Anthracycline-Free Protocol for Favorable-Risk Childhood ALL: A Noninferiority Comparison Between Malaysia-Singapore ALL 2003 and ALL 2010 Studies.

PURPOSE: To investigate whether, for children with favorable-risk B-cell precursor ALL (BCP-ALL), an anthracycline-free protocol is noninferior to a modified Berlin-Frankfurt-Muenster ALL-IC2002 protocol, which includes 120 mg/m2 of anthracyclines. PATIENTS AND METHODS: Three hundred sixty-nine children with favorable-risk BCP-ALL (age 1-9 years, no extramedullary disease, and no high-risk genetics) who cleared minimal residual disease (≤0.01%) at the end of remission induction were enrolled into Ma-Spore (MS) ALL trials. One hundred sixty-seven standard-risk (SR) patients (34% of Malaysia-Singapore ALL 2003 study [MS2003]) were treated with the MS2003-SR protocol and received 120 mg/m2 of anthracyclines during delayed intensification while 202 patients (42% of MS2010) received an anthracycline-free successor protocol. The primary outcome was a noninferiority margin of 1.15 in 6-year event-free survival (EFS) between the MS2003-SR and MS2010-SR cohorts. RESULTS: The 6-year EFS of MS2003-SR and MS2010-SR (anthracycline-free) cohorts was 95.2% ± 1.7% and 96.5% ± 1.5%, respectively (P = .46). The corresponding 6-year overall survival was 97.6% and 99.0% ± 0.7% (P = .81), respectively. The cumulative incidence of relapse was 3.6% and 2.6%, respectively (P = .42). After adjustment for race, sex, age, presenting WBC, day 8 prednisolone response, and favorable genetic subgroups, the hazard ratio for MS2010-SR EFS was 0.98 (95% CI, 0.84 to 1.14; P = .79), confirming noninferiority. Compared with MS2003-SR, MS2010-SR had significantly lower episodes of bacteremia (30% v 45.6%; P = .04) and intensive care unit admissions (1.5% v 9.5%; P = .004). CONCLUSION: In comparison with MS2003-SR, the anthracycline-free MS2010-SR protocol is not inferior and was less toxic as treatment for favorable-risk childhood BCP-ALL.

Digital PCR for Minimal Residual Disease Quantitation Using Immunoglobulin/T-Cell Receptor Gene Rearrangements in Acute Lymphoblastic Leukemia: A Proposed Analytic Algorithm.

In minimal residual disease (MRD), where there are exceedingly low target copy numbers, digital PCR (dPCR) can improve MRD quantitation. However, standards for dPCR MRD interpretation in acute lymphoblastic leukemia are lacking. Here, for immunoglobulin/T-cell receptor-based MRD, we propose an objective, statistics-based analytic algorithm. In 161 postinduction samples from 79 children with acute lymphoblastic leukemia, MRD was performed by dPCR and real-time quantitative PCR (qPCR) using the same markers and primer-probe sets. The dPCR raw data were analyzed by using an automated algorithm. dPCR and qPCR results were highly concordant (P < 0.0001): 98% (50 of 51) of qPCR positive were positive by dPCR, whereas 95% (61 of 64) of qPCR negative results were also negative by dPCR. For MRD quantitation, both qPCR and dPCR were tightly correlated (R2 = 0.94). Using more DNA (1 µg × 7 versus 630 ng × 3), dPCR improved sensitivity of MRD quantitation by one log10 (median MRD positive cutoff 1.6 × 10-5). With dPCR, 83% (29 of 35) of positive-not-quantifiable results by qPCR could be assigned positive/negative MRD status. Seven replicates of tested samples and negative controls were optimal. Compared with qPCR, dPCR could improve MRD sensitivity by one log10. We proposed an automatable, statistics-based algorithm that minimized interoperator variance for dPCR MRD.

Distinct clinical characteristics of DUX4- and PAX5-altered childhood B-lymphoblastic leukemia.

Among the recently described subtypes in childhood B-lymphoblastic leukemia (B-ALL) were DUX4- and PAX5-altered (PAX5alt). By using whole transcriptome RNA sequencing in 377 children with B-ALL from the Malaysia-Singapore ALL 2003 (MS2003) and Malaysia-Singapore ALL 2010 (MS2010) studies, we found that, after hyperdiploid and ETV6-RUNX1, the third and fourth most common subtypes were DUX4 (n = 51; 14%) and PAX5alt (n = 36; 10%). DUX4 also formed the largest genetic subtype among patients with poor day-33 minimal residual disease (MRD; n = 12 of 44). But despite the poor MRD, outcome of DUX4 B-ALL was excellent (5-year cumulative risk of relapse [CIR], 8.9%; 95% confidence interval [CI], 2.8%-19.5% and 5-year overall survival, 97.8%; 95% CI, 85.3%-99.7%). In MS2003, 21% of patients with DUX4 B-ALL had poor peripheral blood response to prednisolone at day 8, higher than other subtypes (8%; P = .03). In MS2010, with vincristine at day 1, no day-8 poor peripheral blood response was observed in the DUX4 subtype (P = .03). The PAX5alt group had an intermediate risk of relapse (5-year CIR, 18.1%) but when IKZF1 was not deleted, outcome was excellent with no relapse among 23 patients. Compared with MS2003, outcome of PAX5alt B-ALL with IKZF1 codeletion was improved by treatment intensification in MS2010 (5-year CIR, 80.0% vs 0%; P = .05). In conclusion, despite its poor initial response, DUX4 B-ALL had a favorable overall outcome, and the prognosis of PAX5alt was strongly dependent on IKZF1 codeletion.

Intracellular vincristine levels in lymphoblasts affect treatment outcome in childhood B-lymphoblastic leukaemia: Ma-Spore ALL 2010 study.

AIMS: Vincristine (VCR) is a key drug in the successful multidrug chemotherapy for childhood acute lymphoblastic leukaemia (ALL). However, it remains unclear how VCR pharmacokinetics affects its antileukaemic efficacy. The objective of this study is to explore the VCR pharmacokinetic parameters and intracellular VCR levels in an up-front window of Ma-Spore ALL 2010 (MS2010) study. METHODS: We randomised 429 children with newly diagnosed ALL to 15-minute vs 3-hour infusion for the first dose of VCR to study if prolonging the first dose of VCR infusion improved response. In a subgroup of 115 B-ALL and 20 T-ALL patients, we performed VCR plasma (n = 135 patients) and intracellular (n = 66 patients) pharmacokinetic studies. The correlations between pharmacokinetic parameters and intracellular VCR levels with early treatment response, final outcome and ABCB1 genotypes were analysed. RESULTS: There was no significant difference between 15-minute and 3-hour infusion schedules in median Day 8 peripheral or bone marrow blast response. Plasma VCR pharmacokinetic parameters did not predict outcome. However, in B-ALL, Day 33 minimal residual disease (MRD) negative patients and patients in continuous complete remission had significantly higher median intracellular VCR24h levels (P = .03 and P = .04, respectively). The median VCR24h intracellular levels were similar among the common genetic subtypes of ALL (P = .4). Patients homozygous for wild-type ABCB1 2677GG had significantly higher median intracellular VCR24h (P = .04) than 2677TT. CONCLUSION: We showed that in childhood B-ALL, the intracellular VCR24h levels in lymphoblasts affected treatment outcomes. The intracellular VCR24h level was independent of leukaemia subtype but dependent on host ABCB1 G2677T genotype.

RAS-protein activation but not mutation status is an outcome predictor and unifying therapeutic target for high-risk acute lymphoblastic leukemia.

Leukemias are routinely sub-typed for risk/outcome prediction and therapy choice using acquired mutations and chromosomal rearrangements. Down syndrome acute lymphoblastic leukemia (DS-ALL) is characterized by high frequency of CRLF2-rearrangements, JAK2-mutations, or RAS-pathway mutations. Intriguingly, JAK2 and RAS-mutations are mutually exclusive in leukemic sub-clones, causing dichotomy in therapeutic target choices. We prove in a cell model that elevated CRLF2 in combination with constitutionally active JAK2 is sufficient to activate wtRAS. On primary clinical DS-ALL samples, we show that wtRAS-activation is an obligatory consequence of mutated/hyperphosphorylated JAK2. We further prove that CRLF2-ligand TSLP boosts the direct binding of active PTPN11 to wtRAS, providing the molecular mechanism for the wtRAS activation. Pre-inhibition of RAS or PTPN11, but not of PI3K or JAK-signaling, prevented TSLP-induced RAS-GTP boost. Cytotoxicity assays on primary clinical DS-ALL samples demonstrated that, regardless of mutation status, high-risk leukemic cells could only be killed using RAS-inhibitor or PTPN11-inhibitor, but not PI3K/JAK-inhibitors, suggesting a unified treatment target for up to 80% of DS-ALL. Importantly, protein activities-based principal-component-analysis multivariate clusters analyzed for independent outcome prediction using Cox proportional-hazards model showed that protein-activity (but not mutation-status) was independently predictive of outcome, demanding a paradigm-shift in patient-stratification strategy for precision therapy in high-risk ALL.

Identifying IGH disease clones for MRD monitoring in childhood B-cell acute lymphoblastic leukemia using RNA-Seq.

Identifying patient-specific clonal IGH/TCR junctional sequences is critical for minimal residual disease (MRD) monitoring. Conventionally these junctional sequences are identified using laborious Sanger sequencing of excised heteroduplex bands. We found that the IGH is highly expressed in our diagnostic B-cell acute lymphoblastic leukemia (B-ALL) samples using RNA-Seq. Therefore, we used RNA-Seq to identify IGH disease clone sequences in 258 childhood B-ALL samples for MRD monitoring. The amount of background IGH rearrangements uncovered by RNA-Seq followed the Zipf's law with IGH disease clones easily identified as outliers. Four hundred and ninety-seven IGH disease clones (median 2, range 0-7 clones/patient) are identified in 90.3% of patients. High hyperdiploid patients have the most IGH disease clones (median 3) while DUX4 subtype has the least (median 1) due to the rearrangements involving the IGH locus. In all, 90.8% of IGH disease clones found by Sanger sequencing are also identified by RNA-Seq. In addition, RNA-Seq identified 43% more IGH disease clones. In 69 patients lacking sensitive IGH targets, targeted NGS IGH MRD showed high correlation (R = 0.93; P = 1.3 × 10-14), better relapse prediction than conventional RQ-PCR MRD using non-IGH targets. In conclusion, RNA-Seq can identify patient-specific clonal IGH junctional sequences for MRD monitoring, adding to its usefulness for molecular diagnosis in childhood B-ALL.

Intensifying Treatment of Childhood B-Lymphoblastic Leukemia With IKZF1 Deletion Reduces Relapse and Improves Overall Survival: Results of Malaysia-Singapore ALL 2010 Study.

Purpose Although IKZF1 deletion ( IKZF1del) confers a higher risk of relapse in childhood B-cell acute lymphoblastic leukemia (B-ALL), it is uncertain whether treatment intensification will reverse this risk and improve outcomes. The Malaysia-Singapore ALL 2010 study (MS2010) prospectively upgraded the risk assignment of patients with IKZF1del to the next highest level and added imatinib to the treatment of all patients with BCR- ABL1 fusion. Patients and Methods In total, 823 patients with B-ALL treated in the Malyasia-Singapore ALL 2003 study (MS2003; n = 507) and MS2010 (n = 316) were screened for IKZF1del using the multiplex ligation-dependent probe amplification assay. The impact of IKZF1del on the 5-year cumulative incidence of relapse (CIR) was compared between the two studies. Results Patient characteristics were similar in both cohorts, including IKZF1del frequencies (59 of 410 [14.4%] v 50 of 275 [18.2%]; P = .2). In MS2003, where IKZF1del was not used in risk assignment, IKZF1del conferred a significantly higher 5-year CIR (30.4% v 8.1%; P = 8.7 × 10-7), particularly in the intermediate-risk group who lacked high-risk features (25.0% v 7.5%; P = .01). For patients with BCR-ABL1-negative disease, IKZF1del conferred a higher 5-year CIR (20.5% v 8.0%; P = .01). In MS2010, the 5-year CIR of patients with IKZF1del significantly decreased to 13.5% ( P = .05) and no longer showed a significant difference in patients with BCR-ABL1-negative disease (11.4% v 4.4%; P = .09). The 5-year overall survival for patients with IKZF1del improved from 69.6% in MS2003 to 91.6% in MS2010 ( P = .007). Conclusion Intensifying therapy for childhood B-ALL with IKZF1del significantly reduced the risk of relapse and improved overall survival. Incorporating IKZF1del screening significantly improved treatment outcomes in contemporary ALL therapy.

Whole-transcriptome sequencing identifies a distinct subtype of acute lymphoblastic leukemia with predominant genomic abnormalities of EP300 and CREBBP.

Chromosomal translocations are a genomic hallmark of many hematologic malignancies. Often as initiating events, these structural abnormalities result in fusion proteins involving transcription factors important for hematopoietic differentiation and/or signaling molecules regulating cell proliferation and cell cycle. In contrast, epigenetic regulator genes are more frequently targeted by somatic sequence mutations, possibly as secondary events to further potentiate leukemogenesis. Through comprehensive whole-transcriptome sequencing of 231 children with acute lymphoblastic leukemia (ALL), we identified 58 putative functional and predominant fusion genes in 54.1% of patients (n = 125), 31 of which have not been reported previously. In particular, we described a distinct ALL subtype with a characteristic gene expression signature predominantly driven by chromosomal rearrangements of the ZNF384 gene with histone acetyltransferases EP300 and CREBBP ZNF384-rearranged ALL showed significant up-regulation of CLCF1 and BTLA expression, and ZNF384 fusion proteins consistently showed higher activity to promote transcription of these target genes relative to wild-type ZNF384 in vitro. Ectopic expression of EP300-ZNF384 and CREBBP-ZNF384 fusion altered differentiation of mouse hematopoietic stem and progenitor cells and also potentiated oncogenic transformation in vitro. EP300- and CREBBP-ZNF384 fusions resulted in loss of histone lysine acetyltransferase activity in a dominant-negative fashion, with concomitant global reduction of histone acetylation and increased sensitivity of leukemia cells to histone deacetylase inhibitors. In conclusion, our results indicate that gene fusion is a common class of genomic abnormalities in childhood ALL and that recurrent translocations involving EP300 and CREBBP may cause epigenetic deregulation with potential for therapeutic targeting.

NUDT15 polymorphisms alter thiopurine metabolism and hematopoietic toxicity.

Widely used as anticancer and immunosuppressive agents, thiopurines have narrow therapeutic indices owing to frequent toxicities, partly explained by TPMT genetic polymorphisms. Recent studies identified germline NUDT15 variation as another critical determinant of thiopurine intolerance, but the underlying molecular mechanisms and the clinical implications of this pharmacogenetic association remain unknown. In 270 children enrolled in clinical trials for acute lymphoblastic leukemia in Guatemala, Singapore and Japan, we identified four NUDT15 coding variants (p.Arg139Cys, p.Arg139His, p.Val18Ile and p.Val18_Val19insGlyVal) that resulted in 74.4-100% loss of nucleotide diphosphatase activity. Loss-of-function NUDT15 diplotypes were consistently associated with thiopurine intolerance across the three cohorts (P = 0.021, 2.1 × 10(-5) and 0.0054, respectively; meta-analysis P = 4.45 × 10(-8), allelic effect size = -11.5). Mechanistically, NUDT15 inactivated thiopurine metabolites and decreased thiopurine cytotoxicity in vitro, and patients with defective NUDT15 alleles showed excessive levels of thiopurine active metabolites and toxicity. Taken together, these results indicate that a comprehensive pharmacogenetic model integrating NUDT15 variants may inform personalized thiopurine therapy.

Profiling of somatic mutations in acute myeloid leukemia with FLT3-ITD at diagnosis and relapse.

Acute myeloid leukemia (AML) with an FLT3 internal tandem duplication (FLT3-ITD) mutation is an aggressive hematologic malignancy with a grave prognosis. To identify the mutational spectrum associated with relapse, whole-exome sequencing was performed on 13 matched diagnosis, relapse, and remission trios followed by targeted sequencing of 299 genes in 67 FLT3-ITD patients. The FLT3-ITD genome has an average of 13 mutations per sample, similar to other AML subtypes, which is a low mutation rate compared with that in solid tumors. Recurrent mutations occur in genes related to DNA methylation, chromatin, histone methylation, myeloid transcription factors, signaling, adhesion, cohesin complex, and the spliceosome. Their pattern of mutual exclusivity and cooperation among mutated genes suggests that these genes have a strong biological relationship. In addition, we identified mutations in previously unappreciated genes such as MLL3, NSD1, FAT1, FAT4, and IDH3B. Mutations in 9 genes were observed in the relapse-specific phase. DNMT3A mutations are the most stable mutations, and this DNMT3A-transformed clone can be present even in morphologic complete remissions. Of note, all AML matched trio samples shared at least 1 genomic alteration at diagnosis and relapse, suggesting common ancestral clones. Two types of clonal evolution occur at relapse: either the founder clone recurs or a subclone of the founder clone escapes from induction chemotherapy and expands at relapse by acquiring new mutations. Relapse-specific mutations displayed an increase in transversions. Functional assays demonstrated that both MLL3 and FAT1 exert tumor-suppressor activity in the FLT3-ITD subtype. An inhibitor of XPO1 synergized with standard AML induction chemotherapy to inhibit FLT3-ITD growth. This study clearly shows that FLT3-ITD AML requires additional driver genetic alterations in addition to FLT3-ITD alone.

Minimal residual disease-guided treatment deintensification for children with acute lymphoblastic leukemia: results from the Malaysia-Singapore acute lymphoblastic leukemia 2003 study.

PURPOSE: To improve treatment outcome for childhood acute lymphoblastic leukemia (ALL), we designed the Malaysia-Singapore ALL 2003 study with treatment stratification based on presenting clinical and genetic features and minimal residual disease (MRD) levels measured by polymerase chain reaction targeting a single antigen-receptor gene rearrangement. PATIENTS AND METHODS: Five hundred fifty-six patients received risk-adapted therapy with a modified Berlin-Frankfurt-Münster-ALL treatment. High-risk ALL was defined by MRD ≥ 1 × 10(-3) at week 12 and/or poor prednisolone response, BCR-ABL1, MLL gene rearrangements, hypodiploid less than 45 chromosomes, or induction failure; standard-risk ALL was defined by MRD ≤ 1 × 10(-4) at weeks 5 and 12 and no extramedullary involvement or high-risk features. Intermediate-risk ALL included all remaining patients. RESULTS: Patients who lacked high-risk presenting features (85.7%) received remission induction therapy with dexamethasone, vincristine, and asparaginase, without anthracyclines. Six-year event-free survival (EFS) was 80.6% ± 3.5%; overall survival was 88.4% ± 3.1%. Standard-risk patients (n = 172; 31%) received significantly deintensified subsequent therapy without compromising EFS (93.2% ± 4.1%). High-risk patients (n = 101; 18%) had the worst EFS (51.8% ± 10%); EFS was 83.6% ± 4.9% in intermediate-risk patients (n = 283; 51%). CONCLUSION: Our results demonstrate significant progress over previous trials in the region. Three-drug remission-induction therapy combined with MRD-based risk stratification to identify poor responders is an effective strategy for childhood ALL.

FLT3 mutation and expression did not adversely affect clinical outcome of childhood acute leukaemia: a study of 531 Southeast Asian children by the Ma-Spore study group.

FMS-like tyrosine kinase 3 (FLT3) is critical for normal haematopoiesis and have been reported to be expressed in the majority of acute myeloid and lymphoid malignancies. We correlated the impact of FLT3 mutations and its expression with age, WHO 2008 classification and treatment outcome in 531 childhood acute leukaemias. Of 150 acute myeloid leukaemia (AMLs), 18 (12%) harboured FLT3-ITD while nine (6%) had FLT3-TKD. FLT3-ITD and -TKD were rare in acute megakaryoblastic leukaemia (AMKL; FLT3-ITD 0/26, FLT3-TKD 1/26) and children below 3 years (n = 2/48). Acute promyelocytic leukaemia (APL) with t(15;17);PML-RARα (n = 7/18; 39%) harboured the highest frequency of FLT3 mutations, followed by myelomonocytic (n = 4/18; 22%) and AML with t(8;21);RUNX1-RUNX1T1 (n = 2/21; 9%). FLT3 expression levels were also lowest in AMKL, both in Down's and non-Down's (p = 0.002) followed by patients <3 years (p = 0.001). The rarity of FLT3 mutations and expression levels in AMKL were independent of age. Conversely, only 2% of childhood acute lymphoblastic leukaemia (ALL) harboured FLT3 mutations (ITD = 1/381; TKD = 6/381). FLT3 was highly expressed in hyperdiploid ALL (p < 0.001). Of the 121 AMLs with clinical history, there were no significant differences in 4-year event-free survival (EFS) (46% vs. 38%; p = 0.46) and overall-survival (OS) (55% vs. 43%; p = 0.30) between FLT3-wildtype and ITD+ patients. Similarly, FLT3 expression levels did not influence survival in AML in both the good risk and non-good risk subgroups. FLT3 does not appear to be involved in the pathogenesis of AMKL, both in Down's and non-Down's. Therapeutic targets using FLT3 inhibitors may not be useful in AMKL and in young children with AML.

Identification of prognostic protein biomarkers in childhood acute lymphoblastic leukemia (ALL).

Early response to 7 days of prednisolone (PRED) treatment is one of the important prognostic factors in predicting eventual outcome in childhood acute lymphoblastic leukemia (ALL). Using proteomic tools and clinically important leukemia cell lines (REH, 697, Sup-B15, RS4; 11), we have identified potential prognostic protein biomarkers as well as discovered promising regulators of PRED-induced apoptosis. After treatment with PRED, the four cell lines can be separated into resistant (REH) and sensitive (697, Sup-B15, RS4;11). Two dimensional gel electrophoresis (2-DE) and MALDI-TOF/TOF MS identified 77 and 17 significantly differentially expressed protein spots (p<0.05) in PRED-sensitive and PRED-resistant cell lines respectively. Several of these were validated by Western blot including proliferating cell nuclear antigen (PCNA), cofilin 1, voltage-dependent anion-channel protein 1 (VDAC1) and proteasome activator subunit 2 (PA28ß). PCNA is a promising protein because of its important roles both in cell cycle regulation and survival control. We subsequently validated PCNA in 43 paired bone marrow samples from children with newly diagnosed ALL (Day 0) and 7 days after PRED treatment (Day 8). ROC curve analysis confirmed that PCNA was highly predictive of PRED response in patients (AUC=0.81, p=0.007) and most interestingly, independent of the molecular subtype, providing a promising universal prognostic marker.

Genetic susceptibility to childhood acute lymphoblastic leukemia shows protection in Malay boys: results from the Malaysia-Singapore ALL Study Group.

To study genetic epidemiology of childhood acute lymphoblastic leukemia (ALL) in the Chinese and Malays, we investigated 10 polymorphisms encoding carcinogen- or folate-metabolism and transport. Sex-adjusted analysis showed NQO1 609CT significantly protects against ALL, whilst MTHFR 677CT confers marginal protection. Interestingly, we observed that NQO1 609CT and MTHFR 1298 C-allele have greater genetic impact in boys than in girls. The combination of SLC19A1 80GA heterozygosity and 3'-TYMS -6bp/-6bp homozygous deletion is associated with reduced ALL risk in Malay boys. Our study has suggested the importance of gender and race in modulating ALL susceptibility via the folate metabolic pathway.

TPMT*26 (208F-->L), a novel mutation detected in a Chinese.

AIMS: Azathioprine, mercaptopurine and thioguanine are commonly used to treat autoimmune disorders, leukaemia and solid organ transplantation. However, azathiopurine and its metabolites can also cause adverse reactions such as myelosuppression. These manifestations may be attributed to polymorphisms or mutations in the thiopurine methyltransferase (TPMT) gene that might result in low TPMT enzyme activity. Our aim was to investigate if azathioprine-related myelosuppression is associated with TPMT polymorphism, which in turn affects its enzyme activity. METHODS: A 61-year-old Chinese man with severe atopic eczema developed moderate myelosuppression with standard doses of azathioprine. His TPMT activity was measured using radiochemical assay. Genotyping of TPMT *3C, *3A and *6 were screened using polymerase chain reaction-restriction fragment length polymorphism. Novel mutation was detected by sequencing. Family studies of his three other siblings were performed. RESULTS: After 4 weeks of azathioprine treatment, the patient's white blood cells and absolute neutrophil count dropped by 40-45%. He was then taken off azathioprine, and blood counts returned to normal. TPMT activity test showed intermediate levels of 9.1 nmol h(-1) ml(-1) peripheral red blood cells (pRBC). Resequencing of the TPMT gene revealed a missense mutation Phe-->Leu at 208 aa position in exon 9 (ss105107120). Two of his three siblings were heterozygous for 208F-->L, which accounts for the decreased enzyme activity (brother 8.9 nmol h(-1) ml(-1) pRBC, sister 8.8 nmol h(-1) ml(-1) pRBC). The remaining sibling had wild-type allele with normal enzyme activity. Screening of 100 normal healthy Chinese subjects did not reveal any individual with this mutation. CONCLUSION: We report a novel mutation TPMT*26 (208F-->L) associated with a decrease in TPMT enzyme activity.

Thiopurine S-methyltransferase activity in three major Asian populations: a population-based study in Singapore.

OBJECTIVE: The distribution of thiopurine methyltransferase (TPMT) activity in Asian populations has not been well documented. We studied the TPMT phenotype in three major Asian ethnic groups in Singapore, namely the Chinese (Ch), Malays (Mal) and Indians (Ind), with the aim of carrying out a comprehensive survey of the distribution of TPMT activity in Asians. METHODS: A radiochemical assay was used to measure the enzymatic activity of TPMT in the red blood cells (RBCs) of 479 healthy adults (Ch=153, Mal=163 and Ind=163). Cut-off points for intermediate TPMT activity were validated using a receiver operating curve (ROC) analysis. PCR-based methods were used to screen for the TPMT*3C, TPMT*3A and TPMT*6 variants. RESULTS: The histogram of the combined population cohort showed a bimodal distribution of TPMT activity, with no subject having low TPMT activity (<5 units). In total, TPMT variants were detected in 14 subjects (*1/*3C in 13 subjects; *1/*3A in one subject). We observed significant inter-ethnic differences in terms of TPMT activity (p<0.001), with the Malays showing a higher median activity than the Chinese or Indians (17.8 units vs 16.4 units). The Malays also showed a higher methylation rate--with a cut-off point for intermediate TPMT activity of 11.3 units--than the Chinese (9.9 units) or Indians (9.4 units). A high phenotype-genotype correlation of >97% was observed in all three races. We also genotyped 418 childhood leukaemias. The combined analysis of subjects participating in this and a previous study--1585 subjects--showed that 4.7% of Chinese (n=30/644), 4.4% of Malays (n=24/540) and 2.7% of Indians (n=11/401) were heterozygous at the TPMT gene locus. CONCLUSION: This is the first comprehensive TPMT phenotype and genotype study in Asian populations, particularly in the Malays and Indians.

Genotyping of eight polymorphic genes encoding drug-metabolizing enzymes and transporters using a customized oligonucleotide array.

Polymorphisms in drug-metabolizing genes may lead to the production of dysfunctional proteins and consequently affect therapeutic efficacy and toxicity of drugs. Different frequencies of polymorphic alleles among the races have been postulated to account for the observed ethnic variations in drug responses. In the current study, we aimed to estimate the frequencies of 14 polymorphisms in eight genes (TPMT, NQO1, MTHFR, GSTP1, CYP1A1, CYP2D6, ABCB1, and SLC19A1) in the Singapore multiracial populations by screening 371 cord blood samples from healthy newborns. To improve genotyping efficacy, we designed an oligonucleotide array based on the principle of allele-specific primer extension (AsPEX) that was capable of detecting the 14 polymorphisms simultaneously. Cross-validation using conventional polymerase chain reaction-restriction fragment-length polymorphism (PCR-RFLP) assays demonstrated 99% concordant results. Measurements on the fluorescent intensity displayed clear distinctions among different genotypes. Statistical analyses showed significantly different allele distributions in several genes among the three races, namely Chinese, Malays, and Indians. Comparing the allelic frequencies in Chinese with previous studies in Caucasian populations, NQO1 609C>T and SLC19A1 80G>A were distinctly different, whereas close similarity was observed for MTHFR 677C>T. We have demonstrated an array-based methodology for rapid multiplex detection of genetic polymorphisms. The allelic frequencies reported in this study may have important therapeutic and prognostic implications in the clinical use of relevant drugs.

Arrayed primer extension: a robust and reliable genotyping platform for the diagnosis of single gene disorders: beta-thalassemia and thiopurine methyltransferase deficiency.

Mutation screenings, which were conventionally carried out individually because of different assay conditions, are usually time consuming and not cost effective. Using microarray technology, simultaneous molecular diagnosis of multiple mutations on a single platform is possible. To evaluate this idea, we developed a DNA chip platform to simultaneously detect 23 mutations of the beta-globin gene and 9 mutations of thiopurine methyltransferase (TPMT) gene based on the principle of arrayed primer extension (APEX). A blinded test consisting of 200 DNA samples with known genotypes was performed to validate this strategy. High genotyping accuracy of 97.3% and 100% for beta-globin and TPMT genes, respectively, were achieved. Further analysis on the fluorescent intensity demonstrated clear separation between the real signal and the background noise, which enabled us to set two cutoff values (V(lower) = 4.0 and V(upper) = 12.0) to determine the genotype quantitatively. Our results showed that APEX is a highly reliable genotyping strategy to detect mutations that cause beta-thalassemia or TPMT enzyme deficiency.