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4. Pediatrics MCQs

Practice Set 305 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 6081

Topic: 4. Pediatrics

A 12-year-old child presents with a mildly short stature and bilateral waddling gait. Radiographs demonstrate a double-layered patella and bilateral flattening of the femoral heads. What is the most likely genetic mutation?

. COL2A1
. COL1A1
. COMP
. CBFA1
. ACVR1

Correct Answer & Explanation

. COMP

Explanation

Multiple epiphyseal dysplasia (MED) most commonly results from a mutation in the COMP gene. A double-layered patella is a classic radiographic hallmark of this condition.

Question 6082

Topic: 4. Pediatrics

Which of the following skeletal dysplasias is characterized by a defect in intramembranous ossification, resulting in delayed closure of cranial sutures, absent or hypoplastic clavicles, and coxa vara?

. Osteogenesis imperfecta
. Achondroplasia
. Spondyloepiphyseal dysplasia congenita
. Cleidocranial dysplasia
. Metaphyseal chondrodysplasia (Schmid type)

Correct Answer & Explanation

. Cleidocranial dysplasia

Explanation

Cleidocranial dysplasia is caused by a mutation in RUNX2 (CBFA1) affecting intramembranous ossification. Hallmarks include open fontanelles, dental anomalies, and absent or hypoplastic clavicles.

Question 6083

Topic: 4. Pediatrics

What is the underlying molecular pathogenesis of fibrous dysplasia?

. Mutation in FGFR3 leading to decreased chondrocyte proliferation.
. Mutation in GNAS leading to constitutive activation of Gs-alpha and increased intracellular cAMP.
. Mutation in EXT1 leading to defective heparan sulfate synthesis.
. Mutation in COMP leading to accumulation of mutant protein in the rough endoplasmic reticulum.

Correct Answer & Explanation

. Mutation in GNAS leading to constitutive activation of Gs-alpha and increased intracellular cAMP.

Explanation

Correct Answer: Mutation in GNAS leading to constitutive activation of Gs-alpha and increased intracellular cAMP.Fibrous dysplasia is caused by a somatic, activating mutation in the GNAS gene. This gene encodes the alpha subunit of the stimulatory G protein (Gs-alpha). The mutation leads to constitutive activation of adenylate cyclase, resulting in high intracellular levels of cyclic AMP (cAMP). This overproduction of cAMP affects the differentiation of osteoblasts, leading to the replacement of normal bone and marrow with fibrous tissue and woven bone. FGFR3 mutations are seen in achondroplasia, EXT1 in multiple hereditary exostoses, and COMP in pseudoachondroplasia.

Question 6084

Topic: 4. Pediatrics

A 6-month-old infant with a known skeletal dysplasia presents with central sleep apnea, hyperreflexia, and clonus. Radiographs show a narrow interpedicular distance in the lumbar spine. Which molecular mechanism primarily drives the underlying condition?

. Loss of function in FGFR3
. Gain of function in FGFR3
. Mutation in COL1A1
. Mutation in COMP
. Defect in osteoclast carbonic anhydrase II

Correct Answer & Explanation

. Gain of function in FGFR3

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3, which inhibits chondrocyte proliferation in the growth plate. Foramen magnum stenosis is a critical complication in infancy that can cause cervicomedullary compression and central sleep apnea.

Question 6085

Topic: 4. Pediatrics

A 7-year-old girl with normal intelligence and no facial dysmorphism presents with a waddling gait. Radiographs show delayed ossification of the capital femoral epiphyses and fragmented epiphyses in multiple joints. Genetic testing reveals a mutation in the COMP gene. What is the diagnosis?

. Achondroplasia
. Multiple Epiphyseal Dysplasia
. Pseudoachondroplasia
. Cleidocranial Dysplasia
. Mucopolysaccharidosis Type IV

Correct Answer & Explanation

. Pseudoachondroplasia

Explanation

Pseudoachondroplasia is primarily caused by a mutation in the Cartilage Oligomeric Matrix Protein (COMP) gene. Unlike achondroplasia, these patients have normal facial features and their skeletal changes become clinically apparent after the first year of life.

Question 6086

Topic: 4. Pediatrics

A 9-year-old girl is evaluated for a significant leg length discrepancy. Physical exam reveals a unilateral port-wine stain over her hypertrophic lower extremity. Superficial varicosities are prominently noted on the same limb. Which genetic mutation is primarily associated with this syndrome?

. GNAS
. PIK3CA
. PTEN
. FGFR3
. EXT1

Correct Answer & Explanation

. PIK3CA

Explanation

Klippel-Trenaunay syndrome consists of the triad of capillary malformations (port-wine stain), venous malformations, and limb overgrowth. It is associated with somatic activating mutations in the PIK3CA gene.

Question 6087

Topic: 4. Pediatrics

A 30-year-old female presents with bilateral knee pain. Radiographs reveal a "double-layer" patella on the lateral view and flattened irregular femoral condyles. She has normal height and normal facial features. Which of the following conditions does she most likely have?

. Achondroplasia
. Nail-Patella Syndrome
. Multiple Epiphyseal Dysplasia
. Spondyloepiphyseal Dysplasia
. Chondrodysplasia Punctata

Correct Answer & Explanation

. Multiple Epiphyseal Dysplasia

Explanation

Multiple Epiphyseal Dysplasia (MED) can be caused by mutations in MATN3, COMP, or COL9. The "double-layer" patella is a classic radiographic sign uniquely seen in the Fairbank type of MED.

Question 6088

Topic: 4. Pediatrics

A 6-month-old male with achondroplasia presents for a routine check-up. The parents report recent episodes of witnessed sleep apnea, profound hypotonia, and poor feeding. Which of the following is the most appropriate next step in management?

. Cervical spine flexion-extension radiographs
. MRI of the craniocervical junction
. Referral for urgent adenotonsillectomy
. Polysomnography as a standalone diagnostic tool
. Prophylactic posterior cervical fusion

Correct Answer & Explanation

. MRI of the craniocervical junction

Explanation

Infants with achondroplasia are at high risk for foramen magnum stenosis, leading to cervicomedullary compression, central sleep apnea, and sudden death. MRI of the craniocervical junction is the gold standard for evaluating this potentially lethal complication.

Question 6089

Topic: 4. Pediatrics

A 4-year-old girl is evaluated for short stature and a waddling gait. Examination reveals normal facial features, marked joint laxity, and disproportionate short-limb dwarfism. Radiographs show delayed epiphyseal ossification and irregular, fragmented metaphyses. A mutation in which of the following genes is most likely responsible?

. FGFR3
. COMP
. COL2A1
. SLC26A2
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is caused by mutations in the COMP (Cartilage Oligomeric Matrix Protein) gene. Unlike achondroplasia, patients have normal craniofacial features and head circumference, but present with joint laxity, early-onset osteoarthritis, and short-limb dwarfism.

Question 6090

Topic: Pediatric Hip
A 9-year-old boy complains of bilateral knee pain and a waddling gait. Radiographs show small, irregular, and fragmented epiphyses, but normal metaphyses and a normal spine. Lateral radiographs of the knee reveal a 'double-layer' appearance of the patella. Which of the following conditions is most likely?
. Multiple Epiphyseal Dysplasia
. Spondyloepiphyseal Dysplasia Congenita
. Legg-Calvé-Perthes Disease
. Meyer Dysplasia
. Chondrodysplasia Punctata

Correct Answer & Explanation

. Multiple Epiphyseal Dysplasia

Explanation

Multiple Epiphyseal Dysplasia (MED) primarily affects the epiphyses, presenting with early-onset joint pain and a waddling gait. The 'double-layer' patella on a lateral radiograph is a pathognomonic finding for this condition, distinguishing it from other dysplasias.

Question 6091

Topic: 4. Pediatrics

A 4-year-old child presents with painful, warm, soft tissue swellings on his back following minor trauma. Physical examination notes bilateral congenital hallux valgus and microdactyly of the first toes. Biopsy of the back lesions is deferred due to the suspicion of a specific genetic condition. What is the pathogenic mutation involved?

. Activating mutation of ACVR1 (ALK2) gene
. Inactivating mutation of EXT1 gene
. Loss-of-function mutation of GNAS1 gene
. Mutation of the COMP gene
. Frameshift mutation in COL1A1

Correct Answer & Explanation

. Activating mutation of ACVR1 (ALK2) gene

Explanation

Fibrodysplasia Ossificans Progressiva (FOP) is caused by an activating mutation in the ACVR1 (ALK2) gene, a BMP type I receptor. It is characterized by congenital malformation of the great toes and progressive heterotopic ossification, which is catastrophically exacerbated by trauma or surgery.

Question 6092

Topic: 4. Pediatrics

A 12-year-old boy with a history of recurrent fractures is diagnosed with Osteogenesis Imperfecta (OI) Type V. Which of the following radiographic or clinical findings is uniquely characteristic of this specific type of OI compared to classic forms?

. Dentinogenesis imperfecta and profound blue sclerae
. Severe basilar invagination with cranial nerve palsies
. Hyperplastic callus formation and radioulnar synostosis
. Normal bone density with isolated severe kyphoscoliosis
. Complete absence of clavicles and delayed dentition

Correct Answer & Explanation

. Hyperplastic callus formation and radioulnar synostosis

Explanation

Osteogenesis Imperfecta Type V is an autosomal dominant non-collagenous form of OI caused by an IFITM5 mutation. It is classically distinguished from other types by the triad of hyperplastic callus formation following fractures, radioulnar synostosis, and an ossified interosseous membrane.

Question 6093

Topic: 4. Pediatrics

A 6-year-old girl is evaluated for disproportionate short stature, waddling gait, and joint laxity. Her facial features are entirely normal. Radiographs demonstrate fragmented, irregular epiphyses and metaphyseal flaring. A mutation in which of the following genes is most likely responsible?

. FGFR3
. COL1A1
. COMP
. COL2A1
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is caused by a mutation in the COMP (Cartilage Oligomeric Matrix Protein) gene. It classically presents with disproportionate short stature and joint laxity but spares the craniofacial skeleton, distinguishing it from achondroplasia.

Question 6094

Topic: Pediatric Hip

A 15-year-old male with delayed closure of cranial sutures and supernumerary teeth is evaluated for a unilateral limp. Examination reveals significant shoulder hypermobility. Which of the following hip abnormalities is most commonly associated with his condition?

. Slipped capital femoral epiphysis
. Coxa vara
. Developmental dysplasia of the hip
. Perthes-like osteonecrosis
. Protrusio acetabuli

Correct Answer & Explanation

. Coxa vara

Explanation

Cleidocranial dysplasia is an autosomal dominant condition caused by a RUNX2 (CBFA1) mutation. Skeletal manifestations typically include absent or hypoplastic clavicles, delayed skull ossification, and developmental coxa vara.

Question 6095

Topic: 4. Pediatrics

A newborn presents with rhizomelic shortening of the extremities, frontal bossing, and midface hypoplasia. What is the specific genetic mutation and its cellular effect on the physeal growth plate in this condition?

. FGFR3 gain-of-function mutation inhibiting chondrocyte proliferation
. FGFR3 loss-of-function mutation promoting chondrocyte apoptosis
. COL1A1 mutation altering type I collagen cross-linking
. COMP mutation causing endoplasmic reticulum stress in chondrocytes
. Runx2 mutation inhibiting osteoblast differentiation

Correct Answer & Explanation

. FGFR3 gain-of-function mutation inhibiting chondrocyte proliferation

Explanation

Achondroplasia is caused by an autosomal dominant gain-of-function mutation in the FGFR3 gene. This constitutive activation paradoxically inhibits chondrocyte proliferation in the proliferative zone of the physis, leading to diminished endochondral ossification.

Question 6096

Topic: 4. Pediatrics

A newborn presents with severe micromelic limb shortening, rigid clubfeet, "hitchhiker" thumbs, and swollen pinnae. What is the affected gene and the expected inheritance pattern for this dysplasia?

. SLC26A2 (DTDST), Autosomal Recessive
. COMP, Autosomal Dominant
. COL2A1, Autosomal Dominant
. FGFR3, Autosomal Dominant
. SOX9, Autosomal Recessive

Correct Answer & Explanation

. SLC26A2 (DTDST), Autosomal Recessive

Explanation

Diastrophic dysplasia is an autosomal recessive disorder caused by mutations in the SLC26A2 (DTDST) gene, which impairs proper cellular sulfate transport. Classical features include the hitchhiker thumb deformity, cauliflower ears, and severe, rigid clubfeet.

Question 6097

Topic: 4. Pediatrics

A child appeared normal at birth but develops severe short-limbed dwarfism by age 3, with normal facial features, joint laxity, and early-onset osteoarthritis. Accumulation of which abnormal protein in the rough endoplasmic reticulum of chondrocytes is responsible?

. Type II collagen
. Cartilage Oligomeric Matrix Protein (COMP)
. Fibroblast growth factor receptor 3
. Type X collagen
. Aggrecan

Correct Answer & Explanation

. Cartilage Oligomeric Matrix Protein (COMP)

Explanation

Pseudoachondroplasia is caused by mutations in the COMP gene. This leads to the accumulation of misfolded COMP in the rough endoplasmic reticulum of chondrocytes, causing premature chondrocyte death and resulting in delayed-onset dwarfism with normal facies.

Question 6098

Topic: 4. Pediatrics
An infant is born with multiple severe fractures, deeply blue sclerae, and profound limb deformity. The child expires shortly after birth due to respiratory failure. According to the Sillence classification, which type of Osteogenesis Imperfecta does this represent?
. Type I
. Type II
. Type III
. Type IV
. Type V

Correct Answer & Explanation

. Type II

Explanation

Sillence Type II is the perinatal lethal form of Osteogenesis Imperfecta. It is characterized by severe osseous fragility, crumpled long bones, and beaded ribs, with death usually occurring secondary to respiratory failure from restricted thoracic volume.

Question 6099

Topic: 4. Pediatrics
A 12-year-old boy presents with bilateral knee and hip pain, mild short stature, and a waddling gait. Radiographs show delayed, fragmented ossification centers of the femoral heads bilaterally, but normal spinal alignment and vertebral body heights. Which condition must this most carefully be differentiated from?
. Achondroplasia
. Bilateral Legg-Calvé-Perthes disease
. Spondyloepiphyseal dysplasia
. Hypochondroplasia
. Mucopolysaccharidosis

Correct Answer & Explanation

. Bilateral Legg-Calvé-Perthes disease

Explanation

Multiple Epiphyseal Dysplasia (MED) often presents with bilateral, symmetric hip involvement that closely mimics bilateral Legg-Calvé-Perthes (LCP) disease. Normal spine radiographs (lack of platyspondyly) help distinguish MED from spondyloepiphyseal dysplasia (SED).

Question 6100

Topic: 4. Pediatrics

A child presents with short-trunk dwarfism, a flat midface, cleft palate, and prominent, stiff joints. Radiographs demonstrate coronal clefts of the vertebral bodies and epiphyseal stippling with a classic "dumbbell" appearance of the long bones. What is the most likely diagnosis?

. Kniest Dysplasia
. Campomelic Dysplasia
. Metaphyseal Chondrodysplasia, Schmid type
. Chondrodysplasia Punctata
. Achondrogenesis

Correct Answer & Explanation

. Kniest Dysplasia

Explanation

Kniest dysplasia is a type II collagenopathy characterized by dumbbell-shaped femora, coronal clefts in the vertebral bodies, and enlarged, stiff joints. Cleft palate and hearing loss are also highly characteristic clinical findings.

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