DNA testing for Down syndrome

Posted by e-Medical PPT
Down syndrome is the Commonest genetic cause of intellectual disability worldwide.
Increased risk with advancing maternal age.
Cause
Non-disjunction / trisomy        95%
Translocation                          4%
  About 50% de novo
Mosaicism                              1%

Clinical features
Craniofacial
Brachycephaly, upslanted eyes, epicanthic folds, flat facial profile, flat nasal bridge, (protruding tongue), (dysplastic ears)
Limbs
Brachydactyly, single palmar crease, clinodactyly, sandle-gap
Cardiac (40%)
ASD, VSD, AVSD, PDA
CNS
Hypotonia, developmental delay, MR
Other
GIT abnormalities (~15%), short stature

Complications
Atlanto-axial instability
Transient neonatal ‘leukaemia’
ALL (20 X greater risk)
Hypothyroidism (antibodies) in 30%
Alzheimer disease

Quantitative fluorescent PCR aneuploidy screen (QF-PCR)
Principle:
Test STR markers on chromosomes
 4-5 on autosomes of choice (13, 18, 21)
 Fewer on X and Y
Used to detect numerical chromosome abnormalities
Can test blood, amniotic fluid, CVS, post-mortem tissue etc...

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