Defective suppressor mutator

The biochemical defect is mutation or loss of the tumor suppressor gene, RB1, encoding the protein pRb. 

Mutations in Tumor Suppressor Genes and Oncogenes Explain why mutations in tumor suppressor genes are recessive (both copies of the gene must be defective for the regulation of cell division to be defective) whereas mutations in oncogenes are dominant. 

A second example of inherited predisposition to cancer is provided by hereditary retinoblastoma. This is a rare tumor of the retina and, when it develops, it generally develops in one eye only. Nonetheless, in children with hereditary retinoblastoma, the cancer develops early in life and generally in both eyes. This is a striking example of the inherited predisposition to develop a tumor. As in the case of hereditary polyposis, the defect is in a tumor suppressor gene, in this case RBI. Here too patients have just one intact gene in each of their cells and a single mutation in that gene may be aU that is required to initiate tumor development. 

The biochemical defect in type I neurofibromatosis (NT) involves ioss-of-function mutations of the NF1 tumor suppressor gene. 

The biochemical defect In families exhibiting this syndrome is a loss-of-function mutation of the tumor suppressor gene, TP53, encoding p53. 

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