W6-L3: Mechanisms of Birth Defects

Question 1

Why do congenical defects occur?

Answer 1

They occur due to abnormal development in a particular part of the embryo at a particular point in time

Question 2

What is congenital defect?

Answer 2

Any abnormality of structure or function that is present,
although not necessarily obvious, at the time of birth

Question 3

What are the characteristics or features of birth defect?

Answer 3

The defect maybe:
-Major (serious) - potential to cause disability/death
-Minor - cosmetic

• May be:
  *Single/isolated
  *Multiple

Question 4

Describe the stages of normal fetal development.

Answer 4

• Pre-embryonic stage (fertilization- end of week 2)
• Embryonic stage- organ formation and development (week 3- week 8)
• Fetus- growth (week 9- birth)

Question 5

Organs susceptible to congenital defect throughout gestation/pregnancy

Answer 5

Central nervous system

*Matures well in the 3rd trimester (week 27) of pregnancy and after birth.

Question 6

What’s a global percentage of babies born with a serious congenital disorders globally?

Answer 6

3-5

Question 7

The rate of congenital abnormalities is higher in South Africa, with a percentage of________

Answer 7

6.8 %

Question 8

What are the 4 main mechanisms causing
structural birth defects?

Answer 8

• Malformations
• Deformations,
• Disruptions,
• Dysplasias

Question 9

Which of the 4 mechanism causing structural birth defect is characterised by a presence of an abnormal structure caused by complete or part failure of development of an organ or limb.

Answer 9

Malformations

Question 10

At which stage of development do we see malformation?

Answer 10

embryonic

Question 11

Majority of known aetiology malformations are caused by what factor/s?

Answer 11

Multifactorial (23%)

Question 11

What are the causes of malformation?

Answer 11

• Chromosome abnormalities
• Single gene abnormalities
• Multifactorial
• Teratogens (e.g. alcohol, Rubella, maternal diabetes)

Question 12

A mechanisms causing
structural birth defects where a normal structure is pushed/ pulled out of shape (external
mechanical force)

Answer 12

Deformation

*Usually occurs later in pregnancy and often involves bone, cartilage and joint

Question 12

What causes deformation?

Answer 12

• abnormal uterus (e.g. large fibroids, bicornuate uterus)
• multiple pregnancy
• oligohydramnio

Question 13

What is a cause of disruption?

Answer 13

• ischaemia (amniotic bands, fetal intravascular accidents)
• necrosis following infection (VZV

Question 13

Normal structure destroyed (limb, organ or tissue)
* particular anatomical area usually involved
* different tissues in that area destroyed – permanent

This is seen with which mechanism of birth defect?

Answer 13

Disruption

Question 14

Describe dysplasia

Answer 14

Abnormal organisation and functioning of a specific tissue type throughout the body

Question 15

What causes dysplasia?

Answer 15

Cause: single gene defects
* Recurrence risks: Mendelian inheritance (AR/AD/XL