Second most common multiple malformation syndrome

Full trisomy 18 in most affected infants: involves an extra (third) copy of chromosome 18 in each cell; partial trisomy 18 (with varying phenotypes) and translocation types also reported

Intrauterine growth retardation, congenital heart defects, microcephaly, and other malformations occurring in most infants with this disorder

Full trisomy 18 syndrome generally fatal or extremely poor prognosis (Thirty to 50% of infants die within the
first 2 months and 90% die within the first year; most surviving patients are profoundly mentally retarded.)

Risk typically increasing with maternal age (mean maternal age 32½)

Incidence ranging from 1 in 3,000 to 8,000 neonates, with three to four females affected for every male

Also known as Edwards’ syndrome

Most cases of trisomy 18 result from spontaneous meitotic nondisjunction, producing an extra copy of chromosome 18 in each cell.