Autosomal trisomies

Drinking at age 21
Election at age 18
Puberty at age 13

Down syndrome trisomy 21

• 95% due to meiotic nondisjunction of homologous chromosome (old women given birth)
• 4% due to Robetson translocation
• 1% due to mosaicism (no maternal association)
  
• FIrst -trimester ultrasound usually show increase nuchal transluency anmd hypoplastic nasal bone,serum PAPP-A is decrease ,free beta-hCG is increase.
• Second trimester quad screen show: decrease alpha-fetoproitin, increase beta-hCG ,decrease estriol and increase inhibin A

Edward syndrome trisomy 18

• death usually within one yr of birth
• PAPP-A and free beta-hCG are decrease in first trimestar 
• quad screen show : decrease alpha fetoprotein and decrease beta-hCG,decrease estriol decrease or normal inhibin A.

Patau syndrome trisomy 13

• death usually within one yr of birth
• first trimester pregnancy screen shows decrease free beta-hCG,decrease PAPP-A,and increase nuchal transluency.