A Comprehensive Genetic Analysis of Slovenian Families with Multiple Cases of Orofacial Clefts Reveals Novel Variants in the Genes IRF6, GRHL3, and TBX22.

Although the aetiology of non-syndromic orofacial clefts (nsOFCs) is usually multifactorial, syndromic OFCs (syOFCs) are often caused by single mutations in known genes. Some syndromes, e.g., Van der Woude syndrome (VWS1; VWS2) and X-linked cleft palate with or without ankyloglossia (CPX), show only minor clinical signs in addition to OFC and are sometimes difficult to differentiate from nsOFCs. We recruited 34 Slovenian multi-case families with apparent nsOFCs (isolated OFCs or OFCs with minor additional facial signs). First, we examined IRF6, GRHL3, and TBX22 by Sanger or whole exome sequencing to identify VWS and CPX families. Next, we examined 72 additional nsOFC genes in the remaining families. Variant validation and co-segregation analysis were performed for each identified variant using Sanger sequencing, real-time quantitative PCR and microarray-based comparative genomic hybridization. We identified six disease-causing variants (three novel) in IRF6, GRHL3, and TBX22 in 21% of families with apparent nsOFCs, suggesting that our sequencing approach is useful for distinguishing syOFCs from nsOFCs. The novel variants, a frameshift variant in exon 7 of IRF6, a splice-altering variant in GRHL3, and a deletion of the coding exons of TBX22, indicate VWS1, VWS2, and CPX, respectively. We also identified five rare variants in nsOFC genes in families without VWS or CPX, but they could not be conclusively linked to nsOFC.

Effects of tyrosine kinase inhibitors on androgen, estrogen α, glucocorticoid and thyroid receptors.

Modern anticancer therapies favor a targeted approach. Tyrosine kinase inhibitors (TKIs) are drugs that target molecular pathways involved in various types of malignancies. Although TKIs are safe and well tolerated, they remain not completely selective; e.g., endocrine-mediated adverse events have been observed with their use. In the present study, the effects of seven TKIs were determined on the activities of androgen receptor, estrogen receptor α (ERα), glucocorticoid receptor and thyroid receptor in vitro using stably transfected cell lines expressing firefly luciferase reporter gene: AR-EcoScreen, hERα-HeLa9903, MDA-kb2, and GH3.TRE-Luc cells, respectively. Antiandrogenic activity was seen for erlotinib, estrogenic activity for imatinib, antiestrogenic activity for dasatinib, erlotinib, nilotinib, regorafenib and sorafenib, glucocorticoid activity for erlotinib and ibrutinib, antiglucocorticoid activity for regorafenib and sorafenib, and antithyroid activity for ibrutinib. Additionally, synergism was seen for 1-5 µM dasatinib and 500 nM hydrocortisone combination for glucocorticoid activity in MDA-kb2 cells. The estrogenic activity of imatinib was confirmed as mediated through ERα, and interference of the TKIs with the reporter gene assays was ruled out in a cell-lysate-based firefly luciferase enzyme inhibition assay. Imatinib in combination with 4-hydroxytamoxifen showed concentration-dependent effects on the metabolic activity of ERα-expressing AN3CA, MCF-7, and SKOV3 cells, and on cell proliferation and adhesion of MCF-7 cells. These findings contribute to the understanding of the endocrine effects of TKIs, in terms of toxicity and effectiveness, and define the need to further evaluate the endocrine disrupting activities of TKIs to safeguard human and environmental health.

Correlation between markers of DNA and lipid oxidative damage in maternal and fetoplacental compartment in the mid-trimester of pregnancy.

OBJECTIVE: To determine the levels of 8-isoprostane (8-IP) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) in urine and in amniotic fluid (AF) of pregnant women and to assess the correlation between oxidative status in the maternal and fetal compartment in the second trimester of pregnancy. METHODS: One hundred and forty-six women with singleton pregnancies, undergoing amniocentesis at the Department of Obstetrics and Gynaecology at the University Medical Centre Ljubljana, were prospectively enrolled. AF and maternal urine were collected in the second trimester of pregnancy. Paired urinary and AF 8-IP and 8-OHdG were measured and evaluated cross-sectionally. RESULTS: 8-IP and 8-OHdG concentrations were higher in maternal urine compared to AF and the ratios were 47:1 and 50:1, respectively. AF 8-OHdG was very low and in 74% was below the limit of detection (LOD). We found a positive correlation between 8-IP in maternal and fetal compartment (ρ=0.217, P=0.008), which stayed unchanged also after adjustment for possible confounding factors. CONCLUSIONS: Oxidative damage to lipids and DNA is also a part of physiologic processes during healthy pregnancy. 8-IP and 8-OHdG are constantly present in urine and AF. A weak positive correlation between maternal and fetal unit suggests a weak reflection of fetal oxidative status in maternal urine in the mid-trimester.

S-Adenosyl Methionine in the Therapy of Depression and Other Psychiatric Disorders.

Preclinical Research S-adenosyl methionine (SAM) is a major methyl donor and as such exerts its influence on CNS function through methylation reactions, such as methylation of several catecholamine moiety-containing neurotransmitters, epigenetic changes through methylation of DNA, RNA, RNA-binding proteins and histones, and phospholipid methylation. Based on available evidence, SAM is currently recommended as a next-step (second-line) treatment option following inadequate treatment response to a first-line antidepressant. It shows significant promise in the treatment of pediatric and perinatal depression, as well as Alzheimer's disease, but to make this a recommendation further clinical trials are needed. SAM is safe to use in most patients, but is contraindicated in those with bipolar disorder. Concerns considering the possible increase of homocysteine levels (and cardiovascular complications) due to long-term SAM therapy need to be further addressed in clinical trials taking into account individual`s ability to metabolize homocysteine and his/her folate status. Drug Dev Res 77 : 336-346, 2016. © 2016 Wiley Periodicals, Inc.

Transcriptome analysis reveals involvement of thiopurine S-methyltransferase in oxidation-reduction processes.

Thiopurine S-methyltransferase (TPMT) is an important enzyme involved in the deactivation of thiopurines and represents a major determinant of thiopurine-related toxicities. Despite its well-known importance in thiopurine metabolism, the understanding of its endogenous role is lacking. In the present study, we aimed to gain insight into the molecular processes involving TPMT by applying a data fusion approach to analyze whole-genome expression data. The RNA profiling was done on whole blood samples from 1017 adult male and female donors to the Estonian biobank using Illumina HTv3 arrays. Our results suggest that TPMT is closely related to genes involved in oxidoreductive processes. The in vitro experiments on different cell models confirmed that TPMT influences redox capacity of the cell by altering S-adenosylmethionine (SAM) consumption and consequently glutathione (GSH) synthesis. Furthermore, by comparing gene networks of subgroups of individuals, we identified genes, which could have a role in regulating TPMT activity. The biological relevance of identified genes and pathways will have to be further evaluated in molecular studies.

Genetic markers for non-syndromic orofacial clefts in populations of European ancestry: a meta-analysis.

To date, the involvement of various genetic markers in the aetiopathogenesis of non-syndromic orofacial cleft (nsOFC) has been extensively studied. In the present study, we focused on studies performed on populations of European ancestry to systematically review the available literature to define relevant genetic risk factors for nsOFC. Eligible studies were obtained by searching Ovid Medline and Ovid Embase. We gathered the genetic markers from population-based case-control studies on nsOFC, and conducted meta-analysis on the repeatedly reported markers. Whenever possible, we performed stratified analysis based on different nsOFC phenotypes, using allelic, dominant, recessive and overdominant genetic models. Effect sizes were expressed as pooled odds ratios (ORs) with 95% confidence intervals (CIs), and p ≤ 0.05 were considered statistically significant. A total of 84 studies were eligible for this systematic review, with > 700 markers included. Of these, 43 studies were included in the meta-analysis. We analysed 47 genetic variants in 30 genes/loci, which resulted in 226 forest plots. There were statistically significant associations between at least one of the nsOFC phenotypes and 19 genetic variants in 13 genes/loci. These data suggest that IRF6, GRHL3, 8q24, VAX1, TGFA, FOXE1, ABCA4, NOG, GREM1, AXIN2, DVL2, WNT3A and WNT5A have high potential as biomarkers of nsOFC in populations of European descent. Although other meta-analyses that included European samples have been performed on a limited number of genetic variants, this study represents the first meta-analysis of all genetic markers that have been studied in connection with nsOFC in populations of European ancestry.

A Common Polymorphism in the MTHFD1 Gene Is a Modulator of Risk of Congenital Heart Disease.

Several environmental and genetic factors may influence the risk of congenital heart defects (CHDs), which can have a substantial impact on pediatric morbidity and mortality. We investigated the association of polymorphisms in the genes of the folate and methionine pathways with CHDs using different strategies: a case-control, mother-child pair design, and a family-based association study. The polymorphism rs2236225 in the MTHFD1 was confirmed as an important modulator of CHD risk in both, whereas polymorphisms in MTRR, FPGS, and SLC19A1 were identified as risk factors in only one of the models. A strong synergistic effect on the development of CHDs was detected for MTHFD1 polymorphism and a lack of maternal folate supplementation during early pregnancy. A common polymorphism in the MTHFD1 is a genetic risk factor for the development of CHD, especially in the absence of folate supplementation in early pregnancy.

Association of Zn and Cu Levels in Cord Blood and Maternal Milk with Pregnancy Outcomes among the Slovenian Population.

Trace elements, including zinc (Zn) and copper (Cu), are known to play important roles in human health. The present study aimed to assess the levels of Zn and Cu in cord blood and maternal milk and to analyze their association with maternal and infant characteristics and pregnancy outcomes in a Slovenian study population of mothers and their neonates recruited within the PHIME prospective cohort study. The study included 324 mothers, but the data on Zn and Cu levels in both cord blood and maternal milk was available for 243 mothers. Questionnaires were used to assess the socio-demographic and health status of the mothers, their lifestyle habits (including detailed nutritional habits), and their residential and occupational histories. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was used to measure Zn and Cu levels in cord blood and maternal milk. Low Zn levels in cord blood were associated with lower gestational age and birth weight and were correlated with an increased probability of the birth of small for gestational age (SGA) infants. Maternal smoking influenced the Cu levels in both cord blood and maternal milk. Cord blood Cu levels were higher and Cu levels in maternal milk were lower in smoking compared to non-smoking mothers. Most importantly, a decreased Zn/Cu ratio in cord blood was associated with lower gestational age and lower birth weight. This indicates the overall positive effects of Zn and negative effects of Cu on pregnancy outcomes.

Vaccinomics and Adversomics in the Era of Precision Medicine: A Review Based on HBV, MMR, HPV, and COVID-19 Vaccines.

Precision medicine approaches based on pharmacogenomics are now being successfully implemented to enable physicians to predict more efficient treatments and prevention strategies for a given disease based on the genetic background of the patient. This approach has already been proposed for vaccines, but research is lagging behind the needs of society, and precision medicine is far from being implemented here. While vaccinomics concerns the effectiveness of vaccines, adversomics concerns their side effects. This area has great potential to address public concerns about vaccine safety and to promote increased public confidence, higher vaccination rates, and fewer serious adverse events in genetically predisposed individuals. The aim here is to explore the contemporary scientific literature related to the vaccinomic and adversomic aspects of the three most-controversial vaccines: those against hepatitis B, against measles, mumps, and rubella, and against human Papilloma virus. We provide detailed information on the genes that encode human leukocyte antigen, cytokines and their receptors, and transcription factors and regulators associated with the efficacy and safety of the Hepatitis B and Measles, Mumps and Rubella virus vaccines. We also investigate the future prospects of vaccinomics and adversomics of a COVID-19 vaccine, which might represent the fastest development of a vaccine ever.

Triclocarban, Triclosan, Bromochlorophene, Chlorophene, and Climbazole Effects on Nuclear Receptors: An in Silico and in Vitro Study.

BACKGROUND: Endocrine-disrupting chemicals can interfere with hormonal homeostasis and have adverse effects for both humans and the environment. Their identification is increasingly difficult due to lack of adequate toxicological tests. This difficulty is particularly problematic for cosmetic ingredients, because in vivo testing is now banned completely in the European Union. OBJECTIVES: The aim was to identify candidate preservatives as endocrine disruptors by in silico methods and to confirm endocrine receptors' activities through nuclear receptors in vitro. METHODS: We screened preservatives listed in Annex V in the European Union Regulation on cosmetic products to predict their binding to nuclear receptors using the Endocrine Disruptome and VirtualToxLab™ version 5.8 in silico tools. Five candidate preservatives were further evaluated for androgen receptor (AR), estrogen receptor (ERα), glucocorticoid receptor (GR), and thyroid receptor (TR) agonist and antagonist activities in cell-based luciferase reporter assays in vitro in AR-EcoScreen, hERα-HeLa-9903, MDA-kb2, and GH3.TRE-Luc cell lines. Additionally, assays to test for false positives were used (nonspecific luciferase gene induction and luciferase inhibition). RESULTS: Triclocarban had agonist activity on AR and ERα at 1µM and antagonist activity on GR at 5µM and TR at 1µM. Triclosan showed antagonist effects on AR, ERα, GR at 10µM and TR at 5µM, and bromochlorophene at 1µM (AR and TR) and at 10µM (ERα and GR). AR antagonist activity of chlorophene was observed [inhibitory concentration at 50% (IC50) IC50=2.4µM], as for its substantial ERα agonist at >5µM and TR antagonist activity at 10µM. Climbazole showed AR antagonist (IC50=13.6µM), ERα agonist at >10µM, and TR antagonist activity at 10µM. DISCUSSION: These data support the concerns of regulatory authorities about the endocrine-disrupting potential of preservatives. These data also define the need to further determine their effects on the endocrine system and the need to reassess the risks they pose to human health and the environment. https://doi.org/10.1289/EHP6596.

Folate Insufficiency Due to MTHFR Deficiency Is Bypassed by 5-Methyltetrahydrofolate.

Adequate levels of folates are essential for homeostasis of the organism, prevention of congenital malformations, and the salvage of predisposed disease states. They depend on genetic predisposition, and therefore, a pharmacogenetic approach to individualized supplementation or therapeutic intervention is necessary for an optimal outcome. The role of folates in vital cell processes was investigated by translational pharmacogenetics employing lymphoblastoid cell lines (LCLs). Depriving cells of folates led to reversible S-phase arrest. Since 5,10-methylenetetrahydrofolate reductase (MTHFR) is the key enzyme in the biosynthesis of an active folate form, we evaluated the relevance of polymorphisms in the MTHFR gene on intracellular levels of bioactive metabolite, the 5-methyltetrahydrofolate (5-Me-THF). LCLs (n = 35) were divided into low- and normal-MTHFR activity groups based on their genotype. They were cultured in the presence of folic acid (FA) or 5-Me-THF. Based on the cells' metabolic activity and intracellular 5-Me-THF levels, we conclude supplementation of FA is sufficient to maintain adequate folate level in the normal MTHFR activity group, while low MTHFR activity cells require 5-Me-THF to overcome the metabolic defects caused by polymorphisms in their MTHFR genes. This finding was supported by the determination of intracellular levels of 5-Me-THF in cell lysates by LC-MS/MS. FA supplementation resulted in a 2.5-fold increase in 5-Me-THF in cells with normal MTHFR activity, but there was no increase after FA supplementation in low MTHFR activity cells. However, when LCLs were exposed to 5-Me-THF, a 10-fold increase in intracellular levels of this metabolite was determined. These findings indicate that patients undergoing folate supplementation to counteract anti-folate therapies, or patients with increased folate demand, would benefit from pharmacogenetics-based therapy choices.

Pharmacogenomics education in medical and pharmacy schools: conclusions of a global survey.

Aim: The need for pharmacogenomic education is becoming more and more urgent. Our aim was to evaluate the progress in pharmacogenomics education since then, and to put forward further recommendations. Methods: A survey was sent to 248 schools of medicine, pharmacy, nursing and health professions around the world. Results: The majority of the study programs (87%) include pharmacogenomics education, which is generally taught as part of the pharmacology curriculum. On average, educators and teachers have selected appropriate and highly relevant pharmacogenomics biomarkers to include in their teaching programs. Conclusions: Based on the results, we can conclude that the state of pharmacogenomics education at the surveyed universities has improved substantially since 2005.

Novel motif of variable number of tandem repeats in TPMT promoter region and evolutionary association of variable number of tandem repeats with TPMT*3 alleles.

AIM: SNPs in the gene for TPMT exemplify one of the most successful translations of pharmacogenomics into clinical practice. This study explains the correlation between common SNPs and variable number of tandem repeats (VNTR) in promoter of the gene. MATERIALS & METHODS: We determined VNTR polymorphisms, as well as TPMT*2 and TPMT*3 SNPs and TPMT activity in Slovenian and Italian individuals and lymphoblastoid cell lines. RESULTS: We observed a previously unreported VNTR allele, AB7C, in a TPMT*3A heterozygous individual. VNTRs with two (AB2C) and three or more (ABnC, n ≥ 3) B motifs were statistically significant in complete linkage disequilibrium (D' = 1, r2 = 1, p < 0.0001) with the TPMT*3C and TPMT*3A alleles, respectively. CONCLUSION: The study provides insights into the stepwise evolution of TPMT*3 alleles from *3C to *3A, with increasing number of B motifs in the VNTR region.

PACSIN2 polymorphism is associated with thiopurine-induced hematological toxicity in children with acute lymphoblastic leukaemia undergoing maintenance therapy.

Adequate maintenance therapy for childhood acute lymphoblastic leukemia (ALL), with 6-mercaptopurine as an essential component, is necessary for retaining durable remission. Interruptions or discontinuations of the therapy due to drug-related toxicities, which can be life threatening, may result in an increased risk of relapse. In this retrospective study including 305 paediatric ALL patients undergoing maintenance therapy, we systematically investigated the individual and combined effects of genetic variants of folate pathway enzymes, as well as of polymorphisms in PACSIN2 and ITPA, on drug-induced toxicities by applying a multi-analytical approach including logistic regression (LR), classification and regression tree (CART) and generalized multifactor dimensionality reduction (GMDR). In addition to the TPMT genotype, confirmed to be a major determinant of drug related toxicities, we identified the PACSIN2 rs2413739TT genotype as being a significant risk factor for 6-MP-induced toxicity in wild-type TPMT patients. A gene-gene interaction between MTRR (rs1801394) and MTHFR (rs1801133) was detected by GMDR and proved to have an independent effect on the risk of stomatitis, as shown by LR analysis. To our knowledge, this is the first study showing PACSIN2 genotype association with hematological toxicity in ALL patients undergoing maintenance therapy.

Lipid-lysine adducts and modified tyrosines as markers of oxidative stress in the second trimester of pregnancy and their association with infant characteristics.

Pregnancy is a physiological state accompanied by excessive levels of oxidative stress (OS), due to the increased demand and utilisation of oxygen. There is increasing evidence that maternally augmented OS exerts an adverse effect on pregnancy outcome. The aim of the present prospective study was to determine the association between the urinary concentration of relatively novel OS markers measured in the second trimester of pregnancy and the infant characteristics at birth. The maternal levels of urinary hexanoyl-lysine (HEL), propanoyl-lysine (PRL), dityrosine (DiY) and 3-nitrotyrosine (NY) were evaluated in generally healthy pregnant subjects to determine their association with birth weight, gestation at delivery and Apgar score. The observed levels of the markers were in agreement with those measured in healthy non-pregnant subjects in a previous study. A positive correlation was detected between HEL and PRL, as well as between HEL and DiY. Although the absence of a correlation between NY and the other markers has been previously noted in a non-pregnant population, a positive correlation in the pair PRL-NY (r=0.367; P<0.001) was observed in the present study. Maternal cigarette smoking was associated with increased urinary PRL levels (P=0.034). The most notable observation in the present study was that high levels of PRL and NY were associated with low Apgar scores at 1 and 5 min after birth (OR, 1.098 and 2.084 for PRL and NY, respectively; P<0.05). However, poor predictive accuracy was shown. For NY, the following results were obtained: Area under the curve (AUC), 0.818; sensitivity, 100%; specificity, 57%; positive predictive value (PPV), 11.54%; and negative predictive value (NPV), 100%. For PLR the values were as follows: AUC, 0.802; sensitivity, 100%; specificity, 62.6%; PPV, 13.05%; and NPV, 100%. DiY was negatively associated with preterm birth risk (OR=0.703; P=0.028). In conclusion, the results of the present study indicated the presence of OS in the second trimester of pregnancy, which was detected with damage to lipids and proteins and associated with an adverse Apgar score; however, the selected urinary markers exhibited poor positive predictive efficacy.

Risk factors for symptomatic osteonecrosis in childhood ALL: A retrospective study of a Slovenian pediatric ALL population between 1970 and 2004.

Treatment induced non-traumatic osteonecrosis (ON) has been reported increasingly in children treated for acute lymphoblastic leukemia (ALL). Several risk factors for ON have been identified in childhood cancer patients; however, their diagnostic and prognostic power is limited and the etiology of the disease remains unclear. Therefore, a continuous effort is focused on the identification of additional ON risk factors. We performed a retrospective study of 313 childhood ALL patients to test the association between the ON occurrence in children receiving ALL therapy and common polymorphisms in potential target genes: Thiopurine S-methyltransferase (TPMT; 460G>A, 719A>G), 5,10-methylenetetrahydrofolate reductase (MTHFR; 677C>T, 1298A>C), estrogen receptor alpha 1 (ESR1; XbaI) and collagen type I, α1 (COL1A1; Sp1). In the present cohort, higher age and more recently developed treatment protocols were independent risk factors for ON. In children >14.5 years old, TPMT genotype modulated the risk of ON. Additionally, in children <12.9 years old ESR1 genotypes were also implicated in the pathogenesis of ON. Besides greater age and more recent treatment protocols, genetic factors (polymorphisms in ESR1 and TPMT genes) were suggested to be implicated in the pathogenesis of ON and could be potentially used as genetic prognostic markers for ON.

Association of ITPA genotype with event-free survival and relapse rates in children with acute lymphoblastic leukemia undergoing maintenance therapy.

Although the treatment of acute lymphoblastic leukemia (ALL) has improved significantly over recent decades, failure due to treatment-related toxicities and relapse of the disease still occur in about 20% of patients. This retrospective study included 308 pediatric ALL patients undergoing maintenance therapy and investigated the effects of genetic variants of enzymes involved in the 6-mercaptopurine (6-MP) metabolism and folate pathway on survival and relapse rates. The presence of at least one of the non-functional ITPA alleles (94C>A and/or IVS2+21A>C variant) was associated with longer event-free survival compared to patients with the wild-type ITPA genotype (p = 0.033). Furthermore, patients carrying at least one non-functional ITPA allele were shown to be at a lower risk of suffering early (p = 0.003) and/or bone marrow relapse (p = 0.017). In conclusion, the ITPA genotype may serve as a genetic marker for the improvement of risk stratification and therapy individualization for patients with ALL.

From pharmacogenetics to pharmacometabolomics: SAM modulates TPMT activity.

AIM: In the present study, the influence of SAM on TPMT activity in vivo on human subjects was investigated. SUBJECTS & METHODS: A total of 1017 donors from the Estonian Genome Center of the University of Tartu (Estonia) were genotyped for common TPMT variants, evaluated for TPMT activity, SAM levels, a set of 19 biochemical and ten hematological parameters and demographic data. RESULTS: After adjustment in multiple regression models and correction for multiple testing, from the 43 factors that were tested, only TPMT genotype (p = 1 × 10(-13)) and SAM levels (p = 1 × 10(-13)) were found to significantly influence TPMT activity. The influence of SAM on TPMT activity was more pronounced in TPMT-heterozygous than wild-type individuals. CONCLUSION: SAM represents a potential pharmacometabolomic marker and therapeutic agent in TPMT-heterozygous subjects.

MTHFR and TYMS genotypes influence TPMT activity and its differential modulation in males and females.

OBJECTIVES: TPMT catalyzes the deactivation of the cytostatic drug 6-mercaptopurine used in treatment of cancer. Patients with low levels of TPMT more often experience severe toxic effects when treated with standard doses of 6-mercaptopurine than patients with high levels who, in turn, may experience inadequate treatment. It is therefore very important to assess factors that could influence TPMT activity. DESIGN AND METHODS: Red blood cell TPMT activity was measured by means of HPLC and genotypes of 86 healthy individuals were analyzed using TaqMan and PCR-RFLP methods, in order to investigate the effect of TPMT, MTHFR and TYMS genotypes on TPMT activity. RESULTS: TPMT activity was higher in TPMT wild-type males than females (p=0.028). Three-way ANOVA interaction analysis revealed a significant interaction effect between MTHFR genotype and gender on TPMT activity (p=0.023). CONCLUSION: Males have higher TPMT activity than females and the trend of influence of MTHFR genotype on TPMT activity is different in the two gender groups.

Individualization of thiopurine therapy: thiopurine S-methyltransferase and beyond.

The metabolism of a given drug depends, not solely on a particular enzyme, but rather on a complex metabolic network. Thiopurine S-methyltransferase (TPMT) catalyzes the methylation, and thus deactivation, of 6-mercaptopurine, a thiopurine used in the treatment of acute lymphoblastic leukemia. Low TPMT activity has been associated with severe toxicity of 6-mercaptopurine. Determination of mutations in the TPMT gene before starting 6-mercaptopurine therapy constitutes a quick, simple and cost-effective strategy to individualize thiopurine dosing. However, TPMT phenotype-to-genotype correlation is not complete, indicating a need for identification of novel biomarkers. Based on our recent findings and reviewing seemingly unrelated literature reports we present a synthesis of the current understanding of factors that influence TPMT activity and consequently modulate responsiveness to thiopurine treatment. Identification and understanding of these factors is crucial for improving the efficacy and safety of acute lymphoblastic leukemia treatment.