicated that there was a 146.1 Mb mosaicism deletion in the p22.31q28 region of the X chromosome (the mosaicism ratio was 70%) and Xp22.31-q28 fragment duplication with Xp22.33p22.31 fragment deletion. Secondary test results detected by whole exome were seq[hg19] del(X)(p22.33p22.31)chrX:60500-9156528del, seq[hg19] del(X) (p22.31q28)chrX:9156529-155270560del[0.45].

We concluded that the fetus was diagnosed as Turner syndrome with mosaic pseudoisodicentric X chromosome. The combination of karyotyping, FISH, CMA even WES were helpful for the differential diagnosis and early intervention and treatment.