Question 1

Q: Radiographic studies of a 2-year-old child reveal a new fracture of the humerus and evidence of multiple old fractures in ribs and long bones. Despite the broken arm, the toddler shows minimal bruising. A physical examination reveals peculiar teeth, a blue tinge to the sclera, and unusually mobile joints. The condition suspected in this child is characterized by an abnormality of which of the following biochemical functions?

Collagen type I synthesis. **Explanation:** The clinical presentation of multiple fractures at various stages of healing, blue sclerae, dental abnormalities (dentinogenesis imperfecta), and joint hypermobility in a 2-year-old is diagnostic of **Osteogenesis Imperfecta (OI)**, specifically Type I. While multiple fractures often raise suspicion for child abuse (Non-Accidental Injury), the presence of blue sclera and dental findings points toward a genetic connective tissue disorder. **1. Why Option A is correct:** Osteogenesis Imperfecta is primarily caused by autosomal dominant mutations in the **COL1A1 or COL1A2 genes**, which encode the alpha chains of **Type I Collagen**. Type I collagen is the major structural protein in bone, skin, tendons, and the sclera. Defective synthesis or structure of this collagen leads to "brittle bones," thin sclera (allowing the underlying choroid to show through as blue), and weak dentin. **2. Why other options are incorrect:** * **Option B (Type II Collagen):** Found primarily in **hyaline cartilage** and vitreous humor. Defects lead to skeletal dysplasias like Achondrogenesis. * **Option C (Type III Collagen):** Found in **blood vessels** and skin. Defects cause the Vascular type of Ehlers-Danlos Syndrome (Type IV EDS), characterized by arterial rupture but not bone fragility. * **Option D (Type IV Collagen):** A key component of the **basement membrane**. Defects lead to Alport Syndrome (nephritis, hearing loss, and ocular issues). **Clinical Pearls for NEET-PG:** * **Differentiate from Child Abuse:** In OI, look for blue sclera, family history, and wormian bones on skull X-ray. In child abuse, look for retinal hemorrhages, posterior rib fractures, and metaphyseal "bucket-handle" fractures. * **Wormian Bones:** Small, irregular bones within the cranial sutures; a classic radiographic sign of OI. * **Hearing Loss:** Conductive hearing loss is common in adults with OI due to otosclerosis of the ossicles.

Question

Radiographic studies of a 2-year-old child reveal a new fracture of the humerus and evidence of multiple old fractures in ribs and long bones. Despite the broken arm, the toddler shows minimal bruising. A physical examination reveals peculiar teeth, a blue tinge to the sclera, and unusually mobile joints. The condition suspected in this child is characterized by an abnormality of which of the following biochemical functions?

Accepted Answer

Collagen type I synthesis

Answer

Collagen type II synthesis

Answer

Collagen type III synthesis

Answer

Collagen type IV synthesis

Child Abuse and Neglect — MCQs

Child Abuse and Neglect — MCQs

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