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
Genetic abnormalities associated with increased risk for male breast cancer
Klinefelter syndrome
DiGeorge syndrome
22q11.2 micro deletion
Catch 22
Cardiac : Conotruncal defect
Abnormal facies -
T. Cell deficiency.
Cleft lip/palate
Hypocalcaemia
