What is Down Syndrome?
Trisomy 21 produces multiple systemic complications as part of the syndrome. It is the most common chromosomal condition, occurring in about 1 in 700 babies in the United States (CDC). Langdon Down first described the condition in 1866, but its cause stayed unknown for years. A chromosomal anomaly was suggested in 1932 and finally demonstrated in 1959.
Pathophysiology
Two hypotheses are proposed for the mechanism of gene action: developmental instability (loss of chromosomal balance) and the gene-dosage effect. Under the gene-dosage effect, genes on chromosome 21 are overexpressed in the cells and tissues of Down syndrome patients, contributing to phenotypic abnormalities. Molecular analysis points to the 21q22.1-q22.3 region, the Down syndrome critical region (DSCR), as containing the gene or genes responsible for the congenital heart disease seen in the syndrome.
Abnormal physiologic functioning affects thyroid metabolism and intestinal absorption; these patients have an increased risk of obesity, frequent infections from impaired immune responses, and a higher incidence of autoimmunity, including hypothyroidism and rare Hashimoto thyroiditis. Decreased buffering of physiologic reactions produces hypersensitivity to pilocarpine and abnormal sensory-evoked EEG tracings, and decreased buffering of metabolic processes predisposes to hyperuricemia and increased insulin resistance. Children with Down syndrome are predisposed to leukemia, particularly transient myeloproliferative disorder and acute megakaryocytic leukemia. Musculoskeletal manifestations include reduced height, atlantooccipital and atlantoaxial hypermobility, and vertebral malformations of the cervical spine. About 5% have GI manifestations, including duodenal atresia, Hirschsprung disease, and celiac disease.
Statistics and Incidences
Down syndrome occurs in nearly all countries and races. About 5,700 babies are born with it each year in the United States (CDC), and it accounts for roughly one-third of all moderate and severe intellectual disability in school-aged children. Worldwide prevalence has risen with increases in lifespan over recent decades. The characteristic morphologic features become obvious in children older than 1 year. The disease occasionally appears in several members of a family, and the recurrence risk in a patient's siblings depends in part on maternal age. The male-to-female ratio is slightly higher (about 1.15:1) in newborns, but only among neonates with free trisomy 21. Perhaps 50% of female patients with trisomy 21 are fertile, and they have up to a 50% chance of a live child who also has trisomy 21.
Causes
The cause is unknown, though Down syndrome arises through 3 cytogenetic variants: three full copies of chromosome 21, a translocation that yields 3 copies of the critical region, and mosaicism. Free trisomy 21 results from nondisjunction during meiosis in one parent and correlates with advanced maternal and paternal age. Translocation occurs when chromosome 21 material attaches to another chromosome, leaving 46 chromosomes with one carrying extra chromosome 21 material. Mosaicism is a postzygotic event, usually a trisomic zygote with mitotic loss of one chromosome, producing two cell lines (one free trisomy, one normal karyotype) and great phenotypic variability from near normal to the classic trisomy 21 phenotype.
Clinical Manifestations
Characteristic craniofacial findings include a flat occiput and flattened facial appearance (most recognizable by age 1 year or older), a small brachycephalic head, epicanthal folds at the inner angle of the eyes, a short flattened nasal bridge, upward-slanting palpebral fissures giving an almond-shaped eye, and Brushfield spots (speckling of the iris). The child often has a small nose and mouth, a thick fissured protruding tongue, small dysplastic ears, and generous nuchal skin that is dry, cracked, fissured, and sometimes mottled.
Assessment and Diagnostic Findings
Diagnosis is most often made by prenatal screening followed by definitive testing.
Order a CBC with differential and bone marrow examination to rule out leukemia. Obtain TSH and thyroxine (T4) at birth, at 6 and 12 months, and annually thereafter to rule out hypothyroidism, and perform Papanicolaou smears every 1-3 years in sexually active women starting at the age of first intercourse. Confirm the clinical diagnosis with cytogenetic studies; karyotyping is essential to determine recurrence risk, and in translocation Down syndrome, karyotyping of parents and other relatives is required for genetic counseling. Fluorescence in situ hybridization (FISH) allows rapid prenatal or neonatal detection of trisomy 21 but does not distinguish translocation, so a FISH result must be confirmed by complete karyotype analysis.
Prenatal screening combining maternal serum biomarkers and ultrasonography detects up to 95% of affected pregnancies. The nuchal translucency (NT) scan measures fluid in the dorsum of the fetal neck, is best assessed at 11-14 weeks, and an increased measurement (linked to higher genetic-syndrome risk) detects up to 70% of Down syndrome pregnancies. Amniocentesis, routinely done at 14-16 weeks' gestation, remains the criterion standard invasive test and is 99.5% accurate for chromosomal disorders. Chorionic villus sampling (CVS) is done at 10-13 weeks' gestation; earlier testing carries a 1 in 300-1000 risk of fetal transverse limb deficiency, a small risk of maternal cell contamination, and a 0.5-1% risk of fetal loss after the procedure.
Medical Management
No notable medical treatment exists for the intellectual disability of Down syndrome, but better medical care has greatly improved quality of life and life expectancy.
Timely surgical treatment of cardiac anomalies found in the newborn period or early infancy can prevent serious complications and is crucial for survival. Surgery may also be needed to reduce atlantoaxial subluxation and stabilize the upper cervical spine when neurologic deficits are significant. Congenital cataracts occur in about 3% of children and must be extracted soon after birth so light reaches the retina. No special diet is needed unless celiac disease is present; a balanced diet and regular exercise maintain appropriate weight, and feeding problems and failure to thrive usually improve after cardiac surgery. No activity restriction is necessary, but counsel parents about sports with higher spinal-injury risk, such as football, soccer, and gymnastics.
Pharmacologic Management
Provide standard immunizations and well-child care, plus targeted treatment for the syndrome's manifestations. Give thyroid hormone for hypothyroidism to prevent intellectual deterioration and improve overall function, academic achievement, and vocational ability. Give digitalis and diuretics as needed for cardiac management. Consider pneumococcal and influenza vaccination for children with chronic cardiac and respiratory disease, and consider prophylactic palivizumab, since infants with Down syndrome are at high risk for hospitalization with respiratory syncytial virus. Give anticonvulsants for tonic-clonic seizures, and treat infantile spasms with steroids.
Nursing Management
Nursing Assessment
Perform a thorough, systematic head-to-toe assessment of the newborn, and obtain a history of the mother's pregnancy, birth, and genetic testing.
Nursing Diagnoses
- Delayed growth and development related to impaired ability to achieve developmental tasks.
- Self-care deficit (bathing and hygiene, dressing, feeding, toileting) related to cognitive impairment.
- Impaired verbal communication related to impaired receptive or expressive skills.
- Risk for infection related to decreased muscle tone and poor mucus drainage.
Nursing Care Planning and Goals
- The child performs motor, social, and expressive skills typical of the age group within present capabilities.
- The child performs age-appropriate self-care and self-control activities.
- The child establishes a method to express needs.
- The child achieves timely wound healing, stays free of purulent drainage or erythema, and remains afebrile.
Nursing Interventions
Provide adequate nutrition. Assess the child's ability to swallow, teach proper feeding technique, and give good nutrition counseling.
Schedule frequent consultations. Encourage parents to have the child's hearing and vision checked regularly.
Assess understanding of the condition. Educate parents about Down syndrome and the child's care.
Provide emotional support. The family needs strong support and guidance from the time the child is born.
Evaluation
Goals are met when the child performs age-typical motor, social, and expressive skills within present capabilities, carries out age-appropriate self-care and self-control, establishes a method to express needs, and achieves timely wound healing while staying free of purulent drainage or erythema and afebrile.
Documentation Guidelines
- Availability and use of support systems and community resources.
- Plan of care.
- Teaching plan.
- Attainment or progress toward desired outcomes.
- Deviations from normal parenting expectations.
Frequently Asked Questions
What is Down syndrome? It is a chromosomal condition in which a person has a full or partial extra copy of chromosome 21 (trisomy 21). The extra genetic material changes how the body and brain develop and drives the physical features and intellectual disability seen in the syndrome (CDC).
How common is Down syndrome? It is the most common chromosomal condition in the United States, occurring in about 1 in 700 babies, which is roughly 5,700 births each year (CDC).
What causes the extra chromosome? Most cases result from nondisjunction, when chromosome 21 fails to separate during egg or sperm formation, producing free trisomy 21. Less often it arises from a translocation or from mosaicism. The risk rises with advanced maternal age.
How is it diagnosed? Prenatal screening that combines maternal serum markers and ultrasound flags higher-risk pregnancies, and diagnostic tests such as chorionic villus sampling or amniocentesis confirm the karyotype. After birth, the diagnosis is confirmed with cytogenetic (chromosome) studies.
What health problems are linked to Down syndrome? Common associated conditions include congenital heart defects, hearing and vision problems, thyroid disease, atlantoaxial instability of the cervical spine, gastrointestinal anomalies, and a higher risk of leukemia (CDC).
What is the nurse's role? Care is lifelong and family-centered: screen for the associated conditions, support development and self-care, coordinate regular hearing, vision, and thyroid checks, and teach and emotionally support the family from the day the child is born.