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4. Pediatrics MCQs

Practice Set 220 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 4381

Topic: 4. Pediatrics

A newborn is evaluated for multiple skeletal deformities including severe short stature, "hitchhiker" thumbs, cauliflower ear deformities, and severe rigid clubfeet. Which gene mutation is responsible for this patient's condition?

. FGFR3
. COMP
. SLC26A2 (DTDST)
. COL1A1
. RUNX2

Correct Answer & Explanation

. SLC26A2 (DTDST)

Explanation

The clinical presentation describes diastrophic dysplasia. It is inherited in an autosomal recessive pattern and caused by mutations in the SLC26A2 gene, which codes for a diastrophic dysplasia sulfate transporter (DTDST).

Question 4382

Topic: 4. Pediatrics

A 7-year-old girl is evaluated for multiple recurrent long bone fractures following minimal trauma. Clinical examination reveals bluish discoloration of the sclerae, joint hypermobility, and opalescent, discolored teeth. This patient's condition is most commonly caused by a mutation affecting which of the following?

. Type II collagen
. Fibroblast growth factor receptor 3 (FGFR3)
. Cartilage oligomeric matrix protein (COMP)
. Type I collagen (COL1A1 or COL1A2)
. Core binding factor alpha 1 (RUNX2)

Correct Answer & Explanation

. Type I collagen (COL1A1 or COL1A2)

Explanation

Osteogenesis imperfecta (OI) is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes. This leads to defective synthesis of Type I collagen, resulting in bone fragility, blue sclerae, and dentinogenesis imperfecta.

Question 4383

Topic: 4. Pediatrics

An 8-year-old child presents with a waddling gait, short stature, and bilateral knee pain. Radiographs demonstrate delayed, irregular, and fragmented ossification centers of the capital femoral epiphyses and distal femoral epiphyses, but the spine and skull appear completely normal. Mutations in which gene are most commonly associated with the autosomal dominant form of this dysplasia?

. COL2A1
. FGFR3
. COMP (Cartilage oligomeric matrix protein)
. SLC26A2 (DTDST)
. SOX9

Correct Answer & Explanation

. COMP (Cartilage oligomeric matrix protein)

Explanation

The clinical and radiographic presentation is classic for Multiple Epiphyseal Dysplasia (MED), which typically spares the spine. The most common genetic cause of the autosomal dominant form is a mutation in the COMP gene on chromosome 19.

Question 4384

Topic: 4. Pediatrics

A 6-year-old child presents with short-limb dwarfism, a normal head circumference, and normal facial features. Radiographs show delayed epiphyseal ossification, flared metaphyses, and platyspondyly with central anterior beaking of the vertebrae. Which of the following best differentiates this condition from classic achondroplasia?

. It is inherited in an autosomal recessive manner.
. The child has normal craniofacial features and is not born with clinical signs of dwarfism.
. It is caused by an activating mutation in the FGFR3 gene.
. Patients have a significantly higher risk of foramen magnum stenosis.
. The rhizomelic shortening of the limbs is more severe.

Correct Answer & Explanation

. The child has normal craniofacial features and is not born with clinical signs of dwarfism.

Explanation

The patient has Pseudoachondroplasia (caused by a COMP mutation). Unlike achondroplasia, children with pseudoachondroplasia have normal craniofacial features, appear normal at birth, and dwarfism becomes apparent only after 1-2 years of age as growth slows.

Question 4385

Topic: 4. Pediatrics

A newborn is noted to have severe short-limb dwarfism, rigid bilateral clubfeet, "hitchhiker" thumbs, and cystic swelling of the pinnae of the ears (cauliflower ear). Radiographs show short, thick tubular bones. This autosomal recessive skeletal dysplasia is caused by a mutation in which of the following genes?

. SLC26A2 (DTDST)
. FGFR3
. COMP
. COL1A1
. RUNX2

Correct Answer & Explanation

. SLC26A2 (DTDST)

Explanation

The clinical triad of hitchhiker thumbs, severe clubfeet, and cystic ear swelling in a short-limbed dwarf is characteristic of Diastrophic Dysplasia. It is an autosomal recessive disorder caused by a mutation in the SLC26A2 (DTDST) sulfate transporter gene.

Question 4386

Topic: 4. Pediatrics

The parents of a child recently diagnosed with achondroplasia ask for genetic counseling. You explain that the condition is caused by a specific mutation in the FGFR3 gene. Which of the following best describes the pathophysiologic consequence of this mutation?

. Gain-of-function inhibiting chondrocyte proliferation
. Loss-of-function increasing chondrocyte hypertrophy
. Defective type I collagen synthesis
. Defective core-binding factor alpha 1 (RUNX2)
. Defective cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. Gain-of-function inhibiting chondrocyte proliferation

Explanation

Achondroplasia is an autosomal dominant skeletal dysplasia caused by a gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. This mutation leads to constitutive, abnormal inhibition of chondrocyte proliferation at the physis.

Question 4387

Topic: 4. Pediatrics
A 6-year-old child with blue sclerae, hearing loss, and a history of multiple low-energy fractures is diagnosed with Sillence Type I Osteogenesis Imperfecta (OI). Which of the following best describes the underlying collagen defect?
. Qualitative defect producing abnormal Type I collagen
. Quantitative defect producing an insufficient amount of normal Type I collagen
. Defect in the synthesis of Type II collagen
. Defect in the synthesis of Type X collagen
. Defect in Cartilage Oligomeric Matrix Protein (COMP)

Correct Answer & Explanation

. Quantitative defect producing an insufficient amount of normal Type I collagen

Explanation

Osteogenesis Imperfecta Type I (the mildest and most common form) is characterized by a quantitative defect, meaning there is decreased production of structurally normal Type I collagen. More severe types (II, III, IV) involve qualitative defects.

Question 4388

Topic: 4. Pediatrics

A 4-year-old boy presents with short-limbed dwarfism, a waddling gait, and normal craniofacial features. Radiographs reveal delayed epiphyseal ossification and platyspondyly, but a normal interpedicular distance in the lumbar spine. Which gene mutation is most likely responsible for this condition?

. FGFR3
. COL1A1
. COL2A1
. COMP
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is caused by a mutation in the Cartilage Oligomeric Matrix Protein (COMP) gene. It is distinguished from achondroplasia by the presence of normal craniofacial features at birth and a normal lumbar interpedicular distance.

Question 4389

Topic: 4. Pediatrics
A 2-year-old girl with blue sclerae and a history of multiple low-energy fractures is diagnosed with Osteogenesis Imperfecta (OI). Which of the following describes the most common underlying biochemical defect in the mildest and most common form of this disease (Type I)?
. Production of abnormal type II collagen
. Decreased quantity of structurally normal type I collagen
. Production of structurally abnormal type I collagen
. Defect in the mineralization of osteoid
. Defect in the conversion of cartilage to bone

Correct Answer & Explanation

. Decreased quantity of structurally normal type I collagen

Explanation

OI Type I is a quantitative defect resulting in a decreased amount of structurally normal type I collagen. In contrast, Types II, III, and IV are qualitative defects where structurally abnormal collagen is produced, leading to more severe phenotypes.

Question 4390

Topic: 4. Pediatrics

A 6-year-old child presents with a short trunk, severe coxa vara, a cleft palate, and high myopia. Radiographs show delayed ossification of the capital femoral epiphyses and platyspondyly. Which of the following mutations is responsible for this skeletal dysplasia?

. FGFR3
. SLC26A2
. COL2A1
. COMP
. RUNX2

Correct Answer & Explanation

. COL2A1

Explanation

Spondyloepiphyseal dysplasia congenita (SEDC) is caused by mutations in the COL2A1 gene, which encodes type II collagen. Clinical features include short-trunk dwarfism, coxa vara, cleft palate, myopia, and a high risk of atlantoaxial instability.

Question 4391

Topic: 4. Pediatrics

A neonate is evaluated for short-limbed dwarfism, bilateral clubfeet, "hitchhiker" thumbs, and cystic swelling of the external ears (cauliflower ears). Which of the following pathophysiologic mechanisms best explains this patient's condition?

. Defective conversion of cartilage to bone due to an FGFR3 mutation
. Defect in type II collagen synthesis
. Defective intracellular sulfate transport leading to undersulfated proteoglycans
. Accumulation of keratan sulfate due to lysosomal enzyme deficiency
. Constitutive activation of the Gs-alpha protein

Correct Answer & Explanation

. Defective intracellular sulfate transport leading to undersulfated proteoglycans

Explanation

Diastrophic dysplasia is an autosomal recessive disorder caused by a mutation in the SLC26A2 gene, which encodes a sulfate transporter. This leads to undersulfated proteoglycans in the cartilage matrix, causing classic features like hitchhiker thumbs and cauliflower ears.

Question 4392

Topic: 4. Pediatrics

A 6-year-old boy presents with short stature, a waddling gait, and bilateral hip pain. Radiographs reveal flattened, irregular, and fragmented capital femoral epiphyses. His spine radiographs are completely normal with no vertebral body abnormalities. A mutation in the gene encoding which of the following proteins is most likely responsible for this patient's condition?

. Type II collagen (COL2A1)
. Cartilage oligomeric matrix protein (COMP)
. Fibroblast growth factor receptor 3 (FGFR3)
. Core-binding factor subunit alpha-1 (CBFA1/RUNX2)
. Diastrophic dysplasia sulfate transporter (SLC26A2)

Correct Answer & Explanation

. Cartilage oligomeric matrix protein (COMP)

Explanation

The patient's presentation of epiphyseal irregularity with normal spine radiographs is classic for Multiple Epiphyseal Dysplasia (MED). MED is most frequently caused by mutations in the COMP gene, unlike Spondyloepiphyseal Dysplasia (SED) which involves COL2A1 mutations and structural spine defects.

Question 4393

Topic: 4. Pediatrics
A 6-year-old child presents with anterolateral bowing of the tibia. Examination reveals six café-au-lait macules and axillary freckling. The underlying genetic mutation for this patient's condition affects a gene located on which chromosome?
. Chromosome 11
. Chromosome 13
. Chromosome 17
. Chromosome 22
. Chromosome X

Correct Answer & Explanation

. Chromosome 17

Explanation

The patient has Neurofibromatosis type 1, indicated by tibial pseudarthrosis, café-au-lait spots, and axillary freckling. NF1 is caused by a mutation in the neurofibromin gene located on chromosome 17.

Question 4394

Topic: 4. Pediatrics

To establish a clinical diagnosis of Neurofibromatosis Type 1 (NF1) in a prepubertal child, the presence of cafe-au-lait macules is a major criterion. What is the minimum requirement for these macules?

. Three spots >5 mm
. Six spots >5 mm
. Six spots >15 mm
. Four spots >10 mm
. Two spots >15 mm

Correct Answer & Explanation

. Six spots >5 mm

Explanation

Diagnostic criteria for NF1 include six or more cafe-au-lait spots. They must measure greater than 5 mm in prepubertal individuals and greater than 15 mm in postpubertal individuals.

Question 4395

Topic: 4. Pediatrics

The fundamental genetic defect in the vast majority of patients with Osteogenesis Imperfecta (OI) involves a mutation affecting the synthesis or structure of Type I collagen. Which of the following genes are most commonly mutated in this condition?

. Type II collagen genes (COL2A1)
. Fibroblast growth factor receptor 3 (FGFR3)
. CBFA1 (Runx2) transcription factor
. COL1A1 or COL1A2 genes
. Cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. COL1A1 or COL1A2 genes

Explanation

Osteogenesis Imperfecta (OI) is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, which encode the alpha-1 and alpha-2 chains of Type I collagen. FGFR3 mutations cause achondroplasia. CBFA1 (Runx2) mutations cause cleidocranial dysplasia. COL2A1 mutations cause conditions like SED or Stickler syndrome. COMP mutations cause multiple epiphyseal dysplasia or pseudoachondroplasia.

Question 4396

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limb dwarfism. It is characterized by an activating mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. How does this specific mutation affect bone growth?

. It inhibits intramembranous ossification in flat bones
. It accelerates chondrocyte proliferation in the resting zone of the physis
. It inhibits chondrocyte proliferation in the proliferative zone of the physis
. It prevents osteoclast formation at the metaphysis
. It causes premature mineralization of the zone of provisional calcification

Correct Answer & Explanation

. It inhibits chondrocyte proliferation in the proliferative zone of the physis

Explanation

Achondroplasia is an autosomal dominant disorder caused by a gain-of-function mutation in FGFR3. Normally, FGFR3 negatively regulates bone growth. The activating mutation causes exaggerated inhibition of chondrocyte proliferation and differentiation in the proliferative zone of the growth plate (physis), leading to impaired endochondral ossification.

Question 4397

Topic: 4. Pediatrics

A newborn is evaluated for severe shortening of the proximal limbs (rhizomelia), frontal bossing, and midface hypoplasia. Genetic testing reveals a mutation in the FGFR3 gene. Which of the following best describes the inheritance pattern and functional effect of this mutation?

. Autosomal dominant, gain-of-function
. Autosomal dominant, loss-of-function
. Autosomal recessive, gain-of-function
. Autosomal recessive, loss-of-function
. X-linked recessive, loss-of-function

Correct Answer & Explanation

. Autosomal dominant, gain-of-function

Explanation

Achondroplasia is the most common form of short-limb dwarfism and is caused by an autosomal dominant, gain-of-function mutation in the Fibroblast Growth Factor Receptor 3 (FGFR3) gene. Normally, FGFR3 negatively regulates chondrocyte proliferation in the growth plate. The gain-of-function mutation results in constitutive over-inhibition of chondrocyte proliferation, leading to profound effects on endochondral ossification.

Question 4398

Topic: 4. Pediatrics

A 45-year-old female refugee presents with generalized bone pain and proximal muscle weakness. Laboratory evaluation reveals low serum calcium, low serum phosphate, elevated alkaline phosphatase, and elevated parathyroid hormone. Radiographs of the pelvis demonstrate symmetric, transverse radiolucent bands perpendicular to the cortex in the pubic rami. Which of the following is the most likely diagnosis?

. Osteitis deformans
. Osteomalacia
. Osteopetrosis
. Hyperparathyroidism secondary to chronic kidney disease
. Osteogenesis imperfecta

Correct Answer & Explanation

. Osteomalacia

Explanation

The patient has osteomalacia, characterized by defective mineralization of osteoid. The radiographic findings are Looser zones (pseudofractures), which are pathognomonic. The lab profile (low/normal Ca, low P, high ALP, high PTH) reflects secondary hyperparathyroidism due to Vitamin D deficiency.

Question 4399

Topic: 4. Pediatrics

A newborn presents with short-limbed dwarfism, bilateral clubfeet, 'hitchhiker' thumbs, and cystic swelling of the external ears (cauliflower ears). Which of the following genes is mutated in this condition?

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

Correct Answer & Explanation

. SLC26A2 (DTDST)

Explanation

Diastrophic dysplasia is an autosomal recessive condition caused by a mutation in the SLC26A2 gene (also known as DTDST), which encodes a sulfate transport protein. This leads to under-sulfation of cartilage proteoglycans. Clinical hallmarks include short stature, hitchhiker thumbs, severe clubfeet, and 'cauliflower' ears.

Question 4400

Topic: 4. Pediatrics

A 10-year-old boy presents with bilateral knee and hip pain, waddling gait, and short stature. Radiographs show delayed, irregular ossification of the epiphyses and a 'double-layer' patella on the lateral knee radiograph. The spine appears radiographically normal. A mutation in which of the following is most likely responsible?

. Type II collagen
. Cartilage oligomeric matrix protein (COMP)
. Type X collagen
. Fibroblast growth factor receptor 3 (FGFR3)
. CBFA1 (RUNX2)

Correct Answer & Explanation

. Cartilage oligomeric matrix protein (COMP)

Explanation

Multiple Epiphyseal Dysplasia (MED) is characterized by delayed and irregular ossification of the epiphyses without spinal involvement (distinguishing it from Spondyloepiphyseal Dysplasia). The 'double-layer' patella is a classic radiographic sign. It is most commonly caused by mutations in the COMP (Cartilage Oligomeric Matrix Protein) gene.

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