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Biology, Genetics & Bone Healing MCQs

Practice Set 194 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 3861

Topic: Biology, Genetics & Bone Healing

Which pharmacological agent has shown efficacy in reducing bone pain and potentially decreasing the rate of abnormal bone turnover in patients with polyostotic fibrous dysplasia?

. Teriparatide
. Intravenous bisphosphonates
. Nonsteroidal anti-inflammatory drugs (NSAIDs) alone
. Methotrexate
. Denosumab

Correct Answer & Explanation

. Intravenous bisphosphonates

Explanation

Intravenous bisphosphonates (such as pamidronate or zoledronic acid) are widely utilized in symptomatic polyostotic fibrous dysplasia. They effectively reduce bone pain and inhibit osteoclastic resorption at the dysplastic sites.

Question 3862

Topic: Biology, Genetics & Bone Healing

A 72-year-old male presents with severe back pain. Radiographs show multiple dense, blastic lesions in the lumbar spine and pelvis.

Which of the following combinations of tumor marker and primary cellular mechanism is characteristic of this malignancy?

. Elevated CEA; Osteoclast stimulation via PTHrP
. Elevated PSA; Direct osteoblast stimulation via endothelin-1
. Elevated Thyroglobulin; Osteoclast inhibition
. Elevated CA-125; RANKL overexpression
. Elevated Bence-Jones protein; Direct osteoblast apoptosis

Correct Answer & Explanation

. Elevated PSA; Direct osteoblast stimulation via endothelin-1

Explanation

Prostate cancer classically produces osteoblastic bone metastases. Prostate cancer cells secrete factors such as endothelin-1 (ET-1), which directly stimulate osteoblast proliferation and bone formation, leading to blastic lesions. PSA is the classic tumor marker.

Question 3863

Topic: Biology, Genetics & Bone Healing

Which of the following best describes the underlying molecular pathophysiology of fibrous dysplasia?

. Mutation in the EXT1 gene causing defective heparan sulfate polymerization
. Somatic activating mutation of the GNAS gene causing elevated intracellular cAMP
. Translocation t(11;22) resulting in the EWS-FLI1 fusion protein
. Mutation in the FGFR3 gene causing impaired endochondral ossification
. Overexpression of the RANKL protein leading to excessive osteoclast activity

Correct Answer & Explanation

. Somatic activating mutation of the GNAS gene causing elevated intracellular cAMP

Explanation

Fibrous dysplasia is caused by a post-zygotic somatic activating mutation in the GNAS gene, which encodes the alpha subunit of the Gs stimulatory protein. This leads to increased intracellular cAMP, causing abnormal proliferation and differentiation of osteoblasts.

Question 3864

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with a history of breast cancer presents with severe thoracic back pain. Imaging demonstrates a blastic and lytic lesion at T8 with posterior element involvement but no spinal cord compression. In addition to localized radiation, what pharmacological agent is indicated to reduce skeletal-related events?

. Teriparatide
. Denosumab or bisphosphonates
. Raloxifene
. Calcitonin
. Methotrexate

Correct Answer & Explanation

. Denosumab or bisphosphonates

Explanation

In patients with bone metastases from breast cancer, antiresorptive agents such as bisphosphonates (e.g., zoledronic acid) or RANKL inhibitors (e.g., denosumab) are indicated to reduce the risk of skeletal-related events. Teriparatide is strictly contraindicated in patients with skeletal malignancies.

Question 3865

Topic: Biology, Genetics & Bone Healing

The pathogenesis of Charcot neuroarthropathy is multifactorial, involving both neurotraumatic and neurovascular pathways. Which of the following best describes the neurovascular theory (French theory) of this disease?

. Loss of protective sensation leads to repetitive microtrauma and joint destruction.
. Autonomic neuropathy causes hyperemic bone resorption and weakening via increased arteriovenous shunting.
. Motor neuropathy causes muscle imbalance resulting in altered plantar pressures.
. Peripheral nerve entrapment leads to ischemic necrosis of the midfoot bones.
. Hyperglycemia directly inhibits osteoclast apoptosis, leading to severe bone loss.

Correct Answer & Explanation

. Autonomic neuropathy causes hyperemic bone resorption and weakening via increased arteriovenous shunting.

Explanation

The neurovascular (French) theory postulates that autonomic neuropathy abolishes sympathetic tone, causing arteriovenous shunting and local hyperemia. This increased blood flow stimulates osteoclastic bone resorption, predisposing the structurally weakened bone to fracture.

Question 3866

Topic: Biology, Genetics & Bone Healing

A 72-year-old man presents with severe back pain. Radiographs reveal multiple osteoblastic lesions in the lumbar spine and pelvis. Laboratory studies show elevated alkaline phosphatase. Which of the following pathophysiologic mechanisms best explains the osteoblastic nature of these specific metastatic bone lesions?

. Tumor-secreted parathyroid hormone-related peptide (PTHrP)
. Production of endothelin-1 (ET-1) by tumor cells
. Inhibition of osteoprotegerin (OPG) by the tumor
. Direct tumor cell synthesis of woven bone matrix
. Secretion of RANK-ligand by tumor cells

Correct Answer & Explanation

. Production of endothelin-1 (ET-1) by tumor cells

Explanation

Prostate cancer metastases are classically osteoblastic. This occurs because prostate carcinoma cells secrete factors such as endothelin-1 (ET-1) and bone morphogenetic proteins (BMPs), which directly stimulate osteoblast proliferation and bone formation.

Question 3867

Topic: Biology, Genetics & Bone Healing

A biopsy of a ground-glass rib lesion in a 14-year-old boy reveals fibrous stroma with irregular, woven bone trabeculae lacking osteoblastic rimming. The pathogenesis of this disease is linked to a somatic mutation leading to the substitution of arginine by histidine or cysteine. Which signaling pathway is directly upregulated by this mutation?

. Wnt/beta-catenin pathway
. RANK/RANKL pathway
. cAMP/Protein Kinase A pathway
. MAPK/ERK pathway
. JAK/STAT pathway

Correct Answer & Explanation

. cAMP/Protein Kinase A pathway

Explanation

Fibrous dysplasia is caused by a somatic activating mutation in the GNAS gene, which encodes the alpha subunit of the Gs stimulatory protein. This mutation leads to constitutive activation of adenylyl cyclase, drastically increasing intracellular cAMP levels and downstream Protein Kinase A activity.

Question 3868

Topic: Biology, Genetics & Bone Healing

A 5-year-old boy presents with progressively worsening varus deformity of both knees. Lab work shows low serum phosphate, normal serum calcium, and elevated alkaline phosphatase. Genetic testing reveals a PHEX gene mutation. Which of the following laboratory values is also expected?

. Decreased FGF-23
. Elevated serum PTH
. Normal urinary phosphate excretion
. Elevated FGF-23
. Decreased 1,25-dihydroxyvitamin D

Correct Answer & Explanation

. Elevated FGF-23

Explanation

X-linked hypophosphatemic rickets (PHEX mutation) leads to an overproduction of FGF-23. Elevated FGF-23 causes renal phosphate wasting and inhibits 1-alpha-hydroxylase, preventing the activation of vitamin D.

Question 3869

Topic: Biology, Genetics & Bone Healing

A 10-year-old boy presents with delayed eruption of secondary teeth and the ability to approximate his shoulders in the midline anteriorly. Radiographs demonstrate absent clavicles and delayed closure of cranial sutures. What bone formation process is primarily impaired in this condition?

. Endochondral ossification
. Intramembranous ossification
. Osteoclastic resorption
. Osteoblastic bone remodeling
. Chondrocyte hypertrophy

Correct Answer & Explanation

. Intramembranous ossification

Explanation

Cleidocranial dysplasia is caused by a mutation in the RUNX2 (CBFA1) gene, which primarily affects intramembranous ossification. This leads to hypoplastic or absent clavicles, open fontanelles, and dental anomalies.

Question 3870

Topic: Biology, Genetics & Bone Healing

A newborn is evaluated for severe micromelic dwarfism, bilateral rigid clubfeet, "hitchhiker" thumbs, and cystic swelling of the pinnae. The genetic mutation responsible for this condition directly affects which of the following cellular processes?

. Sulfate transport
. Type I collagen synthesis
. Chondrocyte proliferation in the resting zone
. Osteoclast ruffled border formation
. Fibroblast growth factor signaling

Correct Answer & Explanation

. Sulfate transport

Explanation

Diastrophic dysplasia is caused by a mutation in the SLC26A2 gene, which encodes a sulfate transporter (DTDST). This results in undersulfated proteoglycans in the cartilage matrix, leading to the classic clinical triad of hitchhiker thumbs, cauliflower ears, and clubfeet.

Question 3871

Topic: Biology, Genetics & Bone Healing

A 12-year-old girl presents with retained deciduous teeth and an ability to bring her shoulders together in the midline anteriorly. Radiographs demonstrate absent clavicles and delayed pubic symphysis ossification. The defective gene in this condition is an essential transcription factor for which of the following?

. Osteoclast differentiation
. Osteoblast differentiation
. Chondrocyte hypertrophy
. Collagen cross-linking
. Mineralization of osteoid

Correct Answer & Explanation

. Osteoblast differentiation

Explanation

Cleidocranial dysplasia results from a mutation in RUNX2 (CBFA1), a master transcription factor required for osteoblast differentiation. Patients classically present with absent clavicles, delayed cranial suture closure, and dental anomalies.

Question 3872

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy has progressive varus bowing of his legs. Lab testing shows low serum phosphate, normal calcium, normal PTH, normal vitamin D, and elevated FGF23 levels. What monoclonal antibody therapy directly targets the underlying pathophysiology of this condition?

. Denosumab
. Burosumab
. Romosozumab
. Infliximab
. Secukinumab

Correct Answer & Explanation

. Burosumab

Explanation

Burosumab is a monoclonal antibody that binds to and inhibits FGF23, directly addressing the underlying pathophysiology of X-linked hypophosphatemic rickets (XLH). This inhibition restores renal phosphate reabsorption and improves serum phosphate levels.

Question 3873

Topic: Biology, Genetics & Bone Healing

A 14-month-old exclusively breastfed infant develops widening of the wrists and bowing of the distal femurs. Laboratory evaluation reveals significantly elevated parathyroid hormone (PTH) and alkaline phosphatase. Which of the following serum calcium and phosphate profiles is most consistent with this diagnosis?

. Normal to low calcium, low phosphate
. High calcium, low phosphate
. Normal calcium, high phosphate
. High calcium, high phosphate
. Low calcium, high phosphate

Correct Answer & Explanation

. Normal to low calcium, low phosphate

Explanation

Nutritional Vitamin D deficiency rickets initially presents with low to normal serum calcium and persistently low phosphate due to secondary hyperparathyroidism. The elevated PTH promotes aggressive renal phosphate wasting.

Question 3874

Topic: Biology, Genetics & Bone Healing

A 4-year-old boy presents with severe bowing of the lower extremities. Labs show normal calcium, low phosphorus, and elevated alkaline phosphatase. Genetic testing reveals a PHEX gene mutation. Which of the following is the primary mechanism of this disease?

. Decreased renal production of 1,25-OH vitamin D
. Increased renal phosphate excretion due to elevated FGF-23
. Impaired osteoclast function due to TCIRG1 mutation
. Defective type I collagen synthesis
. Autoimmune destruction of the parathyroid gland

Correct Answer & Explanation

. Increased renal phosphate excretion due to elevated FGF-23

Explanation

PHEX mutations lead to decreased degradation of FGF-23 in X-linked hypophosphatemic rickets. Elevated FGF-23 causes increased renal phosphate excretion and inhibits 1-alpha-hydroxylase, leading to severe hypophosphatemia and rickets.

Question 3875

Topic: Biology, Genetics & Bone Healing

A 3-year-old girl is diagnosed with oligoarticular Juvenile Idiopathic Arthritis (JIA) affecting her right knee. She has a positive ANA and negative Rheumatoid Factor. What is the most critical screening protocol she must undergo?

. Annual echocardiograms to screen for pericarditis
. Routine slit-lamp examinations every 3-4 months to screen for asymptomatic uveitis
. Monthly liver function tests
. Annual DEXA scans to monitor for osteopenia
. Routine pulmonary function testing for interstitial lung disease

Correct Answer & Explanation

. Routine slit-lamp examinations every 3-4 months to screen for asymptomatic uveitis

Explanation

Young girls with ANA-positive oligoarticular JIA are at the highest risk for asymptomatic anterior uveitis. They require frequent slit-lamp examinations (every 3-4 months) by an ophthalmologist to prevent permanent vision loss.

Question 3876

Topic: Biology, Genetics & Bone Healing

A 7-year-old boy presents for orthopedic evaluation. He is remarkably able to bring his shoulders together anteriorly in the midline. Radiographs reveal absent clavicles and delayed closure of the cranial sutures. A mutation in which of the following transcription factors is responsible?

. SOX9
. RUNX2 (CBFA1)
. GLI3
. HOXD13
. PAX3

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is an autosomal dominant condition caused by mutations in the RUNX2 (CBFA1) gene, an essential transcription factor for osteoblast differentiation. It is characterized by absent or hypoplastic clavicles and delayed cranial suture closure.

Question 3877

Topic: Biology, Genetics & Bone Healing

A 24-month-old toddler presents with a waddling gait and bowing of the legs. Radiographs show widening and cupping of the distal femoral physes, as well as radiolucent bands perpendicular to the cortex in the medial femoral neck. Which of the following is the most likely diagnosis for the radiolucent bands?

. Stress fractures
. Looser zones (pseudofractures)
. Non-ossifying fibromas
. Harris growth arrest lines
. Enchondromas

Correct Answer & Explanation

. Looser zones (pseudofractures)

Explanation

Looser zones, or pseudofractures, are wide transverse radiolucencies traversing part of the bone, representing accumulations of unmineralized osteoid. They are a classic radiographic hallmark of osteomalacia and severe rickets.

Question 3878

Topic: Biology, Genetics & Bone Healing

A 3-year-old child with frequent fractures, blue sclerae, and dentinogenesis imperfecta is started on intravenous bisphosphonate therapy (pamidronate). What is the primary cellular mechanism of action of this medication in treating this disease?

. Stimulates osteoblast differentiation
. Inhibits osteoclast activity by inducing apoptosis
. Promotes type 1 collagen cross-linking
. Stimulates renal production of 1,25-OH vitamin D
. Neutralizes the mutant COL1A1 protein

Correct Answer & Explanation

. Inhibits osteoclast activity by inducing apoptosis

Explanation

Bisphosphonates are analogues of inorganic pyrophosphate that bind to hydroxyapatite and are ingested by osteoclasts. They inhibit osteoclastic bone resorption by disrupting the mevalonate pathway and inducing osteoclast apoptosis, thereby increasing bone mineral density in Osteogenesis Imperfecta.

Question 3879

Topic: Biology, Genetics & Bone Healing
A 3-year-old child presents with progressive varus bowing of the lower extremities. Laboratory studies reveal a normal serum calcium, significantly decreased serum phosphate, normal PTH, and elevated alkaline phosphatase. What is the primary pathophysiologic mechanism of this disease?
. Decreased intestinal calcium absorption
. Inability to convert 25-OH Vitamin D to 1,25-OH Vitamin D
. Mutations in the calcium-sensing receptor (CaSR)
. Deficiency in tissue nonspecific alkaline phosphatase (TNSALP)
. Decreased renal tubular reabsorption of phosphate due to excess FGF23

Correct Answer & Explanation

. Decreased renal tubular reabsorption of phosphate due to excess FGF23

Explanation

X-linked hypophosphatemic rickets is caused by a PHEX gene mutation that leads to excess FGF23 production. FGF23 decreases renal tubular reabsorption of phosphate, resulting in profound hypophosphatemia and secondary rickets.

Question 3880

Topic: Biology, Genetics & Bone Healing

A neonate is noted to have a large anterior fontanelle, delayed closure of cranial sutures, and unusual mobility of the shoulders allowing them to be opposed anteriorly. A mutation in which of the following transcription factors is responsible for this condition?

. SOX9
. RUNX2 (CBFA1)
. GLI3
. SHOX
. HOXD13

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

Cleidocranial dysplasia is caused by an autosomal dominant mutation in the RUNX2 (CBFA1) gene, which regulates osteoblast differentiation. This leads to defective intramembranous ossification, characterized by absent/hypoplastic clavicles and delayed fontanelle closure.

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