How Are SNP‐Array, Karyotyping, and FISH Applied in Prenatal Practice? A Focus on Diagnosis of Mosaicism Involving the Sex Chromosomes

OBJECTIVE: This study conducted a comparative analysis of chromosomal karyotyping, SNP-array, and FISH results in 82 prenatal cases of mosaicism involving the sex chromosomes. METHODS: A retrospective analysis was conducted on 82 cases of mosaicism involving the sex chromosomes; the analysis focused on the concordance and discrepancies among karyotyping, SNP-array, and FISH results. RESULTS: Among 10,825 high-risk pregnancies undergoing amniocentesis, 82 cases (0.76%) of mosaicism involving the sex chromosomes were detected. These included 60 cases (73.2%) of X or Y chromosome aneuploidy mosaicism and 22 cases (26.8%) with mosaicism accompanied by structural abnormalities. Of the 82 cases, 64 showed consistent results across karyotyping, SNP-array, and FISH, while 18 cases exhibited discrepancies between methods. Among the 18 discordant cases, 12 were diagnosed as mosaicism by karyotyping and FISH but showed normal results on SNP-array. SNP-array identified three additional cases of mosaic X chromosome copy number variations (CNVs). In three cases, Turner mosaicism was diagnosed solely by FISH; both karyotype and SNP-array findings were normal. CONCLUSIONS: This study demonstrates that the combination of SNP-array, karyotyping, and FISH can effectively diagnose mosaicism involving the sex chromosomes. Karyotype analysis can effectively identify aneuploidy and balanced translocation mosaicism when X chromosome dosage shows no significant change, whereas SNP array is more effective in detecting mosaic copy number variations < 10 Mb. In cases of discrepant results between the two methods, FISH should be utilized for further verification.