[Prenatal diagnosis of a tetrasomy 18p case using BACs-on-Beads technology and single nucleotide polymorphism array].

Objective To determine the origin of a supernumerary small marker chromosome found in a fetus using prenatal BACs-on-Beads™ (BoBs) and single nucleotide polymorphism array (SNP-array) assays. Methods The fetal sample was subjected to chromosomal karyotyping and BoBs analysis, and the results were validated with genome-wide scanning using a SNP microarray. Results The fetus was found to have a 47, XX, + mar karyotype. BoBs analysis indicated that there was an amplification between 18p11.32 and 18p11.21, which was verified by the SNP-array assay as a 18.3 Mb duplication occurring at 18p11.32q11.1. Conclusion The karyotype of the fetus was determined as 47, XX, + der18(18p11.32→18q11.1∷ 18q11.1→18p11.32). The duplication has involved important genes including SMCHD1, LPIN2 and TGIF1, which may result in severe malformations in the fetus. Key words: Prenatal BACs-on-Beads™; Isochromomosome; Single nucleotide polymorphism array; Tetrasomy 18p