1. General Principles & Basic Science MCQs

A patient diagnosed with Cartilage-Hair Hypoplasia (McKusick type metaphyseal chondrodysplasia) is at a significantly increased risk for which of the following systemic complications?

A 4-year-old boy presents with short stature and metaphyseal flaring on radiographs. His medical history is significant for recurrent bacterial infections and steatorrhea since infancy. A complete blood count reveals severe neutropenia. What is the most likely diagnosis?

A 4-year-old boy presents with short stature, metaphyseal flaring, and a history of recurrent bacterial infections. Laboratory tests reveal chronic neutropenia. He also has a history of steatorrhea and failure to thrive. What is the most likely diagnosis?

A 4-year-old child presents with bowing of the legs and a waddling gait. Radiographs show widening and cupping of the metaphyses, strongly resembling rickets. However, laboratory investigations reveal normal serum calcium, phosphorus, alkaline phosphatase, and vitamin D levels. What is the most likely diagnosis?

A 4-year-old boy presents with short stature, metaphyseal dysplasia, neutropenia, and a history of steatorrhea. Which of the following is the most likely diagnosis?

A 3-year-old boy presents with disproportionate short stature, fine sparse hair, and a history of recurrent severe pulmonary infections. Radiographs demonstrate metaphyseal widening and irregularity. Which of the following systemic manifestations is most closely associated with this condition?

A 2-year-old is evaluated for short stature and prominent metaphyseal flaring. The patient also has a history of steatorrhea and failure to thrive. Complete blood count shows severe neutropenia. Which of the following genes is most likely mutated in this patient?

An infant with severe micromelic dwarfism and prominent eyes is found to have widespread irregular, cupped metaphyses on radiographs. Laboratory studies reveal profound hypercalcemia and hypophosphatemia, yet parathyroid hormone levels are undetectable. The defective receptor in this condition physiologically binds to which of the following ligands?

A 3-year-old girl is diagnosed with nutritional rickets due to bowed legs and cupped, widened metaphyses on radiographs. However, her condition does not improve despite 6 months of high-dose vitamin D therapy. Labs show perfectly normal calcium, phosphorus, alkaline phosphatase, and 25-OH vitamin D levels. What is the most likely diagnosis?

A neonate is diagnosed with Jansen metaphyseal chondrodysplasia. Laboratory studies reveal severe hypercalcemia and hypophosphatemia. The genetic mutation associated with this disorder leads to which of the following mechanisms?

A 5-year-old girl is referred for bilateral bowed legs and a waddling gait. Radiographs show widened, irregular metaphyses and coxa vara. Serum calcium, phosphorus, alkaline phosphatase, and 25(OH) vitamin D levels are strictly within normal limits. Based on the most likely diagnosis, how should her condition be initially managed?

A 10-year-old boy presents with progressive facial paralysis and hearing loss. Radiographs show mild metaphyseal flaring of the long bones and severe hyperostosis of the cranial vault and skull base. A mutation in the ANKH gene is identified. The primary mechanism of this disease involves defective:

A 7-year-old boy is diagnosed with pseudoachondroplasia after presenting with short-limbed dwarfism, a waddling gait, and joint laxity. His facial features are entirely normal. Radiographs show small, irregular epiphyses and widened metaphyses. The pathophysiology of this disease involves the intracellular accumulation of an abnormal protein within the rough endoplasmic reticulum. Which gene is mutated?

A 3-year-old boy presents with profound short stature, micrognathia, and hypercalcemia. Radiographs display wide, irregular, and markedly cupped metaphyses. Laboratory evaluation reveals hypophosphatemia and undetectable levels of endogenous parathyroid hormone (PTH). What is the exact pathophysiologic mechanism for his hypercalcemia?

A 4-year-old girl is diagnosed with a metaphyseal chondrodysplasia. She also suffers from chronic diarrhea, steatorrhea, and recurrent bacterial infections. Complete blood count shows absolute neutropenia. A mutation affecting which of the following cellular processes is most likely responsible?

A rare, autosomal recessive form of metaphyseal chondrodysplasia presents with severe genu varum and metaphyseal irregularities indistinguishable from the Schmid type on plain radiographs. Which of the following describes this specific condition?

A 38-year-old woman with a known history of CREST syndrome presents to the orthopedic clinic with exquisitely painful, pale fingertips triggered by cold weather. Which of the following is the most appropriate first-line pharmacologic therapy to manage the vasospastic component of her condition?

A 4-year-old boy presents with a painful, enlarging scalp mass. Imaging reveals a solitary lytic skull lesion with a "beveled edge" appearance. If an electron microscopic analysis of the lesion tissue were performed, what pathognomonic ultrastructural finding would be expected?

A 52-year-old patient with limited cutaneous systemic sclerosis presents with firm, painful, palpable subcutaneous nodules over the extensor surfaces of the forearms and proximal interphalangeal joints.

What is the primary chemical composition of these particular deposits?

In the management of a staphylococcal periprosthetic joint infection treated with DAIR, rifampin is frequently added to the oral antibiotic regimen after initial intravenous therapy. What is the mechanism of action of rifampin that makes it critical for biofilm-associated infections?