Down
Syndrome (Trisomy 21)
Last
updated 03.11.12
Definition
- Abnormal
genotype of (Aneuploidy) chromosome 21 with three copies (trisomy, triploid)
Features
- Non-disjunction
- Risk
decreases with advancing gestation
- Most
M/C
- 10%
12-16/40
- 20%
16/40 to term
Risk
Factors
- Maternal
age
- 1:1500
at 15-19yrs
- 1:890
at 30yrs
- 1:355
at 35yrs
- 1:90
at 40yrs
- Risk
1/300 at 35 yrs
- If
previous fetus with Trisomy 21 risk = age +0.75%
- Risk
Calculation
- (Age
& gestation) x likelihood ratio by screening tests
Physical
Appearance
- Epicanthic
folds
- Single
palmar crease
- Wide
nose
- Low
set ears
- Curved
5th finger
- Sandal
gap
- Brushfield
spots (iris)
- Large
tongue
- Hypospadius
- Microdontia
- Microcephaly
Associated
Conditions
- Congenital
heart disease: VSD, ASD
- Duodenal
or oesophageal atresia
- Atlanto-occipital/atlanto-axial
instability
- Hypotonia
- Visual
& hearing impairment
- Mental
retardation
- 10-20x
risk
- Typically
<6 yrs (newborn or 3-6yrs)
- Transient
myeloproliferative disorder
- Acute
megakaryocytic leukaemia (AML)
- Prematures
senescence
- Alzhiemers
Disease: Dementia
- Cataracts
- OSA
Antenatal
Screen
- Offered
to all pregnant women in Australia
- To
provide opportunity for TOP if high risk
- Maternal Serum Screening (MSS)
- Combined
First Trimester Screening: blood test + US
- Second
Trimester Screening (Quad Test): blood test
- Detection rates
- 70-80%
with Age + NT
- Increases
to 85-90% with PAPP-A + free Beta hCG (Combined First
Trimester Screening)
- 90%
with Age + NT + NB
- 95%
with Age + NT + NB + PAPP-A + free Beta hCG
- No
nasal bone 60-70%
- No
nuchal fold LR 10 (should be >6mm at 20/40)
- Echogenic
bowel LR 3
- Short
humerus LR 4.1
- Short
femur LR 1.6
- Hydronephrosis
LR 1.1
- Echogenic
focus in ventricle LR 1.1
Ix
- High
risk = >1:300 on Maternal Serum Screening
- CVS
= placental Bx
- Performed
at 11-13/40
- 1%
M/C rate
- Amniocentesis
= fluid sample
- Performed
after 14/40
- 0.5%
M/C rate
- Karyotype
takes 2-3 weeks
- FISH
takes 24hrs
Mx
- Antenatal
Dx: offer TOP
- Dependant
on gestation: suction D&C, D&E, misoprostol & labour
References
www.fetalmedicine.com/fmf/FMF-English.pdf