Down syndrome
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Down syndrome, is a common genetic abnormality. It may also be called Trisomy 21; however, technically this may not be completely correct in all cases.
Genetics
Down syndrome can be the result of three different defects:[1]
| Defect | Percent of DS | Notes |
|---|---|---|
| Extra chromosome 21 (trisomy 21) | ~95% | defect seen more often with increasing maternal age |
| Robertsonian translocation | ~4% | part of chromosome 21 attaches to chromosome 22 or 14; one parent is a carrier -- recurrence virtually 100%; no age dependence |
| Mosaicism | ~1% | some cells have a triple dose of chromosome 21 while others have a normal number of chromosome 21; no age dependence |
Characteristics
Mnemonic CHILD HAS PROBLEM:[2]
- Congenital heart disease / Cataracts.
- Hypothyroidism / Hypotonia.
- Incurved 5th digit (clinodactyly)[3] / Increased gap between 1st and 2nd toe.
- Leukemia risk x2 / Lung problem.
- Duodenal atresia / Delayed development.
- Hirschsprung disease / Hearing loss.
- Alzheimer disease / Alantoaxial instability.
- Short neck / Squint.
- Palmar crease / Protruding tongue.
- Round face / Rolling eye (nystagmus).
- Occiput flat / Oblique eye fissure.
- Brushfield spots / Brachycephaly.
- Low nasal bridge / Language problems.
- Epicanthic fold / Ears folded.
- Mental retardation / Myoclonus.
Notes:
- Brushfield spots = white/grey spots in the iris (the "colour part" of the eye).
- Image: Brushfield spots (WC).
See also
- Trisomy 13 (Patau syndrome).
- Trisomy 18 (Edwards syndrome).
- Chromosomal anomalies.
- Stillbirth.
References
- ↑ Mitchell, Richard; Kumar, Vinay; Fausto, Nelson; Abbas, Abul K.; Aster, Jon (2011). Pocket Companion to Robbins & Cotran Pathologic Basis of Disease (8th ed.). Elsevier Saunders. pp. 99. ISBN 978-1416054542.
- ↑ URL: http://www.valuemd.com/genetics.php. Accessed on: 29 May 2011.
- ↑ URL: http://www.handresearch.com/diagnostics/simian-line-down-syndrome.htm. Accessed on: 29 May 2011.