RESUMEN
Fluoropyrimidines are metabolized mainly by the enzyme dihydropyrimidine dehydrogenase (DPD). Some variants in the coding gene, DPYD, have already been associated with increased toxicity, and their testing is recommended in patients proposed for treatment with these drugs. In this clinical case, a patient without the four variants recommended for testing showed toxicity from the second cycle of capecitabine onwards, requiring hospitalization in the third cycle. Sequencing of the DPYD gene showed the presence of three heterozygous variants which the laboratory interpreted as deleterious to the expression or function of DPD. In the absence of phenotypic testing, the patient stopped treatment, which is also the usual procedure in the case of compound heterozygosity of the variants usually tested. The literature review shows data for and against the role of each variant found in fluoropyrimidine toxicity, but there may be more concrete data in the study of haplotypes with multiple variants and the need to research alterations in other genes to better understand their relationship with toxicity.
RESUMEN
INTRODUCTION: Single Nucleotide Polymorphisms (SNPs) are used as drug susceptibility biomarkers in metabolic diseases. Alterations in the gene encoding triggers the enzyme flavin monooxygenase 3 (FMO3), involved in the Sulindac metabolization, which also is responsible for the inherited metabolic disorder. Trimethylaminuria (TMAu, OMIM: 602079). DPYD gene variants are associated with the enzyme dihydropyrimidine dehydrogenase deficiency (DPD; OMIM: 274270). This autosomal recessive metabolic disorder, ultimately leads to the inability to metabolize fluoropyrimidines, which causes severe toxicity in individuals treated with these drugs. METHODS: Variants in genes responsible for the expression of enzymes that encode transporters or receptors involved in the metabolization pathways of certain drugs may condition the individuals response to certain drugs, compromising the therapeutic response and clinical prognosis. Thus the sequencing and identification of variants become relevant, not only gain knowledge on effects of these variants' on disease causality but also in terms of its side effects resulting from the coding enzymes responsible for drug metabolization. RESULTS: It was found that patients with the c.472G>A (p.Glu158Lys) and c.923A>G (p.Glu308Gly) polymorphisms, in homozygosity, in FMO3 gene did not develop polyps, thus have a protective effect in the treatment of Familial Adenomatous Polyposis (PAF). However, in the case of the DPYD gene, c.1905+1G>A (IVS14+1G>A), c.1679T>G (p.Ile560Ser), c.2846A>T (p.Asp949Val) e c.1236G>A/HapB3 variants can be lethal in cancer patients indicated for fluoropyrimidine-based chemotherapy. CONCLUSION: Knowledge on the drug mechanisms will affect the therapeutic response of patients treated with a given drug. Thus, pharmacogenetics is an essential tool in personalized medicine, since molecular studies allows the clinician to predict the probability of efficacy and toxicity of certain drugs, resulting higher efficiency in individualizing treatment and also improving the safety of the patient. From a personalized medicine perspective, the study of the characteristics of the drug and its metabolization site, the genes involved in the encoding of enzymes responsible for its metabolization will be of great interest.