Pathology In thin basement membrane disease, the defect is in A a1 and a2 chains of type IV collagen B a3 and a4 chains of type IV collagen C a1 and a2 chains of type VI collagen D a3 and a4 chains of type VI collagen 💡 Explanation In thin basement membrane disease, the defect is in ✓ Correct Answer: B. a3 and a4 chains of type IV collagen