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1 in 650 to 700.
This condition derives its name from Dr. Langdon Down ,who first described it in the clinical lecture reports of the London hospital in 1866.
•Abnormality •Frequency (%)Trisomy 21.(nondisjunction of chr.-21 in maternal meiosis – 1).
95
Robertsonian translocation –D/G-(21q/21q , 22q/21q )
4
Mosaicism(Often less severely affected than those with full syndrome.)
1
0
20
40
60
80
100
Category 1Category 2
Category 3
Series 1
Series 2
Series 3
•Cause •Recurrencerisks
Trisomy 21 1/200 to 1/100
Translocation Male:1-3%Female:10-15%
Translocation between 21q & 21q
100%
Newborn period: Hypotonia , sleepy excess nuchal skin .
Craniofacial: Brachycephaly ; epicanthic folds & brush-field spots on eye ; upward sloping palpebral fissures ; protruding tongue ; small ears ; flat nasal bridge .
Limbs: Single palmar crease ( “simian crease” ) , small middle phalanx of 5th finger , wide gap between 1st & 2nd toes .
Cardiac: Atrial & ventricular septal defect ; common atrioventricular canal ; patent ductus arteriosus .
Others: i)Anal atresia , duodenal atresia , Hirsch-prung disease.
ii)Short stature , strabismus .
iii)Average I.Q. of young adults is around 40 to 45 .
iV)Social skills well-developed , most of the children are happy & very affectionate .
They are susceptible to infection & often have congenital heart disease ( in about 50% of all cases ). So , they usually die young . Generally they have a lifetime of about 40 – 50 years , except in severe cases .
i) High resolution USG.
ii) Chorionic villus analysis .
iii) Cultured amniotic cells .
iv) FISH technique .
v) Prenatal screening programmes have been introduced based on the so called “triple” or“quadruple” tests of maternal serum at 16 weeks’ gestation .
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