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Edwards Syndrome Definition
Edwards syndrome – an AUTOSOMAL TRISOMY disorder that results from a REPLICATION ERROR during cell division in which a GAMETE(sex cell) ends up with two copies of CHROMOSOME 18 instead of the normal single copy (as haploid cells, gametes contain one half the complement of chromosomes). At fertilization the ZYGOTE thus ends up with three instead of the normal two copies of chromosome 18, which ultimately produces multiple and lifethreatening congenital anomalies.
When all cells carry the extra chromosome 18), the anomalies are so severe that the defect often is lethal well before birth. Sometimes Edwards syndrome occurs as a mosaic trisomy disorder (some but not all cells contain the third chromosome 18), which tends to produce milder though nonetheless significant symptoms. Edwards syndrome occurs in about 1 in 5,000 live births in the United States, 80 percent of which are females. Researchers do not know whether Edwards syndrome affects females more often or if females are more likely to survive beyond birth.
Anomalies and Deformities of Edwards Syndrome and Diagnosis
Children born with Edwards syndrome have severe and complex physical deformities involving multiple organs and systems that require extensive medical care from the time of birth. Most also have profound intellectual impairment arising from malformations affecting the BRAIN and NERVOUS SYSTEM. A KARYOTYPE confirms the diagnosis. Fewer than 10 percent of infants born with Edwards syndrome survive the first year after birth; those who do require extensive, ongoing medical care and developmental support. Survival beyond five years is extremely rare.
Doctors often can diagnose Edwards syndrome and other autosomal trisomy disorders before birth, through prenatal screening methods such as AMNIOCENTESIS and CHORIONIC VILLI SAMPLING (CVS). These methods retrieve cells from the FETUS from which a geneticist can construct a karyotype. Advanced maternal age (mother’s age over 40) and the previous CONCEPTION of a child with Edwards syndrome or another autosomal trisomy disorder are the leading risks for Edwards syndrome. Whether done prenatally or after birth the karyotype, which presents photomicrographic images of the fetus’s or infant’s chromosomes, provides definitive diagnosis.
Congenital Anomalies Characteristic of Edwards Syndrome
- facial deformities
- fingers curled over one another in clenched fists
- heart defects
- kidney abnormalities
- low, small ears
- microcephaly (small head and BRAIN)
- small MOUTH and cleft deformities
- spina bifida
- TALI PEDES (club foot)
See also AUTOSOME; CHROMOSOME DISORDERS; CONGENITAL ANOMALY; CONGENITAL HEART DISEASE; DOWN SYNDROME; ETHICAL ISSUES IN GENETICS AND MOLECULAR MEDICINE; GENETIC SCREENING; INHERITANCE PATTERNS; MOSAICISM; PATAU’S SYNDROME; PRENATAL CARE.