Maja Stojiljkovic

Systematic documentation and analysis of human genetic variation in hemoglobinopathies using the microattribution approach

We developed a series of interrelated locus-specific databases to store all published and unpublished genetic variation related to hemoglobinopathies and thalassemia and implemented microattribution to encourage submission of unpublished observations of genetic variation to these public repositories. A total of 1,941 unique genetic variants in 37 genes, encoding globins and other erythroid proteins, are currently documented in these databases, with reciprocal attribution of microcitations to data contributors. Our project provides the first example of implementing microattribution to incentivise submission of all known genetic variation in a defined system. It has demonstrably increased the reporting of human variants, leading to a comprehensive online resource for systematically describing human genetic variation in the globin genes and other genes contributing to hemoglobinopathies and thalassemias. The principles established here will serve as a model for other systems and for the analysis of other common and/or complex human genetic diseases.

Functional analysis of the role of the TPMT gene promoter VNTR polymorphism in TPMT gene transcription

AIMS Thiopurine S-methyltransferase (TPMT) activity is polymorphic, and a trimodal distribution has been demonstrated in Caucasians (low, intermediate and high methylator groups). The TPMT gene promoter contains a variable number of three GC-rich tandem repeats, namely A, B and C, ranging from three to nine in length in a A(n)B(m)C architecture. MATERIALS & METHODS Here, we investigated the influence of number and type of TPMT gene promoter tandem repeats on human TPMT gene transcription in K562 cells transiently transfected with reporter constructs bearing various variable number of tandem repeats (VNTR) and addressed the interaction of transcription factor binding to the VNTRs by electrophoretic mobility shift assays. RESULTS We found that the distribution patterns of VNTR alleles do not significantly differ among acute lymphoblastic leukemia patients, acute myeloid leukemia patients and normal individuals. We also demonstrated that the A repeat has a negative effect in TPMT gene transcription and that a positive regulatory element, identified immediately upstream to the VNTR region of the TPMT gene promoter, is indispensable for TPMT gene transcription. Our electrophoretic mobility shift assay analysis indicated that the Sp1 and Sp3 transcription factors bind to the VNTR repeats. CONCLUSION Overall, our data underline that both the number and type of VNTRs, as well as the upstream regulatory region of the TPMT gene promoter, determine the overall level of TPMT gene transcription. It remains to be seen whether these VNTRs can be employed as pharmacogenetic markers to individualize thiopurine therapy.

Molecular and phenotypic characteristics of patients with phenylketonuria in Serbia and Montenegro

Phenylketonuria (PKU) is the most common inborn error of amino acid metabolism in Caucasians. PKU is caused by mutations in the gene encoding phenylalanine hydroxylase (PAH) enzyme. Here, we report the spectrum and the frequency of mutations in the PAH gene and discuss genotype–phenotype correlation in 34 unrelated patients with PKU from Serbia and Montenegro. Using both polymerase chain reaction–restriction fragment length polymorphism and ‘broad‐range’ denaturing‐gradient gel electrophoresis/DNA sequencing analysis, 19 disease‐causing mutations were identified, corresponding to mutation detection rate of 97%. The most frequent ones were L48S (21%), R408W (18%), P281L (9%), E390G (7%) and R261Q (6%), accounting for 60% of all mutant alleles. The genotype–phenotype correlation was studied in homozygous and functionally hemizygous patients. We found that the most frequent mutation, L48S, was exclusively associated with the classical (severe) PKU phenotype. The mutation E390G gave rise to mild PKU. For the mutation R261Q, patients had been recorded in two phenotype categories. Considering allele frequencies, PKU in Serbia and Montenegro is heterogeneous, reflecting numerous migrations over the Balkan Peninsula.

A European spectrum of pharmacogenomic biomarkers: Implications for clinical pharmacogenomics

Pharmacogenomics aims to correlate inter-individual differences of drug efficacy and/or toxicity with the underlying genetic composition, particularly in genes encoding for protein factors and enzymes involved in drug metabolism and transport. In several European populations, particularly in countries with lower income, information related to the prevalence of pharmacogenomic biomarkers is incomplete or lacking. Here, we have implemented the microattribution approach to assess the pharmacogenomic biomarkers allelic spectrum in 18 European populations, mostly from developing European countries, by analyzing 1,931 pharmacogenomics biomarkers in 231 genes. Our data show significant inter-population pharmacogenomic biomarker allele frequency differences, particularly in 7 clinically actionable pharmacogenomic biomarkers in 7 European populations, affecting drug efficacy and/or toxicity of 51 medication treatment modalities. These data also reflect on the differences observed in the prevalence of high-risk genotypes in these populations, as far as common markers in the CYP2C9, CYP2C19, CYP3A5, VKORC1, SLCO1B1 and TPMT pharmacogenes are concerned. Also, our data demonstrate notable differences in predicted genotype-based warfarin dosing among these populations. Our findings can be exploited not only to develop guidelines for medical prioritization, but most importantly to facilitate integration of pharmacogenomics and to support pre-emptive pharmacogenomic testing. This may subsequently contribute towards significant cost-savings in the overall healthcare expenditure in the participating countries, where pharmacogenomics implementation proves to be cost-effective.

Newborn screening in southeastern Europe

The aim of our study was to assess the current state of newborn screening (NBS) in the region of southeastern Europe, as an example of a developing region, focusing also on future plans. Responses were obtained from 11 countries. Phenylketonuria screening was not introduced in four of 11 countries, while congenital hypothyroidism screening was not introduced in three of them; extended NBS programs were non-existent. The primary challenges were identified. Implementation of NBS to developing countries worldwide should be considered as a priority.

6-mercaptopurine influences TPMT gene transcription in a TPMT gene promoter variable number of tandem repeats-dependent manner

AIM TPMT activity is characterized by a trimodal distribution, namely low, intermediate and high methylator. TPMT gene promoter contains a variable number of GC-rich tandem repeats (VNTRs), namely A, B and C, ranging from three to nine repeats in length in an A(n)B(m)C architecture. We have previously shown that the VNTR architecture in the TPMT gene promoter affects TPMT gene transcription. MATERIALS, METHODS & RESULTS: Here we demonstrate, using reporter assays, that 6-mercaptopurine (6-MP) treatment results in a VNTR architecture-dependent decrease of TPMT gene transcription, mediated by the binding of newly recruited protein complexes to the TPMT gene promoter, upon 6-MP treatment. We also show that acute lymphoblastic leukemia patients undergoing 6-MP treatment display a VNTR architecture-dependent response to 6-MP. CONCLUSION These data suggest that the TPMT gene promoter VNTR architecture can be potentially used as a pharmacogenomic marker to predict toxicity due to 6-MP treatment in acute lymphoblastic leukemia patients.

Novel transcriptional regulatory element in the phenylalanine hydroxylase gene intron 8

We present the first transcriptional regulatory element found in a PAH gene intron. The element is located in the PAH gene intron 8, acts as an enhancer specifically in the hepatoma cell line, and binds GATA-1 transcription factor. Herein the presented data could unlock a new area for the analysis of PAH gene expression and could contribute to refining genotype-phenotype correlation.

Acute myeloid leukemia with NUP98-HOXC13 fusion and FLT3 internal tandem duplication mutation: case report and literature review.

The NUP98 gene at chromosome band 11p15 is known to be fused to a number of different partners in various hematological malignancies. The most frequently observed fusion partners of NUP98 are the homeobox family of transcriptional factors (HOX genes). We report a case of de novo AML M4 subtype, with a t(11;12)(p15;q13) translocation, generating a NUP98-HOXC13 chimeric transcript. Molecular analysis showed that the exon 16 of NUP98 was fused in frame with exon 2 of HOXC13. The patient was also positive for FLT3 internal tandem duplication (ITD), another molecular marker for the disease. Comparative study of data on the fusion of HOXC cluster and NUP98 gene revealed that it is a rare event, found exclusively in AML patients. To our knowledge, this is the first case of t(11;12)(p15;q13) in de novo AML-M4 in association with FLT3 ITD mutation. Coexistence of NUP98-HOXC13 fusion and FLT3 ITD mutation is likely relevant in the process of leukemogenesis.

The influence of novel transcriptional regulatory element in intron 14 on the expression of Janus kinase 2 gene in myeloproliferative neoplasms

The expression of Janus kinase 2 (JAK2) gene is altered in myeloproliferative neoplasms (MPN) and the regulation of transcription could be a mechanism that modulates JAK2 gene expression. We analyzed the transcriptional potential of single-nucleotide polymorphism (SNP) rs12343867 T > C in JAK2 intron 14, tagging 46/1 haplotype, and its influence on JAK2 gene expression. Functional analysis of JAK2 intron 14 was performed using the pBLCAT5 reporter system in K562 cells. Identification of the proteins binding to the intron 14 regulatory element was accomplished by electrophoretic mobility shift assay (EMSA) and supershift assays. Quantification of the expression of JAK2 gene in a cohort of 51 MPN patients and 12 healthy controls was performed by real-time quantitative polymerase chain reaction (RQ-PCR). Functional analysis revealed that the intronic DNA element harboring SNP rs12343867 T > C acts as a transcriptional repressor in vitro. The repressor activity was significantly attenuated by the presence of nucleotide C. Supershift analysis showed the enrolment of transcriptional factor Meis1 in this process. RQ-PCR experiments showed increased JAK2 expression in patients with the JAK2V617F mutation, with a significant difference between essential thrombocythemia (ET), polycythemia vera (PV), and myelofibrosis (MF) patients. SNP rs12343867 showed no statistically significant influence on the expression of JAK2 gene in MNP patients.

Clinical applicability of sequence variations in genes related to drug metabolism.

The Human Genome and the Hap Map Projects as well as the extensive use of deep resequencing worldwide, have contributed to a massive catalogue of reported single nucleotide polymorphisms (SNPs) and other genetic variations in the human genome. Pharmacogenomics is an emerging field that combines genetics with pharmacokinetics and pharmacodynamics of the drug in attempt to understand inter-individual differences among patients and develop more accurate drug dosing. However, only for the minority of those variations an association with phenotype has been established. Here, we provide an overview of genes and genetic variants that influence inter-individual dosing of three of the most widely used drugs, namely warfarin, irinotecan and thiopurine drugs, to highlight a tangible benefit of translating genomic knowledge into clinical practice. Therefore, particular SNPs in vitamin K epoxide reductase complex subunit 1 (VKORC1), cytochrome P450 2C9 (CYP2C9), uridine diphosphate glucoronosyltransferase 1A1 (UGT1A1) and thiopurine S-methyltransferase (TPMT) genes has proven to be applicable for optimising the dosage in pursuit of maximum efficacy and minimum adverse effects. Thus, they set an important paradigm of implementation of pharmacogenomics in the mainstream clinical practice.