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4. Pediatrics MCQs

Practice Set 328 of 334

This practice set contains high-yield board review questions covering key concepts in 4. Pediatrics. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 6541

Topic: 4. Pediatrics

A 10-year-old boy presents with bilateral knee and hip pain, waddling gait, and mild short stature. Radiographs demonstrate delayed ossification and irregularity of multiple epiphyses, but the spine appears normal. Which gene mutation is commonly associated with the dominant form of this disease?

. COL2A1
. FGFR3
. COMP
. CBFA1
. SOX9

Correct Answer & Explanation

. COMP

Explanation

Multiple Epiphyseal Dysplasia (MED) primarily affects the epiphyses, sparing the spine (unlike spondyloepiphyseal dysplasia). The most common autosomal dominant form is caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene.

Question 6542

Topic: 4. Pediatrics

A 4-year-old child presents with disproportionate short stature, joint laxity, and normal facial features. Radiographs show delayed epiphyseal ossification and platyspondyly with anterior beaking. Which feature best distinguishes this condition from classical achondroplasia?

. Rhizomelic shortening of the limbs
. Normal craniofacial appearance at birth
. Autosomal dominant inheritance pattern
. Presence of genu varum
. Mutation in the FGFR3 gene

Correct Answer & Explanation

. Normal craniofacial appearance at birth

Explanation

Pseudoachondroplasia presents with a normal birth length and a normal craniofacial appearance, distinguishing it from achondroplasia. It is caused by a mutation in the COMP gene, and growth deceleration typically becomes evident in early childhood.

Question 6543

Topic: 4. Pediatrics

A 4-year-old child presents with a history of recurrent long bone fractures with minimal trauma, blue sclerae, and dentinogenesis imperfecta. The underlying condition is most commonly caused by a mutation resulting in a defect of which of the following?

. Type II collagen synthesis (COL2A1)
. Type I collagen synthesis (COL1A1/COL1A2)
. Fibroblast growth factor receptor 3 (FGFR3)
. Cartilage oligomeric matrix protein (COMP)
. Sulfate transport (SLC26A2)

Correct Answer & Explanation

. Type I collagen synthesis (COL1A1/COL1A2)

Explanation

Osteogenesis Imperfecta (OI) is characterized by a quantitative or qualitative defect in Type I collagen due to COL1A1 or COL1A2 mutations. This results in severe bone fragility, blue sclerae, and dentinogenesis imperfecta.

Question 6544

Topic: 4. Pediatrics

An infant is born with micromelic dwarfism, bilateral 'hitchhiker' thumbs, severe rigid clubfeet, and swelling of the external ears (cauliflower ears). Which of the following genetic mutations is responsible for this condition?

. FGFR3
. COMP
. SLC26A2 (DTDST)
. COL2A1
. SHOX

Correct Answer & Explanation

. SLC26A2 (DTDST)

Explanation

Diastrophic dysplasia is characterized by hitchhiker thumbs, cauliflower ears, cleft palate, and severe clubfeet. It is an autosomal recessive disorder caused by a mutation in the SLC26A2 gene, which encodes a sulfate transporter.

Question 6545

Topic: 4. Pediatrics

A 6-year-old boy presents with bilateral knee pain and a waddling gait. Radiographs show delayed, irregular ossification of multiple epiphyses, notably the proximal femur and knees, with a 'double-layered' appearance of the patella on lateral views. Which gene is most frequently mutated in this dysplasia?

. COL1A1
. COMP
. FGFR3
. COL10A1
. EXT1

Correct Answer & Explanation

. COMP

Explanation

Multiple Epiphyseal Dysplasia (MED) is characterized by delayed, symmetrical ossification of the epiphyses and a pathognomonic double-layered patella. It is most commonly caused by mutations in the COMP (Cartilage Oligomeric Matrix Protein) gene.

Question 6546

Topic: 4. Pediatrics

An infant presents with bowing of the long bones, flail chest, and hypercalcemia. Radiographs show severe defective mineralization mimicking rickets. Laboratory analysis reveals a markedly low serum alkaline phosphatase and elevated urinary phosphoethanolamine. What is the diagnosis?

. Hypophosphatasia
. Nutritional rickets
. Osteogenesis imperfecta
. Achondroplasia
. Jansen metaphyseal chondrodysplasia

Correct Answer & Explanation

. Hypophosphatasia

Explanation

Hypophosphatasia mimics rickets clinically but is characterized by a deficiency in tissue-nonspecific alkaline phosphatase (ALPL mutation). This leads to low serum alkaline phosphatase and accumulation of substrates like urinary phosphoethanolamine and pyridoxal 5'-phosphate (PLP).

Question 6547

Topic: 4. Pediatrics

A 10-year-old girl is evaluated for a waddling gait and joint pain. Radiographs reveal a "double-layer" patella and irregular, fragmented epiphyses in the hips and knees. The spine is radiographically normal. Which of the following genes is most commonly mutated in this condition?

. COL2A1
. COMP
. FGFR3
. DTDST
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Multiple epiphyseal dysplasia (MED) most commonly results from a mutation in the COMP gene. The presence of a double-layer patella is pathognomonic on lateral radiographs, and unlike spondyloepiphyseal dysplasia, the spine is typically spared.

Question 6548

Topic: 4. Pediatrics

A 3-year-old boy has sustained a femoral fracture with minimal trauma. He has a history of severe early-onset bone fragility, blue sclerae, and dentinogenesis imperfecta. Genetic testing reveals a mutation causing substitution of glycine by bulkier amino acids. Which type of collagen is primarily defective?

. Type I
. Type II
. Type IX
. Type X
. Type XI

Correct Answer & Explanation

. Type I

Explanation

Osteogenesis imperfecta is primarily caused by mutations in the COL1A1 or COL1A2 genes, which encode Type I collagen. The substitution of glycine disrupts the formation of the triple helix structure, leading to fragile, brittle bones.

Question 6549

Topic: Pediatric Hip

A newborn is diagnosed with Spondyloepiphyseal Dysplasia Congenita (SEDC). Which of the following physical findings is expected, given the specific genetic mutation associated with this condition?

. Hitchhiker thumbs
. Short trunk with normal-length limbs
. Coxa vara and myopia
. Absent clavicles
. Polydactyly

Correct Answer & Explanation

. Coxa vara and myopia

Explanation

SEDC is caused by a COL2A1 mutation affecting Type II collagen, which is abundant in articular cartilage and the vitreous humor of the eye. Patients characteristically present with a short trunk, severe coxa vara, cleft palate, and ophthalmologic issues like myopia and retinal detachment.

Question 6550

Topic: 4. Pediatrics

A 4-year-old child is being treated for Lyme arthritis of the right knee with a significant effusion. The patient has completed a 28-day course of oral doxycycline but remains symptomatic with severe swelling. What is the next most appropriate step in management?

. Arthroscopic synovectomy
. Repeat a 28-day course of oral doxycycline or amoxicillin
. A 28-day course of intravenous ceftriaxone
. Intra-articular corticosteroid injection
. Serial aspirations without antibiotics

Correct Answer & Explanation

. A 28-day course of intravenous ceftriaxone

Explanation

If Lyme arthritis persists after an initial 28-day course of oral antibiotics, the recommended next step is a 28-day course of intravenous antibiotics (e.g., ceftriaxone). Arthroscopic synovectomy is reserved for refractory cases after multiple courses of appropriate antibiotics.

Question 6551

Topic: 4. Pediatrics

A 6-year-old girl presents with disproportionate short stature, normal facial features, and a waddling gait. Radiographs demonstrate delayed ossification of the epiphyses, metaphyseal flaring, and anterior beaking of the central vertebral bodies. A mutation in the gene encoding which of the following proteins is most likely responsible?

. Type X collagen
. Cartilage oligomeric matrix protein (COMP)
. Fibroblast growth factor receptor 3 (FGFR3)
. Type I collagen
. Core binding factor alpha 1 (CBFA1)

Correct Answer & Explanation

. Cartilage oligomeric matrix protein (COMP)

Explanation

Pseudoachondroplasia is characterized by disproportionate short stature with normal facies and is caused by mutations in the COMP gene. The presence of vertebral anomalies (anterior beaking) differentiates it from Multiple Epiphyseal Dysplasia, though both can involve COMP mutations.

Question 6552

Topic: 4. Pediatrics
A 10-month-old infant is evaluated for a limp and limb length discrepancy. History is notable for a prolonged NICU stay for prematurity and sepsis at birth. Current radiographs of the pelvis show a completely absent right proximal femoral epiphysis and neck with superior displacement of the femoral shaft. What is the most likely diagnosis?
. Developmental dysplasia of the hip
. Proximal focal femoral deficiency
. Tom Smith arthritis
. Slipped capital femoral epiphysis
. Legg-Calvé-Perthes disease

Correct Answer & Explanation

. Tom Smith arthritis

Explanation

Tom Smith arthritis refers to the complete destruction of the proximal femur and hip joint secondary to unrecognized or severe neonatal septic arthritis. The cartilaginous femoral head in a neonate is rapidly destroyed by proteolytic enzymes released during the infection.

Question 6553

Topic: 4. Pediatrics

A 22-year-old asymptomatic male undergoes knee radiographs following mild trauma, revealing an 'Erlenmeyer flask' deformity of the distal femurs and proximal tibias without marked cortical thickening.

What is the most likely genetic defect associated with this condition?

. Mutation in the CBFA1/RUNX2 gene
. Mutation in the FGFR3 gene
. Mutation in the COMP gene
. Mutation in the SFRP4 gene
. Mutation in the COL1A1 gene

Correct Answer & Explanation

. Mutation in the SFRP4 gene

Explanation

The radiograph demonstrates severe undertubulation (Erlenmeyer flask deformity) characteristic of Pyle disease (metaphyseal dysplasia). This rare autosomal recessive condition is caused by loss-of-function mutations in the SFRP4 gene.

Question 6554

Topic: 4. Pediatrics

A 4-year-old child presents with painful soft tissue swellings on her back and a congenital malformation of her great toes. Which of the following gene mutations is most likely responsible for her condition?

. GNAS1
. EXT1
. ACVR1
. FGFR3
. SOX9

Correct Answer & Explanation

. ACVR1

Explanation

The child has Fibrodysplasia Ossificans Progressiva (FOP), characterized by congenital short great toes and progressive, disabling heterotopic ossification. It is caused by an activating mutation in the ACVR1 gene, a BMP type I receptor.

Question 6555

Topic: 4. Pediatrics

A 10-year-old child presents with bilateral knee and hip pain after activity. Radiographs reveal delayed, fragmented, and irregular ossification centers of the femoral heads and knees, but the spine is radiographically normal. A defect in which of the following proteins is most commonly implicated?

. Cartilage oligomeric matrix protein (COMP)
. Fibroblast growth factor receptor 3 (FGFR3)
. Type I collagen
. Bone morphogenetic protein 4 (BMP4)
. Type X collagen

Correct Answer & Explanation

. Cartilage oligomeric matrix protein (COMP)

Explanation

Multiple epiphyseal dysplasia (MED) typically presents with irregular ossification of the epiphyses and a normal spine, differentiating it from spondyloepiphyseal dysplasia. The most common genetic mutation involves the COMP gene.

Question 6556

Topic: 4. Pediatrics

A newborn is noted to have short limbs, rigid clubfeet, 'hitchhiker' thumbs, and cystic swelling of the external ears. Radiographs reveal short, thick tubular bones. What is the underlying pathogenesis of this condition?

. Defective sulfate transport leading to undersulfated proteoglycans
. Abnormal type X collagen synthesis in the hypertrophic zone
. Overactivation of the FGFR3 pathway
. Defective osteoclast function and absence of ruffled borders
. Impaired mineralization of osteoid secondary to ALPL mutation

Correct Answer & Explanation

. Defective sulfate transport leading to undersulfated proteoglycans

Explanation

Diastrophic dysplasia is an autosomal recessive disorder caused by a mutation in the SLC26A2 (DTDST) gene. This defect in sulfate transport leads to undersulfated cartilage proteoglycans and impaired cartilage matrix formation.

Question 6557

Topic: 4. Pediatrics

A 15-year-old presents for evaluation of genu valgum. Radiographs demonstrate marked symmetric widening of the distal femoral and proximal tibial metaphyses with cortical thinning, giving an "Erlenmeyer flask" deformity.

The patient is otherwise asymptomatic with normal intelligence. Which genetic mutation is most commonly associated with this condition?

. COMP
. FGFR3
. SFRP4
. CBFA1
. COL1A1

Correct Answer & Explanation

. SFRP4

Explanation

Pyle disease (metaphyseal dysplasia) features dramatic "Erlenmeyer flask" metaphyseal widening and is caused by loss-of-function mutations in the SFRP4 gene. Unlike osteopetrosis, bone density is typically normal or decreased.

Question 6558

Topic: 4. Pediatrics

A newborn presents with micromelic dwarfism, cleft palate, "hitchhiker" thumbs, and bilateral clubfeet. Radiographs reveal flattened, irregular cervical vertebrae. Which gene mutation is responsible for this condition?

. FGFR3
. COMP
. DTDST (SLC26A2)
. COL2A1
. SOX9

Correct Answer & Explanation

. DTDST (SLC26A2)

Explanation

Diastrophic dysplasia is characterized by hitchhiker thumbs, cauliflower ears, cleft palate, and clubfeet. It is an autosomal recessive disorder caused by mutations in the DTDST (SLC26A2) gene, which encodes a sulfate transporter.

Question 6559

Topic: 4. Pediatrics

A 6-year-old child presents with waddling gait and joint pain. Radiographs show delayed, irregular ossification of the capital femoral epiphyses bilaterally, but normal spine radiographs. Which gene is most commonly mutated in the autosomal dominant form of this disorder?

. COMP
. COL1A1
. FGFR3
. DTDST
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Multiple Epiphyseal Dysplasia (MED) typically spares the spine (unlike Spondyloepiphyseal Dysplasia) and features irregular, fragmented epiphyses. The most common mutation is in the COMP (Cartilage Oligomeric Matrix Protein) gene.

Question 6560

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limbed dwarfism. Which of the following best describes the genetic pathophysiology of this condition?

. Gain-of-function mutation in FGFR3 inhibiting chondrocyte proliferation.
. Loss-of-function mutation in FGFR3 stimulating chondrocyte hypertrophy.
. Mutation in COL1A1 leading to defective type I collagen synthesis.
. Mutation in COMP (Cartilage Oligomeric Matrix Protein).
. Defect in the cbfa1/RUNX2 transcription factor.

Correct Answer & Explanation

. Gain-of-function mutation in FGFR3 inhibiting chondrocyte proliferation.

Explanation

Achondroplasia is caused by an autosomal dominant, gain-of-function mutation in the FGFR3 gene. This constitutively active receptor abnormally inhibits chondrocyte proliferation in the proliferative zone of the physis, restricting endochondral bone growth.

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