Dominant negative mutations: Most individuals with Li–Fraumeni syndrome are heterozygous for a mutant TP53 gene, and some p53 mutants can inhibit the function of the wild-type p53 in a dominant negative manner. Mutated p53 proteins are typically more stable than wild-type, and can inhibit the activity of the wild-type protein in suppressing cell proliferation and in inducing cell cycle arrest. Due to the mutant p53 being able to inhibit some wild-type p53, damaged cells are at an even greater susceptibility to proliferate and become transformed, resulting in cancer.LFS2: mutations in CHEK2
Another variant of Li–Fraumeni that remains somewhat controversial, is a mutation of the CHEK2 (or CHK2) gene. CHK2 is also a tumor suppressor gene; it regulates the action of p53 and is activated by ATM, which detects DNA damage, and in this way, DNA damage information can be conveyed to p53 to indirectly arrest the cell cycle at that point for DNA repair to be able to take place or to cause apoptosis (programmed cell death). LFS-L:
Families who do not conform to the criteria of classical Li–Fraumeni syndrome have been termed "LFS-like". LFS-like individuals generally do not have any detectable p53 mutations, and tend to be diagnosed on either the Birch or Eeles criteria. A third locus has been mapped to the long arm of chromosome 1 (1q23), but no gene has yet been identified.Another locus that has been linked to this syndrome is CDKN2A-CDKN2B.
If these DNA mutations are left unchecked, some cells can divide uncontrollably, forming tumors (cancers). Further mutations in the DNA could lead to malignant cells that can travel to, and develop cancer in, different areas of the body. Many individuals with Li–Fraumeni syndrome have been shown to be heterozygous for a TP53 mutation. Recent studies have shown that 60% to 80% of classic LFS families harbor detectable germ-line TP53 mutations, the majority of which are missense mutations in the DNA-binding domain. These missense mutations cause a decrease in the ability of p53 to bind to DNA, thus inhibiting the normal TP53 mechanism. Unique Brazilian mutation: Although other mutations leading to Li–Fraumeni syndrome have been found outside the DNA-binding domain, a mutation at codon 337 of the tetramerization domain of TP53 has shown a particularly high frequency. The tetramerization domain plays a major role in the oligomerization of the p53 protein, which exists as a tetramer. This mutation has only been found in Brazilian families, and is located in exon 10 of the TP53 gene. The mutation causes an amino acid change from arginine to histidine at codon 337. With pH in the low to normal physiological range (up to 7.5), the mutant protein forms normal oligomers and retains its suppressor function. However, at a high physiological pH, p53 is unable to assemble into a tetramer. This unique feature may contribute to why families with this particular mutation often show incomplete penetrance.