Ch 26: Modeling Abnormalities and Delayed Maturation of Bone

Question 1

A common cause of dwarfism that is the result of overexpression of fibroblast growth factor 3. Extremities are short, but head and chest are normal sized

Answer 1

Achondroplasia

Impaired cartilage proliferation in the growth plate, thus endochondral bone formation of the long bones is affected, but intramembranous bone formation of the flat bones is normal

Question 2

Increased skeletal mass in a child resulting from defective bone resorption. Child presents with bone fractures and extramedullary hematopoiesis to compensate for marrow suppression.

Name the “high yield” mutation involved in the dysfunctional cell.

Answer 2

Osteopetrosis

Dysfuntional osteoclasts- may present with hydrocephalus due to thickening of the foramen magnum. Bones are heavy and dense, but fracture easily
Carbonic Anhydrase II mutation (need acidic environment to reabsorb bone and alkaline to lay it down (alk phos))

Question 3

Patient presents with fractures, blue sclera, and hearing loss. After further studies you determine the patient has a defect in their gene for the production of Type I collagen

Answer 3

Osteogenesis Imperfecta

Defective Type I collagen synthesis is the culprit for all of the defects that the patient presents with. There are four variations of the disease- Type I is the mildest and is represented by the presented vignette, Type II results in death a few days after birth or stillborns, Type III is the most deforming type with many fractures, Type IV is similar to Type I but with normal sclerae

Question 4

Tumor like masses composed of cartilage that lead to many bony deformities present assymetrically throughout the body

Answer 4

Enchondromatosis (aka Ollier disease)

These cartilaginous masses often undergo malignant changes to chondrosarcomas in adulthood