PHARMACOGENETICS

About 3-5% of the population carries the DPYD*2A allele, caused by a splice mutation in intron 14 (IVS14+1G>A). Carriers of the DPYD*2A allele have reduced DPD activity and develop severe to lethal haematological, gastrointestinal or neurological toxicity as a result of 5-FU therapy. It is recommended to test the following variants in the DPYD gene: c.1236G>A (HapB3), c.1679T>G (DPYD*13), c.1905+1G>A (DPYD*2A, IVS14+1G>A), c.2846A>T (p.D949V).

Gene, specification: DPYD gene (c.1905+1G>A, c.1236G>A, c.1679T>G, c.2846A>T)

Type of material to be examined: blood, buccal swab

Indicating specialists: medical genetics, internal medicine, clinical haematology, clinical oncology (excluding radiation oncology)

The TPMT enzyme (thiopurine S-methyltransferase) is essential for the biodegradation of thiopurines into inactive and non-toxic metabolites that are subsequently eliminated from the body. With reduced TPMT activity, thioguanine nucleotides accumulate, leading to adverse effects such as neurotoxicity, hepatotoxicity, myelosuppression, mucosal inflammation, etc. Reduced metabolic activity of the TPMT enzyme is due to functional polymorphisms in the encoding region of the TPMT gene. In the Indo-European population, the most common alleles are TPMT*3A, TPMT*2 and TPMT*3C, less common is TPMT*3B. The TPMT*2 allele contains a single nucleotide substitution in exon 5 (G238C), TPMT*3C substitution in exon 10 (A719G) and TPMT*3B substitution in exon 7 (G460A). In TPMT*3A, the two polymorphisms mentioned above have been described in exon 7 and exon 10 (G460A + A719G).

Gene, specification: TPMT gene (c.238G>C, c.460G>A, c.719A>G)

Type of material to be examined: blood, buccal swab

Indicating specialists: medical genetics, internal medicine, clinical haematology, gastroenterology and hepatology, rheumatology, paediatrics, allergology and clinical immunology

Warfarin is metabolized by the CYP2C9 isoenzyme, which exhibits varying degrees of activity. Up to 20% of the European population has genetically reduced enzyme activity, which necessitates the administration of lower doses of warfarin. Warfarin aims to block the VKOR receptor, which regenerates vitamin K in the body into an active form that restarts the coagulation cascade. Gene variants that reduce the activity of the receptor also reduce blood clotting, so its carriers need less warfarin to achieve the same therapeutic effect. The most significant allelic variants in the CYP2C9 gene are caused by point substitution 416C>T in exon 3 with substitution at the protein level Arg144Cys - CYP2C9*2 allele and 1061A>C with substitution Ileu359Leu - CYP2C9*3 allele. These variants significantly reduce the activity of the enzyme. In the VKORC1 gene, polymorphisms 1173C>T, localized in the first intron, and -1639G>A in the promoter region, are of functional significance and reduce receptor activity. However, these two polymorphisms have been shown to be closely linked and therefore detection of one mutation (more commonly -1639 G>A) is sufficient.

Gene, specification: CYP2C9 gene (c.430C>T, c.1075A>C), VKORC1 (c.-1639G>A)

Type of material to be examined: blood, buccal swab

Indicating specialists: medical genetics, internal medicine, clinical haematology, neurology, paediatric neurology - as part of a healthcare provider with the status of a highly specialised cerebrovascular and stroke centre.

The tested mutation leads to deletion (loss) of a part of the GSTT1/GSTM1gene sequence; this mutated allele is therefore referred to as allele 0. Genotype 00 (presence of two null alleles) causes a missing part of the sequence of the relevant gene and leads to a defect in the production of the corresponding detoxification enzyme. Genotype 00 in the GSTT1 or GSTM1 gene causes a lower ability to detoxify harmful substances and is associated with an increased likelihood of developing various types of cancer, especially when exposed to carcinogens (e.g., smoking). This risk is further increased by the combination of these genotypes with each other and with other risk genotypes of polymorphisms in the genes of other detoxification enzymes, GSTP1 and GSTM3.

The GSTP1 gene encodes the Glutathione-S-transferase P1 enzyme, which plays an important role in the breakdown (detoxification) of hydrophobic and electrophilic substances. This enzyme is involved in the breakdown of carcinogenic substances and metabolites in the body that are produced by the CYP1A1 enzyme. GSTP1 is also considered to be the main deactivator of tobacco smoke toxicants. The ability to neutralize (detoxify) and eliminate excess or potentially harmful substances from the body is very important for life. Substances that are not normally present in the body, are not necessary for its healthy development and do not serve as a source of energy for the body, are called xenobiotics. The main source of xenobiotics is the chemical industry and, in the case of polycyclic aromatic hydrocarbons, smoking and unsuitable diet as well.

Most substances are excreted by the kidneys and liver, but many substances are also excreted through the lungs, skin, and mucous membranes. The organ in which the highest number of detoxification reactions take place is the liver. In humans, there are two main phases of detoxification. In the first phase of detoxification, the substance is modified so that it can combine with amines, acids and alcohols in the subsequent second phase to facilitate its elimination from the body. An important role in conjugation reactions, i.e., the second phase of detoxification, is played by the association of substances with glutathione, where the conjugation of glutathione is enhanced by the GST enzyme present in liver cells. The conjugation of substances with glutathione allows faster elimination of toxic substances from the body. It has been found that individuals who have only one or no alleles of glutathione-S-transferase theta-1 (GSTT1) and Mu-1 (GSTM1) have reduced detoxification capacity and are at higher risk of developing cancer.

Gene, specification: GSTT1 (del), GSTM1 (del), GSTP1 (p.I105V)

Material: buccal swab, blood

Based on genetic analysis, it is possible to estimate the metabolic status of an individual from zero enzyme activity to several-fold increased activity. Humans can be slow to ultra-fast metabolizers. The differences in serum drug levels in these people can even be tenfold. This leads to different drug efficacy depending on genetic predisposition. Therefore, drugs may cause serious side effects in predisposed people or may be completely ineffective.

Gene, specification: CYP2C19, CYP2D6 genes

Type of material to be examined: blood, buccal swab

Indicating specialists: internal medicine, psychiatry, neurology

Based on this comprehensive analysis, the effectiveness of many drugs can be predicted, and dosages can be better adjusted. We base our recommendations on the worldwide pharmacogenomic recommendations that have already been compiled for statins, various antidepressants, NSAIDs, PPIs, metoprolol, allopurinol, clopidogrel, warfarin, some opioids, some antipsychotics, ondansetron, atomoxetine, some antiepileptics, inhalational anaesthetics. 

Gene, specification: panel of about 30 genes 

In terms of the innate predisposition of statins in the human body, the most important membrane transporter is OATP1B1, which ensures the transfer of substances into cells. It is encoded by the SLCO1B1 gene. The drug is then less effective and, in addition, it remains in the blood, where its plasma concentration rises, significantly increasing the risk of side effects. Dosage adjustment is therefore recommended for mutation carriers.

Gene, specifications: SLCO1B1 gene (c.521T>C)