Genetic Disorders Flashcards
M/C common trisomy
M/C genetic cause of low IQ
Down syndrome trisomy of chr 21
Genetic basis of down syndrome
- Maternal meiotic non disjunction of chr 21
- Robertsonian translocation: t(14,21) , t(21,21)
- Mosaicism
Ext characteristics of children with Down syndrome
1. Face
2. Hands
3. Feet
- Mongoloid slant of eyes
Epicanthal fold
Brushfield’s spot : white spot in iris
Low set ears
Brachycephalic skull with flat nose occiput & face
Protruding tongue d/t hypoplastic mandible - Simian crease : single transverse crease
Clinodactyly : curved little finger - Sandal gap
Internal defects in Down syndrome
- Low IQ hypotonia
- Cardiac : Endocardial cusion defect/Atrioventricular septal defect > VSD>ASD
- Gastrointestinal: Duodenal Artesia, Hirschsprung dis, Annular pancreas
- Cancer : ALL, AML
- Increase risk of hypothyroidism
- Atlanto-axial sublaxation with short neck
- Pre senile Alzheimer’s dis
In Down syndrome
1. M/c organ defect
2. M/C cause of morbidity n mortality
3. Cause of Atresia
4. M/C cancer
5. M/C cancer <3yrs
- Heart
- A-V septal defect
- Duodenal
- ALL
- AML
Antenatal screening test for down syndrome
- USG - increased nuchal translucency(1 trimester) or thickness (2trimeater)
- Markers from maternal blood
- Cell free fetal DNA testing/ Non invasive prenatal test (NIPT)
Markers in maternal blood for antenatal screening of down syndrome
- First trimester : double test - beta HCG and pregnancy associated plasma protein - A (PAPP-A)
- Second trimester : triple test - beta HCG, alpha-fetoprotein and unconjugated estriol
- Second trimester : quadruple test - triple test + inhibin A
Interpretation :
Beta HCG and inhibin a increase
Other decrease
Confirmatory test for down syndrome
Karyotyping - invasive procedure
Two methods
1. Amniocentesis - 15 weeks gestation
2. Chorionic Villous sampling. -11 to 13 weeks of gestation
External characteristics of Edward syndrome
- Prominent occiput
- Micro ophthalmia.
- Cleft lip/pallet.
- Clenched fist with overlapping fingers.
- Prominent heel
- Rocker bottom foot.
Internal defects in Edward syndrome
- Heart defect - vSD> PDA> ASD - >90%
- Kidney. - Horseshoe shaped kidney
External characteristics of Pataue syndrome
- Cleft lip./palette
- Micro ophthalmia
- This plastic or malformed ears
- Aplasia cutis.
- Postaxial Polydactyly, Clinodactyly
- Undescended testes.
Organ defects in Patau syndrome
- VSD> PDA> ASD
- Missing ribs
- Holoprosencephaly or arrhiencephaly
External features of Turner syndrome
Short stature
Triangular face
Webbed neck , loose skin folds in neck, low posterior hairline
Flat shield chest, widely spaced nipples
Increased carrying angle > 135 , Cubitus valgus
Short fourth metacarpals
In neonate-dorsal lymphoedema of feet and hands cystic hygroma
Organ defects in Turner syndrome
Heart : bicuspid aortic valve> Coarctation of aorta
Streak ovaries
Normal IQ, but learning disabilities
M/C chromosomal abnormality seen in spontaneous abortion
M/C trisomy associated with spontaneous abortion
Turner syndrome
Trisomy of chromosome 16
