[Prenatal diagnosis of a rare case with de novo partial 21q(21q22.1→ qter) trisomy syndrome and absent nasal bone].

To carry out prenatal diagnosis for a fetus with absent nasal bone by using cytogenetic and molecular techniques.Chromosomal karyotyping, single nucleotide polymorphism array (SNP-array) and fluorescence in situ hybridization (FISH) assays were applied for the diagnoses. Peripheral blood samples were also taken from the parents for chromosomal karyotyping and FISH analysis.The fetus was found to have a 46,XX,add(21)(p11.2) karyotype, and SNP-array has revealed a 11.3 Mb duplication at 21q22.12q22.3 (hg19: 36 762 648-48 093 361), which was confirmed by FISH. Both parents were found to be normal by chromosomal karyotyping and FISH analysis. The fetus was ultimately found to have a karyotype of 46,XX,der(21)t(21;21)(p11.2;q22.1), resulting a de novo partial trisomy of 21q22.1.Combined use of various techniques has enabled accurate prenatal diagnosis and genetic counseling for the fetus.