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
The following diseases have defect in DNA repair mechanism except for - 
Select and explain. 
A. Xeroderma Pigmentosa, B. Fanconi syndrome, C. Huntington's disease, D. Hereditary non polyposis colon cancer
C: Huntington's disease
Answer: C: Huntington's disease 
Explanation: Ans. is 'c' i.e., Huntington's disease Several genetic disorders have defective DNA repair capability due to involvement of DNA repair enzymes. o Mutation caused by defects in DNA repair accumulate as somatic cells divide these type of mutation can cause neoplastic growth. So, all these disorders have significantly increased risk of cancer. o Inherited autosomal recessive syndromes of defective DNA repair Ataxia Telangiectasia Fanconia anemia Hereditary Nonpolyposis cancer (Only Bloom syndrome Xeroderma pi gmentosum autosomal dominant) o These disorders are associated with such a high level of chromosomal instability that they are known as chromosome - breakage syndrome.