Maternal uniparental disomy of chromosome 15 with concurrent paternal non-chromosome 15 marker chromosome: a rare presentation of prader-willi syndrome

Prader-Willi Syndrome (PWS) is a complicated genetic disorder demonstrating a variety of clinical phenotypes. Using molecular cytogenetics approaches to detect the deletions of the paternal 15q11-q13 region and maternal uniparental disomy of chromosome 15 plays an important role in the prenatal diagnosis of PWS. A pregnant woman with advanced maternal age underwent amniocentesis. The amniotic fluid was subjected to karyotyping and chromosomal microarray analysis. A marker without autosomal material and loss of heterozygosity (LOH) of 15q14-q23 were found in the fetus. The LOH was consistent with maternal uniparental isodisomy (UPD) and the marker was inherited from the father. Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) found increased methylation in the fetal 15q11.2-q13 region and fluorescence in situ hybridization confirmed the marker was not originated from chromosome 15. We presented a rare PWS case showing maternal UPD of chromosome 15 with concurrent paternal marker chromosome in the prenatal setting.