Xeroderma pigmentosum is caused due to a defect in:
● Defective DNA - repair syndromes are a set of syndrome due to a defect in DNA repair genes and resultant DNA instability.
● These are autosomal recessive in inheritance and include:
Xeroderma pigmentosum
Bloom syndrome
Ataxia 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; an example for Translocation defect is Philadelphia
chromosome in CML - t (9:22).
Nucleotide excision repair
Base pair
Mismatch repair
Translocation