1. General Principles & Basic Science MCQs

A 4-year-old girl presents with progressive genu varum. Laboratory studies show normal serum calcium, normal PTH, elevated alkaline phosphatase, and low serum phosphate. The defective gene in this condition typically leads to excessive production of which of the following?

A newborn presents with micromelic shortening of the limbs, severe clubfeet, "hitchhiker" thumbs, and cystic swelling of the pinnae. Genetic testing would most likely reveal a mutation affecting which of the following processes?

A 14-year-old boy with chronic kidney disease presents with bilateral hip pain. Radiographs reveal bilateral slipped capital femoral epiphyses. His serum parathyroid hormone (PTH) is markedly elevated. Which primary physiological derangement initiated this cascade?

A 7-year-old boy presents with abnormal mobility of his shoulders, allowing him to appose them anteriorly in the midline. Radiographs reveal hypoplastic clavicles and wide cranial sutures.

Which of the following best describes the underlying pathogenesis of this condition?

A 5-year-old boy presents with progressive bowing of his lower extremities and a waddling gait. Laboratory results show normal serum calcium, markedly low serum phosphate, and elevated alkaline phosphatase. Genetic testing reveals a mutation in the PHEX gene. Which of the following is the primary mechanism leading to his bone disease?

A 10-year-old child presents with a history of recurrent fractures, severe anemia, and hepatosplenomegaly. Radiographs show a 'bone-within-a-bone' appearance and generalized extreme sclerosis. The primary cellular defect in this condition involves a failure to form which of the following structures?

A 55-year-old patient with end-stage renal disease presents with diffuse bone pain and proximal muscle weakness. Laboratory workup reveals elevated BUN/Creatinine. Which of the following best describes the expected serum calcium, phosphate, and intact parathyroid hormone (PTH) levels in untreated renal osteodystrophy?

A 6-month-old infant presents with failure to thrive, hypotonia, and bowing of the long bones. Radiographs demonstrate wide, irregular physes resembling rickets. Laboratory studies reveal hypercalcemia, hypercalciuria, and markedly decreased serum alkaline phosphatase. Which substance would likely be elevated in the patient's urine?

A 65-year-old woman is prescribed teriparatide for severe osteoporosis. Which of the following patient history elements represents an absolute contraindication to the use of this medication?

An 8-year-old boy from a low-income background presents with bleeding gums, petechiae, and progressive leg pain causing him to refuse to walk. Radiographs show a dense zone of provisional calcification and a ring-shaped radiopacity around the epiphyses. The pathogenesis of this condition involves a failure of which step in collagen synthesis?

A 50-year-old woman presents with bone pain and a pathological fracture of the proximal humerus. Radiographs show multiple lytic bone lesions. Laboratory evaluation reveals serum calcium of 11.5 mg/dL (high), phosphate of 2.1 mg/dL (low), and markedly elevated PTH. Biopsy of a lytic lesion would most likely show which of the following?

A patient with suspected Cleidocranial Dysplasia is undergoing dental and orthopedic evaluation.

In addition to clavicular hypoplasia, what is the most common dental manifestation associated with this RUNX2 mutation?

Which of the following phases of Paget's disease is characterized primarily by prominent, disorganized osteoblastic activity leading to woven bone formation, often manifesting radiographically as cortical thickening and bone enlargement?

A 10-year-old boy presents with unusually prominent forehead, delayed tooth eruption, and the ability to approximate his shoulders anteriorly. Radiographs demonstrate the findings below. What is the affected gene in this disorder?

A 5-year-old child presents with bowing of the legs and short stature. Laboratory evaluation reveals normal serum calcium, decreased serum phosphate, normal PTH, and elevated alkaline phosphatase. Which of the following is the most appropriate medical treatment?

An 65-year-old man presents with increasing hat size, hearing loss, and a bowing deformity of his right tibia. Which of the following best describes the initial cellular abnormality in the pathogenesis of his condition?

An infant presents with recurrent fractures, anemia, and cranial nerve palsies. Radiographs show diffuse, uniformly dense bones with a "bone-within-a-bone" appearance. A defect in which of the following mechanisms is responsible for this condition?

A 55-year-old woman with end-stage renal disease on hemodialysis presents with diffuse bone pain. Lab findings reveal high PTH, low serum calcium, and high serum phosphate. Which enzyme's decreased activity in her kidneys is directly responsible for her low calcium?

A 4-year-old boy with a severely restricted diet of only processed foods presents with swollen, bleeding gums, perifollicular hemorrhages, and a refusal to walk due to leg pain. Radiographs reveal a dense zone of provisional calcification and a radiolucent line just proximal to the physis. Which biochemical process is defective?

An infant presents with generalized osteosclerosis, hepatosplenomegaly, and pancytopenia. Bone biopsy reveals numerous osteoclasts that completely lack a ruffled border. This form of malignant infantile osteopetrosis is most commonly caused by a mutation affecting which of the following?