Menu

Biology, Genetics & Bone Healing MCQs

Practice Set 178 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 3541

Topic: Biology, Genetics & Bone Healing

During fracture healing, mesenchymal stem cells must commit to specific lineages. Which of the following transcription factors is considered the "master regulator" for the differentiation of mesenchymal stem cells into the osteoblast lineage?

. Sox9
. Runx2 (Cbfa1)
. HIF-1 alpha
. Beta-catenin
. MyoD

Correct Answer & Explanation

. Runx2 (Cbfa1)

Explanation

Runx2 (also known as Cbfa1) is the essential, master transcription factor for osteoblast differentiation. In contrast, Sox9 is the primary transcription factor required for chondrocyte differentiation.

Question 3542

Topic: Biology, Genetics & Bone Healing

Familial forms of Paget's disease of bone are most frequently associated with genetic mutations that lead to hyperactive osteoclasts. Which of the following genes is most commonly mutated in these familial cases?

. COL1A1
. FGFR3
. SQSTM1 (p62)
. GNAS1
. EXT1

Correct Answer & Explanation

. SQSTM1 (p62)

Explanation

Mutations in the SQSTM1 (p62) gene are the most commonly identified genetic cause of familial Paget's disease. These mutations increase RANK receptor sensitivity to RANKL, leading to massive, hyperactive osteoclasts.

Question 3543

Topic: Biology, Genetics & Bone Healing

Nitrogen-containing bisphosphonates (e.g., Alendronate) are commonly prescribed for osteoporosis. What is the precise intracellular mechanism by which these drugs impair osteoclast function?

. Inhibition of matrix metalloproteinases
. Inhibition of farnesyl pyrophosphate synthase
. Direct binding to the RANK receptor
. Inhibition of carbonic anhydrase II
. Activation of tissue nonspecific alkaline phosphatase

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate synthase

Explanation

Nitrogen-containing bisphosphonates inhibit farnesyl pyrophosphate synthase in the mevalonate pathway. This prevents the prenylation of small GTPase proteins (like Ras and Rho) that are essential for osteoclast survival and ruffled border formation.

Question 3544

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with severe bowing of the lower extremities. Laboratory evaluation reveals X-linked hypophosphatemic rickets. Which of the following serum laboratory profiles is most characteristic of this specific condition prior to treatment?

. Low calcium, low phosphorus, high PTH
. Normal calcium, low phosphorus, normal PTH
. Normal calcium, high phosphorus, low PTH
. Low calcium, normal phosphorus, high PTH
. High calcium, low phosphorus, normal PTH

Correct Answer & Explanation

. Normal calcium, low phosphorus, normal PTH

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX gene mutation leading to excess FGF23 and subsequent renal phosphate wasting. Typical labs show low phosphorus, normal calcium, and normal parathyroid hormone (PTH) levels.

Question 3545

Topic: Biology, Genetics & Bone Healing

When a massive structural cortical bone allograft is utilized in reconstruction, it incorporates via a process known as creeping substitution. Which of the following best describes the initial cellular sequence of this process in dense cortical bone?

. Rapid vascular ingrowth followed by enchondral ossification
. Osteoclast cutting cones followed by osteoblast bone deposition
. Woven bone formation followed by lamellar remodeling
. Hematoma organization followed by direct intramembranous ossification
. Direct appositional bone growth from host periosteum

Correct Answer & Explanation

. Osteoclast cutting cones followed by osteoblast bone deposition

Explanation

In dense cortical bone grafts, creeping substitution is initiated by osteoclastic resorption via cutting cones, followed by osteoblastic new bone deposition. This sequential remodeling temporarily weakens the structural allograft before it fully incorporates.

Question 3546

Topic: Biology, Genetics & Bone Healing

According to Perren's strain theory, what is the maximum allowable interfragmentary strain necessary to achieve primary bone healing via cutting cones?

. Less than 2%
. 2% to 10%
. 10% to 15%
. 15% to 30%
. Greater than 30%

Correct Answer & Explanation

. Less than 2%

Explanation

Primary bone healing requires absolute stability, which is defined as an interfragmentary strain of less than 2%. This environment allows for direct osteonal remodeling via cutting cones without the formation of an intermediate fracture callus.

Question 3547

Topic: Biology, Genetics & Bone Healing
A patient with a history of multiple low-energy fractures and a 'rugger-jersey' spine appearance on plain radiographs is diagnosed with a metabolic bone disorder. This condition is primarily characterized by a defect in which of the following cellular mechanisms?
. Osteoblast differentiation via Runx2 mutation
. Type I collagen alpha chain synthesis
. Osteoclast ruffled border formation and acidification
. Fibroblast growth factor receptor 3 (FGFR3) hyperactivity
. Excessive production of unmineralized osteoid

Correct Answer & Explanation

. Osteoclast ruffled border formation and acidification

Explanation

The patient has Osteopetrosis (Albers-Schönberg disease), characterized by dense, brittle bones and a 'rugger-jersey' spine. It is caused by impaired osteoclast function. Mutations affecting the proton pump (TCIRG1), chloride channel (CLCN7), or carbonic anhydrase II impair the formation of the acidic microenvironment needed at the osteoclast ruffled border for bone resorption.

Question 3548

Topic: Biology, Genetics & Bone Healing

Which bone morphogenetic protein (BMP) is an FDA-approved osteoinductive agent commonly used in anterior lumbar interbody fusion (ALIF), and which cell surface receptor type does it primarily bind to?

. BMP-2; Serine/threonine kinase receptor
. BMP-7; Tyrosine kinase receptor
. BMP-2; G-protein coupled receptor
. BMP-7; Ion channel receptor
. BMP-4; Tyrosine kinase receptor

Correct Answer & Explanation

. BMP-2; Serine/threonine kinase receptor

Explanation

Recombinant human BMP-2 (rhBMP-2) is FDA-approved for ALIF procedures (delivered via an absorbable collagen sponge). BMPs are part of the TGF-beta superfamily and exert their cellular effects by binding to transmembrane serine/threonine kinase receptors (Types I and II), which subsequently phosphorylate intracellular Smad proteins to alter gene transcription.

Question 3549

Topic: Biology, Genetics & Bone Healing

During the endochondral ossification phase of secondary fracture healing, which factor secreted by hypertrophic chondrocytes is most responsible for triggering vascular invasion into the cartilaginous callus?

. Vascular Endothelial Growth Factor (VEGF)
. Transforming Growth Factor Beta (TGF-beta)
. Fibroblast Growth Factor 2 (FGF-2)
. Insulin-like Growth Factor 1 (IGF-1)
. Platelet-Derived Growth Factor (PDGF)

Correct Answer & Explanation

. Vascular Endothelial Growth Factor (VEGF)

Explanation

During endochondral ossification, hypertrophic chondrocytes secrete Vascular Endothelial Growth Factor (VEGF), which is essential for angiogenesis. The invasion of blood vessels brings osteoprogenitor cells and osteoclasts into the cartilaginous callus, triggering chondrocyte apoptosis and the replacement of cartilage with woven bone.

Question 3550

Topic: Biology, Genetics & Bone Healing

Bone morphogenetic proteins (BMPs) play a crucial role in osteoinduction. Which of the following is a key intracellular signaling molecule directly activated by BMP receptors?

. cAMP
. Smad
. Beta-catenin
. NF-kappa B
. JAK/STAT

Correct Answer & Explanation

. Smad

Explanation

BMPs bind to serine/threonine kinase cell surface receptors, which phosphorylate intracellular Smad proteins (specifically R-Smads 1, 5, and 8). These then form a complex with Smad4, translocate to the nucleus, and regulate the transcription of osteogenic genes such as Runx2.

Question 3551

Topic: Biology, Genetics & Bone Healing

In the pathogenesis of Rheumatoid Arthritis, the interaction between RANKL and RANK leads to characteristic periarticular bone erosions. Which cell type is the primary source of RANKL in the inflamed rheumatoid synovium?

. Osteoblasts
. Osteoclasts
. Synovial fibroblasts and T cells
. Chondrocytes
. Neutrophils

Correct Answer & Explanation

. Synovial fibroblasts and T cells

Explanation

In Rheumatoid Arthritis, the inflamed synovium (pannus) is rich in synovial fibroblasts and activated T-lymphocytes, both of which secrete copious amounts of RANKL. This drives massive local osteoclastogenesis and the characteristic marginal bone erosions.

Question 3552

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the physiological effect of continuous high-dose administration of Parathyroid Hormone (PTH) on bone remodeling?

. Net increase in bone formation via direct stimulation of osteoblasts
. Net increase in bone resorption via direct stimulation of osteoclasts
. Net increase in bone resorption via osteoblast-mediated activation of osteoclasts
. Net decrease in bone turnover by inhibiting both osteoblasts and osteoclasts
. Induction of osteocyte apoptosis leading to woven bone formation

Correct Answer & Explanation

. Net increase in bone resorption via osteoblast-mediated activation of osteoclasts

Explanation

Continuous high-dose PTH leads to a net increase in bone resorption. PTH receptors are located on osteoblasts (not osteoclasts). The osteoblasts respond to continuous PTH by upregulating RANKL and downregulating OPG, which in turn activates osteoclasts. Intermittent low-dose PTH (e.g., teriparatide), conversely, favors bone formation.

Question 3553

Topic: Biology, Genetics & Bone Healing

A child presents with recurrent fractures, anemia, and cranial nerve palsies. Radiographs reveal generalized osteosclerosis with a "bone-within-bone" appearance. The primary cellular defect in this condition involves a failure of which mechanism?

. Defective collagen type I synthesis
. Inability to acidify the resorption pit via carbonic anhydrase II
. Overactive osteoblast function due to Wnt signaling
. Defective mineralization of osteoid
. Fibroblast growth factor receptor 3 (FGFR3) mutation

Correct Answer & Explanation

. Inability to acidify the resorption pit via carbonic anhydrase II

Explanation

This presentation is characteristic of osteopetrosis, a disease of osteoclast dysfunction. The most common underlying defect is a mutation in carbonic anhydrase II, which prevents osteoclasts from creating the acidic environment necessary for bone resorption.

Question 3554

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with a lytic, eccentrically located lesion in the distal femur epiphysis. Biopsy confirms Giant Cell Tumor (GCT) of bone. Denosumab is considered for neoadjuvant therapy. What is the specific target of this medication?

. Osteoprotegerin (OPG)
. RANK receptor on osteoclasts
. RANK Ligand (RANKL) on stromal cells
. Vascular Endothelial Growth Factor (VEGF)
. Macrophage colony-stimulating factor (M-CSF)

Correct Answer & Explanation

. RANK Ligand (RANKL) on stromal cells

Explanation

Denosumab is a monoclonal antibody that binds to and inhibits RANK Ligand (RANKL), which is secreted by the neoplastic stromal cells in a GCT. This prevents RANKL from activating the RANK receptor on normal osteoclast precursors, stopping bone destruction.

Question 3555

Topic: Biology, Genetics & Bone Healing

A 55-year-old female immigrant presents with diffuse bone pain and proximal muscle weakness. Laboratory studies reveal low serum calcium, low serum phosphorus, elevated alkaline phosphatase, and elevated parathyroid hormone (PTH). What is the most likely diagnosis?

. Osteoporosis
. Paget's disease
. Osteomalacia
. Primary hyperparathyroidism
. Multiple myeloma

Correct Answer & Explanation

. Osteomalacia

Explanation

This laboratory profile (low Ca, low PO4, high ALP, and secondary hyperparathyroidism) is the hallmark of osteomalacia, typically caused by severe Vitamin D deficiency. Paget's and osteoporosis generally feature normal calcium and phosphorus levels.

Question 3556

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with a history of malabsorption presents with diffuse bone pain. Radiographs show bilateral Looser zones in the femoral necks. Labs reveal low calcium, low phosphate, and elevated alkaline phosphatase. Which histologic finding is diagnostic of this metabolic bone disease?

. Decreased osteoclast activity and retained primary spongiosa
. Increased thickness and volume of unmineralized osteoid seams
. Thinning of normal trabeculae with normal mineralization ratios
. Extensive formation of disorganized woven bone
. Increased multinucleated giant cells within brown tumors

Correct Answer & Explanation

. Increased thickness and volume of unmineralized osteoid seams

Explanation

The patient has osteomalacia (adult rickets) caused by vitamin D deficiency or malabsorption. Histologically, it is characterized by defective mineralization of newly formed bone matrix, resulting in thick, unmineralized osteoid seams.

Question 3557

Topic: Biology, Genetics & Bone Healing

Alendronate is prescribed to a patient for the treatment of postmenopausal osteoporosis. What is the primary cellular mechanism of action for this nitrogen-containing bisphosphonate?

. Inhibition of osteoblast apoptosis
. Direct binding and neutralization of RANKL
. Inhibition of farnesyl pyrophosphate (FPP) synthase
. Stimulation of the Wnt signaling pathway
. Direct inhibition of cathepsin K

Correct Answer & Explanation

. Inhibition of farnesyl pyrophosphate (FPP) synthase

Explanation

Nitrogen-containing bisphosphonates (like alendronate and zoledronic acid) act by inhibiting farnesyl pyrophosphate (FPP) synthase in the mevalonate pathway. This prevents prenylation of small GTPase proteins in osteoclasts, leading to osteoclast apoptosis.

Question 3558

Topic: Biology, Genetics & Bone Healing

A 30-year-old female presents with knee pain. Radiographs reveal an eccentric, lytic, expansile lesion in the distal femoral epiphysis extending to the subchondral bone. Histology shows multinucleated giant cells in a background of mononuclear stromal cells. What targeted medical therapy has shown high efficacy for unresectable cases of this tumor?

. Imatinib
. Denosumab
. Methotrexate
. Rituximab
. Doxorubicin

Correct Answer & Explanation

. Denosumab

Explanation

The patient has a Giant Cell Tumor (GCT) of bone. The neoplastic mononuclear stromal cells overexpress RANKL, which recruits osteoclast-like giant cells. Denosumab, a monoclonal antibody against RANKL, is an effective targeted therapy to halt bone destruction.

Question 3559

Topic: Biology, Genetics & Bone Healing

A 14-year-old male sustains a subtrochanteric femur fracture. Radiographs show diffusely dense, 'chalk-like' bones with loss of the medullary canal. He has a history of multiple cranial nerve palsies. A defect in which of the following mechanisms is most likely responsible?

. Type I collagen synthesis
. Osteoclastic carbonic anhydrase II
. Fibroblast growth factor receptor 3
. Osteoblast differentiation
. Matrix metalloproteinase activity

Correct Answer & Explanation

. Osteoclastic carbonic anhydrase II

Explanation

Osteopetrosis is caused by defective osteoclast function, commonly due to a mutation in carbonic anhydrase II or TCIRG1. This leads to dense but brittle bones and narrowed neural foramina causing cranial nerve palsies.

Question 3560

Topic: Biology, Genetics & Bone Healing

Which of the following bone graft materials possesses osteoconductive, osteoinductive, and osteogenic properties?

. Demineralized bone matrix (DBM)
. Cancellous allograft
. Recombinant human bone morphogenetic protein-2 (rhBMP-2)
. Iliac crest autograft
. Calcium phosphate ceramics

Correct Answer & Explanation

. Iliac crest autograft

Explanation

Autograft (like iliac crest) is the only graft material that possesses all three properties: osteoconduction (scaffold), osteoinduction (growth factors like BMPs), and osteogenesis (live osteoblasts and progenitor cells).

Test Yourself

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

On this Page