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Difference between revisions of "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. | '''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:<ref name=Ref_PCPBoD8_99>{{Ref PCPBoD8|99}}</ref> | |||
{| class="wikitable sortable" | |||
! 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== | ==Characteristics== | ||