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4. Pediatrics MCQs

Practice Set 302 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 6021

Topic: 4. Pediatrics

A 4-year-old boy presents with short stature, waddling gait, and joint laxity. Unlike classic achondroplasia, his craniofacial appearance is completely normal. Radiographs reveal delayed epiphyseal ossification and platyspondyly. A mutation in which of the following genes is most likely responsible?

. FGFR3
. COMP
. COL1A1
. GNAS1
. EXT2

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is characterized by short-limbed dwarfism with a normal craniofacial appearance. It is caused by a mutation in the Cartilage Oligomeric Matrix Protein (COMP) gene.

Question 6022

Topic: 4. Pediatrics

Achondroplasia is the most common form of short-limbed dwarfism. The underlying pathophysiology involves a defect in the proliferative zone of the physis. Which of the following describes the genetic mechanism?

. Loss of function in FGFR3
. Gain of function in FGFR3
. Loss of function in COMP
. Gain of function in COMP
. Dominant negative mutation in COL2A1

Correct Answer & Explanation

. Gain of function in FGFR3

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in the FGFR3 gene. This mutation causes a continuous inhibitory signal that suppresses chondrocyte proliferation in the proliferative zone of the physis.

Question 6023

Topic: 4. Pediatrics

A neonate is born with severe micromelia, rigid clubfeet, and a "hitchhiker" thumb. The external ears show marked cystic swelling that later develops into a classic deformity. The genetic defect involves SLC26A2. What is the diagnosis?

. Campomelic dysplasia
. Diastrophic dysplasia
. Achondroplasia
. Osteogenesis imperfecta type II
. Ellis-van Creveld syndrome

Correct Answer & Explanation

. Diastrophic dysplasia

Explanation

Diastrophic dysplasia is caused by a defect in the sulfate transporter gene (SLC26A2/DTDST). Classic features include cauliflower ears, hitchhiker thumbs, severe rigid clubfeet, and cervical kyphosis.

Question 6024

Topic: 4. Pediatrics

Both achondroplasia and pseudoachondroplasia present with short-limbed dwarfism. Which of the following clinical features most reliably differentiates pseudoachondroplasia from true achondroplasia?

. Presence of rhizomelic shortening
. Normal craniofacial appearance
. Autosomal dominant inheritance pattern
. Development of lumbar lordosis
. Short stature

Correct Answer & Explanation

. Normal craniofacial appearance

Explanation

Unlike achondroplasia, patients with pseudoachondroplasia have a normal craniofacial appearance. This is because pseudoachondroplasia (caused by COMP mutations) spares intramembranous ossification, which forms the facial bones and skull vault.

Question 6025

Topic: 4. Pediatrics

A 9-year-old boy sustains a minor fall and presents with arm pain. X-rays reveal a centralized, radiolucent lesion in the proximal humerus metaphysis with a "fallen leaf" sign. Which of the following factors indicates the cyst is in the "active" phase?

. Proximity of less than 0.5 cm to the physis
. Presence of a pathologic fracture
. Multiloculated appearance on MRI
. Cortical expansion greater than 2 cm
. Location in the diaphysis

Correct Answer & Explanation

. Proximity of less than 0.5 cm to the physis

Explanation

Unicameral bone cysts are considered "active" when they are adjacent to the physis (typically less than 0.5 cm) and carry a higher risk of recurrence after treatment. "Latent" cysts have migrated distally into the diaphysis as normal bone grows between the cyst and the physis.

Question 6026

Topic: 4. Pediatrics

A 10-year-old boy presents with waddling gait, knee pain, and short stature. Radiographs demonstrate flattened, irregular epiphyses in the hips and knees, and a double-layered patella. His intelligence is normal. Which of the following genes is most commonly mutated in this condition?

. COL2A1
. COMP
. FGFR3
. SLC26A2
. CBFA1

Correct Answer & Explanation

. COMP

Explanation

Multiple epiphyseal dysplasia (MED) is most commonly caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene. A double-layered patella is a classic, highly specific radiographic finding for MED.

Question 6027

Topic: 4. Pediatrics

A 4-year-old child with short-trunk dwarfism presents with progressive weakness in all four extremities. Radiographs show coxa vara, flattened vertebral bodies, and delayed ossification of the odontoid. What is the most likely genetic defect?

. Mutation in the COMP gene
. Mutation in the COL2A1 gene
. Mutation in the FGFR3 gene
. Mutation in the GNAS1 gene
. Mutation in the RUNX2 gene

Correct Answer & Explanation

. Mutation in the COL2A1 gene

Explanation

Spondyloepiphyseal dysplasia (SED) congenita is an autosomal dominant disorder caused by a mutation in the COL2A1 gene, affecting type II collagen. Odontoid hypoplasia is common and can lead to atlantoaxial instability, presenting as myelopathy.

Question 6028

Topic: 4. Pediatrics

A newborn presents with short-limbed dwarfism, rigid clubfeet, "hitchhiker" thumbs, and cystic swelling of the pinnae (cauliflower ears). Which of the following is the underlying genetic anomaly?

. Defect in the sulfate transporter SLC26A2
. Defect in fibroblast growth factor receptor 3 (FGFR3)
. Defect in the CBFA1/RUNX2 transcription factor
. Defect in type 1 collagen synthesis
. Defect in the COMP gene

Correct Answer & Explanation

. Defect in the sulfate transporter SLC26A2

Explanation

Diastrophic dysplasia is an autosomal recessive condition caused by mutations in the SLC26A2 sulfate transporter gene. Classic features include hitchhiker thumbs, severe clubfeet, and cauliflower ears.

Question 6029

Topic: 4. Pediatrics

A 7-year-old girl presents with short stature, waddling gait, and ligamentous laxity. Her facial features and head circumference are normal. Radiographs demonstrate irregular epiphyses and fragmented metaphyses. Which of the following distinguishes pseudoachondroplasia from achondroplasia?

. Inheritance pattern
. Presence of normal facial appearance and head circumference
. Presence of short-limbed dwarfism
. Development of spinal stenosis in adulthood
. Mutation in the FGFR3 gene

Correct Answer & Explanation

. Presence of normal facial appearance and head circumference

Explanation

Pseudoachondroplasia is caused by a COMP gene mutation, whereas achondroplasia is caused by an FGFR3 mutation. Unlike achondroplasia, patients with pseudoachondroplasia have a normal facial appearance and normal head circumference.

Question 6030

Topic: 4. Pediatrics

A male and a female, both diagnosed with heterozygous achondroplasia, are expecting a child. They are seeking genetic counseling regarding the risk of their baby inheriting the lethal form of the disease. What is the probability that the child will be born with lethal homozygous achondroplasia?

. 0%
. 25%
. 50%
. 75%
. 100%

Correct Answer & Explanation

. 25%

Explanation

Achondroplasia is an autosomal dominant disorder caused by an FGFR3 mutation. When two heterozygous individuals mate, there is a 25% chance of the offspring inheriting the homozygous dominant genotype, which is universally lethal in utero or shortly after birth.

Question 6031

Topic: 4. Pediatrics

A newborn infant is evaluated for short-limbed dwarfism, bilateral rigid clubfeet, 'hitchhiker thumbs', and cystic swelling of the external pinnae (cauliflower ears). This condition is inherited in an autosomal recessive pattern. What is the underlying genetic mutation?

. FGFR3
. SLC26A2
. COMP
. COL1A1
. RUNX2

Correct Answer & Explanation

. SLC26A2

Explanation

The clinical presentation is pathognomonic for diastrophic dysplasia. It is caused by a mutation in the SLC26A2 gene, which encodes a sulfate transporter crucial for cartilage proteoglycan synthesis.

Question 6032

Topic: 4. Pediatrics

A 10-year-old boy presents with a waddling gait and bilateral knee pain. He has short stature but normal facial features. Radiographs show delayed, irregular ossification of the epiphyses with a 'double-layered' patella, but the spine is completely normal. A mutation in which of the following genes is most likely responsible?

. COMP
. FGFR3
. COL2A1
. GNAS
. EXT1

Correct Answer & Explanation

. COMP

Explanation

The patient has Multiple Epiphyseal Dysplasia (MED), characterized by irregular epiphyses, a double-layered patella, and a normal spine (unlike spondyloepiphyseal dysplasia). The most common mutation in MED involves the COMP (Cartilage Oligomeric Matrix Protein) gene.

Question 6033

Topic: 4. Pediatrics

A 30-year-old male presents with severe, early-onset bilateral hip osteoarthritis. He has disproportionate short stature, but a completely normal facial appearance and normal intelligence. Radiographs show platyspondyly with anterior beaking of the vertebral bodies. What is the most likely diagnosis?

. Achondroplasia
. Pseudoachondroplasia
. Morquio syndrome
. Cleidocranial dysplasia
. Osteogenesis imperfecta

Correct Answer & Explanation

. Pseudoachondroplasia

Explanation

Pseudoachondroplasia presents with short-limbed dwarfism and severe early-onset osteoarthritis, but unlike classic achondroplasia, patients have normal facies and head circumference. It is caused by a COMP mutation.

Question 6034

Topic: 4. Pediatrics

A 9-year-old boy presents with severe leg pain, easy fatigability, and a waddling gait. Radiographs reveal symmetrical, bilateral cortical thickening of the diaphyseal regions of the femur and tibia, sparing the epiphyses.

What is the genetic mutation associated with this condition?

. COL1A1
. FGFR3
. TGFB1
. GNAS1
. COMP

Correct Answer & Explanation

. TGFB1

Explanation

The clinical and radiographic presentation is classic for Camurati-Engelmann disease (progressive diaphyseal dysplasia). It is an autosomal dominant condition caused by mutations in the TGFB1 gene, leading to increased bone formation in the diaphyses.

Question 6035

Topic: 4. Pediatrics

A newborn is diagnosed with a skeletal dysplasia characterized by rhizomelic shortening of the limbs, a large head with frontal bossing, and a midface hypoplasia. The condition is inherited in an autosomal dominant pattern, though 80% are de novo mutations linked to advanced paternal age. What is the fundamental cellular defect?

. Gain-of-function mutation in FGFR3 leading to decreased chondrocyte proliferation
. Loss-of-function mutation in FGFR3 leading to increased chondrocyte proliferation
. Defect in processing of type I procollagen
. Inability of osteoclasts to resorb bone due to lacking carbonic anhydrase II
. Defect in the SOX9 transcription factor

Correct Answer & Explanation

. Loss-of-function mutation in FGFR3 leading to increased chondrocyte proliferation

Explanation

Achondroplasia is caused by a gain-of-function mutation in the FGFR3 gene. FGFR3 normally acts to inhibit cartilage proliferation; thus, a gain-of-function mutation constitutively suppresses enchondral ossification, leading to dwarfism.

Question 6036

Topic: 4. Pediatrics

A 6-year-old girl is evaluated for multiple recurrent long bone fractures with minimal trauma. Examination reveals blue sclerae and mild hearing loss. Radiographs show osteopenia and multiple healed fractures. Which of the following genes is most likely mutated in this patient?

. FGFR3
. COL1A1 or COL1A2
. GNAS
. COMP
. Runx2/CBFA1

Correct Answer & Explanation

. COL1A1 or COL1A2

Explanation

This patient has Osteogenesis Imperfecta (OI), primarily characterized by brittle bones, blue sclerae, and hearing loss. Approximately 90% of OI cases are caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes, affecting Type I collagen.

Question 6037

Topic: 4. Pediatrics

A 9-year-old boy presents with severe, aching bilateral leg pain, a waddling gait, and progressive muscle weakness. Radiographs demonstrate marked, symmetrical cortical thickening of the diaphyseal regions of the femurs and tibias.

What is the genetic mutation responsible for this specific condition?

. COMP
. FGFR3
. TGFB1
. COL1A1
. RUNX2

Correct Answer & Explanation

. TGFB1

Explanation

The clinical and radiographic presentation is characteristic of Camurati-Engelmann disease (progressive diaphyseal dysplasia). This condition is inherited in an autosomal dominant pattern and is caused by a gain-of-function mutation in the TGFB1 gene. The mutation leads to increased osteoblastic activity, resulting in marked cortical thickening of the long bone diaphyses.

Question 6038

Topic: 4. Pediatrics

A 10-year-old child presents with bilateral leg pain and a waddling gait. Radiographs show symmetric, severe cortical thickening of the diaphyseal regions of the long bones.

What is the genetic mutation associated with this skeletal dysplasia?

. COMP
. FGFR3
. TGFB1
. COL1A1
. RUNX2

Correct Answer & Explanation

. TGFB1

Explanation

This presentation is classic for Progressive Diaphyseal Dysplasia (Camurati-Engelmann disease). It is an autosomal dominant condition caused by mutations in the TGFB1 gene, leading to increased bone formation and characteristic cortical thickening.

Question 6039

Topic: 4. Pediatrics

A 6-year-old girl with blue sclerae, normal stature, and a history of three long bone fractures is diagnosed with Osteogenesis Imperfecta (OI) Type I. Which of the following best describes the underlying collagen defect?

. Decreased quantity of structurally normal Type I collagen
. Normal quantity of structurally abnormal Type I collagen
. Complete absence of Type II collagen
. Defect in the cross-linking of Type IX collagen
. Abnormal endochondral ossification at the physis

Correct Answer & Explanation

. Decreased quantity of structurally normal Type I collagen

Explanation

OI Type I is the mildest and most common form. It is characterized by a quantitative defect (null allele) resulting in decreased production of structurally normal Type I collagen.

Question 6040

Topic: 4. Pediatrics



A 12-year-old boy presents with severe leg pain, waddling gait, and muscle weakness. Radiographs demonstrate bilateral cortical thickening of the femoral and tibial diaphyses. A mutation in which of the following genes is responsible for this condition?

. COMP
. FGFR3
. TGFB1
. COL1A1
. RUNX2

Correct Answer & Explanation

. TGFB1

Explanation

The image and clinical presentation are characteristic of progressive diaphyseal dysplasia (Camurati-Engelmann disease). This autosomal dominant condition is caused by a mutation in the TGFB1 gene, leading to increased bone formation in the diaphyses.

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