<prompt> Xeroderma pigmentosum is caused due to defect in: RepeatBase pairNucleotide excision repairMismatch repairTranslocation  <response>: Ref: Chapter 7. Neoplasia; page: 275; Robbins and Cot ran Pathologic Basis of Disease: 8t? editionExplanation: Defective DNA - repair syndromes are set of syndrome due to defect in DNA repair genes and resultant DNA instability. These are autosomal recessive in inheritance and include:Xeroderma pigmentosumBloom syndromeAtaxia telangiectasia. Whereas, HNPCC is associated with inactivation of DNA mismatch repair gene, resulting in increased susceptibility to colon cancer, and cancers of Endometrium, ovary etc., Example for Base pair defect is Sickle cell anemia; example for Translocation defect is Philadelphia chromosome in CML - t 9:22. 