Trisomy 21 (Down Syndrome)

Trisomy 21, also called Down syndrome, occurs when cells contain extra chromosome 21 material. Most cases result from meiotic nondisjunction, in which chromosome 21 does not separate normally during formation of an egg or sperm. Less often, the extra material results from a Robertsonian translocation or mosaicism, where only some cells carry the additional chromosome material. The extra genetic material affects development across organ systems. A newborn may have hypotonia, characteristic facial features, a single transverse palmar crease, short broad hands, or a wide gap between the first and second toes. These findings support clinical suspicion but do not establish the diagnosis. Physical features vary, as do developmental abilities, communication, and independence over time. Experienced nurses look beyond the recognizable appearance. Hypotonia can interfere with feeding and motor development, while congenital heart disease can make feeding feel like exercise. An infant who sweats, becomes tachypneic, or tires after a few minutes of bottle-feeding may be showing cardiac or respiratory compromise rather than simple poor feeding.