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Cutaneous Malignant Melanoma - Genes CDKN2A, CDK4, MC1R, BRAF and TRRAP

Malignant cutaneous melanoma represents the about 10% of cutaneous neoplasms and is responsible for over 90% of deaths from skin cancer. Its incidence increases with the passage of time, especially in Caucasians exposed to solar radiation. They have identified some genes that confer increased susceptibility to the development of melanomas.

The gene associated with the development of cutaneous melanomas most important is the CDKN2A (Cyclin-dependent kinase inhibitor 2A), located on the short arm of chromosome 9 (9p21). This gene has the ability to generate two proteins by splicing (cuts and joints) alternative first exon: p16, encoded by 1? exons 2 and 3, is involved in cell cycle control and apoptosis, and p14 ARF, encoded by exons 1?, 2 and 3, whose role is in cell cycle regulation through a p53 - dependent pathway. P16 protein binds to and competitively inhibits cyclin dependent kinases (CDK4 and CDK6). For this reason it is also sometimes called INK4a (kinase inhibitor 4). Thus achieved prevent complex formation formed by the union of CDK4 and cyclin D1, necessary for the transition from the G1 phase of the cell cycle phase S.

Mutations in CDKN2A, usually specific amino acid changes or deletions may be generated sporadically or be hereditary and associated therefore sporadic cases of melanomas without family history and cases of families with multiple cases of melanomas. In general, it seems that point mutations are predominant in cases of melanomas family while deletions are the most common form of inactivation in sporadic melanomas. Mutations in p16 are transmitted with an autosomal dominant inheritance and can occur at any of the three exons that comprise the gene. The degree of penetrance of mutations in CDKN2A has been estimated at 0.30 to 0.67 to 50 and 80 years, although there are differences depending on the country, so it is suspected that the penetrance may depend on exposure environmental, mainly ultraviolet (UV). UV radiation causes direct DNA damage and induces the formation of thymine dimers and free radicals and also stops the melanocytes in the G1 and G2 phases of cell cycle. This can cause genetic disorders and chromosomal deletions in tumor suppressor genes, which inactivate p16 in this case, contributing to the progression and development of melanoma.

Another gene associated with the development of cutaneous melanoma and intimately related to the regulation of CDKN2A is CDK4, located on the long arm of chromosome 12 (12q14). This gene encodes a catalytic subunit of the very important for cell cycle progression protein kinase. The activity of this kinase is limited to the G1 phase and is controlled by p16. Mutations reported so far in it, rare and minority are located in the p16 binding site, generating resistance to normal physiological inhibition by p16 performed.

Up to 60% of melanomas have been described somatic alterations in the BRAF oncogene, located on the long arm of chromosome 7 (7q34). They have been identified mutations in the BRAF gene in acquired melanocytic nevi, primary melanomas and melanoma metastases. However, the presence of these mutations in the radial growth phase is low (5-10%) and, above all, much less to the presence of mutations in the vertical growth phase and metastatic melanoma (65-75%) . So these mutations do not appear to be involved in predisposition or the generation of melanoma, but in melanoma progression to more aggressive forms and metastatic capacity. In the sequence encoding the kinase domain, in exon 15, there is a "hotspot" hot - spot that has more than 90% of localized mutations in the BRAF gene. The mutation consists of the substitution of valine for glutamic acid molecule at residue 600 (V600E). The protein resulting from this genetic alteration has 10 times more activity than the same protein in normal conditions.

Alterations in other genes as in the MC1R gene, located on the long arm of chromosome 16 (16q24.3) or TRRAP, located on the long arm of chromosome 7 (7q21.2-q22.1), have been described in some cases of cutaneous malignant melanoma people. Alterations in the MC1R gene disrupt capacity melanocortin receptor 1 to trigger the production of eumelanin in melanocytes. Because eumelanin normally protects the skin from the harmful effects of UV radiation, deficiency or absence of this pigment leaves the most vulnerable to damage from sun exposure skin. Variations in the MC1R gene can also increase the risk of developing melanoma in the absence of damage associated with UV radiation. Meanwhile, a particular mutation in the TRRAP, Phe-722 gene has been identified frequently in people with malignant cutaneous melanoma.

Tests performed in IVAMI: in IVAMI perform mutation detection associated with the development of malignant cutaneous melanomas, by complete PCR amplification of the exons of the CDKN2A, CDK4, MC1R, BRAF and TRRAP genes, respectively, and subsequent sequencing. It is suggested to start the study by PCR amplification followed by sequencing CDKN2A if prior family history of melanomas and, if found necessary, proceed to study after using the technique of quantitative real - time PCR (qPCR Real Time ) looking for deletions or duplications. If no family history might be more interesting to use, first, the method of quantitative real - time PCR to search for deletions in the CDKN2A gene and, if found necessary, then proceed to PCR amplification followed by sequencing. Should be negative both sequencing CDKN2A as for deletions, it offers the possibility of sequencing by other genes complete PCR amplification and subsequent sequencing.

Samples recommended: EDTA blood collected for separation of blood leukocytes, or impregnated sample card with dried blood (IVAMI may mail the card to deposit the blood sample) for detection of germline mutations. For detection of somatic mutations, tissue from biopsy.