This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Recessive dystrophic epidermolysis Bullosa occurs due to alteration in: 
Select and explain. 
A. Type 4 collagen, B. Type 6 collagen, C. Type 7 collagen, D. Type 8 collagen
C: Type 7 collagen
Answer: C: Type 7 collagen 
Explanation: "Nikolsky's sign" is positive in: 

Pemphigus
Familial benign chronic pemphigus (hailey-hailey disease)
Recessive dystrophic epidermolvsis bullosa [Epidermolysis bullosa occurs due to alteration in structure of type VII  collagen.