Trisomy 18 (Edwards Syndrome)

This newborn has trisomy 18, as manifested by intrauterine growth retardation (birth weight, 2350 g; length, 47.2 cm), microcephaly (head circumference, 31.5 cm), short neck, hypotonia, feeding difficulties, high-pitched cry, micrognathia, cleft palate, low-set ears, short sternum, widely spaced nipples, clenched hands with ulnar deviation and overlapping digits, micromelia, and a single umbilical artery.

Other features of this syndrome include failure to thrive, mental retardation, hypertonia after the neonatal period, lack of subcutaneous fat, cutis marmorata, wide fontanels, prominent occiput, narrow bifrontal diameter of the forehead, ptosis, epicanthal folds, narrow palpebral fissures, corneal opacity, malformed ears, upturned nose, limited hip abduction, rocker-bottom feet, syndactyly of second and third toes, low arch dermal ridge pattern on 6 or more fingertips, hypoplasia of nails, simian crease, short dorsiflexed hallux, inguinal hernia, umbilical hernia, diaphragmatic hernia, omphalocele, cardiac defect (especially ventricular septal defect, atrial septal defect, or patent ductus arteriosus), renal anomalies (particularly horseshoe kidney, polycystic kidney, hydronephrosis, or hydroureter), Meckel diverticulum, cryptorchidism, hypoplasia of labia majora, and prominent clitoris.

Trisomy 18 occurs in approximately 1 in 3000 to 7000 live births. The female to male ratio is 3:1. Approximately 80% of cases are caused by chromosomal nondisjunction and are associated with advanced maternal age. The remainder are caused by translocation. In the latter case, parental karyotypes should be obtained to determine whether one of the parents is a balanced translocation carrier.