[Cytogenetic and molecular genetic analysis of the amniotic fluid cells of a fetus with pseudodicentric isochromosome 22 resulting in partial tetraploidy of 22q].

OBJECTIVE: To diagnose chromosomal abnormalities in amniotic fluid cells by combining karyotyping and single nucleotide polymorphism array (SNP-array) analysis, and to explore the application of SNP-array in routine clinical practice.

METHODS: Conventional G banding was used to karyotype a fetal amniotic fluid sample and the corresponding peripheral blood samples from the parents, followed by SNP-array analysis of the fetal genomic DNA from the amniotic fluid.

RESULTS: The karyotype of the amniocytes was 47, XX, +mar. The marker chromosome was further identified as psu idic (22) (q11.2) by SNP-array analysis, revealing tetraploidy of a 1.7 Mb fragment in 22q11.1-q11.2 interval that involves the critical region for Cat eye syndrome.

CONCLUSION: A rare chromosomal abnormality was identified by combining conventional G banding and SNP-array. The high resolution SNP-array could provide more detailed information for determining the origin of chromosomal abnormalities.