Menu

Biology, Genetics & Bone Healing MCQs

Practice Set 212 of 212

This practice set contains high-yield board review questions covering key concepts in Biology, Genetics & Bone Healing. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 4221

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with severe, aching pain and progressive joint contracture in her right lower extremity. Radiographs demonstrate asymmetric, dense cortical hyperostosis flowing down the medial aspect of the femur and tibia, resembling "dripping candle wax". What gene is typically mutated in this disorder?

. TGFB1
. LEMD3
. COMP
. SOX9
. GNAS

Correct Answer & Explanation

. LEMD3

Explanation

Melorheostosis is a non-hereditary, sclerosing bone dysplasia often linked to somatic mutations in the LEMD3 or MAP2K1 genes. The classic "dripping candle wax" radiographic appearance is associated with severe pain, stiffness, and joint contractures.

Question 4222

Topic: Biology, Genetics & Bone Healing

A 2-year-old boy is evaluated for severe bowing of the lower extremities, prominent joints, and short stature. Laboratory tests reveal profound, asymptomatic hypercalcemia, hypophosphatemia, and undetectable PTH levels. Radiographs show extensively cupped and frayed metaphyses. What is the underlying pathogenesis?

. Loss-of-function mutation in the calcium-sensing receptor (CaSR)
. Activating mutation of the PTH/PTHrP receptor (PTH1R)
. Deficiency of 1-alpha-hydroxylase
. Inactivating mutation of the PHEX gene
. Autoantibodies against the osteoprotegerin (OPG) receptor

Correct Answer & Explanation

. Activating mutation of the PTH/PTHrP receptor (PTH1R)

Explanation

Jansen metaphyseal chondrodysplasia is caused by a gain-of-function mutation in the PTH1R gene. This leads to constitutive activation of the PTH receptor, resulting in severe hypercalcemia, hypophosphatemia, and metaphyseal changes despite suppressed systemic PTH levels.

Question 4223

Topic: Biology, Genetics & Bone Healing

A 2-year-old girl is evaluated for recurrent fractures, hepatosplenomegaly, and severe anemia. Skeletal survey demonstrates uniformly dense bones with a "bone-within-bone" appearance and loss of the medullary canal. The most common genetic mutation causing this severe infantile condition primarily affects which osteoclast component?

. Receptor activator of nuclear factor kappa-B ligand (RANKL)
. Proton pump required for ruffled border acidification
. Cathepsin K enzyme secretion
. Carbonic anhydrase II enzyme
. Tartrate-resistant acid phosphatase (TRAP)

Correct Answer & Explanation

. Proton pump required for ruffled border acidification

Explanation

Malignant infantile osteopetrosis is most commonly caused by a TCIRG1 mutation, leading to a defective vacuolar proton pump. This results in the failure of osteoclasts to acidify the resorption pit and form a ruffled border, causing dense, brittle bones and marrow obliteration.

Question 4224

Topic: Biology, Genetics & Bone Healing

An 8-year-old girl is brought to the orthopedic clinic due to unusual hypermobility of her shoulders. Physical examination demonstrates the ability to approximate her shoulders in the anterior midline. She also has delayed eruption of permanent teeth and a wide, open sagittal suture. A mutation in which of the following transcription factors is the primary cause of her condition?

. RUNX2 (CBFA1)
. SOX9
. COMP
. EXT1
. SH3BP2

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is an autosomal dominant condition caused by a mutation in the RUNX2 (CBFA1) gene, a master transcription factor for osteoblast differentiation. It predominantly impairs intramembranous bone formation, leading to absent or hypoplastic clavicles and delayed cranial suture closure.

Test Yourself

Switch to an interactive, timed exam simulation to truly master this topic.

On this Page