Scientific background
Edwards syndrome, which is based on trisomy 18, has an average incidence of 1:3,000 in newborns. In 80% a free trisomy 18 is found, in 10% a mosaic trisomy and in another 10% there is an unbalanced translocation. There is clear gynecotrophy with 75% female patients. External symptoms are variable; they include dolichocephaly with prominent occiput and a small face, ear dysplasia, microcephaly, microretrognathia, and a prominent calcaneus. Overlapping of the 3rd and 4th fingers by the 2nd and 5th fingers is characteristic, especially in newborns. Furthermore, heart defects, horseshoe kidney, muscle hypertonia and joint contractures are found. Psychomotor development is also severely delayed. Mortality usually occurs within the first few months of life, with over 90% dying within the first year of life. As with all autosomal trisomies, there is a maternal age effect.
References
Vendola et al. 2010, Am J Med Genet 152A:360 / Baty et al. 1994, Am J Med Genet 49:175 / Van Dyke and Allen 1990, Pediatrics 85:753 / Carter et al. 1983, Clin Genet 27:59