What is the role of inactive MLH1 in the development of some forms of inherited colon cancer?
a. Deletion of a nucleotide repeat in the DUX4 gene.
b. DNA damage is left unrepaired.
c. Expansion in the number of cyto-sine-guanine (CG) dinucleotide.
d. Abnormalities of chromosome 11p15.5 that lead to downregulation of IGF2.
ANS: B
A major cause of one form of inherited colon cancer (hereditary nonpolyposis colorectal cancer [HNPCC]) is the methylation of the promoter region of a gene, MLH1, whose protein product repairs damaged DNA. When MLH1 becomes inactive, DNA damage accumulates, eventually resulting in colon tumors. Facioscapulohumeral muscular dystrophy (FSHMD) is associated with the DUX4 gene. Fragile X is associated with the cytosine-guanine (CG) dinucleotide. Downreg-ulation of IGF2 is associated with Russell-Silver syndrome.
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