Down syndrome, Down’s syndrome, or trisomy 21 is a chromosomal disorder caused by the presence of all or part of an extra 21st chromosome. It is the most common chromosomal abnormality.
- It is named after John Langdon Down, the British doctor who described the syndrome in 1866.
- The disorder was identified as a chromosome 21 trisomy by Jérôme Lejeune in 1959.
- The condition is characterized by a combination of major and minor differences in structure.
- Often Down syndrome is associated with some impairment of cognitive ability and physical growth as well as facial appearance.
- Down syndrome in a baby can be identified with amniocentesis during pregnancy or at birth.
- Individuals with Down syndrome tend to have a lower than average cognitive ability, often ranging from mild to moderate developmental disabilities.
- A small number have severe to profound mental disability.
- The incidence of Down syndrome is estimated at 1 per 800 to 1,000 births, although these statistics are heavily influenced by the age of the mother. Other factors may also play a role.
- Health concerns for individuals with Down syndrome include a higher risk for congenital heart defects, gastroesophageal reflux disease, recurrent ear infections, obstructive sleep apnea, and thyroid dysfunctions.
- Early childhood intervention, screening for common problems, medical treatment where indicated, a conducive family environment, and vocational training can improve the overall development of children with Down syndrome. Although some of the physical genetic limitations of Down syndrome cannot be overcome, education and proper care will improve quality of life.
The cause is unknown and multiple theories exist. The concept of multiple causality is most accepted.
- Cytogenetics of the disorder are well established.
- Approximately 92% to 95% of cases are attributed to an extra chromosome 21 hence the name trisonomy 21.
- About 3-6% of cases maybe caused by translocation of chromosomes 15 (21 or 22).
- From 1-3% of persons demonstrate mosaicsm (cells with both normal and abnormal chromosomes).
- Children with down syndrome are born to parents of all ages. Although there is a higher incidence among mothers over age 35, most are born to mothers under age 35 (80%).
The degree of cognitive and physical impairment is related to the percentage of cells with the abnormal chromosome makeup.
1. Separated sagittal suture
2. Oblique palpebral fissures
3. Small nose
4. Depressed nasal bridge
5. High-arched palate
6. Skin excess laxity
7. Wide space and plantar crease between the big and second toe.
8. Hyperextensible and lax joints
9. Muscle weakness
Other common findings include a small penis, short, broad hands (transverse (simian) palmar crease), a protruding tongue, small ears, Brushfield spots, and dry skin.
Associated problems and features:
- Intelligence varies from severely retarded to low normal but is usually in the mild to moderate range.
- Social development may be 2 to 3 years beyond mental age; temperament range is similar to normal children, with a trend toward the easy child.
- Congenital anomalies include congenital heart disease (especially septal defects), renal agenesis, duodenal atresia. Hirschsprung disease, tracheoesophageal fistula, and skeletal deformities.
- Sensory problems include strabismus, nystagmus, myopia, hyperopia, excessive tearing and cataracts, and conductive hearing loss.
Other physical disorders inlcudes:
- Respiratory infections, leukemia, and thyroid dysfunction.
- Growth is reduced and there is rapid weight gain.
- Sexual development maybe delayed, incomplete or both. Male genitalia and secondary characteristics are underdeveloped. Breast development is mild to moderate with menarche at appropriate age. Women may be fertile, men are infertile.
- Assess for associated problems.
- Administer medications which maybe prescribed for associated problems.
- Implement a plan of care that is the same as for mental retardation. Include planning and intervention strategies for associated problems and features.
- Encourage genetic counseling.
- Explain hypertonicity and joint hyperextensibility to parents, and that the child’s resultant lack of clinging is physiologic and not a sign of detachment.
- Prevent respiratory infections by clearing the nose with a bulb syringe, using a cool mist vaporizer, performing chest physiotherapy when needed, providing good handwashing and avoiding exposure to infection.
- When feeding infants and young children, use a small, straight-handled spoon to push food to the side and back of the mouth. Feeding difficulties occur due to a protruding tongue and hypotonia.
- Encourage fluids and foods rich in fiber. Constipation results from decreased muscle tone, which affects gastric motility.
- Provide good skin care because the skin is dry and prone to infection.
Lippincott Review Series
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