Trisomies Flashcards
What is the most common live-born chromosomal anomaly
Down syndrome
most common cause of intellectual disability
down syndrome
key physical clinical features of Down Syndrome
- flat, wide set NASAL BRIDGE
- low set, small ears
- brachycephaly (flat posterior skull)
- prominent EPICANTHAL folds
- UPSLANTING palpebral fissures
- brushfield spots (white spots on iris)
- short, broad hands
- transverse palmar crease
- “sandal gap”
- DYSTONIA (low muscle tone)
- short stature
congenital heart disease in down syndrome
- about 50%
* most commonly endocardial cushion defects (primum ASD or VSD ->holosystolic murmur)
GI anomalies in down syndrome
- about 5%
* duodenal atresia or stenosis
alzheimer’s in down syndrome
- common, and early onset (<50yo)
* amyloid precursor protein (APP) on chromosome 21
malignancy in down syndrom
- increased risk
- 1-1.5 percent
- leukemias
most common cause of down syndrome
- meiotic nondisjunction (95%)
- 90% meiosis I
- 90% extra chromosome from mother
rare cause of down syndrome
- robertsonian translocation (2-3%)
- risk does NOT increase with maternal age
- high recurrence risk in families
rarest cause of down syndrome
- mitotic error post fertilization (<2%)
* somatic mosaicism
fetal karyotype in down syndrome prenatal screening
- invasive and carries risks
- only done in cases when high risk
- 1st trimester -> chorionic villus sampling (from placenta)
- 2nd trimester -> amniocentesis
ultrasound testing in down syndrome
- non-invasive, can be predictive but not confirmatory
- small, poorly formed nasal bones
- nuchal translucency (fluid under back of neck)
maternal serum testing in down syndrome (1st trimester)
- pregnancy associated plasma protein A (PAPP-A) -> LOW
* β-hCG -> HIGH
maternal serum testing in down syndrome (2nd trimester)
- “quad test”
- α-fetoprotein (AFP) -> LOW
- estriol (uE3) -> LOW
- β-hCG -> HIGH
- Inhibin-A -> HIGH
commonalities of all trisomies
- associated with maternal age
- commonly due to meiotic NDJ
- intellectual disabilities
- physical deformities
- congenital heart defects
trisomies in order of how common they are (live births)
Down syndrome (21) > Edward syndrome (18) > patau syndrome (13)
male and female occurrence of Edward syndrome
3:1 female:male
key physical clinical features of Edward syndrome
- low birth weight
- SMALL HEAD, prominent occiput
- low set ears
- SMALL JAW, MOUTH
- clenched fist w/ overlapping fingers
- “rockerbottom” feet
congenital heart disease in Edward syndrome
- about 50%
- VSD
- patent ductus arteriosus (PDA)
GI defects in Edward syndrome
- about 75%
- meckel’s diverticulum (most common)
- malrotation
- omphalacele
survival rates with edward syndrome
- many die in utero
- 50% die in 2 weeks
- only 5-10% survive first year
ultrasound in edward syndrome diagnosis prenatally
- usually can diagnose physical deformities
- limb defects
- congenital heart defects
maternal serum testing in edward syndrome (1st trimester)
- pregnancy associated plasma protein A (PAPP-A) -> LOW
* β-hCG -> LOW
maternal serum testing in edward syndrome (2nd trimester)
- “quad test”
- α-fetoprotein (AFP) -> LOW
- estriol (uE3) -> LOW
- β-hCG -> LOW
- Inhibin-A -> LOW
most severe trisomy
patau syndrome (13)
detection of patau syndrome by ultrasound
90% can be diagnosed
key physical clinical features of patau syndrome
- microphthalmia or anophthalmia
- cleft lip/palate
- post-axial (away from midline of body) polydactyly
- holoprosencephaly (hemispheres of brain)
congenital heart disease in patau syndrome
- about 80%
- VSD
- ASD
- patent ductus arteriosus (PDA)
survival rates with patau syndrome
- most die in utero
- median survival after birth ~7 days
- 91% die within first year
maternal serum testing in patau syndrome (1st trimester)
•pregnancy associated plasma protein A (PAPP-A) -> LOW
•β-hCG -> LOW
(usually diagnosed by US though)
