Clinical and echocardiographic predictors of embolism in infective endocarditis: systematic review and meta-analysis

OBJECTIVES

Prediction of embolic events (EEs) in infective endocarditis (IE) could inform clinical decisions, such as surgical timing. We conducted a systematic review to more precisely define associations between risk factors and EEs.

METHODS

We searched two bibliographic databases (1994-2018) for observational studies that reported EEs in IE patients and considered clinical, microbiological or echocardiographic risk factors. Studies that did not use Duke criteria or only investigated a subset of IE patients were excluded. Study quality was assessed using the Newcastle-Ottawa scale. A pooled risk ratio (RR) for each risk factor was estimated using random-effects models; statistical heterogeneity was estimated using I².

RESULTS

Of 3862 unique citations, 47 cohort studies (11 215 IE cases) were included; 54 risk factors were analysed in at least two studies, with nine studies reporting other individual factors. Most studies were of high methodological quality. Major predictors of EEs were intravenous drug use (RR 1.69, 95% CI 1.32-2.17; I² = 46%), Staphylococcus aureus infection (RR 1.64, 95% CI 1.45-1.86, I² = 32%), mitral valve vegetation (RR 1.24, 95% CI 1.11-1.37, I² = 30%), and vegetation size >10 mm (RR 1.87, 95% CI 1.57-2.21, I² = 48%). EE risk was also higher with human immunodeficiency virus, chronic liver disease, elevated C-reactive protein, Staphylococcus spp. infection, vegetation presence, and multiple, mobile or prosthetic mechanical valve vegetation, and lower with Streptococcus spp. infection. Most findings were unchanged in sensitivity analyses that removed studies with pulmonary EEs from the outcome.

CONCLUSIONS

Given the serious consequences of embolism, surgical evaluation may be considered in patients with these risk factors.

First Korean Case of Renpenning Syndrome with Novel Mutation in PQBP1 Diagnosed by Targeted Exome Sequencing, and Literature Review

Renpenning syndrome is a rare X-linked disorder characterized by mental retardation, leanness, microcephaly, facial dysmorphism, short stature, and small testes. This disease is caused by PQBP1 mutations. Herein, we present a literature review and describe the clinical and molecular findings in a Korean boy with Renpenning syndrome. A 23-month-old boy presented with mental retardation, narrow face, bulbous nose, and cardiac anomaly. Interestingly, targeted exome sequencing identified a novel mutation c.559delT (p.Tyr187llefs*8) in the PQBP1 gene, and he was diagnosed as having Renpenning syndrome. In line with previously reported studies, our case suggests that men with mental retardation, short stature, and microcephaly should include Renpenning syndrome as a differential diagnosis.

Etiological trends in male central precocious puberty

PURPOSE

In the present study, the etiological trends in male central precocious puberty (CPP) were examined, and annual distribution was evaluated.

METHODS

Seventy-one male CPP subjects who started puberty before 9 years of age were included in this study. All individuals were diagnosed as having CPP at Samsung Medical Center between 2001 and 2016. Chronological age at puberty onset, diagnosis of CPP, bone age, weight (kg), height (cm), puberty stage, brain magnetic resonance imaging findings, testosterone level, basal gonadotropin level, and gonadotropin level after gonadotropin releasing hormone stimulation were analyzed.

RESULTS

The 71 patients were divided into 2 groups: idiopathic (group I) and organic (group II) when the lesion was identified as associated with the central nervous system (CNS) or when the patient received chemotherapy for non-CNS tumors before CPP diagnosis, respectively. Forty-four cases (62%) were idiopathic, and 27 (38%) were organic. The proportion of idiopathic CPP was higher than that of organic CPP during the study period. In 51.9% of organic cases, puberty started before 8 years of age, whereas it started after that age in 93.2% of the idiopathic cases.

CONCLUSION

In the present study, among all male CPP cases, 62% were idiopathic. The probability of idiopathic CPP prevalence was higher in males when the puberty onset was after 8 years of age with no history of cranial radiotherapy or chemotherapy.

Lymphopenia is associated with late onset Pneumocystis jirovecii pneumonia in solid organ transplantation

BACKGROUND

Pneumocystis jirovecii pneumonia (PJP) affected 5%-15% of solid organ transplant (SOT) recipients prior to universal prophylaxis, classically with trimethoprim-sulfamethoxazole (TMP-SMX). Guidelines generally recommend 6-12 months of prophylaxis post-SOT, yet optimal duration and robust PJP risk stratification have not been established.

METHODS

A retrospective, single-center, case-control study of PJP among SOT recipients from January 1998 to December 2013 was conducted. Cases had positive PJ direct fluorescent antibody assay of respiratory specimens. Controls were matched 4:1 by nearest date of SOT. Univariate testing and multivariate logistic regressions were performed.

RESULTS

Fifteen cases were identified among 5505 SOT recipients (0.27% rate) and analyzed vs 60 controls. PJP occurred on average 6.1 years (range 0.9-13.8) post-SOT; no case was receiving PJP prophylaxis at diagnosis. Most were treated with reduced immunosuppression and TMP-SMX plus steroids (80%). Six patients (40%) required critical care; 3 (20%) died. There were no significant demographic differences, though cases tended to be older at SOT (54 vs 48 years, P = .1). In univariate analysis, prior viral infection was more common among cases (67% vs 37%, P = .08). Lower absolute lymphocyte count (ALC) at diagnosis date was strongly associated with PJP (400 vs 1230 × 10⁶  cells/μL, P < .001); odds of infection were high with ALC ≤ 500 × 10⁶ cells (OR 18.7, P < .01).

CONCLUSION

Pneumocystis jirovecii pneumonia is a rare, late complication of SOT with significant morbidity and mortality. Severe lymphopenia may be useful in identifying SOT recipients who warrant continued or reinstated PJP prophylaxis.

Abstract P3-07-08: Temozolomide as a targeted therapy strategy for triple negative breast cancer

BACKGROUND:

Approximately 15% of newly diagnosed breast cancers are classified as triple negative (TNBC). TNBCs are considered more aggressive and have a worse prognosis as no targeted therapies are currently available. These tumors are routinely treated with chemotherapy agents with only modest proven efficacy.

Temozolomide (TMZ) is an oral chemotherapy agent commonly used for the treatment of brain tumors and melanoma. TMZ is an alkylating agent, and its therapeutic benefit depends on its ability to alkylate/methylate DNA, most commonly at the N-7 or O-6 positions of guanine residues. This process leads to DNA damage and subsequently triggers cell death. Cells that express the enzyme O6-Methylguanine-DNA Methyltransferase (MGMT) are able to repair damage caused by TMZ. Tumors that lack expression of MGMT, owing to methylation of the gene promoter, demonstrate a better response to TMZ treatment as a result of synthetic lethality.

It was first reported in 2012 that TNBCs were more likely to be MGMT methylated, which was confirmed by another group that reported up to 64% of wild-type BRCA1 TNBC exhibited MGMT gene methylation. In 2013 it was found that basal-like breast cancers were more likely to be MGMT methylated and linked to larger tumor size. Together these findings suggest that a sub-population of TNBCs lack MGMT expression, due to promoter methylation.

Currently, TMZ is not a treatment option for breast cancers given the modest efficacy of TMZ noted in breast cancer clinical trials; however, most of these trials have focused on using this agent to either treat or prevent brain metastases, due to TMZs ability to cross the blood-brain barrier. Importantly, none of these trials investigated MGMT expression or specifically TNBC populations.

We hypothesize that TMZ may be a viable and efficacious treatment option for TNBCs that lack MGMT expression, due to promoter methylation.

METHODS:

We analyzed 12 archival specimens and 4 TNBC cell lines (HTB132, HTB26, HTB126 and HCC1806) for MGMT expression using a qRT-PCR clinical assay available from Calgary Laboratory Services. Additionally, we also looked at MGMT protein expression in the cell lines using Western Blot analysis to confirm the qRT-PCR results. Finally, we performed an in vitro assay with TNBC cell lines to determine cytotoxicity of TMZ.

RESULTS:

Analysis of the archival specimens found that 33% of samples analyzed had MGMT promoter methylation by qRT-PCR. Additionally, we found that HTB26 and HTB126 cell lines showed MGMT promoter methylation by qRT-pCR analysis. Western Blot analysis confirmed lack of MGMT expression in these two cell lines, and also identified another cell line (HCC1806) lacking MGMT protein that was classified as unmethylated by the qRT-PCR clinical assay. Moreover, our in vitro assay found that two cell lines (HTB26 and HCC1806) showed a noticeable response to treatment with TMZ. Interestingly, HTB126 did not show response to TMZ, suggesting that there may be another putative resistance pathway.

CONCLUSIONS:

Preliminary findings suggest that TMZ may be a viable targeted treatment option for TNBCs. Currently, we are investigating drug response using in vivo mouse models, as well as investigating synergistic combination therapy options.

Citation Format: Kornaga EN, Gratton K, Shi Q, Yang A, Nixon NA, Roldan Urgoiti G, Morris DG. Temozolomide as a targeted therapy strategy for triple negative breast cancer [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P3-07-08.

HDR syndrome with a novel mutation in GATA3 mimicking a congenital X-linked stapes gusher: a case report

Background

Hypoparathyroidism, sensorineural hearing loss, and renal disease (HDR) syndrome, also known as Barakat syndrome, is a rare genetic disorder with high phenotypic heterogeneity caused by haploinsufficiency of the GATA3 gene on chromosome 10p14-p15. For these reasons, the diagnosis of HDR syndrome is challenging and requires a high index of suspicion as well as genetic analysis.

Case presentation

A 14-month-old boy, with sensorineural hearing loss in both ears, showed typical radiological features of X-linked stapes gusher on preoperative temporal bone computed tomography (CT) for cochlear implantations. Then after his discharge from hospital, he suffered a hypocalcemic seizure and we discovered a renal cyst during investigation of hypocalcemia. He was finally diagnosed with HDR syndrome by clinical findings, which were confirmed by molecular genetic testing. Direct sequencing of the GATA3 gene showed a heterozygous 2-bp deletion (c.1201_1202delAT), which is predicted to cause a frameshift of the reading frame (p.Met401Valfs*106).

Conclusions

To our knowledge, this is the first case of HDR syndrome with a novel de novo variant mimicking a congenital X-linked stapes gusher syndrome. Novel mutations and the diversity of clinical manifestations expand the genotypic and phenotypic spectrum of HDR syndrome.

Diagnosis of HDR syndrome is still challenging, but clinicians should consider it in their differential diagnosis for children with a wide range of clinical manifestations including hypocalcemia induced seizures and deafness. We hope that this case will contribute to further understanding and studies of HDR-associated GATA3 mutations.

Electronic supplementary material

The online version of this article (10.1186/s12881-017-0484-6) contains supplementary material, which is available to authorized users.

Prevalence and Epidemiological Characteristics of Endoscopically Proven Reflux Esophagitis in Children in Korea

PURPOSE

The prevalence of reflux esophagitis (RE) has increased recently in Korea. Little is known concerning the prevalence and characteristics of RE in pediatric patients. This study investigated the prevalence and influence of risk factors in endoscopically proven RE in Korea in pediatric patients over a period of 14 years.

METHODS

A retrospective chart review of all patients between the ages of 1 month and 20 years who underwent esophagogastroduodenoscopy at Samsung Medical Center between 2001 and 2014 was carried out. Univariate and multivariate analyses were conducted to identify independent risk factors for RE.

RESULTS

The prevalence rate of endoscopically proven RE in this study was 28.7% (978/3,413). The prevalence of RE increased from 11.8% from 2001 to 2007 to 37.7% from 2008 to 2014. Multivariate logistic regression analysis revealed that residency in the Greater Gangnam area (odds ratio [OR], 1.21; 95% confidence interval [CI], 1.02-1.44) and age (OR, 1.13; 95% CI, 1.11-1.15) were significant predictive factors for the presence of RE.

CONCLUSION

The prevalence rate of endoscopically proven pediatric RE has increased over the past 14 years. Residency and older age are more important independent risk factors for pediatric RE in Korea.

An atypical case of Noonan syndrome with KRAS mutation diagnosed by targeted exome sequencing

Noonan syndrome (NS) is a genetic disorder caused by autosomal dominant inheritance and is characterized by a distinctive facial appearance, short stature, chest deformity, and congenital heart disease. In individuals with NS, germline mutations have been identified in several genes involved in the RAS/mitogen-activated protein kinase signal transduction pathway. Because of its clinical and genetic heterogeneity, the conventional diagnostic protocol with Sanger sequencing requires a multistep approach. Therefore, molecular genetic diagnosis using targeted exome sequencing (TES) is considered a less expensive and faster method, particularly for patients who do not fulfill the clinical diagnostic criteria of NS. In this case, the patient showed short stature, dysmorphic facial features suggestive of NS, feeding intolerance, cryptorchidism, and intellectual disability in early childhood. At the age of 16, the patient still showed extreme short stature with delayed puberty and characteristic facial features suggestive of NS. Although the patient had no cardiac problems or chest wall deformities, which are commonly present in NS and are major concerns for patients and clinicians, the patient showed several other characteristic clinical features of NS. Considering the possibility of a genetic disorder, including NS, a molecular genetic study with TES was performed. With TES analysis, we detected a pathogenic variant of c.458A > T in KRAS in this patient with atypical NS phenotype and provided appropriate clinical management and genetic counseling. The application of TES enables accurate molecular diagnosis of patients with nonspecific or atypical features in genetic diseases with several responsible genes, such as NS.

Prevalence and risk factors for type 2 diabetes mellitus with Prader-Willi syndrome: a single center experience

BACKGROUND

Prader-Willi syndrome (PWS) is often related to severe obesity and type-2 diabetes mellitus (T2DM). However, few studies, and none in Korea, have examined prevalence of T2DM and other variables in PWS. The aim of this study was to identify the prevalence and associated risk factors for T2DM in Korean patients with PWS.

METHODS

We performed a retrospective cohort study of the 84 PWS patients aged 10 or over (10.3-35.8 years of age) diagnosed with PWS at Samsung Medical Center from 1994 to 2016. We estimated occurrence of T2DM according to age (10-18 years versus >18 years), body mass index (BMI), genotype, history of growth hormone therapy, homeostasis model of assessment-insulin resistance (HOMA-IR), and the presence of dyslipidemia, hypogonadism, or central precocious puberty. Additionally, we investigated cutoff values of risk factors for development of T2DM.

RESULTS

Twenty-nine of a total 211 patients, diagnosed with PWS over the study period, were diagnosed as having T2DM (13.7%, mean age 15.9 ± 3.6 years). In the >18 years group, obesity, HOMA-IR, and presence of dyslipidemia, hypogonadism, or central precocious puberty were associated with the occurrence of T2DM in univariate analysis. In multivariate logistic regression analysis, only obesity (p = 0.001) and HOMA-IR (p < 0.001) were significant predictive factors for T2DM. Based on the receiver operating a characteristic curve analysis, the cutoff values of HOMA-IR and BMI for predicting T2DM were >2.7 and >28.49 kg/m2, respectively. Of the 29 patients, seven had ≥1 microvascular complication, with non-proliferative diabetic retinopathy in 6 of 7 cases. Advanced age and HOMA-IR were positively correlated with diabetic microvascular complications (p < 0.05, Spearman correlation coefficient 0.393 and 0.434, respectively).

CONCLUSIONS

The prevalence of diabetes in Korean PWS was similar to that in previous results. BMI and HOMA-IR were strong predictive factors for the development of T2DM in PWS. We specifically suggest the regular monitoring of glucose homeostasis parameters through a detailed settlement of ethnically specific cutoff values for BMI and HOMA-IR in PWS to prevent progression of T2DM and diabetic microvascular complications.

2q37 Deletion syndrome confirmed by high-resolution cytogenetic analysis

Chromosome 2q37 deletion syndrome is a rare chromosomal disorder characterized by mild to moderate developmental delay, brachydactyly of the third to fifth digits or toes, short stature, obesity, hypotonia, a characteristic facial appearance, and autism spectrum disorder. Here, we report on a patient with 2q37 deletion presenting with dilated cardiomyopathy (DCMP). Congenital heart malformations have been noted in up to 20% of patients with 2q37 deletions. However, DCMP has not been reported in 2q37 deletion patients previously. The patient exhibited the characteristic facial appearance (a flat nasal bridge, deep-set eyes, arched eyebrows, and a thin upper lip), developmental delay, mild mental retardation, peripheral nerve palsy, and Albright hereditary osteodystrophy (AHO)-like phenotypes (short stature and brachydactyly). Conventional chromosomal analysis results were normal; however, microarray-based comparative genomic hybridization revealed terminal deletion at 2q37.1q37.3. In addition, the patient was confirmed to have partial growth hormone (GH) deficiency and had shown a significant increase in growth rate after substitutive GH therapy. Chromosome 2q37 deletion syndrome should be considered in the differential diagnosis of patients presenting with AHO features, especially in the presence of facial dysmorphism. When patients are suspected of having a 2q37 deletion, high-resolution cytogenetic analysis is recommended.

Occupational metal exposures, smoking and risk of diabetes and prediabetes

BACKGROUND

Metal exposure and tobacco smoking have been independently associated with diabetes, but no study has been conducted to investigate the interaction between them on the risk of diabetes.

AIMS

To investigate the effect of occupational exposure to metals, and potential effect modification by smoking, on the risk of diabetes and prediabetes in a cohort of Chinese male workers.

METHODS

We assessed metal exposure and tobacco smoking at baseline in the Jinchang Cohort of male workers. We used Poisson regression analyses to estimate the interaction between smoking and metal exposures based on occupations, which we grouped according to the measured urinary metal levels.

RESULTS

Among the 26008 study subjects, compared with non-smokers, the adjusted prevalence ratio (PR) for diabetes was 1.8 [95% confidence interval (CI) 1.3-2.4] for smokers of >40 pack-years. The adjusted PRs were 1.2 (95% CI 1.1-1.4) among mining/production workers and 2.7 (95% CI 2.4-3.0) among smelting/refining workers, both compared with office workers. There was significant effect modification under the additive model between smoking and metal exposure on the prevalence of diabetes (Pinteraction = 0.001), with an adjusted PR of 3.6 (95% CI 2.4-5.4) for those with >40 pack-years of smoking who had the highest metal exposures, whereas no significant interaction was observed for prediabetes.

CONCLUSIONS

Both exposure to metals and heavy smoking were associated with an increased prevalence of diabetes in this large cohort of male workers. There was also strong interaction between these two exposures in affecting diabetes risk that should be confirmed in future studies.

Use of Nested and Real-Time PCR for the Detection of Ceratocystis fagacearum in the Sapwood of Diseased Oak Species in Minnesota

Oak wilt caused by Ceratocystis fagacearum is a significant disease of Quercus spp. in the eastern United States. Early and accurate detection of the pathogen is particularly important when disease control is planned. Nested and real-time polymerase chain reaction (PCR) methods utilizing fungal DNA extracted from sapwood drill shavings of red, bur, and white oak at different stages of disease development were compared with culture-based detection from sapwood. The pathogen was detected in all (n = 3) actively wilting branches of each of nine red oak trees using all three methods. The lowest detection rate (33% of assayed branches; 6 of 8 trees) for actively wilting branches was found for white oak using isolation while nested PCR had a branch detection rate of 100% (8 of 8 trees) and real-time PCR of 87% (8 of 8 trees) for the same samples. For both bur and white oak, the pathogen was not detected by isolation in branches over 1 year after their death but was detected using both PCR methods. Only the PCR assays detected the fungus in sapwood samples underlying remnants of sporulation mats (n = 21; 90%, nested and 62%, real-time) on red oak. These PCR methods offer several significant improvements for laboratory-based detection methods of C. fagacearum.

Quantitative Characterization of the Exposure-Response Relationship for Cancer Immunotherapy: A Case Study of Nivolumab in Patients With Advanced Melanoma

To inform the benefit-risk assessment of nivolumab in patients with advanced melanoma, analyses of efficacy and safety exposure-response (E-R) relationships were conducted with data from patients with advanced melanoma enrolled in two clinical studies (phase I and phase III) who received nivolumab 0.1-10.0 mg/kg every 2 weeks. E-R efficacy analyses were performed by relating the nivolumab time-averaged concentration after the first dose (Cavg1 ) to two endpoints: RECIST objective response (OR) and overall survival (OS). E-R safety analyses characterized the relationship between nivolumab Cavg1 and the hazard of all-causality adverse events leading to discontinuation or death (AE-DC/D). Nivolumab exposure represented by Cavg1 was not a significant predictor of OR, OS, or the hazard of AE-DC/D. E-R efficacy and safety relationships were relatively flat over the exposure range.

Rebalance between 7S and 11S globulins in soybean seeds of differing protein content and 11SA4

Protein content and globulin subunit composition of soybean seeds affect the quality of soy foods. In this proteomic study, the protein profile of soybean seeds with high (∼45.5%) or low (∼38.6%) protein content and with or without the glycinin (11S) subunit 11SA4 was examined. 44 unique proteins and their homologues were identified and showed that both protein content and 11SA4 influenced the abundance of a number of proteins. The absence of 11SA4 exerted a greater impact than the protein content, and led to a decreased abundance of glycinin G2/A2B1 and G5/A5A4B3 subunits, which resulted in lower total 11S with a concomitant higher total β-conglycinin (7S). Low protein content was associated with higher glycinin G3/A1aB1b and lower glycinin G4/A5A4B3. Using the proteomic approach, it was demonstrated that 11SA4 deficiency induced compensatory accumulation of 7S globulins and led to a similar total abundance for 7S+11S irrespective of protein content or 11SA4.

Clinical and endocrine characteristics and genetic analysis of Korean children with McCune-Albright syndrome: a retrospective cohort study

Background

McCune–Albright syndrome (MAS) is a rare disease defined by the triad of fibrous dysplasia (FD), café au lait spots, and peripheral precocious puberty (PP). Because of the rarity of this disease, only a few individuals with MAS have been reported in Korea. We describe the various clinical and endocrine manifestations and genetic analysis of 14 patients with MAS in Korea.

Methods

Patients’ clinical data—including peripheral PP, FD, and other endocrine problems—were reviewed retrospectively. In addition, treatment experiences of letrozole in five patients with peripheral PP were described. Mutant enrichment with 3′-modified oligonucleotides - polymerase chain reaction (MEMO-PCR) was performed on eight patients to detect mutation in GNAS using blood. MEMO-PCR is a simple and practical method that enables the nondestructive selection and enrichment of minor mutant alleles in blood.

Results

The median age at diagnosis was 5 years 2 months (range: 18 months to 16 years). Eleven patients were female, and three were male. Thirteen patients showed FD. All female patients showed peripheral PP at onset, and three patients subsequently developed central PP. There was a significant decrease in estradiol levels after two years of letrozole treatment. However, bone age was advanced in four patients. Two patients had clinical hyperthyroidism, and two patients had growth hormone (GH) excess with pituitary microadenoma. c.602G > A (p.Arg201His) in GNAS was detected in two patients in blood, and c.601C > T (p.Arg201Cys) in GNAS was detected in one patient in pituitary adenoma.

Conclusions

This study described the various clinical manifestations of 14 patients with MAS in a single center in Korea. This study first applied MEMO-PCR on MAS patients to detect GNAS mutation. Because a broad spectrum of endocrine manifestations could be found in MAS, multiple endocrinopathies should be monitored in MAS patients. Better treatment options for peripheral PP with MAS are needed.

A genomics-led approach to deciphering the mechanism of thiotetronate antibiotic biosynthesis

Thiolactomycin (TLM) is a thiotetronate antibiotic that selectively targets bacterial fatty acid biosynthesis through inhibition of the β-ketoacyl-acyl carrier protein synthases (KASI/II) that catalyse chain elongation on the type II (dissociated) fatty acid synthase. It has proved effective in in vivo infection models of Mycobacterium tuberculosis and continues to attract interest as a template for drug discovery. We have used a comparative genomics approach to uncover the (hitherto elusive) biosynthetic pathway to TLM and related thiotetronates. Analysis of the whole-genome sequence of Streptomyces olivaceus Tü 3010 producing the more ramified thiotetronate Tü 3010 provided initial evidence that such thiotetronates are assembled by a novel iterative polyketide synthase-nonribosomal peptide synthetase, and revealed the identity of other pathway enzymes, encoded by adjacent genes. Subsequent genome sequencing of three other thiotetronate-producing actinomycetes, including the Lentzea sp. ATCC 31319 that produces TLM, confirmed that near-identical clusters were also present in these genomes. In-frame gene deletion within the cluster for Tü 3010 from Streptomyces thiolactonus NRRL 15439, or within the TLM cluster, led to loss of production of the respective thiotetronate, confirming their identity. Each cluster houses at least one gene encoding a KASI/II enzyme, suggesting plausible mechanisms for self-resistance. A separate genetic locus encodes a cysteine desulfurase and a (thiouridylase-like) sulfur transferase to supply the sulfur atom for thiotetronate ring formation. Transfer of the main Tü 3010 gene cluster (stu gene cluster) into Streptomyces avermitilis led to heterologous production of this thiotetronate, showing that an equivalent sulfur donor can be supplied by this host strain. Mutational analysis of the Tü 3010 and TLM clusters has revealed the unexpected role of a cytochrome P450 enzyme in thiotetronate ring formation. These insights have allowed us to propose a mechanism for sulfur insertion, and have opened the way to engineering of the biosynthesis of TLM and other thiotetronates to produce novel analogues.