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Biology, Genetics & Bone Healing MCQs

Practice Set 195 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 3881

Topic: Biology, Genetics & Bone Healing

A 2-year-old child recently immigrated to the US presents with irritability, delayed walking, and widening of the wrists. Radiographs show cupping and fraying of the metaphyseal-physeal junctions. Which of the following laboratory profiles confirms the diagnosis of nutritional rickets?

. Decreased 25-OH Vitamin D, Increased PTH, Decreased Phosphate
. Normal 25-OH Vitamin D, Increased PTH, Increased Phosphate
. Normal 25-OH Vitamin D, Normal PTH, Decreased Phosphate
. Increased 1,25-OH Vitamin D, Decreased PTH, Normal Phosphate
. Decreased 25-OH Vitamin D, Decreased PTH, Decreased Calcium

Correct Answer & Explanation

. Decreased 25-OH Vitamin D, Increased PTH, Decreased Phosphate

Explanation

Nutritional rickets results from Vitamin D deficiency, leading to decreased calcium absorption. This triggers secondary hyperparathyroidism, which increases serum calcium toward normal but causes profound renal phosphate wasting.

Question 3882

Topic: Biology, Genetics & Bone Healing

A 45-year-old male with end-stage renal disease on hemodialysis presents with diffuse bone pain. Radiographs demonstrate 'rugger jersey' spine and osteopenia. What is the primary driving mechanism for his metabolic bone disease?

. Primary hyperparathyroidism due to an adenoma
. Hypophosphatemia inducing osteomalacia
. Hyperphosphatemia causing secondary hyperparathyroidism
. Excessive production of 1,25-OH Vitamin D
. Aluminum toxicity impairing osteoid mineralization

Correct Answer & Explanation

. Hyperphosphatemia causing secondary hyperparathyroidism

Explanation

In renal osteodystrophy, failing kidneys cannot excrete phosphate or adequately synthesize 1,25-dihydroxyvitamin D. The resulting hyperphosphatemia and hypocalcemia drive severe secondary hyperparathyroidism, leading to high-turnover bone disease.

Question 3883

Topic: Biology, Genetics & Bone Healing

A 4-year-old female is recently diagnosed with oligoarticular Juvenile Idiopathic Arthritis. Her laboratory workup is positive for Antinuclear Antibody (ANA). Which of the following represents the most critical screening protocol for this patient?

. Echocardiogram every 6 months to monitor for pericarditis
. Ophthalmology referral for slit-lamp examinations every 3 to 4 months
. Monthly complete blood counts to check for macrophage activation syndrome
. Annual DXA scans to monitor for systemic osteoporosis
. Routine pulmonary function tests to detect interstitial lung disease

Correct Answer & Explanation

. Ophthalmology referral for slit-lamp examinations every 3 to 4 months

Explanation

Young females with ANA-positive oligoarticular JIA carry the highest risk of developing asymptomatic anterior uveitis. Routine slit-lamp examinations every 3 to 4 months are critical to prevent permanent visual impairment or blindness.

Question 3884

Topic: Biology, Genetics & Bone Healing

A 5-year-old girl with severe bowing of the lower extremities is diagnosed with X-linked hypophosphatemic rickets (XLH). Which laboratory profile is most specific to the pathophysiology of her disease?

. Elevated PTH, low calcium
. Elevated FGF23, low phosphate
. Low 1,25-dihydroxyvitamin D, normal phosphate
. Low alkaline phosphatase, high calcium
. Normal FGF23, high PTH

Correct Answer & Explanation

. Elevated FGF23, low phosphate

Explanation

XLH is caused by a PHEX gene mutation that leads to excess production of FGF23. Elevated FGF23 causes profound renal phosphate wasting, resulting in hypophosphatemia with normal serum calcium and normal PTH levels.

Question 3885

Topic: Biology, Genetics & Bone Healing

A 1-year-old exclusively breastfed infant presents with bowing of the distal radius and widening of the physes. Which laboratory profile is most consistent with the early symptomatic stages of nutritional rickets?

. Normal Calcium, Normal Phosphate, Normal PTH, Low Alk Phos
. Low Calcium, Low Phosphate, Elevated PTH, Elevated Alk Phos
. High Calcium, Low Phosphate, Low PTH, Normal Alk Phos
. Normal Calcium, High Phosphate, High PTH, High Alk Phos
. Low Calcium, High Phosphate, Low PTH, Normal Alk Phos

Correct Answer & Explanation

. Low Calcium, Low Phosphate, Elevated PTH, Elevated Alk Phos

Explanation

Vitamin D deficiency rickets initially presents with decreased enteral calcium absorption, leading to hypocalcemia. This triggers secondary hyperparathyroidism (elevated PTH), which normalizes calcium slightly but causes renal phosphate wasting (hypophosphatemia) and elevates alkaline phosphatase.

Question 3886

Topic: Biology, Genetics & Bone Healing

A 12-year-old girl presents with excessive shoulder mobility, allowing her to touch her shoulders together anteriorly. Radiographs reveal aplastic clavicles. What other clinical finding is most characteristic of this genetic condition?

. Blue sclerae
. Supernumerary teeth
. Ligamentous laxity of the knees
. Short bowed femurs
. Cauliflower ears

Correct Answer & Explanation

. Supernumerary teeth

Explanation

Cleidocranial dysplasia is an autosomal dominant condition caused by a RUNX2 (CBFA1) mutation. It is classically associated with absent or hypoplastic clavicles, delayed skull suture closure, and supernumerary or delayed eruption of teeth.

Question 3887

Topic: Biology, Genetics & Bone Healing
A 6-month-old infant presents with bowing of the extremities and failure to thrive. Radiographs show severe osteopenia and widened, irregular physes resembling rickets. Labs reveal hypercalcemia and an exceptionally low serum alkaline phosphatase. What is the primary underlying defect?
. ALPL gene mutation
. PHEX gene mutation
. Vitamin D receptor mutation
. Deficient 1-alpha-hydroxylase
. FGFR3 mutation

Correct Answer & Explanation

. ALPL gene mutation

Explanation

Hypophosphatasia mimics rickets clinically but is caused by an ALPL gene mutation leading to deficient tissue-nonspecific alkaline phosphatase (TNSALP). This prevents the cleavage of inorganic pyrophosphate, a potent inhibitor of bone mineralization.

Question 3888

Topic: Biology, Genetics & Bone Healing

A 10-year-old boy presents with a femur fracture after a minor fall. Radiographs demonstrate a 'bone-within-a-bone' appearance and an absence of medullary canals. He also has a history of cranial nerve palsies. The pathogenesis involves failure of which cellular mechanism?

. Type 1 collagen synthesis
. Osteoblast proliferation
. Osteoclast ruffled border acidification
. Cartilage proteoglycan sulfation
. Chondrocyte hypertrophy

Correct Answer & Explanation

. Osteoclast ruffled border acidification

Explanation

Osteopetrosis (Albers-Schonberg disease) results from defective osteoclast function, commonly due to an inability to form a ruffled border or acidify the resorption pit (e.g., Carbonic Anhydrase II mutations). This leads to dense, brittle bones and cranial nerve entrapment from narrowed foramina.

Question 3889

Topic: Biology, Genetics & Bone Healing
A 2-year-old boy presents with bowing of the lower extremities and delayed walking. Laboratory studies demonstrate hypercalcemia, normal phosphorus, and markedly decreased serum alkaline phosphatase. Urine phosphoethanolamine is elevated. What is the primary biochemical defect?
. Tissue-nonspecific alkaline phosphatase (TNSALP) gene mutation
. PHEX gene mutation
. FGF-23 overproduction
. 1-alpha-hydroxylase deficiency
. Vitamin D receptor mutation

Correct Answer & Explanation

. Tissue-nonspecific alkaline phosphatase (TNSALP) gene mutation

Explanation

This clinical profile is pathognomonic for hypophosphatasia, an inborn error of metabolism caused by a mutation in the TNSALP gene. It leads to impaired skeletal mineralization resembling rickets, but uniquely presents with profoundly low alkaline phosphatase.

Question 3890

Topic: Biology, Genetics & Bone Healing

A 10-year-old girl is evaluated for delayed dental eruption and abnormal shoulder mobility. Examination shows she can bring her anterior shoulders together in the midline. Which of the following transcription factors is deficient in this condition?

. SOX9
. RUNX2 (CBFA1)
. Osterix
. TRAP
. NFATc1

Correct Answer & Explanation

. RUNX2 (CBFA1)

Explanation

The patient has cleidocranial dysplasia, characterized by absent or hypoplastic clavicles, delayed cranial suture closure, and dental abnormalities. It is caused by a mutation in the RUNX2 (CBFA1) gene, an essential transcription factor for osteoblast differentiation.

Question 3891

Topic: Biology, Genetics & Bone Healing

A 55-year-old patient with end-stage renal disease presents with severe bone pain and proximal muscle weakness. Radiographs of the spine demonstrate a rugger jersey appearance. Lab results show hypocalcemia, hyperphosphatemia, and markedly elevated PTH. Which of the following pathophysiologic mechanisms best explains these findings?

. Decreased renal excretion of calcium
. Impaired hepatic hydroxylation of Vitamin D
. Decreased renal 1-alpha-hydroxylase activity leading to decreased calcitriol
. Primary overproduction of parathyroid hormone
. Overproduction of calcitonin

Correct Answer & Explanation

. Decreased renal 1-alpha-hydroxylase activity leading to decreased calcitriol

Explanation

Renal osteodystrophy is driven by a failing kidney's inability to excrete phosphate and its lack of 1-alpha-hydroxylase activity. This results in low active Vitamin D (calcitriol), causing hypocalcemia and severe secondary hyperparathyroidism, leading to bone resorption and osteitis fibrosa cystica.

Question 3892

Topic: Biology, Genetics & Bone Healing

A 3-year-old girl presents with severe bowing of the legs, growth retardation, and total alopecia. Lab testing reveals hypocalcemia, hypophosphatemia, and markedly elevated levels of 1,25-dihydroxyvitamin D. What is the underlying pathophysiology?

. Deficiency of 25-hydroxylase
. Deficiency of 1-alpha-hydroxylase
. Defect in the vitamin D receptor
. Mutation in the PHEX gene
. Mutation in FGF23

Correct Answer & Explanation

. Defect in the vitamin D receptor

Explanation

Vitamin D dependent rickets Type II is characterized by end-organ resistance to active Vitamin D due to a mutation in the Vitamin D receptor. This leads to markedly elevated 1,25-dihydroxyvitamin D levels and is uniquely associated with total alopecia.

Question 3893

Topic: Biology, Genetics & Bone Healing

Which medication class is currently considered the most effective first-line medical therapy for managing severe bone pain associated with polyostotic fibrous dysplasia?

. Denosumab
. Bisphosphonates
. Teriparatide
. NSAIDs
. Methotrexate

Correct Answer & Explanation

. Bisphosphonates

Explanation

Intravenous bisphosphonates (such as pamidronate or zoledronic acid) are the mainstay of medical treatment for symptomatic fibrous dysplasia. They inhibit osteoclast activity, effectively reducing bone pain and potentially slowing lesion progression.

Question 3894

Topic: Biology, Genetics & Bone Healing

Under microscopic examination, the septations in a primary aneurysmal bone cyst typically contain which of the following cellular components?

. Atypical endothelial cells with frequent mitoses
. Fibroblasts, multinucleated giant cells, and reactive woven bone
. Atypical chondrocytes with double nuclei
. Malignant osteoblasts producing osteoid
. Lipid-laden foamy histiocytes

Correct Answer & Explanation

. Fibroblasts, multinucleated giant cells, and reactive woven bone

Explanation

The septa of an ABC lack an endothelial lining and are instead composed of fibroblasts, myofibroblasts, and multinucleated giant cells. Reactive woven bone is also frequently seen within these fibrous septations.

Question 3895

Topic: Biology, Genetics & Bone Healing

Histopathologic examination of a diaphyseal bone lesion shows irregular spicules of woven bone distributed within a bland fibrous stroma. A classic diagnostic feature of this pathology is the absence of which of the following?

. Osteoclasts
. Chondrocytes
. Osteoblastic rimming
. Fibroblasts
. Collagen fibers

Correct Answer & Explanation

. Osteoblastic rimming

Explanation

The classic histologic appearance of fibrous dysplasia is "Chinese character" trabeculae of woven bone emerging directly from a fibrous stroma without the normal osteoblastic rimming, distinguishing it from conditions like osteofibrous dysplasia.

Question 3896

Topic: Biology, Genetics & Bone Healing

A 22-year-old female with polyostotic fibrous dysplasia presents with new-onset, deep, aching bone pain in her affected femur, without evidence of acute fracture or deformity progression. Which pharmacological intervention has been shown to be most effective in alleviating this specific type of bone pain?

. Oral NSAIDs
. Intravenous bisphosphonates
. Subcutaneous denosumab
. Oral systemic corticosteroids
. Methotrexate

Correct Answer & Explanation

. Intravenous bisphosphonates

Explanation

Intravenous bisphosphonates (like pamidronate or zoledronic acid) are the mainstay of medical treatment for symptomatic fibrous dysplasia, effectively reducing bone pain and potentially decreasing the rate of localized osteolysis.

Question 3897

Topic: Biology, Genetics & Bone Healing

When performing surgical treatment on a standard, accessible aneurysmal bone cyst in the proximal tibia of a 15-year-old, the current standard of care to minimize local recurrence involves intralesional curettage followed by which critical intraoperative step?

. Immediate structural allografting without further margin treatment
. Use of a high-speed burr to extend the margin
. En bloc wide resection with endoprosthetic reconstruction
. Application of bone morphogenetic protein (BMP) alone
. Prophylactic radiation therapy to the cavity

Correct Answer & Explanation

. Use of a high-speed burr to extend the margin

Explanation

The standard of care for an accessible ABC is extended intralesional curettage. Extending the margin using a high-speed burr (and often chemical or thermal adjuvants like phenol or argon beam) significantly reduces the recurrence rate compared to curettage alone.

Question 3898

Topic: Biology, Genetics & Bone Healing

A 12-year-old boy presents with a limp. Radiographs show a proximal femur lesion with a ground-glass appearance and a varus deformity. Which of the following genetic abnormalities is most likely responsible?

. Translocation t(11;22)
. Mutation of the GNAS gene
. Translocation t(16;17)
. Mutation in the EXT1 gene
. RUNX2 gene mutation

Correct Answer & Explanation

. Mutation of the GNAS gene

Explanation

Fibrous dysplasia is caused by a somatic, activating mutation in the GNAS gene encoding the alpha subunit of the Gs stimulatory protein. This leads to increased intracellular cAMP and impaired osteoblast differentiation.

Question 3899

Topic: Biology, Genetics & Bone Healing

A 15-year-old male presents with back pain. Imaging shows an expansile, lytic lesion involving the posterior elements of L3. Biopsy reveals blood-filled cystic spaces lacking endothelial lining. Which of the following adjuvant therapies is most appropriate if the lesion is surgically inaccessible?

. Methotrexate
. Imatinib
. Denosumab
. Bisphosphonates
. Teriparatide

Correct Answer & Explanation

. Denosumab

Explanation

The histology describes an Aneurysmal Bone Cyst (ABC). In surgically inaccessible locations like the spine or sacrum, denosumab (a RANKL inhibitor) or selective arterial embolization can be used as effective treatments.

Question 3900

Topic: Biology, Genetics & Bone Healing

Fibrous dysplasia is driven by a somatic mutation in the GNAS gene. This mutation directly leads to the constitutive activation of which of the following cellular pathways?

. Wnt/beta-catenin signaling
. RANK/RANKL pathway
. Adenylate cyclase/cAMP pathway
. Tyrosine kinase/JAK-STAT pathway
. Hedgehog signaling

Correct Answer & Explanation

. Adenylate cyclase/cAMP pathway

Explanation

The GNAS mutation results in a constitutively active Gs-alpha protein. This leads to continuous activation of adenylate cyclase and an overproduction of intracellular cAMP, which disrupts normal osteoblast differentiation.

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