Down's syndrome
Chromosomal abnormality
Three copies of chromosome 21
- Non-disjunction (esp mothers > 40 years)
- Non-disjunction of a gamete: one progeny gets TWO chromosomes (and the other one gets none) which is then fertilised by a normal gamete from the other parent enduing up with THREE copies of chromosomes.
- Usually maternally derived extra copy
- Translocation (rare)
- Parents phenotypically normal but have a balanced translocation
- Chr 23 +Chr 23 / Ab Cr 22; get's one Chr 23 from mum, one Chr23 from dad and AbCr22+Down's shit
- Mosaism
- 1/100 cases
- Normal ovum
- Non-disjunction after the blastocysts starts to develop
Associations
- Congenital heart defects: PDA, VSD, ASD
- Neoplasia
- Increased incidence glue ear
