Sometimes referred to as trisomy 18 as it arises as a consequence of an extra copy of chromosome 18 (see figure below). It occurs in about 1 in every 3000 to 5000 births, affecting girls more than boys. As with Down’s syndrome (after which it is the second most common trisomy), the risk of conceiving a child with Edwards syndrome becomes much greater after the age of 35. And as with Down’s syndrome, mosaic and translocated forms can occur. Most children (90-95%) with the syndrome die within the first year after birth, and the mean lifespan is less than 2 months for 50% of them. It is characterized by dysmorphic features and organ malformations, as well as by severe mental retardation. The syndrome is named after John Hilton Edwards (1928-2007) who first described it in 1960.
