Clinical meaning
Trisomy 21 occurs when nondisjunction during meiosis produces a gamete with an extra chromosome 21, resulting in 47 chromosomes instead of 46. The overexpression of genes on chromosome 21 leads to disrupted embryogenesis affecting the cardiac septum (endocardial cushion defects), craniofacial development, GI tract (duodenal atresia, Hirschsprung disease), and central nervous system (reduced neuronal density). Approximately 95% of cases are full trisomy 21, while 3-4% result from Robertsonian translocation and 1-2% from mosaicism. The nurse must coordinate comprehensive multidisciplinary care, manage cardiac and respiratory complications, perform developmental screening, and educate families on long-term health surveillance.
Exam relevance
Risk factors: - Advanced maternal age (risk increases exponentially after age 35) - Prior pregnancy with trisomy 21 - Parental balanced translocation carrier - Family history of chromosomal abnormalities - Abnormal prenatal screening markers (low AFP, high hCG, low estriol)
Diagnostics: - Interpret prenatal screening: nuchal translucency, quad screen, cell-free fetal DNA - Coordinate postnatal karyotype analysis for definitive diagnosis - Order and interpret echocardiogram to evaluate for congenital heart defects - Monitor thyroid function tests (TSH, free T4) annually - Screen for celiac disease with tissue transglutaminase antibodies - Coordinate cervical spine radiography for atlantoaxial instability screening - Monitor CBC for hematologic abnormalities (transient myeloproliferative disorder, leukemia)