Genetic mutations and phenotype characteristics in peripheral vascular malformations: A systematic review.

Vascular malformations (VMs) are clinically diverse with regard to the vessel type, anatomical location, tissue involvement and size. Consequently, symptoms and disease impact differ significantly. Diverse causative mutations in more and more genes are discovered and play a major role in the development of VMs. However, the relationship between the underlying causative mutations and the highly variable phenotype of VMs is not yet fully understood. In this systematic review, we aimed to provide an overview of known causative mutations in genes in VMs and discuss associations between the causative mutations and clinical phenotypes. PubMed and EMBASE libraries were systematically searched on November 9th, 2022 for randomized controlled trials and observational studies reporting causative mutations in at least five patients with peripheral venous, lymphatic, arteriovenous and combined malformations. Study quality was assessed with the Newcastle-Ottawa Scale. Data were extracted on patient and VM characteristics, molecular sequencing method and results of molecular analysis. In total, 5667 articles were found of which 69 studies were included, reporting molecular analysis in a total of 4261 patients and 1686 (40%) patients with peripheral VMs a causative mutation was detected. In conclusion, this systematic review provides a comprehensive overview of causative germline and somatic mutations in various genes and associated phenotypes in peripheral VMs. With these findings, we attempt to better understand how the underlying causative mutations in various genes contribute to the highly variable clinical characteristics of VMs. Our study shows that some causative mutations lead to a uniform phenotype, while other causal variants lead to more varying phenotypes. By contrast, distinct causative mutations may lead to similar phenotypes and result in almost indistinguishable VMs. VMs are currently classified based on clinical and histopathology features, however, the findings of this systematic review suggest a larger role for genotype in current diagnostics and classification.

Appearance-related concerns and their impact on health-related quality of life in patients with peripheral vascular malformations.

BACKGROUND: Peripheral vascular malformations (VMs) may lead to disfigurement of the body and face, potentially impairing aesthetic appearance. Yet, data on appearance in this population is limited. This study aimed to examine appearance-related concerns and their impact on health-related quality of life (HR-QoL) in patients with VMs. METHODS: In this cross-sectional study, 384 adults and 194 children with VMs were invited to complete the Outcome Measures for VAscular MAlformations (OVAMA) questionnaire to evaluate potential appearance-related concerns on a five-point verbal-rating scale, with higher scores indicating more appearance-related concerns (e.g., colour-difference, facial-distortion, reduced self-esteem, and dissatisfaction with appearance). HR-QoL was evaluated using Patient-Reported Outcome Measurement Information System (PROMIS). Subgroups of patients reporting more appearance-related concerns were identified using univariate analysis. Associations between appearance-related concerns and various HR-QoL domains (e.g., anxiety and social participation) were assessed. RESULTS: A total of 184 patients (32%) completed the questionnaires; 121 patients (66%) reported that one or more appearance outcome was severely affected (i.e., 4-5 out of 5). The following factors statistically significant associated with more appearance-related concerns: capillary/combined origin, facial localization, subcutaneous tissue involvement, larger size, overgrowth, and diagnosis of a syndrome. In adults, dissatisfaction with appearance and reduced self-esteem due to the appearance of the VM correlated with more anxiety and depression symptoms. Reduced self-esteem correlated with less social participation. In children, bodily distortion and being stared at were correlated with less peer relationships. CONCLUSION: Severe appearance-related concerns were present in two-thirds of patients with VMs, impairing their mental HR-QoL. Clinicians should acknowledge appearance-related aspects, monitor psychological well-being, and offer intervention aimed at improving satisfaction with appearance.

Development of a condition-specific patient-reported outcome measure for measuring symptoms and appearance in vascular malformations: the OVAMA questionnaire.

BACKGROUND: The symptoms and appearance of vascular malformations can severely harm a patient's quality of life. The aim of treatment of vascular malformations generally is to improve condition-specific symptoms and/or appearance. Therefore, it is highly important to start testing treatment effects in clinical studies from the patient's perspective. OBJECTIVES: To develop a patient-reported outcome measure for measuring symptoms and appearance in patients with vascular malformations. METHODS: A first draft of the patient-reported outcome measure was based on the previously internationally developed core outcome set. The qualitative part of this study involved interviews with 14 patients, which led to a second draft. The second draft was field tested cross-sectionally, after which groups of items were evaluated for adequate internal consistency (Cronbach's alpha > 0·7) to form composite scores. Construct validity was evaluated by testing 13 predefined hypotheses on known-group differences. RESULTS: The patient interviews ensured adequate content validity and resulted in a general symptom scale with six items, a head and neck symptom scale with eight items, and an appearance scale with nine items. Cronbach's alpha was adequate for two composite scores: a general symptom score (0·88) and an appearance score (0·85). Ten out of 13 hypotheses on known-group differences were confirmed, confirming adequate construct validity. CONCLUSIONS: With the development of the OVAMA questionnaire, outcomes of patients with vascular malformations can now be evaluated from the patient's perspective. This may help improve the development of evidence-based treatments and the overall care for patients with vascular malformations.

Development of a core outcome domain set for clinical research on capillary malformations (the COSCAM project).

BACKGROUND: Due to a large variety in treatment outcomes reported in therapeutic trials and lacking patient-relevant outcomes, it is hard to adequately compare and improve current therapies for patients with capillary malformations (CMs). The Core Outcome Set for Capillary Malformations (COSCAM) project aims to develop a core outcome set (COS) for use in future CM trials, in which we will first develop a core outcome (sub)domain set (CDS). Here, we describe the methods for the development of a CDS and present the results of the first development stage. METHODS: The COSCAM project is carried out according to the recommendations of the Cochrane Skin Core OUtcomes Set INitiative (CS-COUSIN) and the Core Outcome Measures in Effectiveness Trials (COMET) initiative. During the first stage, we identified all potentially relevant outcome subdomains based on a systematic review, two focus group sessions and input from patient representatives of Dutch patient organizations and the COSCAM-founding group. In stage two, we will present the subdomains in a three-round e-Delphi study and online consensus meeting, in which CM patients, parents/caregivers and CM experts worldwide rate the importance of the proposed subdomains, hereby finalizing the core outcome (sub)domains of the CDS. RESULTS: A total of 67 potential outcome subdomains were included; sixteen were previously used in the literature, 20 were proposed by Dutch patients and their parents/caregivers (n = 13) in focus group sessions and 38 were suggested by the experts of the COSCAM-founding group. Seven were excluded because of overlap. CONCLUSION: The final CDS may serve as a minimum standard in future CM trials, thereby facilitating adequate comparison of treatment outcomes. After this CDS development, we will select appropriate outcome measurement instruments to measure the core outcome subdomains.

Responsiveness of quality of life measures in children with peripheral vascular malformations: The OVAMA project.

BACKGROUND: The OVAMA (Outcome Measures for VAscular MAlformations) project determined quality of life (QoL) as a core outcome domain for evaluating treatment effect in vascular malformations. To correctly evaluate treatment effect on QoL, patient-reported outcome measures (PROMs) are needed that are responsive to changes. In children with vascular malformations, we explored if two widely used PROMs were responsive to changes: the Pediatric Quality of Life Inventory (PedsQL) and the Children's Dermatology Life Quality Index (CDLQI). METHODS: In an international multicenter prospective study, conservatively and invasively treated children completed the PedsQL and CDLQI at baseline and after follow-up of 6-8 weeks. At follow-up, change in health was assessed by a global rating of change (GRC) scale. Responsiveness was assessed by testing hypotheses on expected correlation strength between change scores of the PROMs and the GRC scale, and by calculating the area under the receiver operating characteristics curve (AUC). The PROMs were considered responsive if ≥75% of the hypotheses were confirmed or if the AUC was ≥0.7. RESULTS: Twenty-nine children were recruited in three centers in the Netherlands and United States, of which 25 completed all baseline and follow-up measurements. For both the PedsQL and CDLQI, less than 75% of the hypotheses were confirmed and the AUC was <0.7. DISCUSSION: The results suggest that these PROMs are not sufficiently responsive for evaluating treatment effect in peripheral vascular malformations. Our study emphasizes the need for assessing responsiveness before using a PROM in evaluating treatment effect.

Responsiveness of quality-of-life measures in patients with peripheral vascular malformations: the OVAMA project.

BACKGROUND: The OVAMA (Outcome Measures for Vascular Malformations) project determined quality of life (QoL) as a core outcome domain for patients with vascular malformations. In order to measure how current therapeutic strategies alter QoL in these patients, a patient-reported outcome measurement (PROM) responsive to changes in QoL is required. OBJECTIVES: To assess the responsiveness of two widely used generic QoL PROMs, the Medical Outcomes Study Short Form 36 (SF-36) and Skindex-29, in adult patients with vascular malformations. METHODS: In an international multicentre prospective study, treated and untreated patients completed the SF-36 and Skindex-29 at baseline and after a follow-up period of 6-8 weeks. Global rating of change (GRC) scales assessing various QoL-related outcome domains were additionally completed. Per subscale, responsiveness was assessed using two methods: by testing hypotheses on expected correlation strength between change scores of the questionnaires and the GRC scales, and by calculating the area under the receiver operating characteristics curve (AUC). The questionnaires were considered responsive if ≥ 75% of the hypotheses were confirmed or if the AUC was ≥ 0·7. RESULTS: Eighty-nine participants were recruited in three centres in the Netherlands and the U.S.A., of whom 67 completed all baseline and follow-up questionnaires. For all subscales of the SF-36 and Skindex-29, < 75% of the hypotheses were confirmed and the AUC was < 0·7. CONCLUSIONS: Our findings suggest that the SF-36 and Skindex-29 seemed unresponsive to change in QoL. This suggests that alternative PROMs are needed to measure - and ultimately improve - QoL in patients with vascular malformations. What's already known about this topic? Quality of life is often impaired in patients with vascular malformations. Quality of life is considered a core outcome domain for evaluating treatment of vascular malformations. To measure the effect of treatment on quality of life, a patient-reported outcome measure is required that is responsive to changes in quality of life. What does this study add? This is the first study assessing the responsiveness of quality-of-life measures in patients with vascular malformations. The results seem to indicate that the Medical Outcomes Study Short Form 36 (SF-36) and Skindex-29 are not responsive to changes in quality of life in patients with vascular malformations. What are the clinical implications of this work? Medical Outcomes Study Short Form 36 (SF-36) and Skindex-29 are not ideal to assess the effect on quality of life over time, of treatment strategies for peripheral vascular malformations.

The ability of different peer review procedures to flag problematic publications.

There is a mounting worry about erroneous and outright fraudulent research that gets published in the scientific literature. Although peer review's ability to filter out such publications is contentious, several peer review innovations attempt to do just that. However, there is very little systematic evidence documenting the ability of different review procedures to flag problematic publications. In this article, we use survey data on peer review in a wide range of journals to compare the retraction rates of specific review procedures, using the Retraction Watch database. We were able to identify which peer review procedures were used since 2000 for 361 journals, publishing a total of 833,172 articles, of which 670 were retracted. After addressing the dual character of retractions, signalling both a failure to identify problems prior to publication, but also the willingness to correct mistakes, we empirically assess review procedures. With considerable conceptual caveats, we were able to identify peer review procedures that seem able to detect problematic research better than others. Results were verified for disciplinary differences and variation between reasons for retraction. This leads to informed recommendations for journal editors about strengths and weaknesses of specific peer review procedures, allowing them to select review procedures that address issues most relevant to their field.

Correction to: The changing forms and expectations of peer review.

[This corrects the article DOI: 10.1186/s41073-018-0051-5.].

The changing forms and expectations of peer review.

The quality and integrity of the scientific literature have recently become the subject of heated debate. Due to an apparent increase in cases of scientific fraud and irreproducible research, some have claimed science to be in a state of crisis. A key concern in this debate has been the extent to which science is capable of self-regulation. Among various mechanisms, the peer review system in particular is considered an essential gatekeeper of both quality and sometimes even integrity in science. However, the allocation of responsibility for integrity to the peer review system is fairly recent and remains controversial. In addition, peer review currently comes in a wide variety of forms, developed in the expectation they can address specific problems and concerns in science publishing. At present, there is a clear need for a systematic analysis of peer review forms and the concerns underpinning them, especially considering a wave of experimentation fuelled by internet technologies and their promise to improve research integrity and reporting. We describe the emergence of current peer review forms by reviewing the scientific literature on peer review and by adding recent developments based on information from editors and publishers. We analyse the rationale for developing new review forms and discuss how they have been implemented in the current system. Finally, we give a systematisation of the range of discussed peer review forms. We pay detailed attention to the emergence of the expectation that peer review can maintain 'the integrity of science's published record', demonstrating that this leads to tensions in the academic debate about the responsibilities and abilities of the peer review system.

Patient-Reported Outcomes of Bleomycin Sclerotherapy for Low-Flow Vascular Malformations and Predictors of Improvement.

PURPOSE: There is paucity of data on patient-perceived outcomes of bleomycin sclerotherapy for low-flow vascular malformations. In this study, the long-term outcomes of bleomycin sclerotherapy were investigated in terms of quality of life (QoL) and patient-perceived changes in health. MATERIALS AND METHODS: A cohort of Dutch patients with vascular malformations treated with bleomycin sclerotherapy (June 2010-November 2015) completed a questionnaire evaluating disease symptoms, QoL (Short Form 36), patient-perceived change in health status (Global Rating of Change scales) and treatment satisfaction. QoL was assessed for the patient's status before and after treatment and was analyzed relative to an age and sex-matched Dutch reference population. Predictive factors associated with QoL and patient-perceived improvement in overall health status were assessed using multivariable linear and logistic regression analyses, respectively. RESULTS: Seventy-seven patients, with a median follow-up of 22 months, were enrolled. About half of the respondents (49.3%) indicated that they perceived (any form of) improvement in their overall health status. Most often improved were the specific health aspects 'pain' (54.5%) and 'overall severity of symptoms' (57.1%). No factors were significantly predictive for patient-perceived improvement in health with respect to the vascular malformation. Impairment in work- or study-related activities prior to sclerotherapy was found to negatively impact physical QoL at follow-up (p = 0.03). CONCLUSION: Approximately half of patients with low-flow vascular malformations indicate an improvement in overall health status following bleomycin sclerotherapy, particularly concerning pain and severity of symptoms. However, most patients only perceived little to moderate improvement to their health and desire further treatment.

Core outcome sets in dermatology: report from the second meeting of the International Cochrane Skin Group Core Outcome Set Initiative.

Results of clinical trials are the most important information source for generating external clinical evidence. The use of different outcomes across trials, which investigate similar interventions for similar patient groups, significantly limits the interpretation, comparability and clinical application of trial results. Core outcome sets (COSs) aim to overcome this limitation. A COS is an agreed standardized collection of outcomes that should be measured and reported in all clinical trials for a specific clinical condition. The Core Outcome Set Initiative within the Cochrane Skin Group (CSG-COUSIN) supports the development of core outcomes in dermatology. In the second CSG-COUSIN meeting held in 2017, 11 COS development groups working on skin diseases presented their current work. The presentations and discussions identified the following overarching methodological challenges for COS development in dermatology: it is not always easy to define the disease focus of a COS; the optimal method for outcome domain identification and level of detail needed to specify such domains is challenging to many; decision rules within Delphi surveys need to be improved; appropriate ways of patient involvement are not always clear. In addition, there appear to be outcome domains that may be relevant as potential core outcome domains for the majority of skin diseases. The close collaboration between methodologists in the Core Outcome Set Initiative and the international Cochrane Skin Group has major advantages for trialists, systematic reviewers and COS developers.

Development of an international core outcome set for peripheral vascular malformations: the OVAMA project.

BACKGROUND: An important limitation in vascular malformation research is the heterogeneity in outcome measures used for the evaluation of treatment outcome. OBJECTIVES: To reach international consensus on a core outcome set (COS) for clinical research on peripheral vascular malformations: lymphatic (LM), venous (VM) and arteriovenous malformations (AVM). In this consensus study, we determined what domains should constitute the COS. METHODS: Thirty-six possibly relevant outcome domains were proposed to an international group of physicians, patients and the parents of patients. In a three-round e-Delphi process using online surveys, participants repeatedly rated the importance of these domains on a five-point Likert scale. Participants could also propose other relevant domains. This process was performed for LM, VM and AVM separately. Consensus was predefined as 80% agreement on the importance of a domain among both the physician group and the patient/parent group. Outcomes were then re-evaluated in an online consensus meeting. RESULTS: 167 physicians and 134 patients and parents of patients with LM (n = 50), VM (n = 71) and AVM (n = 29) participated in the study. After three rounds and a consensus meeting, consensus was reached for all three types of vascular malformations on the core domains of radiological assessment, physician-reported location-specific signs, patient-reported severity of symptoms, pain, quality of life, satisfaction and adverse events. Vascular malformation type-specific signs and symptoms were included for LM, VM and AVM, separately. CONCLUSIONS: Our recommendation is that therapeutic-efficacy studies on peripheral vascular malformations should measure at least these core outcome domains.

Complications of pregnancy and labour in women with Klippel-Trénaunay syndrome: a nationwide cross-sectional study.

OBJECTIVE: To evaluate complications of pregnancy, including thromboembolism, in women with extensive vascular malformations associated with Klippel-Trénaunay syndrome (KTS). DESIGN: Nationwide cross-sectional study. SETTING: Two tertiary expert centres and the Dutch Klippel-Trénaunay patient organisation. SAMPLE: Adult women with KTS. METHODS: Patients with KTS were invited to participate in a comprehensive online survey about their obstetric history. Reference data on pregnancy outcomes and complications of non-diseased women were collected from population-based cohorts from the literature. MAIN OUTCOME MEASURES: Prevalence of complications, specifically venous thromboembolism and postpartum haemorrhage. RESULTS: Sixty women completed the survey. Seventeen patients did not conceive, of whom three refrained from pregnancy because of KTS. A total of 97 pregnancies and 86 deliveries were reported in 43 patients. KTS-related symptoms were aggravated during pregnancy in 43% of patients. Deep vein thrombosis was present in 5.8% and pulmonary embolism was present in 2.3% of pregnancies, which was extremely high compared with the reference population (P < 0.0001), with a relative risk of 108.9 (95% confidence interval, 95% CI 46.48-255.03) and 106.2 (95% CI 26.97-418.10), respectively. Severe postpartum haemorrhage (PPH) occurred in 11% of KTS pregnancies, compared with 5.8% of pregnancies in the reference population (relative risk, RR 1.81, 95% CI 0.97-3.37, P = 0.06). CONCLUSIONS: Our data suggest that women with KTS have a significant risk of venous thromboembolic events, severe postpartum haemorrhage, and aggravation of KTS symptoms during pregnancy, and in early postpartum period. Obstetricians should counsel patients about these risks in the preconception phase. Antithrombotic prophylaxis should be considered in the obstetric management of patients with KTS. TWEETABLE ABSTRACT: High risk of complications during pregnancy and labour in women with Klippel-Trénaunay syndrome.

Promoting Virtue or Punishing Fraud: Mapping Contrasts in the Language of 'Scientific Integrity'.

Even though integrity is widely considered to be an essential aspect of research, there is an ongoing debate on what actually constitutes research integrity. The understanding of integrity ranges from the minimal, only considering falsification, fabrication and plagiarism, to the maximum, blending into science ethics. Underneath these obvious contrasts, there are more subtle differences that are not as immediately evident. The debate about integrity is usually presented as a single, universal discussion, with shared concerns for researchers, policymakers and 'the public'. In this article, we show that it is not. There are substantial differences between the language of research integrity in the scientific arena and in the public domain. Notably, scientists and policymakers adopt different approaches to research integrity. Scientists tend to present integrity as a virtue that must be kindled, while policy documents and newspapers stress norm enforcement. Rather than performing a conceptual analysis through philosophical reasoning and discussion, we aimed to clarify the discourse of 'scientific integrity' by studying its usage in written documents. To this end, large numbers of scientific publications, policy documents and newspaper articles were analysed by means of scientometric and content analysis techniques. The texts were analysed on their usage of the term 'integrity' and of frequently co-occurring terms and concepts. A comparison was made between the usage in the various media, as well as between different periods in which they were published through co-word analysis, mapping co-occurrence networks of significant terms and themes.

Analysis of deformity in scaphoid non-unions using two- and three-dimensional imaging.

UNLABELLED: Pre-operative assessment of the deformity in scaphoid non-unions influences surgical decision-making. To characterize deformity, we used three-dimensional computed tomographic modelling in 28 scaphoid non-unions, and quantified bone loss, dorsal osteophyte volume and flexion deformity. We further related these three-dimensional parameters to the intrascaphoid and capitate-lunate angles, and stage of scaphoid non-union advanced collapse assessed on conventional two-dimensional images and to the chosen surgical procedure. Three-dimensional flexion deformity (mean 26°) did not correlate with intrascaphoid and capitate-lunate angles. Osteophyte volume was positively correlated with bone loss and stage of scaphoid non-union advanced collapse. Osteophyte volume and bone loss increased over time. Three-dimensional modelling enables the quantification of bone loss and osteophyte volume, which may be valuable parameters in the characterization of deformity and subsequent decision-making about treatment, when taken in addition to the clinical aspects and level of osteoarthritis. TYPE OF STUDY/LEVEL OF EVIDENCE: Level IV.

Sleep-disordered breathing and chronic atrial fibrillation.

BACKGROUND: Little has been known about the prevalence of sleep apnea in patients with atrial fibrillation (AF). Studies have suggested that the prevalence of AF is increasing in patients with sleep-disordered breathing. We hypothesize that the prevalence of OSA is higher in chronic persistent and permanent AF patients than a sub-sample of the general population without this arrhythmic disorder. OBJECTIVE: Evaluate the frequency of Obstructive Sleep Apnea in a sample of chronic AF compared to a sub-sample of the general population. METHODS: Fifty-two chronic AF patients aged (60.5 +/- 9.5, 33 males) and 32 control (aged 57.3 +/- 9.6, 15 males). All subjects were evaluated by a staff cardiologist for the presence of medical conditions and were referred for polysomnography. The differences between groups were analyzed by ANOVA for continuous variables, and by the Chi-square test for dichotomous variables. Statistical significance was established by alpha=0.05. RESULTS: There were no differences in age, gender, BMI, sedentarism, presence of hypertension, type 2 diabetes mellitus, abdominal circumference, systolic and diastolic blood pressure, and sleepiness scoring between groups. Despite similar BMI, AF patients had a higher neck circumference compared to control group (39.9cm versus 37.7cm, p=0.01) and the AF group showed higher percentage time of stage 1 NREM sleep (6.4% versus 3.9%, p=0.03). Considering a cut-off value for AHI >= 10 per hour of sleep, the AF group had a higher frequency of OSA compared to the control group (81.6% versus 60%, p=0.03). All the oxygen saturation parameters were significantly worse in the AF group, which had lower SaO(2) nadir (81.9% versus 85.3%, p=0.01) and mean SaO(2) (93.4% versus 94.3%, p=0.02), and a longer period of time below 90% (26.4min versus 6.7min, p=0.05). CONCLUSION: Sleep-disordered breathing is more frequent in chronic persistent and permanent AF patients than in age-matched community dwelling subjects.

Relative efficacies of gastric proton pump inhibitors: their clinical and pharmacological basis.

The present review will verify by intra-study rank orders, and their comparison between studies, that the different gastric proton pump inhibitors (PPIs) display similar dose-response relationships with similar potencies and efficacies on a milligram basis, i.e., at the same milligram doses. This is in line with their basic pharmacology which suggests that, primarily, the serum AUCs of the free pro-drugs and their chemical activation half lives at pH 1 relative to their serum elimination half lives determine the efficacies of PPIs. According to the literature, these drug characteristics are similar for all PPIs. Although PPIs have been introduced into the therapy of acute peptic ulcer disease at different daily, oral doses of 20 mg (omeprazole and rabeprazole), 30 mg (lansoprazole) and 40 mg (pantoprazole), the data suggest that the optimal dose of lansoprazole, omeprazole and pantoprazole, with respect to the acute treatment of peptic ulcers and moderate to severe gastroesophageal reflux disease (GERD), is about 30-40 mg daily. The data base of rabeprazole appears to be too small at present to make any definite statement. Lower daily doses of the PPIs of about 15-20 mg are sufficient in less severe cases of GERD and in maintenance therapy. It appears that different dose recommendations were based on different strategies to balance optimal drug dosage and safety, rather than on real differences in milligram-related efficacies.

Isoprenoid biosynthesis in bacteria: two different pathways?

The biosynthesis of isopentenylpyrophosphate, a central intermediate of isoprenoid formation, was investigated in six different bacterial organisms. Cell-free extracts of Myxococcus fulvus, Staphylococcus carnosus, Lactobacillus plantarum and Halobacterium cutirubrum converted [14C]acetyl-CoA or [14C]hydroxymethylglutaryl-CoA to [14C]mevalonic acid. Furthermore, [14C]mevalonic acid, [14C]mevalonate-5-phosphate and [14C]mevalonate-5-pyrophosphate were metabolized to [14C]isopentenylpyrophosphate. These data demonstrated the in vitro operation of acetoacetate pathway for the formation of isopentenylpyrophosphate in bacteria. In contrast, no intermediates of this reaction sequence could be detected using cell-free extracts of Zymomonas mobilis and Escherichia coli. These results indicate that at least two different pathways for the biosynthesis of isopentenylpyrophosphate are present in bacteria.