Clinical Pathology: Genetic Testing

• Trisomy 18, also known as Edward syndrome, is the second most common congenital malformation syndrome after Down syndrome.

• Trisomy 18 occurs with a frequency of 1:3333 to 1:6000 births.

• Although trisomy 18 infants can survive to term, spontaneous abortion is the more likely outcome; thus, the prevalence of this chromosome abnormality is greater at the time of chorionic villus sampling and decreases all the way to term.

• The median postnatal survival time is 14.5 days.

• Only 5% to 10% of trisomy 18 newborns survive the first year.

• Those who survive have severe mental deficiency.

Jones KL, Smith DW: Smith’s Recognizable Patterns of Human Malformation. 6th ed. Philadelphia: Elsevier Saunders, 2006.

Gardner RJM, Sutherland GR, Shaffer LG, eds: Chromosome Abnormalities and Genetic Counseling. New York: Oxford University Press. 2012.

Menasha J, Levy B, Hirschhorn K, et al: Incidence and spectrum of chromosome abnormalities in spontaneous abortions: new insights from a 12-year study. Genet Med 2005;7:251–263.

Wyandt HE, Tonk VS: Atlas of Human Chromosome Heteromorphisms. Dordrecht/Boston: Kluwer Academic; 2004.

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