Reproductive Genetics 3

Question 1

What is confined placental mosaicism?

Answer 1

• Found in approximately 1% of CVS samples
• Confirmed in fetus in 23% of cases
• Amniocentesis often recommended
• CPM may be associated with IUGR
• Trisomy 17 will always indicate CPM

Question 2

What is spinal muscular atrophy (SMA)?

Answer 2

• Autosomal recessive progressive neurodegenerative disorder
  
  • lower motor neurons in anterior horn of spinal cord
• Symmetric proximal msucle weakness
  
  • progresses to hypotonia and respiratory failure at age 2
• Most common form of a result of homozygous absence of functional SMN1 gene
• Incidence is 1 in 6000

Question 3

Describe the risks of osme of the common aneuploidies in liveborn babies.

Answer 3

• Trisomy 21 (Down syndrome) - 1 in 700
• Trisomy 18 (Edward syndrome) - 1 in 3000
• Trisomy 13 (Patau syndrome) - 1 in 5000
• 45, X (Turner syndrome) - 1 in 2500 females and 600 males
• 47,XXY (Klinefelter syndrome) - similar to Turner
• 47, XYY and 47, XXX - 1 in 1500

Question 4

What fetal chromosome abnormality does not increase with maternal age?

Answer 4

Polyploidies or microdeletions

Question 5

What is the risk for recurrence in aneuploidy?

Answer 5

• If women have miscarriages that are due to chromosome abnormality the first time around, the second one will have an increased risk of aneuploidy
• Risk is much lower for someone who is a carrier, not 33%
  
  • most aneuploidy pregnancies spontaneously miscarry
• Risk is much higher if the mother is the carrier of the translocation versus the father
  
  • sperm carrying extra chromosomes aren’t as able to fertilize the eggs