pediatrics
Down Syndrome (Trisomy 21)
Key Points
Down syndrome involves an extra chromosome 21, either a separate chromosome or a translocation onto another chromosome. Diagnosis may be suspected prenatally based on anomalies detected by fetal ultrasonography (eg, increased nuchal translucency, heart defect, duodenal atresia) or based on cell-free fetal DNA analysis of maternal blood or maternal multiple marker screening for levels of plasma protein A in late first trimester and levels of alpha-fetoprotein, beta-human chorionic gonadotropin(beta-hCG), unconjugated estriol, and inhibin in early second trimester. Karyotype analysis is the confirmatory test of choice and can be done prenatally by chorionic villus sampling in the first trimester or amniocentesis in the second trimester, or postnatally on a blood sample. Life expectancy is decreased primarily because of heart disease and, to a lesser degree, increased susceptibility to infections, acute myelocytic leukemia, and early-onset Alzheimer disease; however, it has increased remarkably in recent decades, and some affected people live into their 80s. Do routine age-specific screening to detect associated medical conditions (eg, cardiac anomalies, hypothyroidism). Treat specific manifestations, and provide social and educational support and genetic counseling. 