Review Question - QID 237

Achondropasia is caused by a mutation in the FGFR-3 receptor in the zone of proliferation. This is a gain of function mutation which enhances tyrosine kinase activity resulting in increased inhibition of chondrocyte proliferation and differentiation.

Shirley and Ain reviewed the features of achondroplasia which include rhizomelic dwarfism (proximal shortening) and genu varum. It is helpful to remember that spinal manifestations develop at different ages: foramen magnum stenosis during infancy, thoracolumbar kyphosis when sitting begins, and spinal stenosis as early as the second decade.

Illustration A shows the zone of proliferation, which is affected in Achondroplasia.

Incorrect Answers:
Answer 2 & 4: Apert's syndrome is caused by a genetic defect in the FGFR-2
Answer 5: COMP defects cause pseudoachondroplasia, multiple epiphyseal dysplasia type I, and McKusick's metaphyseal chondrodysplasia.