MD Musculoskeletal and Connective Tissue 4

Question 1

A 16-year-old boy has tall stature, arachnodactyly, lens dislocation upward, and an aortic root diameter of 4.8 cm. Mutation in which gene is responsible?

Accepted Answer

FBN1 (fibrillin-1)

Answer

Marfan syndrome is caused by mutations in FBN1 encoding fibrillin-1, disrupting microfibrils and TGF-β signaling, affecting connective tissue in multiple organ systems.

Question 2

A 10-year-old girl has hyperextensible skin, hypermobile joints, and easy bruising. Skin biopsy shows abnormal collagen cross-linking. She likely has a defect in which enzyme?

Accepted Answer

Lysyl oxidase

Answer

Ehlers-Danlos syndrome (classical type) involves defective lysyl oxidase or collagen genes, impairing collagen cross-linking and resulting in skin and joint laxity.

Question 3

A 2-year-old child has multiple fractures, blue sclerae, dentinogenesis imperfecta, and hearing loss. What is the underlying molecular defect?

Accepted Answer

Mutation in COL1A1 or COL1A2 causing defective type I collagen

Answer

Osteogenesis imperfecta results from mutations in type I collagen genes (COL1A1/COL1A2), producing structurally abnormal collagen that weakens bone, sclerae, and teeth.

Question 4

A 35-year-old woman with diffuse systemic sclerosis develops progressive dyspnea. High-resolution CT shows basal-predominant ground-glass opacities and honeycombing. Which antibody is most associated with this pulmonary complication?

Accepted Answer

Anti-Scl-70 (anti-topoisomerase I)

Answer

Anti-Scl-70 antibodies are associated with diffuse cutaneous systemic sclerosis and a higher risk of interstitial lung disease.

Question 5

A 60-year-old woman develops proximal muscle weakness, elevated CK, and an EMG showing myopathic changes. Muscle biopsy reveals perifascicular atrophy. What is the diagnosis?

Accepted Answer

Dermatomyositis

Answer

Perifascicular atrophy is pathognomonic for dermatomyositis, reflecting ischemia from complement-mediated microangiopathy of muscle capillaries.

MD - Doctor of Medicine Practice Test

MD - Doctor of Medicine Practice Test

MD Musculoskeletal and Connective Tissue 4