Limb development defects

Question 1

What is amelia?

Answer 1

Complete absence of a limb

Question 2

What is meromelia?

Answer 2

Partial absence of one or more limb structures

Question 3

What is phocomelia?

Answer 3

Absence of long bones with rudimentary hands and feet attached to trunk by small irregular bones

Question 4

What is polydactyly?

Answer 4

Extra digits

Genetic recessive trait

Question 5

What is syndactyly? What are the 2 types?

Answer 5

Fusion of digits

• Cutaneous: webbing between digits (just involves CT)
• Osseous: fusion of bones (synostosis)

Question 6

What is the structural defect underlying congenital dislocation of the hip (CHD)/developmental dysplasia of hip?

Answer 6

Underdevelopment of the hip bone acetabulum and head of femur. Joint capsule is very relaxed and dislocation almost always occurs after birth.

Question 7

What is CHD often associated with? Suggest a reason for this.

Answer 7

Breech presentation at birth.

Delivery of buttocks first could push head of femur out of acetabulum due to pressure in birth canal.

Question 8

What are the 3 main types of underlying problems in morphogenesis?

Answer 8

1. Malformation: intrinsic error in coordination of morphogenesis (genetic).
2. Deformation: constriction bands (strands of amniotic membrane tear off and constrict limb).
3. Disruption: effect of external agent, e.g. thalidomide , TORCH infections (toxoplasmosis, other, rubella, cytomegalovirus, herpes).

Question 9

What is the effect of thalidomide on limb development?

Answer 9

Acts as a teratogen - induces oxidative stress to ROS-dependent signaling pathways in AER (and ZPA). So no development of limb buds = phocomelia.