Polimorfizam gena tiopurinmetiltransferaze u bolesnika s upalnom bolešću crijeva [Polymorphism of thiopurinementhyltranserase gene in patients with the inflammatory bowel disease]

Ladić, Agata (2018) Polimorfizam gena tiopurinmetiltransferaze u bolesnika s upalnom bolešću crijeva [Polymorphism of thiopurinementhyltranserase gene in patients with the inflammatory bowel disease]. PhD thesis, Sveučilište u Zagrebu.

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Abstract

Thiopurine S-methyltransferase (TPMT) is an enzyme that converts thiopurine drugs into inactive metabolites. 37 variant TPMT-encoding alleles have been discovered so far. These variants produce enzyme with reduced enzymatic activity. Wild-type enzyme is denoted TPMT*1/*1, while variants were given numbers successively as they were discovered. The latest variant, TPMT*37, was discovered in 2014. The most common variant alleles of TPMT gene are: TPMT*2, TPMT*3A, TPMT*3B and TPMT*3C. Patients who are heterozygous for the enzyme, should have a thiopurine drug dose reduction, while homozygous patients should either stay free of this drug, or should have up to 10x drug dose reduction. Furthermore, blood parameters should be checked regularly. According to early studies of this enzyme, variant homozygosity is present in 1/300 persons; however – further population studies have revealed different ratios in Caucasian, Asiatic and African population. The first aim of this study was to investigate frequencies of the most common variant alleles in Croatian inflammatory bowel disease (IBD) patients and in healthy individuals. 685 participants are included, out of whom 459 are IBD patients (338 Crohn’s disease patients and 221 ulcerative colitis patients) and 226 are healthy volunteers. 94.55% IBD of patients and 94.25% of healthy volunteers have homozygous wild-type enzyme (TPMT*1/*1). TPMT*1/*2 and TPMT*1/*3C are present in 0.87% and 1.53% IBD patients, respectively; these variants are not present in healthy volunteers. TPMT*1/*3A is present in 3.05% IBD patients and 5.75% healthy volunteers. TPMT*3B allele is not found in any group. Variant genotypes are statistically significantly more common in Crohn's disease than in ulcerative colitis subgroup (p=0.032). We also compared frequencies of variant TPMT alleles in our population to selected countries which had had results published earlier. We found the overall frequency of variant alleles in our population statistically nonsignificantly lower when compared with other populations of Caucasian origin. Azathioprine is a thiopurine drug registered in IBD treatment in Croatia. Patients who have variant TPMT genotype, i.e. reduced enzyme activity, possibly develop severe adverse effects. The most common azathioprine adverse effect is myelotoxicity. Additionaly, concomitant therapy possibly influences adverse effects occurrence. Regarding aforementioned, the other aim of the study was to investigate a relationship between the most common TPMT polymorphisms, AZA adverse effects and concomitant therapy that is regularly applied in IBD. Out of 263 patients treated with AZA, 64 have developed adverse effects (24%). The most common adverse effects is myelotoxicity, with thrombocytopenia slightly more prevalent than leukopenia. The most common toxic hepatic manifestation is diffuse liver lesion, while pancreatic toxicity usually presents with acute pancreatitis. The majority of adverse effects occurs in patients with wild-type genotype. Statistical analysis shows that only TPMT genotype influences adverse effects occurrence (p=0.0038), notably TPMT*3A variant (p=0.0036). There is no influence of concomitant therapy – either aminosalicylate, corticosteroid or anti-TNF – on AZA-related toxicity.

Abstract in Croatian

Tiopurin-metiltransferaza (TPMT) je enzim koji sudjeluje u razgradnji tiopurinskih lijekova. Do sada je opisano 37 varijanti ovog enzima. Radi se o polimorfizmima koji nastaju zamjenom određenih aminokiselina u genu TPMT, a čiji produkt je enzim reducirane aktivnosti. Divlji genotip se označava kraticom TPMT*1/*1, dok su ostali varijantni oblici dobivali nazive prema slijedu otkrivanja, s posljednjom varijantom otkrivenom 2014.godine, naziva TPMT*37. Najčešći varijantni aleli ovog gena su: TPMT*2, TPMT*3A, TPMT*3B i TPMT*3C. Bolesnicima s heterozigotnom konstelacijom ovog enzima potrebno je reducirati dozu tiopurinskih lijekova, dok se homozigotima ili lijek ne treba davati, ili je dozu potrebno smanjiti 10 puta u odnosu na dozu lijeka kod divljeg genotipa i trajno monitorirati krvne parametre. Prema ranim istraživanjima ovog enzima, varijantna homozigotnost prisutna je u 1/300 osoba, no kasnije su populacijske studije pokazale da je odnos različit za bjelačke, azijatske i crnačke populacije. Prvi je cilj ove studije bio istražiti raspodjelu najčešćih polimorfizama u populaciji hrvatskih bolesnika s upalnim bolestima crijeva (IBD prema engl.inflammatory bowel disease) te u hrvatskih zdravih dobrovoljaca. U istraživanje je uključeno 685 ispitanika, od kojih je 459 IBD bolesnika (338 bolesnika s Crohnovom bolešću te 221 s ulceroznim kolitisom) te 226 zdravih dobrovoljaca. 94,55% IBD bolesnika i 94,25% zdravih dobrovoljaca su homozigoti za divlji tip alela (TPMT*1/*1). U IBD bolesnika su nađeni TPMT*1/*2 (0,87% bolesnika) i TPMT*1/*3C (1,53%), za razliku od zdravih dobrovoljaca u kojih ovaj genotip nije nađen. TPMT*1/TPMT*3A genotip je nađen u 3,05% IBD bolesnika te u 5,75% zdravih dobrovoljaca. TPMT*1/*3B i varijantni homozigoti nisu nađeni niti u jednoj skupini. Sa statističkom smo značajnošću našli veću učestalost varijantnih genotipova u bolesnika s Crohnovom bolešću u odnosu na grupu s ulceroznim kolitisom (p=0,032). Usporedili smo rezultate hrvatske populacije s drugim populacijama za koje su do trenutka pisanja disertacije objavljeni rezultati. Našli smo da je ukupna prevalencija varijantnih genotipova u našoj populaciji niža u odnosu na druge bjelačke populacije. U Hrvatskoj je za liječenje upalnih bolesti crijeva od tiopurinskih lijekova registriran azatioprin. Kod osoba s varijantnim genotipom TPMT i reduciranom aktivnošću enzima, moguć je razvoj značajnih nuspojava, od kojih je najčešća mijelotoksičnost. Također, prepoznat je i mogući utjecaj konkomitantne terapije u liječenju IBD, kao dodatni negativni čimbenik u razvoju nuspojava na ovaj lijek. Drugi je cilj bio ispitati utjecaj varijantnih genotipova TPMT na razvoj najčešćih nuspojava azatioprina (mijelotoksičnosti, hepatotoksičnosti te pankreasne toksičnosti) te utjecaj konkomitantne terapije azatioprinu na razvoj navedenih nuspojava. Od 263 bolesnika koji su liječeni azatioprinom, 64 su razvila nuspojave (24%). Najveći broj nuspojava je mijelotoksične naravi, od kojih je u našoj populaciji nešto češća trombocitopenija, potom slijedi leukopenija. Najčešća manifestacije hepatotoksičnosti je difuzna jetrena lezija, dok je kod afekcije gušterače najčešće zabilježen akutni pankreatitis. Najveći dio nuspojava je zabilježen u bolesnika s divljim genotipom TPMT. Od konkomitantne terapije analizirali smo lijekove koji se najčešće daju uz azatioprin - aminosalicilate, kortikosteroide te anti-TNF. Niti jedan lijek nije imao utjecaja na razvoj nuspojava azatioprinu. Statističkom smo obradom utvrdili da između spola, dijagnoze, konkomitantne terapije i genotipa TPMT, jedino genotip TPMT ima utjecaja na razvoj nuspojava (p=0,0038); post-hoc analizom utvrđeno je da je TPMT*1/*3A statistički značajno vezan uz razvoj nuspojava.

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