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ALL / Clinical Sciences
Down's syndrome: epidemiology and genetics
Down's syndrome: epidemiology and genetics
Risk of Down's syndrome with increasing maternal age| Age (years) | Risk |
|---|---|
| 20 | 1 in 1,500 |
| 30 | 1 in 800 |
| 35 | 1 in 270 |
| 40 | 1 in 100 |
| 45 | 1 in 50 or greater |
One way of remembering this is by starting at 1/1,000 at 30 years and then dividing the denominator by 3 (i.e. 3 times more common) for every extra 5 years of age
Cytogenetics
| Mode | % of cases | Risk of recurrence |
|---|---|---|
| Nondisjunction | 94% | 1 in 100 if under mother < 35 years |
| Robertsonian translocation (usually onto 14) | 5% | 10-15% if mother is translocation carrier 2.5% if father is translocation carrier |
| Mosaicism* | 1% |
The chance of a further child with Down's syndrome is approximately 1 in 100 if the mother is less than 35 years old. If the trisomy 21 is a result of a translocation the risk is much higher
*Mosaicism is defined as the presence of two genetically different populations of cells in the body
+PassMedicine Notes
Risk of Down's syndrome with increasing maternal age
Age (years) _Risk | 20 _ 1 in 1,500 | 30 _ 1 in 800 | 35 _ 1 in 270 | 40 _ 1 in 100 | 45 _ 1 in 50 or greater|One way of remembering this is by starting at 1/1,000 at 30 years and then dividing the denominator by 3 (i.e. 3 times more common) for every extra 5 years of age
Cytogenetics
Mode _ % of cases _ Risk of recurrence| Nondisjunction _ 94% _ 1 in 100 if under mother < 35 years| Robertsonian translocation (usually onto 14) _ 5% _ 10-15% if mother is translocation carrier 2.5% if father is translocation carrier| Mosaicism* _ 1%_|The chance of a further child with Down's syndrome is approximately 1 in 100 if the mother is less than 35 years old. If the trisomy 21 is a result of a translocation the risk is much higher
*Mosaicism is defined as the presence of two genetically different populations of cells in the body
