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: Skin
Xeroderma pigmentosum is caused due to: 
Select and explain. 
A. DNA synthesis defect, B. Ectodermal cell migration defect, C. Abnormal nucleotide excision repair, D. Melanocyte proliferation
C: Abnormal nucleotide excision repair
Answer: C: Abnormal nucleotide excision repair 
Explanation: Xeroderma pigmentosum (XP) is a rare autosomal recessive disease characterized by photosensitivity, pigmentary changes, premature skin ageing, neoplasia and abnormal Nucleotide excision repair. Ref: Rook's textbook of dermatology, 8th edition, Pg15.71.