Background
Coronavirus disease 19 (COVID‐19)–associated coagulopathy is a hallmark of disease severity and poor prognosis. The key manifestations of this prothrombotic syndrome—microvascular ...thrombosis, stroke, and venous and pulmonary clots—are also observed in severe and catastrophic antiphospholipid syndrome. Antiphospholipid antibodies (aPL) are detectable in COVID‐19 patients, but their association with the clinical course of COVID‐19 remains unproven.
Objectives
To analyze the presence and relevance of lipid‐binding aPL in hospitalized COVID‐19 patients.
Methods
Two cohorts of 53 and 121 patients from a single center hospitalized for PCR‐proven severe acute respiratory syndrome–coronavirus 2 infection were analyzed for the presence of aPL and clinical severity of COVID‐19.
Results
We here demonstrate that lipid‐binding aPL are common in COVID‐19. COVID‐19 patients with lipid‐binding aPL have higher median concentrations of C‐reactive protein and D‐dimer, and are more likely to have a critical clinical course and fatal outcome. Lipid‐binding aPL isolated from COVID‐19 patients target the recently described cell surface complex of lysobisphosphatidic acid (LBPA) with the protein C receptor (EPCR) to induce prothrombotic and inflammatory responses in monocytes and endothelial cells. We show that B1a cells producing lipid‐reactive aPL of the IgG isotype circulate in the blood of COVID‐19 patients. In vivo, COVID‐19 aPL accelerate thrombus formation in an experimental mouse model dependent on the recently delineated signaling pathway involving EPCR‐LBPA.
Conclusions
COVID‐19 patients rapidly expand B1a cells secreting pathogenic lipid‐binding aPL with broad thrombotic and inflammatory effects. The association with markers of inflammation and coagulation, clinical severity, and mortality suggests a causal role of aPL in COVID‐19–associated coagulopathy.
Background & Aims: HCO3− supply to the enterocyte is rate limiting for duodenal HCO3− secretion (JHCO3−). This study defines the molecular nature of the major HCO3− uptake pathways in rabbit ...duodenocytes and investigates their physiologic significance and regulation during basal and stimulated JHCO3−. Methods & Results: pH gradient–driven 22Na+ uptake into duodenal basolateral membrane vesicles was partly HCO3− dependent, stilbene sensitive, and therefore mediated by Na+HCO3− cotransport, and partly HCO3− independent, Hoechst 642 sensitive, and therefore mediated by the Na+/H+ exchanger isoform NHE1. Semiquantitative polymerase chain reaction (PCR) revealed high duodenal expression levels for the NBC1 isoform of the Na+HCO3− cotransporter gene family and NHE1. Cloning and comparison of full-length rabbit with human gastrointestinal and kidney NBC1 subtype revealed a conserved protein kinase A consensus sequence in the cytoplasmic N-terminus of the gastrointestinal NBC1. Inhibition of either Na+HCO3− cotransport or carbonic anhydrase reduced ouabain-sensitive JHCO3− in in vitro rabbit duodenal mucosae by approximately 50%, but did not affect 8-Br-cAMP–induced ΔJHCO3−, suggesting cAMP-mediated up-regulation of the alternative pathway. However, inhibition of both Na+HCO3− cotransport and either carbonic anhydrase or NHE1 strongly reduced ΔJHCO3−. Conclusions: NBC1 and NHE1 are the major base importers in rabbit duodenocytes. Na+HCO3− cotransport and CO2 hydration/Na+/H+ exchange are equally important pathways for duodenal HCO3− supply and are up-regulated during cAMP-mediated stimulation.
GASTROENTEROLOGY 2000;119:406-419
Insulin resistance (IR) is a hallmark of type 2 diabetes mellitus (DM). The homeostatic model assessment of insulin resistance (HOMA-IR) provides an estimate for IR from fasting glucose and insulin ...serum concentrations. The aim of this study was to obtain a reference interval for HOMA-IR for a specific insulin immunoassay.
The Gutenberg Health Study (GHS) is a population-based, prospective, single-center cohort study in Germany with 15,030 participants aged 35-74 years. Fasting glucose, insulin, and C-peptide were available in 10,340 participants. HOMA-IR was calculated in this group and three reference subgroups with increasingly more stringent inclusion criteria. Age- and sex-dependent distributions of HOMA-IR and reference intervals were obtained. In a substudy three insulin assays were compared and HOMA-IR estimated for each assay.
Among the 10,340 participants analyzed there were 6,590 non-diabetic, 2,901 prediabetic, and 849 diabetic individuals. Median (interquartile range IQR) HOMA-IR was 1.54 (1.13/2.19), 2.00 (1.39/2.99), and 4.00 (2.52/6.51), respectively. The most stringently selected reference group consisted of 1,065 persons. Median (IQR) HOMA-IR was 1.09 (0.85/1.42) with no significant difference between men and women. The 97.5th percentile was 2.35. There was a non-significant trend towards higher values with older age. Comparison of three immunoassays for insulin showed an unsatisfactory correlation among the assays and systematic differences in calculated HOMA-IR.
We present HOMA-IR reference intervals for adults derived by more or less stringent selection criteria for the reference cohort. In addition we show that assay specific reference intervals for HOMA-IR are required.
The anion exchanger isoform 2 (AE2) gene encodes three subtypes (AE2a, b and c), which have different N-termini and tissue distributions. AE2 is expressed at
high levels in the stomach, where it is ...thought to mediate basolateral base exit during acid production. The present study
investigated if the three AE2 subtypes are differentially expressed and regulated in different cell types within the gastric
mucosa.
The cloning strategy to obtain rabbit AE2a, b and c cDNAs combined genomic PCR and RT-PCR based on primers deduced from the
rat sequences. Semiquantitative RT-PCR using homologous primers revealed much higher AE2 mRNA expression in rabbit parietal
cells (PCs) than in mucous cells (MCs). The subtype expression pattern was AE2b ⫠AE2c ⥠AE2a in PCs and AE2a >AE2b ⫠AE2c
in MCs. Sequence analysis revealed the presence of a highly conserved protein kinase C (PKC) consensus sequence in the AE2a
alternative N-terminus.
Maximal Cl â -HCO 3 â exchange rates, measured fluorometrically in BCECF-loaded cultured gastric cells, were much higher in PCs than MCs. PKC activation
by phorbol ester stimulated maximal Cl â -HCO 3 â exchange rates in MCs but not in PCs, whereas forskolin had no effect in each cell type.
In summary, rabbit PCs and MCs, which originate from the same gastric stem cell population, display a completely different
AE2 subtype expression pattern. Therefore, AE2 subtype expression is not organ specific but cell type specific. The different
regulation of anion exchange in parietal and mucous cells suggests that AE2 subtypes may be differentially regulated.
ADAMTS-13 adopts an open conformation in patients with immune-mediated thrombotic thrombocytopenic purpura (iTTP) in acute phase while being closed in healthy donors. We reported that a substantial ...number of patients with iTTP in remission with restored ADAMTS-13 activity (>50%) still had an open ADAMTS-13 conformation, although a closed conformation is expected given the extent of remission.
To investigate whether open ADAMTS-13, represented by a conformation index >0.5, is associated with a risk of earlier ADAMTS-13 and/or clinical relapse.
We collected follow-up data (ADAMTS-13 parameters, ADAMTS-13 and clinical relapse, and treatment) from 81 patients with iTTP in remission with ADAMTS-13 activity >50%.
During follow-up, 19 ADAMTS-13 and 10 clinical relapses were reported (median follow-up period, 20 months). First, open or closed ADAMTS-13 conformation was dichotomized based on the 0.5 conformation index cutoff. Open ADAMTS-13 (conformation index, >0.5) was not identified as a risk factor for ADAMTS-13 and clinical relapse (log-rank test and Cox regression model). In contrast, by identifying the optimal conformation index cutoff for relapse prediction, using classification and regression tree analysis, a conformation index >0.645 and >0.835 was shown to be a risk factor for ADAMTS-13 relapse (hazard ratio, 3.3; 95% CI, 1.3-8.3; P = .01) and clinical relapse (hazard ratio, 4.4; 95% CI, 1.3-15.3; P = .02), respectively.
Patients with open ADAMTS-13 with a conformation index >0.645 and >0.835 have a >3- and >4-fold higher risk of earlier ADAMTS-13 and clinical relapse, respectively. Hence, ADAMTS-13 conformation index could be used to complement ADAMTS-13 activity monitoring to timely notice ADAMTS-13 relapse and prevent clinical relapse.
Background
Severe plasma prekallikrein (PK) deficiency is an autosomal‐recessive defect characterized by isolated activated partial thromboplastin time prolongation. To date, no comprehensive ...methodologically firm analysis has investigated the diagnostic, clinical, and genetic characteristics of PK deficiency, and its prevalence remains unknown.
Patients/Methods
We described new families with PK deficiency, retrieved clinical and laboratory information of cases systematically searched in the (gray) literature, and collected blood of these cases for complementary analyses. The Genome Aggregation Database (gnomAD) and the population‐based Gutenberg Health Study served to study the prevalence of mutations and relevant genetic variants.
Results
We assembled a cohort of 111 cases from 89 families and performed new genetic analyses in eight families (three unpublished). We identified new KLKB1 mutations, excluded the pathogenicity of some of the previously described ones, and estimated a prevalence of severe PK deficiency of 1/155 668 overall and 1/4725 among Africans. One individual reported with PK deficiency had, in fact, congenital kininogen deficiency associated with decreased PK activity. One quarter of individuals had factor XII clotting activity below the reference range. Four major bleeding events were described in 96 individuals, of which 3 were provoked, for a prevalence of 4% and an annualized rate of 0.1%. The prevalence of cardiovascular events was 15% (6% <40 years; 21% 40‐65 years; 33% >65 years) for an annualized rate of 0.4%.
Conclusions
We characterized the genetic background of severe PK deficiency, critically appraised mutations, and provided prevalence estimates. Our data on laboratory characteristics and clinical course of severe PK deficiency may have clinical implications.
Essentials
Prekallikrein (PK) deficiency is a recessive trait with isolated aPTT prolongation.
KLKB1 c.451dupT is common in Nigerians (7/600 alleles) and absent in a European group (0/600).
To date, ...all genotyped PK‐deficient patients of African ancestry were homozygous for 451dupT.
Diagnostics of isolated aPTT prolongation in African descendants should include PK testing.
Background
Severe prekallikrein deficiency (PK deficiency) is an autosomal‐recessive condition thought to be very rare. Recently we reported that the previously unnoticed variant c.451dupT, p.Ser151Phefs*34 in KLKB1, which is listed in databases aggregating genome data, causes PK deficiency and is common in Africans according to gnomAD (allele frequency 1.43%).
Patients/Methods
The most common African (c.451dupT) and European (c.1643G>A, p.Cys548Tyr) PK deficiency causing KLKB1 variants were analyzed in two population‐based collectives of 300 Nigerian and 300 German subjects. Genome databases were evaluated for variant frequencies and ethnicity of the subjects. The geographic origin of PK‐deficient cases due to 451dupT was assessed.
Results
Two of five patients with PK deficiency caused by homozygous 451dupT were African, one African American, one from Oman, and one of unknown origin. The frequency of 451dupT was 1.17% in the Nigerian collective (7/600 alleles); none had Cys548Tyr. Subjects with 451dupT were found among different Nigerian ethnicities. Both variants were absent in the European collective. Database research was compatible with these findings, even though mainly data of African Americans (451dupT: 1.12%‐1.78%) was accessible. A relevant number of non‐American Africans are included only in the 1000Genomes collective: 451dupT frequency was 1.29% in native Africans and 1.56% in African Caribbeans.
Conclusions
This study underlines the higher prevalence of PK deficiency among people with African descent compared to Europeans. In order to avoid delay of necessary surgical procedures in patients of African origin, diagnostic algorithms for isolated, unexplained, activated partial thromboplastin time prolongation in these subjects should include PK deficiency screening.
Severe high-molecular-weight kininogen (HK) deficiency is a poorly studied autosomal recessive contact system defect caused by pathogenic, biallelic KNG1 variants.
We performed the first ...comprehensive analysis of diagnostic, clinical, genetic, and epidemiological aspects of HK deficiency.
We collected clinical information and blood samples from a newly detected HK-deficient individual and from published cases identified by a systematic literature review. Activity and antigen levels of coagulation factors were determined. Genetic analyses of KNG1 and KLKB1 were performed by Sanger sequencing. The frequency of HK deficiency was estimated considering truncating KNG1 variants from GnomAD.
We identified 48 cases of severe HK deficiency (41 families), of these 47 have been previously published (n = 19 from gray literature). We genotyped 3 cases and critically appraised 10 studies with genetic data. Ten HK deficiency–causing variants (one new) were identified. All of them were truncating mutations, whereas the only known HK amino acid substitution with a relevant phenotype instead causes hereditary angioedema. Conservative estimates suggest an overall prevalence of severe HK deficiency of approximately one case per 8 million population, slightly higher in Africans. Individuals with HK deficiency appeared asymptomatic and had decreased levels of prekallikrein and factor XI, which could lead to misdiagnosis.
HK deficiency is a rare condition with only few known pathogenic variants. It has an apparently good prognosis but is prone to misdiagnosis. Our understanding of its clinical implications is still limited, and an international prekallikrein and HK deficiency registry is being established to fill this knowledge gap.
•High-molecular-weight kininogen (HK) deficiency is a recessive benign trait leading to isolated activated partial thromboplastin time prolongation.•We performed the first comprehensive analysis of HK deficiency (n = 48).•Only truncating variants are known, and HK deficiency significantly reduces prekallikrein and factor XI.•Our estimates suggest an overall prevalence of 1 case per 8 million population.
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