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4. Pediatrics MCQs

Practice Set 329 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 6561

Topic: 4. Pediatrics

A 4-year-old child is evaluated for progressive stiffness and painful soft tissue swellings. Physical examination reveals bilateral hallux valgus and uniquely shortened great toes. Radiographs show early ectopic bone formation in the paraspinal muscles. What is the underlying genetic mutation?

. GNAS1
. ACVR1
. EXT1
. FGFR3
. COL1A1

Correct Answer & Explanation

. ACVR1

Explanation

The patient has Fibrodysplasia Ossificans Progressiva (FOP), characterized by congenital malformation of the great toes and progressive heterotopic ossification. FOP is caused by an activating mutation in the ACVR1 (ALK2) gene, a BMP type I receptor.

Question 6562

Topic: 4. Pediatrics

A 5-year-old boy presents with short stature, coxa vara, and pronounced bowing of the lower extremities. Laboratory tests (calcium, phosphorus, alkaline phosphatase, and Vitamin D) are completely normal. Radiographs show widened, irregular metaphyses but normal epiphyses. What is the genetic mutation responsible for the Schmid type of this dysplasia?

. Type X collagen (COL10A1)
. Type I collagen (COL1A1)
. Type II collagen (COL2A1)
. Fibroblast growth factor receptor 3 (FGFR3)
. Cartilage oligomeric matrix protein (COMP)

Correct Answer & Explanation

. Type X collagen (COL10A1)

Explanation

Metaphyseal chondrodysplasia, Schmid type, presents similarly to rickets but with normal laboratory values. It is caused by a mutation in the COL10A1 gene, which affects type X collagen located in the hypertrophic zone of the physis.

Question 6563

Topic: 4. Pediatrics

Which of the following genes is mutated in Schmid type metaphyseal chondrodysplasia?

. COMP
. FGFR3
. COL10A1
. RUNX2
. SLC26A2

Correct Answer & Explanation

. COL10A1

Explanation

Schmid type metaphyseal chondrodysplasia is caused by an autosomal dominant mutation in the COL10A1 gene, which encodes type X collagen. It typically presents with short stature, coxa vara, and bowing of the long bones.

Question 6564

Topic: 4. Pediatrics

A 10-year-old asymptomatic child undergoes knee radiographs following minor trauma, revealing an 'Erlenmeyer flask' deformity of the distal femurs.

History reveals early dental caries and genu valgum. What is the most likely diagnosis?

. Osteopetrosis
. Achondroplasia
. Pyle disease (Familial metaphyseal dysplasia)
. Multiple epiphyseal dysplasia
. Cleidocranial dysplasia

Correct Answer & Explanation

. Pyle disease (Familial metaphyseal dysplasia)

Explanation

Pyle disease is an autosomal recessive disorder characterized by a defect in metaphyseal modeling, leading to the classic 'Erlenmeyer flask' deformity. Patients are typically asymptomatic but may have genu valgum and dental anomalies.

Question 6565

Topic: 4. Pediatrics

A 6-month-old infant with a known FGFR3 mutation presents with failure to thrive, apnea, and hypotonia. What is the most common cause of mortality in this patient population during infancy?

. Atlantoaxial instability
. Cervicomedullary compression at the foramen magnum
. Severe thoracic kyphosis causing cor pulmonale
. Hydrocephalus
. Tracheal stenosis

Correct Answer & Explanation

. Cervicomedullary compression at the foramen magnum

Explanation

Infants with achondroplasia (FGFR3 mutation) can experience severe stenosis of the foramen magnum. This cervicomedullary compression can lead to central apnea, hypotonia, quadriparesis, and is a leading cause of sudden death in these infants.

Question 6566

Topic: 4. Pediatrics

A 4-year-old child presents with short stature, a waddling gait, and bowing of the lower extremities. Radiographs show flaring and irregularity of the metaphyses with normal epiphyses and spine. Genetic testing reveals a mutation in the COL10A1 gene. What is the most likely diagnosis?

. Multiple epiphyseal dysplasia
. Schmid metaphyseal chondrodysplasia
. Jansen metaphyseal chondrodysplasia
. Achondroplasia
. Pseudoachondroplasia

Correct Answer & Explanation

. Schmid metaphyseal chondrodysplasia

Explanation

Schmid metaphyseal chondrodysplasia is an autosomal dominant disorder caused by a mutation in the COL10A1 gene, which affects type X collagen in the hypertrophic zone of the physis. It presents with short stature, coxa vara, and bowed legs, but normal epiphyses and spine.

Question 6567

Topic: 4. Pediatrics

A 6-month-old infant is evaluated for rhizomelic short stature, frontal bossing, and midface hypoplasia. Radiographs reveal narrowing of the interpedicular distances in the lumbar spine. Which of the following represents the underlying cellular defect in this condition?

. Defect in type I collagen synthesis
. Defect in the hypertrophic zone of the physis
. Decreased proliferation of chondrocytes in the proliferative zone of the physis
. Defect in osteoclast function and ruffled border formation
. Mutation in the COMP gene affecting the extracellular matrix

Correct Answer & Explanation

. Decreased proliferation of chondrocytes in the proliferative zone of the physis

Explanation

Achondroplasia is caused by an activating mutation in the FGFR3 gene. This overactivity inhibits chondrocyte proliferation in the proliferative zone of the physis, leading to severely impaired endochondral ossification and rhizomelic dwarfism.

Question 6568

Topic: 4. Pediatrics

The radiograph of a 5-year-old child with short stature demonstrates metaphyseal flaring and lucencies, as shown in the image.

If this patient has McKusick type metaphyseal chondrodysplasia (cartilage-hair hypoplasia), which of the following systemic manifestations is most commonly associated?

. Hypercalcemia
. Cellular immunodeficiency
. Deafness
. Retinitis pigmentosa
. Congenital heart defects

Correct Answer & Explanation

. Cellular immunodeficiency

Explanation

McKusick type metaphyseal chondrodysplasia, or cartilage-hair hypoplasia, is an autosomal recessive disorder caused by an RMRP gene mutation. It is classically associated with fine, sparse hair and defective T-cell function leading to cellular immunodeficiency.

Question 6569

Topic: 4. Pediatrics

A 7-year-old girl presents with short stature, a waddling gait, and joint laxity. Unlike achondroplasia, her facial features are completely normal. Radiographs reveal delayed, fragmented epiphyseal ossification centers and irregular metaphyses. Which of the following genes is most likely mutated in this patient?

. FGFR3
. COMP
. COL1A1
. RUNX2
. SOX9

Correct Answer & Explanation

. COMP

Explanation

Pseudoachondroplasia is caused by a mutation in the COMP (Cartilage Oligomeric Matrix Protein) gene. Patients present with short stature and joint laxity but, unlike true achondroplasia, they have normal facies and normal intelligence.

Question 6570

Topic: 4. Pediatrics

A newborn is noted to have short-limbed dwarfism, bilateral clubfeet, "hitchhiker" thumbs, and cystic swelling of the external ears. Radiographs show a short, thick first metacarpal. What is the underlying genetic mutation for this condition?

. SLC26A2
. FGFR3
. COMP
. COL2A1
. CBFA1

Correct Answer & Explanation

. SLC26A2

Explanation

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

Question 6571

Topic: 4. Pediatrics

A 5-year-old child presents with short stature and a waddling gait. Radiographs are shown below.

Genetic testing is most likely to reveal a mutation in which of the following genes?

. FGFR3
. COMP
. COL10A1
. COL1A1
. RUNX2

Correct Answer & Explanation

. COL10A1

Explanation

The radiograph shows coxa vara and flaring/irregularity of the metaphyses, classic for Schmid metaphyseal chondrodysplasia. This condition is inherited in an autosomal dominant pattern and is caused by a mutation in the COL10A1 gene, affecting type X collagen in the hypertrophic zone.

Question 6572

Topic: 4. Pediatrics

A 4-year-old girl is diagnosed with the most common form of short-limb dwarfism. Her parents are of average height. The underlying mutation results in an abnormality in which specific zone of the physis?

. Resting zone
. Proliferative zone
. Hypertrophic zone
. Zone of provisional calcification
. Primary spongiosa

Correct Answer & Explanation

. Proliferative zone

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3, which inhibits normal chondrocyte proliferation. This directly affects the proliferative zone of the physis, leading to decreased endochondral ossification and rhizomelic shortening.

Question 6573

Topic: Pediatric Hip

A 9-year-old girl presents with short stature, sparse hair, a bulbous pear-shaped nose, and finger joint deformities. Radiographs of her hands show cone-shaped epiphyses in the phalanges.

What other orthopedic manifestation is highly characteristic of this syndrome?

. Multiple osteochondromas
. Premature hip osteoarthritis resembling Legg-Calve-Perthes
. Atlantoaxial instability
. Scoliosis with rib fusions
. Osteosclerosis of the skull base

Correct Answer & Explanation

. Premature hip osteoarthritis resembling Legg-Calve-Perthes

Explanation

Trichorhinophalangeal syndrome (TRPS) Type 1 is caused by a TRPS1 gene mutation. Alongside the classic facial features and cone-shaped phalangeal epiphyses, patients frequently develop severe early-onset hip dysplasia and Perthes-like changes.

Question 6574

Topic: 4. Pediatrics

Children with severe infantile autosomal recessive osteopetrosis frequently develop blindness and deafness. What is the primary pathophysiological mechanism for these sensory deficits?

. Direct neurotoxicity from elevated serum calcium
. Compression of cranial nerves due to failure of neural foramina to widen
. Ischemic neuropathy from extensive vascular calcification
. Associated central nervous system demyelination
. Congenital absence of cranial nerve nuclei

Correct Answer & Explanation

. Compression of cranial nerves due to failure of neural foramina to widen

Explanation

In osteopetrosis, the lack of osteoclastic bone resorption prevents the normal enlargement of cranial neural foramina during growth. This leads to bony compression of cranial nerves, resulting in blindness, deafness, and facial palsies.

Question 6575

Topic: Pediatric Hip

A 10-year-old boy with Trichorhinophalangeal syndrome type 1 (TRPS1) complains of bilateral groin pain. Radiographs reveal flattening and fragmentation of both femoral heads. What is the expected long-term orthopedic outcome if this hip pathology is left untreated?

. Spontaneous resolution with normal spherical femoral heads
. Development of secondary osteosarcoma
. Premature secondary osteoarthritis requiring early arthroplasty
. Progression to slipped capital femoral epiphysis (SCFE)
. High-output cardiac failure

Correct Answer & Explanation

. Premature secondary osteoarthritis requiring early arthroplasty

Explanation

TRPS1 is associated with Legg-Calve-Perthes-like changes in the hips. These skeletal dysplasias lead to early joint incongruity and severe premature osteoarthritis.

Question 6576

Topic: 4. Pediatrics

A 12-year-old girl presents with bilateral hip pain. Exam reveals sparse scalp hair and a bulbous, pear-shaped nose. Radiographs demonstrate cone-shaped epiphyses of the phalanges.

What is the underlying genetic mutation?

. TRPS1 gene
. COMP gene
. COL2A1 gene
. FGFR3 gene
. SOX9 gene

Correct Answer & Explanation

. TRPS1 gene

Explanation

The clinical presentation is classic for Trichorhinophalangeal syndrome (TRPS) Type 1, which is caused by a mutation in the TRPS1 gene. This gene encodes a zinc-finger transcription repressor involved in chondrocyte and perichondrium development.

Question 6577

Topic: Pediatric Hip
A 10-year-old boy has bilateral Legg-Calvé-Perthes-like hip changes, a bulbous nasal tip, and cone-shaped epiphyses on hand radiographs. This syndrome is caused by a defect in a gene that functions primarily as a:
. Structural collagen component
. Zinc-finger transcription repressor
. Fibroblast growth factor receptor
. Matrix metalloproteinase
. Transmembrane ion channel

Correct Answer & Explanation

. Zinc-finger transcription repressor

Explanation

TRPS Type 1 is caused by a mutation in the TRPS1 gene, which functions as a zinc-finger transcription repressor. This regulates the development of the perichondrium and articular cartilage.

Question 6578

Topic: 4. Pediatrics
A 15-year-old girl with confirmed TRPS Type 1 presents with hand radiographs showing brachydactyly and distinctive cone-shaped epiphyses. Which of the following lower extremity pathologies is she at highest risk for developing prematurely?
. Slipped capital femoral epiphysis
. Early-onset hip osteoarthritis mimicking sequelae of Perthes disease
. Bilateral genu varum with medial physeal beaking
. Recurrent patellar dislocations
. Tarsal coalition

Correct Answer & Explanation

. Early-onset hip osteoarthritis mimicking sequelae of Perthes disease

Explanation

Patients with TRPS Type 1 frequently develop severe, early-onset hip dysplasia and osteoarthritis. The femoral head changes heavily mimic Legg-Calvé-Perthes disease but are often bilateral and progressive.

Question 6579

Topic: 4. Pediatrics

An infant with diffuse skeletal sclerosis and hepatosplenomegaly develops progressive vision loss. What is the most likely pathophysiologic mechanism for this complication?

. Retinal detachment secondary to collagen defect
. Primary optic nerve hypoplasia
. Bony encroachment of the optic neural foramina
. Intraocular calcification
. Vitamin A deficiency from malabsorption

Correct Answer & Explanation

. Bony encroachment of the optic neural foramina

Explanation

Osteopetrosis involves a failure of osteoclastic bone resorption, leading to narrowed cranial nerve foramina. This commonly causes blindness and deafness due to cranial nerve compression.

Question 6580

Topic: Pediatric Hip
TRPS Type II (Langer-Giedion syndrome) shares many features with TRPS Type I, including sparse hair and cone-shaped epiphyses. Which of the following clinical findings uniquely distinguishes TRPS Type II from Type I?
. Legg-Calvé-Perthes-like hip disease
. Multiple osteochondromas
. Mandibular hypoplasia
. Blue sclerae
. Severe scoliosis

Correct Answer & Explanation

. Multiple osteochondromas

Explanation

TRPS Type II (Langer-Giedion syndrome) is caused by a contiguous gene deletion involving both the TRPS1 gene and the EXT1 gene, leading to the unique development of multiple osteochondromas not seen in Type I.

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