Laboratory approach for vaccine-induced thrombotic thrombocytopenia diagnosis in the Netherlands

BACKGROUND AND OBJECTIVES

Vaccine-induced thrombotic thrombocytopenia (VITT) is a rare adverse effect characterized by thrombocytopenia and thrombosis occurring after COVID-19 vaccination. VITT pathophysiology is not fully unravelled but shows similarities to heparin-induced thrombocytopenia (HIT). HIT is characterized by the presence of antibodies against platelet factor 4 (PF4)/heparin complex, which can activate platelets in an FcγRIIa-dependent manner, whereas IgG-antibodies directed against PF4 play an important role in VITT.

MATERIALS AND METHODS

We characterized all clinically suspected VITT cases in the Netherlands from a diagnostic perspective and hypothesized that patients who developed both thrombocytopenia and thrombosis display underlying mechanisms similar to those in HIT. We conducted an anti-PF4 ELISA and a functional PF4-induced platelet activation assay (PIPAA) with and without blocking the platelet-FcγRIIa and found positivity in both tests, suggesting VITT with mechanisms similar to those in VITT.

RESULTS

We identified 65 patients with both thrombocytopenia and thrombosis among 275 clinically suspected VITT cases. Of these 65 patients, 14 (22%) tested positive for anti-PF4 and PF4-dependent platelet activation. The essential role of platelet-FcγRIIa in VITT with mechanisms similar to those in HIT was evident, as platelet activation was inhibited by an FcγRIIa-blocking antibody in all 14 patients.

CONCLUSION

Our study shows that only a small proportion of clinically suspected VITT patients with thrombocytopenia and thrombosis have anti-PF4-inducing, FcɣRIIa-dependent platelet activation, suggesting an HIT-like pathophysiology. This leaves the possibility for the presence of another type of pathophysiology ('non-HIT like') leading to VITT. More research on pathophysiology is warranted to improve the diagnostic algorithm and to identify novel therapeutic and preventive strategies.

Diagnostic accuracy of four different D-dimer assays: A post-hoc analysis of the YEARS study

INTRODUCTION

For exclusion of pulmonary embolism (PE) clinical decision rules in combination with a D-dimer assay are applied. Currently available D-dimer assays are not standardized and it is unknown whether these differences have an impact on diagnostic management of suspected PE. Therefore, the aim is to explore differences between D-dimer assays and their impact on diagnostic outcome.

METHODS

Data from all patients included in the YEARS study were collected. The YEARS study is a prospective, multicentre, cohort outcome study evaluating 3462 patients with suspected PE in which four different D-dimer assays were applied (Liatest, Innovance, Tinaquant, Vidas). Median D-dimer concentrations were calculated for each D-dimer assay. Sensitivity, specificity, PPV and NPV for detection of PE of all four assays were determined in patients without YEARS items and in those with ≥1 YEARS items (i.e. symptomatic deep vein thrombosis, haemoptysis, and whether PE is the most likely diagnosis).

RESULTS

A total of 1323, 1100, 768 and 271 D-dimer concentrations were collected using the Liatest Innovance, Tinaquant and Vidas assay, respectively. Median D-dimer concentrations differed significantly between assays, with lowest values in the Tinaquant assay. In patients without YEARS items using a cutoff level of 1000 ng/mL, the NPV varied from 99,5 to 100%. In patients with ≥1 YEARS items using a 500 ng/mL cutoff, the NPV varied from 97,0 to 100% depending on the assay.

CONCLUSIONS

The overall high NPV for all assays demonstrates the clinical value of the D-dimer assay. However, these results confirm differences between D-dimer assays, which have an impact on follow-up imaging. This emphasizes the need for standardization of D-dimer assays.

Diagnostic Yield of One-Time Colonoscopy vs One-Time Flexible Sigmoidoscopy vs Multiple Rounds of Mailed Fecal Immunohistochemical Tests in Colorectal Cancer Screening

BACKGROUND & AIMS

We compared the diagnostic yields of colonoscopy, flexible sigmoidoscopy, and fecal immunochemical tests (FITs) in colorectal cancer (CRC) screening.

METHODS

A total of 30,007 asymptomatic persons, 50-74 years old, were invited for CRC screening in the Netherlands. Participants were assigned to groups that received 4 rounds of FIT (mailed to 15,046 participants), once-only flexible sigmoidoscopy (n = 8407), or once-only colonoscopy (n = 6600). Patients with positive results from the FIT (≥10 μg Hb/g feces) were referred for colonoscopy. Patients who underwent flexible sigmoidoscopy were referred for colonoscopy if they had a polyp of ≥10 mm; adenoma with ≥25% villous histology or high-grade dysplasia; sessile serrated adenoma; ≥3 adenomas; ≥20 hyperplastic polyps; or invasive CRC. The primary outcome was number of advanced neoplasia detected (diagnostic yield) by each test. Secondary outcomes were number of colonoscopies needed to detect advanced neoplasia and number of interval CRCs found during each primary screening test. Patients with interval CRCs were found through linkage with Netherlands Cancer Registry. Advanced neoplasia were defined as CRC, adenomas ≥ 10 mm, adenomas with high-grade dysplasia, or adenomas with a villous component of at least 25%.

RESULTS

The cumulative participation rate was significantly higher for FIT screening (73%) than for flexible sigmoidoscopy (31%; P < .001) or colonoscopy (24%; P < .001). The percentage of colonoscopies among invitees was higher for colonoscopy (24%) compared to FIT (13%; P < .001) or flexible sigmoidoscopy (3%; P < .001). In the intention to screen analysis, the cumulative diagnostic yield of advanced neoplasia was higher with FIT screening (4.5%; 95% CI 4.2-4.9) than with colonoscopy (2.2%; 95% CI, 1.8-2.6) or flexible sigmoidoscopy (2.3%; 95% CI, 2.0-2.7). In the as-screened analysis, the cumulative yield of advanced neoplasia was higher for endoscopic screening with colonoscopy (9.1%; 95% CI, 7.7-10.7) or flexible sigmoidoscopy (7.4%; 95% CI, 6.5-8.5) than with the FIT (6.1%; 95% CI, 5.7-6.6). All 3 screening strategies detected a similar proportion of patients with CRC. Follow-up times differed for each test (median 8.3 years for FIT and flexible sigmoidoscopy and 5.8 years for colonoscopy). Proportions of patients that developed interval CRC were 0.13% for persons with a negative result from FIT, 0.09% for persons with a negative result from flexible sigmoidoscopy, and 0.01% for persons with a negative result from colonoscopy.

CONCLUSIONS

Mailed multiple-round FITs detect significantly more advanced neoplasia, on a population level, compared with once-only flexible sigmoidoscopy or colonoscopy screening. Significantly fewer colonoscopies are required by individuals screened by multiple FITs. Trialregister.nl numbers: first round, NTR1096; second round and additional invitees, NTR1512; fourth round, NTR5874; COCOS trial NTR1829.

A randomised comparison of two faecal immunochemical tests in population-based colorectal cancer screening

OBJECTIVE

Colorectal cancer screening programmes are implemented worldwide; many are based on faecal immunochemical testing (FIT). The aim of this study was to evaluate two frequently used FITs on participation, usability, positivity rate and diagnostic yield in population-based FIT screening.

DESIGN

Comparison of two FITs was performed in a fourth round population-based FIT-screening cohort. Randomly selected individuals aged 50-74 were invited for FIT screening and were randomly allocated to receive an OC -Sensor (Eiken, Japan) or faecal occult blood (FOB)-Gold (Sentinel, Italy) test (March-December 2014). A cut-off of 10 µg haemoglobin (Hb)/g faeces (ie, 50 ng Hb/mL buffer for OC-Sensor and 59 ng Hb for FOB-Gold) was used for both FITs.

RESULTS

In total, 19 291 eligible invitees were included (median age 61, IQR 57-67; 48% males): 9669 invitees received OC-Sensor and 9622 FOB-Gold; both tests were returned by 63% of invitees (p=0.96). Tests were non-analysable in 0.7% of participants using OC-Sensor vs 2.0% using FOB-Gold (p<0.001). Positivity rate was 7.9% for OC-Sensor, and 6.5% for FOB-Gold (p=0.002). There was no significant difference in diagnostic yield of advanced neoplasia (1.4% for OC-Sensor vs 1.2% for FOB-Gold; p=0.15) or positive predictive value (PPV; 31% vs 32%; p=0.80). When comparing both tests at the same positivity rate instead of cut-off, they yielded similar PPV and detection rates.

CONCLUSIONS

The OC-Sensor and FOB-Gold were equally acceptable to a screening population. However, FOB-Gold was prone to more non-analysable tests. Comparison between FIT brands is usually done at the same Hb stool concentration. Our findings imply that for a fair comparison on diagnostic yield between FIT's positivity rate rather than Hb concentration should be used.

TRIAL REGISTRATION NUMBER

NTR5385; Results.

Fecal immunochemical testing results and characteristics of colonic lesions

BACKGROUND AND STUDY AIMS

Fecal immunochemical tests (FIT) are used to detect blood in feces, which might indicate the presence of colorectal neoplasia. The aim of this study was to investigate whether FIT results vary depending on the characteristics of colonic lesions.

PATIENTS AND METHODS

This was a retrospective analysis of lesions detected in a cohort of asymptomatic individuals (aged 50 - 75 years) who were invited to participate in a FIT-based screening pilot in The Netherlands. The mean FIT result was compared across subgroups of individuals defined by histopathology of the most advanced lesion detected. In addition, the results were compared with data from a primary colonoscopy screening trial, in which participants also completed a FIT.

RESULTS

In three rounds of FIT-based screening, a total of 877 FIT-positive individuals underwent colonoscopy. Higher mean FIT results (hemoglobin [Hb]/g feces) were observed in individuals with carcinomas (199 μg Hb/g) and advanced adenomas (87 μg Hb/g) compared with participants with nonadvanced adenomas (50 μg Hb/g) or those with serrated lesions (46 μg Hb/g) (P < 0.001). In the primary colonoscopy trial, 1256 participants completed a FIT test and underwent colonoscopy. The number of participants with nonadvanced adenomas as the most advanced lesion was comparable between this group and the FIT-based screening group (20 % vs. 22 %).

CONCLUSION

In FIT-based screening, the mean FIT results varied depending on the characteristics of the most advanced colonic lesion. The proportion of participants with a nonadvanced adenoma as the most advanced lesion was similar in the FIT-based screening group and in the primary colonoscopy screening group, suggesting that these lesions are coincidental findings rather than FIT-detected findings.

CLINICAL TRIAL REGISTRATION

www.trialregister.nl number NTR2755.

Two novel haemoglobin variants that affect haemoglobin A1c measurement by ion-exchange chromatography

BACKGROUND

Haemoglobin (Hb) variants are well-known factors interfering with accurate HbA1c testing. This report describes two novel Hb variants leading to inappropriate quantification of HbA1c by ion-exchange chromatography.

METHODS

Glycated forms of novel Hb variants were recognised in the blood of two patients with diabetes mellitus screened by HbA1c ion-exchange chromatography. Dedicated high-resolution cation-exchange chromatography and subsequent DNA sequencing revealed the exact nature of the variants. Other common techniques for quantifying HbA1c were applied on both samples and haematological parameters were determined to judge possible pathology associated with the novel Hb variants.

RESULTS

A fraction of 15% of abnormal Hb was observed in a 37-year-old female. DNA sequencing revealed a heterozygous mutation in the α1-globin gene, resulting in a leucine-to-phenylalanine amino-acid substitution (HBA1: c.301C>T, p.Leu101Phe). We named this variant Hb Weesp. The other novel variant, Hb Haelen, presented as a 40% fraction in a 63-year-old male and resulted from a heterozygous amino acid substitution in the β-globin gene (HBB: c.335T>C, p.Val112Gly). The presence of both Hb variants resulted in aberrant separation of the Hb components, leading to an inadequate quantification of HbA1c.

CONCLUSIONS

Close examination of HbA1c chromatograms revealed two novel, clinically silent Hb variants that interfere with HbA1c quantification. Healthcare providers need to be aware of the potential of such Hb variants when interpreting HbA1c results.

Admission lipoprotein-associated phospholipase A2 activity is not associated with long-term clinical outcomes after ST-segment elevation myocardial infarction

Background

Lipoprotein-associated phospholipase A₂ (Lp-PLA₂) activity is a biomarker predicting cardiovascular diseases in a real-world. However, the prognostic value in patients undergoing primary percutaneous coronary intervention (pPCI) for ST-segment elevation myocardial infarction (STEMI) on long-term clinical outcomes is unknown.

Methods

Lp-PLA₂ activity was measured in samples obtained prior to pPCI from consecutive STEMI patients in a high-volume intervention center from 2005 until 2007. Five years all-cause mortality was estimated with the Kaplan-Meier method and compared among tertiles of Lp-PLA2 activity during complete follow-up and with a landmark at 30 days. In a subpopulation clinical endpoints were assessed at three years. The prognostic value of Lp-PLA₂, in addition to the Thrombolysis In Myocardial Infarction or multimarker risk score, was assessed in multivariable Cox regression.

Results

The cohort (n = 987) was divided into tertiles (low <144, intermediate 144–179, and high >179 nmol/min/mL). Among the tertiles differences in baseline characteristics associated with long-term mortality were observed. However, no significant differences in five years mortality in association with Lp-PLA₂ activity levels were found; intermediate versus low Lp-PLA₂ (HR 0.97; CI 95% 0.68–1.40; p = 0.88) or high versus low Lp-PLA₂ (HR 0.75; CI 95% 0.51–1.11; p = 0.15). Both in a landmark analysis and after adjustments for the established risk scores and selection of cases with biomarkers obtained, non-significant differences among the tertiles were observed. In the subpopulation no significant differences in clinical endpoints were observed among the tertiles.

Conclusion

Lp-PLA₂ activity levels at admission prior to pPCI in STEMI patients are not associated with the incidence of short and/or long-term clinical endpoints. Lp-PLA₂ as an independent and clinically useful biomarker in the risk stratification of STEMI patients still remains to be proven.

Measuring direct thrombin inhibitors with routine and dedicated coagulation assays: which assay is helpful?

The use of direct thrombin inhibitors (DTIs) for prophylactic or therapeutic anticoagulation is increasing because of the predictable bioavailability and short half-life of these DTIs. However, in certain situations, indication of the concentration is warranted. We investigated the effects of 3 DTIs (lepirudin, argatroban, and bivalirudin) in 6 pooled plasma specimens on routine coagulation assays (activated partial thromboplastin time [aPTT], prothrombin time [PT], and thrombin time [TT]) and dedicated DTI assays (Hemoclot, HemosIL, the ecarin clotting time, and a chromogenic ecarin clotting time) on 2 coagulation analyzers. We found routine tests to be nondiscriminative between concentrations of different DTIs in the aPTT. Moreover, for PT and TT, the responses for different DTIs differed. This was similar for ecarin clotting assays. The Hemoclot and HemosIL assays showed identical linear increases for all 3 DTIs. We conclude that dedicated calibrated assays based on a diluted TT (Hemoclot and HemosIL) appear to be the most suitable for monitoring purposes.

Implementation of population screening for colorectal cancer by repeated Fecal Immunochemical Test (FIT): third round

Background

Colorectal cancer (CRC) is the most common cancer in Europe with a mortality rate of almost 50%. The prognosis of patients is largely determined by the clinical and pathological stage at the time of diagnosis. Population screening has been shown to reduce CRC-related mortality rate. Most screening programs worldwide rely on fecal immunochemical testing (FIT). The effectiveness of a FIT screening program is not only influenced by initial participation rate, but also by program adherence during consecutive screening rounds. We aim to evaluate the participation rate in and yield of a third CRC screening round using FIT.

Methods and design

Four years after the first screening round and two years after the second round, a total number of approximately 11,000 average risk individuals (50 to 75 years of age) will be invited to participate in a third round of FIT-based CRC screening. We will select individuals in the same target area as in the previous screening rounds, using the electronic database of the regional municipal administration registrations. We will invite all FIT-negatives and all non-participants in previous screening rounds, as well as eligible first time invitees who have moved into the area or have become 50 years of age.

FITs will be analyzed in the special technique laboratory of the Academic Medical Center of the University of Amsterdam. All FIT-positives will be invited for a consultation at the outpatient clinic. In the absence of contra-indications, a colonoscopy will follow at the Academic Medical Center or at the Flevohospital. The primary outcome measures are the participation rate, defined as the proportion of invitees that return a FIT in this third round of FIT-screening, and the diagnostic yield of the program.

Implications

This study will provide precise data on the participation in later FIT screening rounds. This enables to estimate the effectiveness of CRC screening programs that rely on repeated FIT- screening, such as the one that will be implemented in the Netherlands in 2013.

The influence of aspirin dose and glycemic control on platelet inhibition in patients with type 2 diabetes mellitus

BACKGROUND

Low-dose aspirin seems to offer no benefit in the primary prevention of cardiovascular disease in type 2 diabetes mellitus (DM2). The anti-platelet effect may be diminished by poor glycemic control or inadequate dosing of aspirin.

OBJECTIVES

To study the effects of both glycemic control and increasing aspirin dose on platelet response to aspirin in DM2 patients and matched controls.

PATIENTS/METHODS

Platelet effects of increasing doses of aspirin (30, 100 and 300 mg daily) were prospectively assessed in 94 DM2 patients and 25 matched controls by measuring thromboxane levels in urine (11-dhTxB2) and platelet aggregation using VerifyNow(®) and light transmission aggregometry (LTA). DM2 patients were stratified for glycemic control (hemoglobin-A1c [HbA1c] ≤ 53, 53-69, ≥ 69 mmol mol(-1)).

RESULTS

At baseline, median 11-dhTxB2 excretion was higher in the poorly controlled patients (77 ng mmol(-1)), and the moderately controlled (84 ng mmol(-1)) compared with the well-controlled patients (64 ng mmol(-1)) and controls (53 ng mmol(-1)), P < 0.01. Next, 30 mg of aspirin reduced 11-dhTxB2 excretion to 31, 29 and 24 ng mmol(-1) in the poorly, moderately and well-controlled patients, respectively, and to 19 ng mmol(-1) in controls, P < 0.001. VerifyNow(®) and LTA were also incompletely suppressed in DM2 patients using 30 mg of aspirin, but 100 mg resulted in similar platelet suppression in all groups, with no additional effect of 300 mg.

CONCLUSIONS

DM2 patients with inadequate glycemic control (HbA1c > 53 mmol mol(-1)) have higher baseline platelet activity and incomplete suppression of platelet activity with 30 mg of aspirin. However, 100 mg of aspirin leads to optimal inhibition irrespective of glycemic control, and 300 mg does not further improve platelet suppression.

Lower risk of advanced neoplasia among patients with a previous negative result from a fecal test for colorectal cancer

BACKGROUND & AIMS

Consecutive rounds of fecal occult blood tests (FOBTs) are used to screen for colorectal cancer (CRC); they detect precursor lesions and early-stage disease. We assessed whether the positivity rate and the positive predictive values (PPVs) for advanced neoplasia and CRC decrease with repeated testing by using fecal immunochemical tests (FITs).

METHODS

Data were collected from 2 rounds of screening. In the first round, average-risk persons (50 to 74 years old) were randomly assigned to groups that received the guaiac FOBT or FIT. In the second round, the subjects received only FIT (1594 received FIT after guaiac FOBT and 2022 received FIT after FIT). The positivity rate and PPV for advanced neoplasia and CRC were compared between second-round participants with a previous negative test result (FIT after guaiac FOBT or FIT after FIT) and first-round participants (guaiac FOBT or FIT).

RESULTS

The rate of positive results from FIT was 7.4% in the FIT-after-FIT group, compared with 8.1% in the first-round FIT group (P = .34). A significant decrease was observed in the PPV for advanced neoplasia between the first and second round from 55% (132/239) to 44% (112/252; P = .017). The PPV for CRC was 8% (20/239) in the first round versus 4% (9/252) in the second round (P = .024). Ten interval cancers were diagnosed. There were no significant differences in stages of cancers detected in the first and second round or the interval cancers.

CONCLUSIONS

The rate of positive results from FIT does not decrease after repeated CRC screening, but the PPVs of FIT for advanced neoplasia and for CRC are significantly lower among second-round participants who tested negative in the first round.

Catastrophic antiphospholipid syndrome mimicking a malignant pancreatic tumour – a case report

Abstract

The catastrophic antiphospholipid syndrome is characterised by rapid onset thromboses, often resistant to conventional anticoagulant treatment, and resulting in life threatening multiple organ dysfunction. The diagnosis of catastrophic antiphospholipid syndrome may be difficult, predominantly due to its frequently atypical presentation. We report a case of a 35-year-old female who presented with a pancreatic tumour and extensive thromboses. Following a storm of ischemic events due to thrombotic occlusions in spite of therapeutic heparin dose, the suspicion of catastrophic antiphospholipid syndrome emerged. The patient was successfully treated with anticoagulants, immunuglobulins, plasmapheresis and rituximab. The present report shows that the use of the diluted Russell’s viper venom time can be helpful in providing additional information on the lupus anticoagulans antibody status, allowing careful monitoring of lupus anticoagulans conversion and hence response to therapy.

Error budget calculations in laboratory medicine: linking the concepts of biological variation and allowable medical errors

BACKGROUND

Random, systematic and sporadic errors, which unfortunately are not uncommon in laboratory medicine, can have a considerable impact on the well being of patients. Although somewhat difficult to attain, our main goal should be to prevent all possible errors. A good insight on error-prone steps in the laboratory process is essential to achieving a structured system for error reduction.

METHODS

Here, the process of laboratory medicine is divided into phases, and for each phase, an error frequency is presented. While error frequencies in the laboratory (pre-analytical to post-analytical) have been reported elsewhere, we also include them in the present paper. In order to investigate error frequencies in the pre-pre- and post-post-analytical phases, clinicians were asked to carefully answer questions concerning their ordering strategies for laboratory investigation and their interpretation of results.

RESULTS

In the present study, the overall error rate in laboratory medicine was found to be 20.0%. The error percentages in the pre-pre- and post-post-analytical phase were about 12.0% and 5.0%, respectively. This indicates that, also on the clinical side, error reduction is desirable, especially in the requesting of laboratory investigation. Error reduction can be achieved through process redesigning by, for example, applying the Hazard Analysis and Critical Control Points approach. The error budget that clinicians might spend, based upon critical differences, is 26.9%. For the same test set and production circumstances, the overall biological variation is 7.9%. Clinicians thus take the error rates into account in their practical, daily use, and the ultimate achievable in laboratory medicine is biological variation.

CONCLUSIONS

Several currently available software applications can aid error reduction in clinical chemistry. Both laboratory consultants and the use of information and communication technology are essential tools in optimizing the efficiency of laboratory medicine.

Involvement of the endoplasmic reticulum in peroxisome formation

The traditional view holds that peroxisomes are autonomous organelles multiplying by growth and division. More recently, new observations have challenged this concept. Herein, we present evidence supporting the involvement of the endoplasmic reticulum (ER) in peroxisome formation by electron microscopy, immunocytochemistry and three-dimensional image reconstruction of peroxisomes and associated compartments in mouse dendritic cells. We found the peroxisomal membrane protein Pex13p and the ATP-binding cassette transporter protein PMP70 present in specialized subdomains of the ER that were continuous with a peroxisomal reticulum from which mature peroxisomes arose. The matrix proteins catalase and thiolase were only detectable in the reticula and peroxisomes. Our results suggest the existence of a maturation pathway from the ER to peroxisomes and implicate the ER as a major source from which the peroxisomal membrane is derived.

Pex15p of Saccharomyces cerevisiae provides a molecular basis for recruitment of the AAA peroxin Pex6p to peroxisomal membranes

The gene products (peroxins) of at least 29 PEX genes are known to be necessary for peroxisome biogenesis but for most of them their precise function remains to be established. Here we show that Pex15p, an integral peroxisomal membrane protein, in vivo and in vitro binds the AAA peroxin Pex6p. This interaction functionally interconnects these two hitherto unrelated peroxins. Pex15p provides the mechanistic basis for the reversible targeting of Pex6p to peroxisomal membranes. We could demonstrate that the N-terminal part of Pex6p contains the binding site for Pex15p and that the two AAA cassettes D1 and D2 of Pex6p have opposite effects on this interaction. A point mutation in the Walker A motif of D1 (K489A) decreased the binding of Pex6p to Pex15p indicating that the interaction of Pex6p with Pex15p required binding of ATP. Mutations in Walker A (K778A) and B (D831Q) motifs of D2 abolished growth on oleate and led to a considerable larger fraction of peroxisome bound Pex6p. The nature of these mutations suggested that ATP-hydrolysis is required to disconnect Pex6p from Pex15p. On the basis of these results, we propose that Pex6p exerts at least part of its function by an ATP-dependent cycle of recruitment and release to and from Pex15p.

Involvement of the endoplasmic reticulum in peroxisome formation

The traditional view holds that peroxisomes are autonomous organelles multiplying by growth and division. More recently, new observations have challenged this concept. Herein, we present evidence supporting the involvement of the endoplasmic reticulum (ER) in peroxisome formation by electron microscopy, immunocytochemistry and three-dimensional image reconstruction of peroxisomes and associated compartments in mouse dendritic cells. We found the peroxisomal membrane protein Pex13p and the ATP-binding cassette transporter protein PMP70 present in specialized subdomains of the ER that were continuous with a peroxisomal reticulum from which mature peroxisomes arose. The matrix proteins catalase and thiolase were only detectable in the reticula and peroxisomes. Our results suggest the existence of a maturation pathway from the ER to peroxisomes and implicate the ER as a major source from which the peroxisomal membrane is derived.

Enlargement of the endoplasmic reticulum membrane in Saccharomyces cerevisiae is not necessarily linked to the unfolded protein response via Ire1p

Conditions that stress the endoplasmic reticulum (ER) in Saccharomyces cerevisiae can elicit a combination of an unfolded protein response (UPR) and an inositol response (IR). This results in increased synthesis of ER protein-folding factors and of enzymes participating in phospholipid biosynthesis. It was suggested that in cells grown on glucose or galactose medium, the UPR and the IR are linked and controlled by the ER stress sensor Ire1p. However, our studies suggest that during growth on oleate the IR is controlled both by an Ire1p-dependent pathway and by an Ire1p-independent pathway.

Structural organization of the human short-chain L-3-hydroxyacyl-CoA dehydrogenase gene

The third step in the mitochondrial beta-oxidation spiral of short-chain fatty acids is catalyzed by short-chain L-3-hydroxyacyl-CoA dehydrogenase (HADHSC; EC 1.1.1.35). We have determined the structural organization of the human HADHSC gene by sequencing of cloned genomic amplification products, obtained using HADHSC-specific cDNA-based primers, as well as by direct sequencing of an isolated PAC clone containing the HADHSC gene. Upon comparison with the HADHSC cDNA sequence, HADHSC was shown to encompass at least eight exons, ranging in size from 73 to 158 bp, and 7 introns. The total HADHSC gene spans approximately 49 kb. The HADHSC 5'-flanking region was characterized with an AluI plasmid library constructed from a partially AluI-digested PAC clone containing the human HADHSC gene. Several typical promoter elements such as a CAAT-box, Sp1, AP1, and AP2 sites were found, while a TATA-box was apparently absent. Among other putative regulatory elements, a NRRE-1 site was identified. By radiation hybrid panel, assisted fine-mapping HADHSC was linked to marker AFM070TH5, corresponding to Chromosome (Chr) 4q22-26, and a putative HADHSC pseudogene was linked to marker D15S1324, located at Chr 15q17-21. Knowledge of the genomic organization and 5'-flanking region of HADHSC will enable genomic mutation analysis of patients suspected of HADHSC deficiency, as well as facilitate the investigation into the transcriptional regulation of short-chain fatty acid oxidizing gene products in general and HADHSC expression in particular.

Human short-chain L-3-hydroxyacyl-CoA dehydrogenase: cloning and characterization of the coding sequence

The cDNA encompassing the complete coding sequence of human liver short-chain L-3-hydroxyacyl-CoA dehydrogenase (SCHAD) was isolated and characterized. Screening of a cDNA library combined with rapid amplification of 5' cDNA ends resulted in a SCHAD cDNA sequence of 1877 bp. It encodes a protein of 314 amino acids with a calculated molecular weight of 34.3 kDA containing a mitochondrial import signal peptide of 12 amino acids and 302 amino acids of mature SCHAD protein. The deduced amino acid sequence of the mature protein shows a 92 percent identity with SCHAD from pig heart. Northern blot analysis reveals SCHAD mRNA to be expressed in liver, kidney, pancreas, heart and skeletal muscle. The human SCHAD gene was mapped by fluorescence in situ hybridization to chromosome 4q22-26.