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Li-Fraumeni syndrome (LFS) is a clinically and genetically heterogeneous inherited cancer syndrome. LFS is characterized by autosomal dominant inheritance and early onset of tumors, multiple tumors within an individual, and multiple affected family members. In contrast to other inherited cancer syndromes, which are predominantly characterized by site-specific cancers, LFS presents with a variety of tumor types.

The most common types are soft tissue sarcomas and osteosarcomas, breast cancer, brain tumors, leukemia, and adrenocortical carcinoma. Classic LFS is defined as a proband with a sarcoma before the age of 45 years and a first-degree relative with any cancer before the age of 45 years and 1 additional first- or second-degree relative in the same lineage with any cancer before the age of 45 years or a sarcoma at any age (Li et al., 1988).

Approximately 70% of LFS cases and 40% of LFL cases contain germline mutations in the p53 gene on chromosome 17p13.1

Olivier et al. (2003) described a database for collecting information on families carrying a germline mutation in the TP53 gene and on families affected with Li-Fraumeni syndromes, both Li-Fraumeni and Li-Fraumeni-like syndromes.They described analysis of 265 families/individuals with LFS/LFL. In classic LFS families with a germline TP53 mutation (83 families), the mean age of onset of breast cancer was significantly lower than in LFS families (16 families) without a TP53 mutation (34.6 vs. 42.5 years; P = 0.0035). In individuals with a TP53 mutation, a correlation between the genotype and phenotype was found: brain tumors were associated with missense TP53 mutations located in the DNA-binding loop that contact the minor groove of DNA (P = 0.01).

The molecular mechanisms invoveld in the Li-Fraumeni syndrome is TP53 tumor suppressor gene is the most frequent target for genetic alterations in human cancer. TP53 gene alterations may result in the gain of oncogenic functions such as neoangiogenesis and resistance to therapy. The TP53 germ line mutation c.659A>C (p.Y220S) was identified in stored DNA from related patients with Li-Fraumeni syndrome. This Tp53 gene is present in all human there is no chance of its absence in the Human genome, the onset of this syndrome is due to activation of transcription factors to trigger the Tp53 gene.

Oncogenic signalling activates p53 not only through the DNA damage response pathways, but also through the transcriptional activation of p14ARF (ARF). The levels of ARF protein are found to be increased upon aberrant expression of oncogenes such as Ras and Myc20. One of the key roles of the ARF protein is to bind to Mdm2 and inhibit its ubiquitin ligase activity, thus promoting p53 stabilization.

The turning on p53 gene can be stopped by inactivating the transcroption factors which activate the oncogenic gene.

Conclusion : the Tp53 gene will be present as default in the genome only turn on/off can take place. if the p53 gene is identifies at the germline level and removed then there will no chances of this syndrome.