trisomy 18, a congenital condition caused by the presence of an extra chromosome 18, characterized by severe cognitive impairment and multiple deformities. Among the most common defects are scaphocephaly or other skull abnormalities; micrognathia; abnormal facies with low-set malformed ears and prominent occiput; cleft lip and palate; clenched fists with overlapping fingers, especially the index over the third finger; clubfeet; and syndactyly. Ventricular septal defect, patent ductus arteriosus, atrial septal defect, and renal anomalies are also common. The condition occurs in about 1 in 3000 births and predominantly in females, at a 3:1 sex ratio, and survival for more than a few months is rare. Also called Edwards’ syndrome, trisomy E syndrome, trisomy 16-18.
