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4. Pediatrics MCQs

Practice Set 303 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 6041

Topic: 4. Pediatrics
A child is diagnosed with osteogenesis imperfecta type I, which presents with mild bone fragility and blue sclerae. Which of the following best describes the underlying collagen defect in this specific type?
. Production of an abnormal, truncated Type I collagen chain
. Decreased production of structurally normal Type I collagen
. Inability to cross-link Type II collagen fibrils
. Defective hydroxylation of proline residues
. Overproduction of poorly organized Type III collagen

Correct Answer & Explanation

. Decreased production of structurally normal Type I collagen

Explanation

Osteogenesis imperfecta Type I is caused by a quantitative defect (a null allele), resulting in a decreased amount of structurally normal Type I collagen. In contrast, Types II, III, and IV involve qualitative (structural) defects, leading to more severe phenotypes.

Question 6042

Topic: 4. Pediatrics

A 10-year-old boy presents with progressive, deep-aching leg pain and a waddling gait. Radiographs reveal symmetrical, bilateral cortical thickening of the long bone diaphyses, sparing the metaphyses and epiphyses.

The pathogenesis of this disease is linked to a mutation in which of the following genes?

. COL1A1
. FGFR3
. GNAS
. TGFB1
. COMP

Correct Answer & Explanation

. TGFB1

Explanation

Progressive diaphyseal dysplasia (Camurati-Engelmann disease) is caused by a mutation in the TGFB1 gene, which encodes transforming growth factor-beta 1. This leads to increased bone formation primarily along the diaphyseal cortices.

Question 6043

Topic: 4. Pediatrics

A 6-month-old infant is evaluated for short limbs and a prominent forehead. Genetic testing confirms an activating mutation in the FGFR3 gene. At the cellular level within the physis, this mutation primarily results in which of the following?

. Decreased chondrocyte proliferation in the proliferative zone
. Defective calcification in the zone of provisional calcification
. Accelerated hypertrophy of chondrocytes in the hypertrophic zone
. Failure of primary spongiosa resorption by osteoclasts
. Impaired stem cell recruitment in the reserve zone

Correct Answer & Explanation

. Decreased chondrocyte proliferation in the proliferative zone

Explanation

Achondroplasia is caused by a gain-of-function mutation in FGFR3. Paradoxically, this receptor normally acts as a negative regulator of bone growth; its overactivation profoundly inhibits chondrocyte proliferation in the proliferative zone of the physis.

Question 6044

Topic: 4. Pediatrics

A 12-year-old boy with a family history of bone bumps presents with multiple cartilage-capped bony outgrowths around his knees and wrists. He is diagnosed with Multiple Hereditary Exostoses. The genetic mutations responsible for this condition disrupt normal physeal growth by impairing which cellular process?

. Type X collagen synthesis in the hypertrophic zone
. Heparan sulfate synthesis in the Golgi apparatus
. Indian hedgehog (Ihh) cleavage in the endoplasmic reticulum
. Lysyl oxidase cross-linking of Type I collagen
. Sulfate transport across the cell membrane

Correct Answer & Explanation

. Heparan sulfate synthesis in the Golgi apparatus

Explanation

Multiple Hereditary Exostoses (MHE) is caused by mutations in the EXT1 or EXT2 genes. These genes act in the Golgi apparatus to synthesize heparan sulfate. Deficient heparan sulfate disrupts the diffusion of Indian hedgehog (Ihh) signaling at the growth plate, leading to exostosis formation.

Question 6045

Topic: 4. Pediatrics

A 4-year-old child presents with short-limbed dwarfism, frontal bossing, and midface hypoplasia. Radiographs show narrowing of the interpedicular distances in the lumbar spine. Which genetic mutation and receptor anomaly are responsible for this condition?

. FGFR3 activating mutation
. COL1A1 mutation
. RUNX2 mutation
. COMP mutation
. EXT1 mutation

Correct Answer & Explanation

. FGFR3 activating mutation

Explanation

Achondroplasia is caused by a gain-of-function (activating) mutation in the FGFR3 gene. This leads to the inhibition of chondrocyte proliferation in the proliferative zone of the physis.

Question 6046

Topic: 4. Pediatrics

An 8-month-old infant with achondroplasia is brought to the clinic by his parents who are concerned about a noticeable bump on his lower back. Examination reveals a flexible thoracolumbar kyphosis. Neurological examination is normal. What is the most appropriate initial management?

. Immediate posterior spinal fusion
. Anterior and posterior spinal fusion
. Avoidance of unsupported sitting and observation
. Thoracolumbosacral orthosis (TLSO) bracing
. Foramen magnum decompression

Correct Answer & Explanation

. Avoidance of unsupported sitting and observation

Explanation

Correct Answer: Avoidance of unsupported sitting and observationThoracolumbar kyphosis is present in over 90% of infants with achondroplasia. It is primarily postural and related to hypotonia and a large head size. The vast majority of these deformities resolve spontaneously when the child begins walking. The recommended management is to avoid unsupported sitting (which exacerbates the kyphosis) and to observe. Bracing or surgery is reserved for progressive, rigid deformities or those with neurological compromise.

Question 6047

Topic: 4. Pediatrics

A 6-year-old girl presents with short-limb dwarfism and a waddling gait. Her facial features are normal. Radiographs of the spine reveal platyspondyly with anterior tongue-like projections of the vertebral bodies. A mutation in which of the following genes is the most likely cause of her condition?

. FGFR3
. COL2A1
. COMP
. SLC26A2
. RUNX2

Correct Answer & Explanation

. COMP

Explanation

Correct Answer: COMPThe clinical picture of short-limb dwarfism with normal facies and specific radiographic findings (platyspondyly with anterior tongue-like projections) is characteristic of pseudoachondroplasia. This condition is caused by mutations in the Cartilage Oligomeric Matrix Protein (COMP) gene. Unlike achondroplasia (FGFR3), patients with pseudoachondroplasia have normal facial features and head size.

Question 6048

Topic: Pediatric Hip

A 4-year-old boy is diagnosed with Spondyloepiphyseal Dysplasia Congenita (SEDC). He has a barrel chest, severe coxa vara, and a shortened trunk. The underlying genetic defect in this condition primarily affects which of the following structural proteins?

. Type I collagen
. Type II collagen
. Type X collagen
. Cartilage oligomeric matrix protein
. Fibroblast growth factor receptor

Correct Answer & Explanation

. Type II collagen

Explanation

Correct Answer: Type II collagenSpondyloepiphyseal Dysplasia Congenita (SEDC) is a type II collagenopathy, caused by mutations in the COL2A1 gene. Type II collagen is the primary structural protein in articular cartilage and the nucleus pulposus of intervertebral discs. Defects lead to abnormal epiphyseal development, platyspondyly, and severe joint deformities like coxa vara.

Question 6049

Topic: 4. Pediatrics

An 8-month-old infant with achondroplasia is noted to have a prominent thoracolumbar kyphosis when sitting. Neurological examination is normal. What is the most appropriate initial management?

. Immediate posterior spinal fusion
. Application of a Milwaukee brace
. Avoidance of unsupported sitting and observation
. Anterior spinal release and fusion

Correct Answer & Explanation

. Avoidance of unsupported sitting and observation

Explanation

Correct Answer: Avoidance of unsupported sitting and observationThoracolumbar kyphosis is present in over 90% of infants with achondroplasia. It is primarily postural, exacerbated by hypotonia and a large head size. The most appropriate initial management is to avoid unsupported sitting. In the vast majority of cases, the kyphosis resolves spontaneously once the child develops adequate trunk strength and begins to walk. Bracing or surgery is reserved for progressive, rigid deformities that persist after walking age.

Question 6050

Topic: 4. Pediatrics

A neonate is evaluated for disproportionate short stature, prominent joints, and a cleft palate. Spinal radiographs reveal characteristic coronal clefts in the vertebral bodies. Which of the following is the most likely diagnosis?

. Achondroplasia
. Kniest dysplasia
. Pseudoachondroplasia
. Cleidocranial dysplasia

Correct Answer & Explanation

. Kniest dysplasia

Explanation

Correct Answer: Kniest dysplasiaKniest dysplasia is a type II collagenopathy characterized by short-trunk dwarfism, prominent joints, midface hypoplasia, cleft palate, and myopia. Radiographically, it is uniquely associated with coronal clefts in the vertebral bodies during infancy, as well as dumbbell-shaped femora. Achondroplasia presents with narrowing interpedicular distances, and pseudoachondroplasia typically presents later in childhood with normal facial features.

Question 6051

Topic: 4. Pediatrics

An 8-month-old infant with achondroplasia is noted to have a flexible thoracolumbar kyphosis of 35 degrees. Neurological examination is normal. Which of the following is the most appropriate management recommendation to prevent progression of this deformity?

. Immediate application of a rigid thoracolumbosacral orthosis (TLSO)
. Prohibiting unsupported sitting until the child develops adequate trunk strength
. Prophylactic posterior spinal fusion from T10 to L3
. Encouraging early use of a baby walker to stimulate spinal extensor muscles

Correct Answer & Explanation

. Prohibiting unsupported sitting until the child develops adequate trunk strength

Explanation

Correct Answer: Prohibiting unsupported sitting until the child develops adequate trunk strengthThoracolumbar kyphosis is present in over 90% of infants with achondroplasia. It is primarily postural, resulting from hypotonia, a large head, and ligamentous laxity. The deformity is usually flexible and resolves in the vast majority of children once they begin walking and develop lumbar lordosis. The most effective preventative measure against fixed anterior vertebral wedging and progressive kyphosis is to avoid unsupported sitting in the first 12-18 months of life. Bracing is reserved for persistent or rigid curves, and surgery is rarely needed unless the curve becomes severe and fixed.

Question 6052

Topic: 4. Pediatrics

A neonate is evaluated for a skeletal dysplasia. Radiographs reveal coronal clefts of the vertebral bodies, dumbbell-shaped femora, and severe platyspondyly. The patient later develops progressive kyphoscoliosis and enlarged, stiff joints. A mutation in which of the following genes is most likely responsible for this condition?

. FGFR3
. COMP
. COL2A1
. SLC26A2

Correct Answer & Explanation

. COL2A1

Explanation

Correct Answer: COL2A1The clinical and radiographic presentation describes Kniest dysplasia, which is a type II collagenopathy caused by mutations in the COL2A1 gene. Hallmark radiographic findings in neonates include coronal clefts of the vertebral bodies and dumbbell-shaped long bones (especially femora) with broad metaphyses. Patients typically develop severe platyspondyly, progressive kyphoscoliosis, and prominent, stiff joints. FGFR3 is associated with achondroplasia, COMP with pseudoachondroplasia, and SLC26A2 with diastrophic dysplasia.

Question 6053

Topic: 4. Pediatrics

A 1-year-old child with achondroplasia presents with central sleep apnea, hyperreflexia, and delayed motor milestones. Magnetic resonance imaging confirms severe cervicomedullary compression. What is the primary anatomical cause of this compression?

. Odontoid hypoplasia leading to atlantoaxial subluxation
. Premature fusion of the neurocentral synchondroses of the atlas and axis
. Stenosis of the foramen magnum due to abnormal endochondral ossification of the cranial base
. Hypertrophy of the posterior longitudinal ligament and ligamentum flavum

Correct Answer & Explanation

. Stenosis of the foramen magnum due to abnormal endochondral ossification of the cranial base

Explanation

Correct Answer: Stenosis of the foramen magnum due to abnormal endochondral ossification of the cranial baseInfants with achondroplasia are at significant risk for foramen magnum stenosis, which can lead to cervicomedullary compression, central sleep apnea, myelopathy, and even sudden infant death. The skull base develops via endochondral ossification (which is defective in achondroplasia due to the FGFR3 mutation), leading to a congenitally small foramen magnum. The cranial vault, however, develops via intramembranous ossification and is relatively large. Odontoid hypoplasia and AAI are characteristic of SEDC and Morquio syndrome, not achondroplasia.

Question 6054

Topic: 4. Pediatrics

An 8-month-old infant with achondroplasia presents with a prominent thoracolumbar kyphosis. Neurologic examination is normal. What is the most appropriate management strategy at this stage?

. Immediate anterior and posterior spinal fusion
. Application of a Milwaukee brace for 23 hours a day
. Avoidance of unsupported sitting and observation
. Posterior column osteotomies
. Halo gravity traction

Correct Answer & Explanation

. Avoidance of unsupported sitting and observation

Explanation

Correct Answer: Avoidance of unsupported sitting and observationThoracolumbar kyphosis is very common in infants with achondroplasia, primarily due to hypotonia and a large, heavy head. The vast majority (over 90%) will resolve spontaneously when the child begins to walk and develops lumbar lordosis. Management consists of avoiding unsupported sitting (which exacerbates the deformity) and observation. Bracing or surgery is reserved for progressive, rigid deformities persisting into early childhood.

Question 6055

Topic: 4. Pediatrics

A 12-year-old boy presents with back pain and a progressively worsening short-trunk appearance. Radiographs reveal platyspondyly with a characteristic hump-shaped buildup of bone on the central and posterior portions of the vertebral endplates. His maternal uncle has a similar body habitus. What is the most likely diagnosis and its inheritance pattern?

. Spondyloepiphyseal dysplasia congenita; Autosomal dominant
. Spondyloepiphyseal dysplasia tarda; X-linked recessive
. Multiple epiphyseal dysplasia; Autosomal dominant
. Morquio syndrome; Autosomal recessive
. Achondroplasia; Autosomal dominant

Correct Answer & Explanation

. Spondyloepiphyseal dysplasia tarda; X-linked recessive

Explanation

Correct Answer: Spondyloepiphyseal dysplasia tarda; X-linked recessiveSpondyloepiphyseal dysplasia tarda (SEDT) typically presents in late childhood or early adolescence, distinguishing it from SED congenita which is present at birth. It is characterized by short-trunk dwarfism, premature osteoarthritis, and classic radiographic findings of platyspondyly with a hump-shaped buildup of bone on the posterior/central endplates. The classic form is X-linked recessive (TRAPPC2 gene mutation), which aligns with the presentation in a boy and his maternal uncle.

Question 6056

Topic: 4. Pediatrics

A 9-month-old infant with achondroplasia presents with a prominent thoracolumbar kyphosis. Neurological examination is completely normal. Radiographs confirm a flexible thoracolumbar kyphosis without fixed wedging of the apical vertebrae. What is the most appropriate initial management?

. Immediate posterior spinal fusion
. Anterior and posterior spinal fusion
. Avoidance of unsupported sitting
. Thoracolumbosacral orthosis (TLSO) for 23 hours a day
. Observation with no restrictions on positioning

Correct Answer & Explanation

. Avoidance of unsupported sitting

Explanation

Correct Answer: Avoidance of unsupported sittingThoracolumbar kyphosis is extremely common in infants with achondroplasia, occurring in over 90% of cases. It is primarily postural, related to hypotonia and a large head size. The most appropriate initial management is the avoidance of unsupported sitting and avoiding carrying the child in a flexed posture (e.g., in a soft sling). With these precautions and the eventual onset of walking, the kyphosis resolves spontaneously in the vast majority of patients. Bracing or surgery is reserved for progressive, rigid deformities or those with neurological compromise.

Question 6057

Topic: 4. Pediatrics

Spondyloepiphyseal dysplasia congenita (SEDC) is characterized by disproportionate short-trunk dwarfism and major spinal involvement, including a high risk of atlantoaxial instability. This condition is primarily caused by a mutation affecting which of the following?

. Fibroblast growth factor receptor 3 (FGFR3)
. Type I collagen
. Type II collagen
. Cartilage oligomeric matrix protein (COMP)
. Diastrophic dysplasia sulfate transporter (DTDST)

Correct Answer & Explanation

. Type II collagen

Explanation

Correct Answer: Type II collagenSpondyloepiphyseal dysplasia congenita (SEDC) is an autosomal dominant disorder caused by mutations in the COL2A1 gene, which encodes for Type II collagen. This leads to abnormal cartilage formation, affecting the spine and epiphyses. FGFR3 mutations cause achondroplasia. Type I collagen mutations cause osteogenesis imperfecta. COMP mutations cause pseudoachondroplasia and multiple epiphyseal dysplasia. DTDST mutations cause diastrophic dysplasia.

Question 6058

Topic: 4. Pediatrics

A neonate is evaluated for a skeletal dysplasia. Radiographs reveal coronal clefts in the vertebral bodies, dumbbell-shaped femora, and severe platyspondyly. The child also has a cleft palate and prominent, enlarged joints. Which of the following is the most likely diagnosis?

. Achondroplasia
. Diastrophic dysplasia
. Kniest dysplasia
. Cleidocranial dysplasia
. Osteogenesis imperfecta

Correct Answer & Explanation

. Kniest dysplasia

Explanation

Correct Answer: Kniest dysplasiaKniest dysplasia is a type II collagenopathy characterized by short trunk and limbs, prominent joints, and midface hypoplasia (often with cleft palate). Radiographically, it is classically associated with coronal clefts in the vertebral bodies during infancy, severe platyspondyly, and 'dumbbell-shaped' long bones (especially the femora) due to broad metaphyses and epiphyses.

Question 6059

Topic: 4. Pediatrics

A 2-year-old child presents with a prominent thoracolumbar gibbus deformity, corneal clouding, and hepatosplenomegaly. Radiographs show anterior beaking of the inferior aspect of the lumbar vertebrae. A deficiency in which of the following enzymes is the most likely cause of this patient's skeletal dysplasia?

. Galactosamine-6-sulfatase
. Alpha-L-iduronidase
. Iduronate-2-sulfatase
. Arylsulfatase B
. Beta-galactosidase

Correct Answer & Explanation

. Alpha-L-iduronidase

Explanation

Correct Answer: Alpha-L-iduronidaseThe clinical picture of a thoracolumbar gibbus, corneal clouding, hepatosplenomegaly, and inferior anterior vertebral beaking is classic for Hurler syndrome (Mucopolysaccharidosis type I). Hurler syndrome is caused by a deficiency in the enzyme alpha-L-iduronidase. Morquio syndrome A (MPS IVA) is caused by galactosamine-6-sulfatase deficiency and typically features central anterior vertebral beaking. Hunter syndrome (MPS II) is caused by iduronate-2-sulfatase deficiency and lacks corneal clouding.

Question 6060

Topic: 4. Pediatrics

An infant with achondroplasia is being evaluated in the clinic. The parents report that the child has episodes of sleep apnea, loud snoring, and exhibits hyperreflexia in the lower extremities. Which of the following is the most appropriate next step in management?

. Reassurance and routine follow-up
. Polysomnography and MRI of the craniocervical junction
. Immediate application of a cervical collar
. Genetic testing to confirm the FGFR3 mutation
. Thoracolumbosacral orthosis (TLSO) fitting

Correct Answer & Explanation

. Polysomnography and MRI of the craniocervical junction

Explanation

Correct Answer: Polysomnography and MRI of the craniocervical junctionInfants with achondroplasia are at high risk for foramen magnum stenosis, which can cause cervicomedullary compression. Symptoms include central sleep apnea, hyperreflexia, clonus, and delayed motor milestones. This is a potentially life-threatening complication (sudden infant death). The appropriate workup includes a sleep study (polysomnography) to evaluate for central apnea and an MRI of the craniocervical junction to assess the degree of stenosis and cord signal changes. Surgical decompression may be urgently required.

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