Prenatal detection of full monosomy 21 in a fetus with increased nuchal translucency: molecular cytogenetic analysis and review of the literature.

Full monosomy 21 is an extremely rare chromosomal disorder. A 38-year-old woman attended a first trimester scan. Ultrasound (U/S) imaging of the fetus at 12 weeks of gestation showed features of increased nuchal translucency measurement (12 mm). Chorionic villi sampling (CVS) was performed after genetic counseling. At 16 weeks of gestation the fetus showed U/S characteristics of severe intrauterine growth restriction, generalized edema and hydrothorax. Cytogenetic examination was performed using quantitative fluorescent polymerase chain reaction analysis, standard Giesma banding and fluorescent in situ hybridization analysis. Non-mosaic full monosomy 21 was detected and the parents opted to terminate the pregnancy. Microsatellite analysis demonstrated maternal origin of the single chromosome. This case represents one of the few cases of prenatally diagnosed full monosomy 21 confirmed only by CVS, in which the parental origin of the single chromosome was determined.