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4. Pediatrics MCQs

Practice Set 191 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 3801

Topic: 4. Pediatrics

A 4-year-old boy presents with a history of recurrent low-energy long bone fractures. Examination reveals blue sclerae and mild hearing loss. A genetic defect in which of the following is most likely responsible for this condition?

. FGFR3
. COL1A1
. COMP
. RUNX2
. PHEX

Correct Answer & Explanation

. COL1A1

Explanation

Osteogenesis imperfecta is most commonly caused by an autosomal dominant mutation in the COL1A1 or COL1A2 genes, affecting type I collagen synthesis. Clinical hallmarks include fragile bones, blue sclerae, and early-onset hearing loss.

Question 3802

Topic: 4. Pediatrics

A 6-year-old girl presents with short stature, waddling gait, and joint pain. Radiographs show fragmented, flattened epiphyses of the hips and knees, but the spine and skull are radiographically normal. A mutation in which gene is most likely responsible?

. COMP
. FGFR3
. COL1A1
. CBFA1
. SOX9

Correct Answer & Explanation

. COMP

Explanation

Multiple epiphyseal dysplasia (MED) and pseudoachondroplasia are both associated with mutations in the COMP (Cartilage Oligomeric Matrix Protein) gene. MED presents with irregular, delayed ossification of the epiphyses but classically spares the spine, differentiating it from spondyloepiphyseal dysplasia.

Question 3803

Topic: 4. Pediatrics
A neonate is born with multiple fractures, severe bowing of long bones, and a beaded appearance of the ribs. The neonate expires shortly after birth from respiratory failure. Based on the Sillence classification for this condition, what is the inheritance pattern and type?
. Type I, Autosomal Dominant
. Type II, Autosomal Dominant (New mutation)
. Type III, Autosomal Recessive
. Type IV, Autosomal Dominant
. Type V, Autosomal Dominant

Correct Answer & Explanation

. Type II, Autosomal Dominant (New mutation)

Explanation

Sillence Type II osteogenesis imperfecta is the perinatal lethal form, presenting with beaded ribs, severe long bone deformities, and death from pulmonary hypoplasia. It predominantly arises from a spontaneous new autosomal dominant mutation in COL1A1/COL1A2.

Question 3804

Topic: 4. Pediatrics

A 12-year-old boy presents with progressive loss of forearm pronation and supination following a minor distal radius fracture treated in a cast. Radiographs demonstrate exuberant, hypertrophic callus formation and calcification of the interosseous membrane. Which of the following genes is most likely mutated in this patient?

. COL1A1
. COL1A2
. IFITM5
. COMP
. FGFR3

Correct Answer & Explanation

. IFITM5

Explanation

This patient has Osteogenesis Imperfecta Type V, which is characterized by hyperplastic callus formation and calcification of the interosseous membranes. It is uniquely caused by an autosomal dominant mutation in the IFITM5 gene.

Question 3805

Topic: 4. Pediatrics

A 5-year-old girl presents with disproportionate short stature, joint laxity, and a waddling gait. Examination reveals perfectly normal craniofacial features. Radiographs demonstrate delayed ossification of the epiphyses and irregular metaphyses. Which of the following clearly differentiates this condition from true achondroplasia?

. Presence of rhizomelic shortening
. Mutation in the FGFR3 gene
. Normal craniofacial features
. Autosomal recessive inheritance pattern
. Presence of a champagne glass pelvis

Correct Answer & Explanation

. Normal craniofacial features

Explanation

Pseudoachondroplasia presents with disproportionate short stature and limb deformities similar to achondroplasia, but patients have entirely normal craniofacial features and intelligence. It is caused by a mutation in the COMP gene, unlike achondroplasia (FGFR3).

Question 3806

Topic: 4. Pediatrics

A 6-year-old child presents with short-trunk dwarfism, a barrel-shaped chest, and progressive coxa vara. Genetic testing confirms a mutation in the COL2A1 gene, consistent with Spondyloepiphyseal Dysplasia Congenita (SEDC). Which of the following extra-skeletal manifestations must be critically screened for in this patient?

. Renal failure
. Sensorineural hearing loss
. Retinal detachment
. Congenital heart defects
. Hepatomegaly

Correct Answer & Explanation

. Retinal detachment

Explanation

SEDC is a type II collagenopathy. Type II collagen is abundant in articular cartilage and the vitreous humor of the eye; therefore, these patients are at high risk for severe myopia and retinal detachment.

Question 3807

Topic: 4. Pediatrics

A newborn is evaluated in the NICU and is noted to have micromelic short stature, bilateral severe clubfeet, radially deviated "hitchhiker" thumbs, and cystic swelling of the pinnae. What is the underlying genetic defect in this condition?

. Defect in type II collagen synthesis
. Mutation in the sulfate transporter gene (SLC26A2)
. Mutation in the fibroblast growth factor receptor 3 (FGFR3) gene
. Defect in the core binding factor alpha-1 (CBFA1) gene
. Mutation in the cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. Mutation in the sulfate transporter gene (SLC26A2)

Explanation

Diastrophic dysplasia presents with "hitchhiker" thumbs, cauliflower ears, and severe clubfeet. It is an autosomal recessive disorder caused by a mutation in the SLC26A2 gene, which encodes a sulfate transporter essential for cartilage matrix formation.

Question 3808

Topic: 4. Pediatrics
A 2-year-old child presents with markedly bowed legs, early loss of deciduous teeth with intact roots, and poor weight gain. Laboratory tests reveal hypercalcemia and unexpectedly low serum alkaline phosphatase levels. Accumulation of which of the following substances in the serum is diagnostic for this condition?
. Uric acid
. Pyridoxal 5'-phosphate
. 1,25-dihydroxyvitamin D
. Homocysteine
. Parathyroid hormone

Correct Answer & Explanation

. Pyridoxal 5'-phosphate

Explanation

Hypophosphatasia is caused by a mutation in the ALPL gene encoding tissue-nonspecific alkaline phosphatase (TNSALP). Defective enzyme function leads to an accumulation of its substrates, notably pyridoxal 5'-phosphate (the active form of Vitamin B6) and phosphoethanolamine.

Question 3809

Topic: 4. Pediatrics

A neonate is evaluated for disproportionate dwarfism. Examination reveals a flat midface, a cleft palate, extremely short limbs, and prominent, enlarged joints. Radiographs demonstrate "dumbbell-shaped" femora and coronal clefts in the vertebral bodies. Which of the following is the most likely diagnosis?

. Kniest dysplasia
. Achondroplasia
. Cleidocranial dysplasia
. Campomelic dysplasia
. Multiple epiphyseal dysplasia

Correct Answer & Explanation

. Kniest dysplasia

Explanation

Kniest dysplasia is a type II collagenopathy characterized by prominent joints, cleft palate, and hearing loss. Radiographically, the classic findings are dumbbell-shaped femora and coronal clefts in the vertebrae.

Question 3810

Topic: 4. Pediatrics
An infant presents with asymmetrical limb shortening, thick scaly skin (ichthyosis), and bilateral congenital cataracts. Radiographs reveal diffuse, stippled, calcific spots in the cartilaginous epiphyses. This presentation is most characteristic of which condition?
. Multiple epiphyseal dysplasia
. Chondrodysplasia punctata
. Diastrophic dysplasia
. Achondroplasia
. Pseudoachondroplasia

Correct Answer & Explanation

. Chondrodysplasia punctata

Explanation

Chondrodysplasia punctata (Conradi-Hünermann syndrome) classically presents with asymmetric limb shortening, ichthyosis, cataracts, and radiographic findings of stippled epiphyses in infancy.

Question 3811

Topic: 4. Pediatrics

A 5-year-old child with a known diagnosis of Osteogenesis Imperfecta presents with progressive anterolateral bowing of the femur, limiting ambulation.

What is the preferred surgical management for long-term correction of this deformity in a growing child?

. Fassier-Duval telescoping intramedullary rodding
. External fixation with gradual correction
. Rigid unreamed intramedullary nail
. Locking plate osteosynthesis
. Corrective osteotomy followed by serial casting

Correct Answer & Explanation

. Fassier-Duval telescoping intramedullary rodding

Explanation

Telescoping intramedullary rods, such as the Fassier-Duval system, are the gold standard for long bone deformity correction in growing children with Osteogenesis Imperfecta. They expand as the child grows, protecting the entire length of the bone and decreasing the need for revision surgeries.

Question 3812

Topic: Pediatric Hip

A 7-year-old girl is evaluated for delayed eruption of secondary dentition and an unusual ability to appose her shoulders anteriorly. Radiographs confirm absent clavicles.

Which of the following orthopaedic manifestations is most commonly associated with this genetic syndrome?

. Coxa vara
. Slipped capital femoral epiphysis
. Acetabular protrusio
. Bilateral hip dislocation
. Avascular necrosis of the femoral head

Correct Answer & Explanation

. Coxa vara

Explanation

Cleidocranial dysplasia (RUNX2 gene mutation) classically presents with delayed ossification of the skull, aplastic or hypoplastic clavicles, and pelvic abnormalities. Coxa vara and a widened pubic symphysis are the most common associated hip/pelvic manifestations.

Question 3813

Topic: 4. Pediatrics

A neonate is evaluated in the NICU for multiple long bone fractures sustained during a normal vaginal delivery. Physical examination reveals soft, deformable skull bones and deep blue sclerae.

The underlying molecular defect most commonly results in a deficiency or qualitative defect of which structural component?

. Type II collagen
. Type I collagen
. Type IX collagen
. Cartilage oligomeric matrix protein (COMP)
. Fibroblast growth factor receptor 3 (FGFR3)

Correct Answer & Explanation

. Type I collagen

Explanation

Osteogenesis imperfecta is primarily caused by autosomal dominant mutations in the COL1A1 or COL1A2 genes. This leads to defective or reduced Type I collagen, the major structural protein of bone, skin, tendons, and sclerae.

Question 3814

Topic: 4. Pediatrics

A newborn presents with short-limbed dwarfism, bilateral rigid clubfeet, "hitchhiker" thumbs, and cystic swelling of the external ears. What is the genetic inheritance pattern and affected gene for this syndrome?

. Autosomal dominant; FGFR3
. Autosomal recessive; SLC26A2
. X-linked recessive; PHEX
. Autosomal dominant; COMP
. Autosomal recessive; ALPL

Correct Answer & Explanation

. Autosomal recessive; SLC26A2

Explanation

Diastrophic dysplasia is an autosomal recessive disorder caused by a mutation in the SLC26A2 (DTDST) gene, which encodes a sulfate transporter. Hallmarks include cauliflower ears, hitchhiker thumbs, and severe, rigid clubfeet.

Question 3815

Topic: 4. Pediatrics

A 6-year-old child presents with short stature, a waddling gait, and joint pain. Radiographs demonstrate delayed, irregular epiphyseal ossification and normal vertebrae. The facial features are completely normal. A mutation in the COMP gene is identified. Which of the following is a classic radiographic finding of the patella in this patient's condition?

. Double-layer patella
. Patella alta
. Patella baja
. Bipartite patella
. Absent patella

Correct Answer & Explanation

. Double-layer patella

Explanation

Multiple Epiphyseal Dysplasia (MED) can be caused by mutations in the COMP gene. A "double-layer" patella seen on a lateral knee radiograph is a classic pathognomonic finding for MED.

Question 3816

Topic: 4. Pediatrics

A 5-year-old boy with achondroplasia presents with progressive, symptomatic genu varum. Clinical examination shows significant bowing with prominent fibular heads. What is the primary anatomic etiology of the varus alignment in this condition?

. Premature closure of the medial proximal tibial physis
. Relative overgrowth of the fibula compared to the tibia
. Vitamin D deficiency leading to physeal widening
. Laxity of the lateral collateral ligament
. Hypoplasia of the medial femoral condyle

Correct Answer & Explanation

. Relative overgrowth of the fibula compared to the tibia

Explanation

In achondroplasia, genu varum primarily results from a disparity in growth between the tibia and fibula. The relative overgrowth of the fibula tethers the lateral side of the leg, driving the tibia into a varus deformity.

Question 3817

Topic: 4. Pediatrics
A 1-year-old infant presents with severe bowing of the long bones, craniosynostosis, and premature loss of primary incisors. Laboratory studies reveal hypercalcemia, hypercalciuria, and a markedly decreased serum alkaline phosphatase level. Which of the following substrates is most likely elevated in this patient's urine?
. Homogentisic acid
. Phosphoethanolamine
. Hydroxyproline
. Methylmalonic acid
. Glycosaminoglycans

Correct Answer & Explanation

. Phosphoethanolamine

Explanation

Hypophosphatasia is an inherited disorder caused by mutations in the ALPL gene, resulting in deficient tissue-nonspecific alkaline phosphatase (TNSALP). This causes an accumulation of inorganic pyrophosphate, pyridoxal 5'-phosphate, and phosphoethanolamine (PEA) in the urine.

Question 3818

Topic: 4. Pediatrics
An 18-month-old child presents with anterolateral bowing of the left tibia and multiple café-au-lait spots. An X-ray is shown demonstrating the classic deformity. What is the underlying genetic mutation associated with this condition?
. Mutation in the NF2 gene on chromosome 22
. Mutation in the COL1A1 gene
. Mutation in the NF1 gene on chromosome 17 coding for neurofibromin
. GNAS1 gene mutation
. EXT1 gene mutation

Correct Answer & Explanation

. Mutation in the NF1 gene on chromosome 17 coding for neurofibromin

Explanation

Neurofibromatosis type 1 is associated with a mutation in the NF1 gene on chromosome 17, which encodes neurofibromin. Anterolateral bowing of the tibia is highly characteristic and often progresses to congenital pseudarthrosis.

Question 3819

Topic: 4. Pediatrics

A 2-year-old boy presents with an anterolateral bowing of the tibia. Radiographs show medullary sclerosis and a narrow canal at the apex of the deformity.

What is the underlying genetic mutation most commonly associated with this specific condition?

. NF2 gene on chromosome 22
. NF1 gene on chromosome 17
. GNAS gene on chromosome 20
. EXT1 gene on chromosome 8
. FGFR3 gene on chromosome 4

Correct Answer & Explanation

. NF1 gene on chromosome 17

Explanation

Anterolateral bowing of the tibia and subsequent congenital pseudarthrosis are highly associated with Neurofibromatosis type 1 (NF1). NF1 is an autosomal dominant disorder caused by a mutation in the neurofibromin gene on chromosome 17.

Question 3820

Topic: 4. Pediatrics

A 2-year-old boy with multiple cafe-au-lait spots presents with the severe lower extremity deformity shown in the clinical and radiographic context.

What is the underlying genetic mutation most commonly associated with this specific osseous manifestation?

. Mutation in the neurofibromin gene on chromosome 17
. Mutation in the merlin gene on chromosome 22
. Activating mutation in the FGFR3 gene
. Mutation in the COL1A1 gene
. Inactivating mutation in the EXT1 gene

Correct Answer & Explanation

. Mutation in the neurofibromin gene on chromosome 17

Explanation

Congenital anterolateral bowing of the tibia and subsequent pseudarthrosis are hallmark orthopedic manifestations of Neurofibromatosis type 1 (NF1). NF1 is caused by a mutation in the neurofibromin gene on chromosome 17.

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