Non-mosaic trisomy 20 in cultures of amniotic fluid from a fetus with serious congenital malformation.

We present a case of non-mosaic trisomy 20 in amniotic fluid associated with major congenital anomalies. A detailed prenatal ultrasonic examination was performed, and revealed dilatation of the cisterna magna and the fourth ventricle with hypoplasia of the vermis of the cerebellum. Fetal echocardiography showed overriding aorta and ventricular septal defects with pulmonary atresia. However, the karyotype of the lymphocyte in the cord blood was normal female 46, XX. The occurrence of the Dandy-Walker malformation in non-mosaic trisomy 20 has not been reported before, and the clinical significance of this major defect for prenatal diagnosis is discussed.