Trisomy 18 syndrome (also known as Edwards' syndrome) is the second most common multiple malformation syndrome. Most affected infants 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 infants 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 infants with full trisomy 18 syndrome die within the first 2 months of life; 90% die within the first year. Most patients who survive exhibit profound mental retardation.
Most cases of trisomy 18 syndrome are caused by spontaneous meiotic nondisjunction. The risk of chromosomal abnormalities typically increases with maternal age; however, the mean maternal age for this disorder is 32½. Incidence is 1 in 3,000 neonates, with females three times more likely to be affected than males.
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 (usually seen on ultrasound as well); neural tube defects; omphalocele; cystic hygroma; choroid plexus cysts (also seen in some healthy 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 aren't 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 or using peripheral blood of skin fibroblasts after birth.
Treatment is aimed at providing comfort for the infant and emotional support for the parents. Because the infant's sucking reflex is poor, nutrition is maintained using gavage feedings. Teach parents about home care and feeding techniques.
❑ Allow adequate time for the parents to bond with and hold their child.
❑ Refer the parents to early intervention if the infant is medically stable.
❑ Refer the parents of an affected child for genetic counseling to explore the cause of the disorder and discuss the risk of recurrence in a future pregnancy.
❑ Refer the parents to a social worker or grief counselor for additional support if needed.
❑ Refer the parents to the Support Organization for Trisomy 18, 13 and Related Disorders (S.O.F.T.) national support group to allow them interaction with other parents of infants with trisomy 18 and trisomy 13.
Review other book chapters online related to Sex chromosome conditions:
Copyright notice for book excerpts: Copyright © 2008 Lippincott Williams & Wilkins. All rights reserved.
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More About This Book:
Title: Professional Guide to Diseases (Eighth Edition) Authors: Springhouse Publisher: Lippincott Williams & Wilkins Copyright: 2005 ISBN: 1-58255-370-X 
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