Trisomy 18 Syndrome (Edwards syndrome)
Trisomy 18 syndrome (also known as Edwards' syndrome) is the second most common multiple malformation syndrome. Most affected neonates have full trisomy 18, involving an extra (third) copy of chromosome 18 in each cell, but partial trisomy 18 (with varying phenotypes) and translocation types have also been reported. Most neonates with this disorder present with intrauterine growth retardation, congenital heart defects, microcephaly, and other malformations.
Full trisomy 18 syndrome is generally fatal or has an extremely poor prognosis; 30% to 50% of these infants die within the first 2 months of life, and 90% die within the first year. Most surviving patients are profoundly mentally retarded.
CausesMost cases of trisomy 18 syndrome are caused by spontaneous meiotic non-disjunction. The risk of chromosomal abnormalities typically increases with maternal age; however, the mean maternal age for this disorder is 32.5. Incidence ranges from 1 in 3,000 to 8,000 neonates, with 3 to 4 females affected for every male.
Signs and symptoms
Growth retardation begins in utero, and remains significant after birth. Initial hypotonia may soon give way to hypertonia. Common findings include microcephaly and dolichocephaly, micrognathia, genital and perineal abnormalities (including imperforate anus), diaphragmatic hernia, and various renal defects. Congenital heart defects, such as ventricular septal defect, tetralogy of Fallot, transposition of the great vessels, and coarctation of the aorta, occur in 80% to 90% of patients and may be the cause of death in many infants.
Other findings may include a short and narrow nose with upturned nares; unilateral or bilateral cleft lip and palate; low-set, slightly pointed ears; a short neck; a conspicuous clenched hand with overlapping fingers (often seen on ultrasound as well); neural tube defects; omphalocele; cystic hygroma; choroid plexus cysts (also seen in some normal infants); and oligohydramnios.
Multiple marker maternal serum screening tests involving different combinations of alpha-fetoprotein, human chorionic gonadotropin, and unconjugated estriol may be abnormal in many pregnant women with an affected fetus; however, these tests are not diagnostic. Fetal ultrasound may reveal varying degrees of abnormalities, but many fetuses have few detectable defects.
Diagnosis should be based on karyotype, done either prenatally (by amniocentesis) or using peripheral blood or skin fibroblasts after birth.
Medical care for individuals with Trisomy 18 is supportive, and focuses on providing nutrition, treating infections, and managing heart problems. During the first months of life, infants with Trisomy 18 require skilled medical care. Due to the complex medical problems, including heart defects and overwhelming infections, infants have a 5% chance of surviving to age 1 year. Advances in medical care over time will, in the future, help more infants with Trisomy 18 live into childhood and beyond.
Prenatal diagnosis of trisomy 18 is possible with an amniocentesis and chromosome studies on amniotic cells. Parents who have a child with translocational trisomy 18 and want additional children should have chromosome studies, because they are at increased risk to have another child with trisomy 18.
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