<prompt> Xeroderma pigmentosum is caused due to abnormalities in:A SOS repairNucleotide excision repairBase excision repairMismatch repair  <response>: Ans. B. Nucleotide excision repaira. It is transmitted as autosomal recessive and DNA repair mechanism is defective. DNA damage is produced by UV irradiation especially thymine dimers, cannot be incised. Inborn deficiency of the enzyme nicking endonuclease is there.b. Clinical manifestations: produces blisters on the skin.c. Dry keratosis, hyperpigmentation and atrophy of skin.d. May produce corneal ulcers. 