Thiopurine-induced toxicity is associated with dysfunction variant of the human molybdenum cofactor sulfurase gene (xanthinuria type II)

Studying the role of Bombyx mori molybdenum cofactor sulfurase in Bombyx mori nucleopolyhedrovirus infection

Molybdenum cofactor sulfurase (MoCoS) is a key gene involved in the uric acid metabolic pathway that activates xanthine dehydrogenase to synthesise uric acid. Uric acid is harmful to mammals but plays crucial roles in insects, one of which is the immune responses. However, the function of Bombyx mori MoCoS in response to BmNPV remains unclear. In this study, BmMoCoS was found to be relatively highly expressed in embryonic development, gonads and the Malpighian tubules. In addition, the expression levels of BmMoCoS were significantly upregulated in three silkworm strains with different levels of resistance after virus infection, suggesting a close link between them. Furthermore, RNAi and overexpression studies showed that BmMoCoS was involved in resistance to BmNPV infection, and its antivirus effects were found to be related to the regulation of uric acid metabolism, which was uncovered by inosine- and febuxostat-coupled RNAi and overexpression. Finally, the BmMoCoS-mediated uric acid pathway was preliminarily confirmed to be a potential target to protect silkworms from BmNPV infection. Overall, this study provides new evidence for elucidating the molecular mechanism of silkworms in response to BmNPV infection and new strategies for the prevention of viral infections in sericulture.

Three cases of xanthinuria identified by gas chromatography/mass spectrometry-based urine metabolomics

Introduction

Early diagnosis of patients with urolithiasis or hypouricemia owing to inborn errors of hypoxanthine metabolism is important in preventing renal failure or drug-induced toxicity.

Case presentation

We identified three patients with xanthinuria using gas chromatography/mass spectrometry-based urine metabolomics: a 72-year-old male with bladder stone, a severe hypouricemic 59-year-old female with type 2 diabetes mellitus, and an 8-year and 9-month-old female who was first discovered to harbor a mutation in the xanthine dehydrogenase gene using whole-exome sequencing, but had a normal molybdenum cofactor sulfurase gene. Hydantoin-5-propionate was detected in the first and third patients but not in the second, suggesting that the first and second patients had type I and II xanthinuria, respectively.

Conclusion

Gas chromatography/mass spectrometry-based metabolomics can be used for undiagnosed patients with xanthinuria, identification of the type of xanthinuria without allopurinol loading, and the quick functional evaluation of mutations in the xanthinuria-related genes.

Genetic variants of genes involved in thiopurine metabolism pathway are associated with 6-mercaptopurine toxicity in pediatric acute lymphoblastic leukemia patients from Ethiopia

Introduction: Genetic variation in the thiopurine S-methyltransferase (TPMT) gene by and large predicts variability in 6-mercaptopurine (6-MP) related toxicities. However, some individuals without genetic variants in TPMT still develop toxicity that necessitates 6-MP dose reduction or interruption. Genetic variants of other genes in the thiopurine pathway have been linked to 6-MP related toxicities previously. Objective: The aim of this study was to evaluate the effect of genetic variants in ITPA, TPMT, NUDT15, XDH, and ABCB1 on 6-MP related toxicities in patients with acute lymphoblastic leukemia (ALL) from Ethiopia. Methods: Genotyping of ITPA, and XDH was performed using KASP genotyping assay, while that of TPMT, NUDT15, and ABCB1 with TaqMan^® SNP genotyping assays. Clinical profile of the patients was collected for the first 6 months of the maintenance phase treatment. The primary outcome was the incidence of grade 4 neutropenia. Bivariable followed by multivariable cox regression analysis was performed to identify genetic variants associated with the development of grade 4 neutropenia within the first 6 months of maintenance treatment. Results: In this study, genetic variants in XDH and ITPA were associated with 6-MP related grade 4 neutropenia and neutropenic fever, respectively. Multivariable analysis revealed that patients who are homozygous (CC) for XDH rs2281547 were 2.956 times (AHR 2.956, 95% CI = 1.494-5.849, p = 0.002) more likely to develop grade 4 neutropenia than those with the TT genotype. Conclusion: In conclusion, in this cohort, XDH rs2281547 was identified as a genetic risk factor for grade 4 hematologic toxicities in ALL patients treated with 6-MP. Genetic polymorphisms in enzymes other than TPMT involved in the 6-mercaptopurine pathway should be considered during its use to avoid hematological toxicity.

XDH genotypes through gene-gene interactions with NUDT15 affect azathioprine-induced leukopenia in Chinese patients

Aim: To investigate whether genotypes of XDH, GMPS and MOCOS were associated with azathioprine-induced adverse drug reaction (ADR) and had the gene-gene interactions with NUDT15 rs116855232 to induce leukopenia. Methods: Patients who had taken azathioprine were recruited. Genotyping of those gene was performed. Risk factor to ADR was analyzed by logistic regression. The generalized multifactor dimensionality reduction (GMDR) was assessed based on gene-gene interactions with ADR. Results: A total of 111 patients were included in this study, all of whom were Han Chinese. XDH rs2295475 was a risk factor of myelotoxicity (p = 0.022). NUDT15 rs116855232 was a risk factor of myelotoxicity, grade ≥2 leukopenia and drug treatment termination (p-values were <0.05). Rs2295475 and rs116855232 had a gene-gene interaction. The model was associated with grade ≥2 leukopenia (OR: 17.99; 95% CI: 4.11-78.81). Conclusion: Combined testing genotype for rs2295475 and rs116855232 could improve the prediction of azathioprine-induced leukopenia.

The Examination of a TPMT Gene Before Administration of Azathioprine in Rheumatology Practice and Identification of a Novel Variant p.W29R

METHODS

Two-hundred patients were assessed for the presence of genetic allelic variants using PCR amplification and direct sequencing.

RESULTS

In 19 patients, we detected genetic allelic variants affecting TPMT activity; in 1 case, it was an unpublished heterozygous variant c.85T>C (p.W29R); of those, 15 patients were switched from AZA to a different medication, and 1 patient was prescribed a reduced dose of AZA.

CONCLUSIONS

Our findings show the importance of testing for variants of the TPMT gene before the administration of AZA in clinical rheumatology practice. Patients with documented episodes of leukopenia or elevated liver biochemical tests while on AZA should undergo TPMT genotype testing and/or TPMT enzyme activity testing.

Classical Xanthinuria in Nine Israeli Families and Two Isolated Cases from Germany: Molecular, Biochemical and Population Genetics Aspects

Classical xanthinuria is a rare autosomal recessive metabolic disorder caused by variants in the XDH (type I) or MOCOS (type II) genes. Thirteen Israeli kindred (five Jewish and eight Arab) and two isolated cases from Germany were studied between the years 1997 and 2013. Four and a branch of a fifth of these families were previously described. Here, we reported the demographic, clinical, molecular and biochemical characterizations of the remaining cases. Seven out of 20 affected individuals (35%) presented with xanthinuria-related symptoms of varied severity. Among the 10 distinct variants identified, six were novel: c.449G>T (p.(Cys150Phe)), c.1434G>A (p.(Trp478*)), c.1871C>G (p.(Ser624*)) and c.913del (p.(Leu305fs*1)) in the XDH gene and c.1046C>T (p.(Thr349Ileu)) and c.1771C>T (p.(Pro591Ser)) in the MOCOS gene. Heterologous protein expression studies revealed that the p.Cys150Phe variant within the Fe/S-I cluster-binding site impairs XDH biogenesis, the p.Thr349Ileu variant in the NifS-like domain of MOCOS affects protein stability and cysteine desulfurase activity, while the p.Pro591Ser and a previously described p.Arg776Cys variant in the C-terminal domain affect Molybdenum cofactor binding. Based on the results of haplotype analyses and historical genealogy findings, the potential dispersion of the identified variants is discussed. As far as we are aware, this is the largest cohort of xanthinuria cases described so far, substantially expanding the repertoire of pathogenic variants, characterizing structurally and functionally essential amino acid residues in the XDH and MOCOS proteins and addressing the population genetic aspects of classical xanthinuria.

An ancestral variant causing type I xanthinuria in Turkmen and Arab families is predicted to prevail in the Afro-Asian stone-forming belt

Classical xanthinuria is a rare autosomal recessive metabolic disorder characterized by lack of xanthine dehydrogenase activity that often manifests as xanthine urolithiasis and risk of drug toxicity. Variants in the XDH or HMCS gene underlie classical xanthinuria type I and type II, respectively. Here we present two Israeli Arab families affected by type I xanthinuria in whom a c.2164A>T (Lys722Ter) variant in the XDH gene, previously reported in a Turkish family of Turkmen origin, was identified. Analysis of polymorphic markers surrounding the variant site revealed common haplotypes spanning 0.6 Mbp shared by all three, and 1.7 Mbp shared by two of the studied families. By applying Bayesian methods to a simple model of crossover events through generations in the chromosomes carrying the variant, the most recent common ancestor of these families was found to be 179 (95% credible limit 70) generations old. The estimated antiquity of the variant, the historical genealogy of the affected families and the history and present day dispersion of their people strongly suggest prevalence of this variant in the Afro-Asian stone-forming belt. As far as we are aware, this is a first report of an ancient variant causing xanthinuria with potential wide geographical dispersion.

Amplicon targeted resequencing for SLC2A9 and SLC22A12 identified novel mutations in hypouricemia subjects

Background

To identify potential causative mutations in SLC2A9 and SLC22A12 that lead to hypouricemia or hyperuricemia (HUA).

Methods

Targeted resequencing of whole exon regions of SLC2A9 and SLC22A12 was performed in three cohorts of 31 hypouricemia, 288 HUA and 280 normal controls.

Results

A total of 84 high‐quality variants were identified in these three cohorts. Eighteen variants were nonsynonymous or in splicing region, and then included in the following association analysis. For common variants, no significant effects on hypouricemia or HUA were identified. For rare variants, six single nucleotide variations (SNVs) p.T21I and p.G13D in SLC2A9, p.W50fs, p.Q382L, p.V547L and p.E458K in SLC22A12, occurred in totally six hypouricemia subjects and were absent in HUA and normal controls. Allelic and genotypic frequency distributions of the six SNVs differed significantly between the hypouricemia and normal controls even after multiple testing correction, and p.G13D in SLC2A9 and p.V547L in SLC22A12 were newly reported. All these mutations had no significant effects on HUA susceptibility, while the gene‐based analyses substantiated the significant results on hypouricemia.

Conclusion

Our study first presents a comprehensive mutation spectrum of hypouricemia in a large Chinese cohort.