Coronavirus disease 2019 (COVID-19) causes a spectrum of disease; some patients develop a severe proinflammatory state which can be associated with a unique coagulopathy and procoagulant endothelial phenotype. Initially, COVID-19 infection produces a prominent elevation of fibrinogen and D-dimer/fibrin(ogen) degradation products. This is associated with systemic hypercoagulability and frequent venous thromboembolic events. The degree of D-dimer elevation positively correlates with mortality in COVID-19 patients. COVID-19 also leads to arterial thrombotic events (including strokes and ischemic limbs) as well as microvascular thrombotic disorders (as frequently documented at autopsy in the pulmonary vascular beds). COVID-19 patients often have mild thrombocytopenia and appear to have increased platelet consumption, together with a corresponding increase in platelet production. Disseminated intravascular coagulopathy (DIC) and severe bleeding events are uncommon in COVID-19 patients. Here, we review the current state of knowledge of COVID-19 and hemostasis.

We study the two-dimensional localization problem for (i) a classical diffusing particle advected by a quenched random mean-zero vorticity field, and (ii) a quantum particle in a quenched random mean-zero magnetic field. Through a combination of numerical and analytical techniques we argue that both systems have extended eigenstates at a special point in the spectrum invariant under particle-hole symmetry, where a sublattice decomposition obtains. In a neighborhood of this point, the Lyapunov exponents of the transfer matrices acquire ratios characteristic of conformal invariance allowing an indirect determination of 1͞r for the typical spatial decay of eigenstates. PACS numbers: 46.10.+z, 05.40.+j, 05.45.+b In this paper we study two simple models for passive advection of a diffusing field: (I) a diffusing scalar density n͑x͒ advected by a quenched random velocity field A͑x͒ described by the Fokker-Planck equation [1]:where D is the diffusivity; and (II) the random-flux model [2] for a noninteracting quantum particle propagating in a spatially random, zero-mean magnetic fieldwhere A now denotes the vector potential, described by the Schrödinger equationc being the (complex) quantum wave function, p ϵ 2i= = = the momentum operator, and V ͑x͒ the (scalar) potential [3]. Model (II) has received much attention recently in the context of the quantum Hall effect at filling factor n 1 2[2]. An unresolved question is whether the system has properties of a Fermi liquid, and, in particular, extended states. Previous work has addressed the energy dependence of the localization length j͑E͒ moving inward from the band edge, with authors arriving at opposite conclusions. The most careful numerical study of model (II) to date concludes that all states are localized [2(b)], whereas others find a central band of extended states [2(a)]. An analytic calculation using a replicated nonlinear sigma model with a topological term [4] also obtains a band of extended states.Our purpose is twofold. First, we explore the consequences of particle-hole symmetry at the band center of these models, E c , and describe numerical and analytical evidence for a divergent localization length at this point. Previous studies [2(b),5] did not allow for this symmetry at the band center [6]. Second, we demonstrate that the properties of random flux that have drawn so much attention are exhibited by a much larger class of models, among them the passive scalar model (I).Magnetic field and vorticity are distinguished from potential fields by their transformation under time reversal [7]. Writing the velocity in model (I) as A = = =x 1 = = = 3 f, we observe that x, like V, is even under time reversal, whereas f, (the source of vorticity v = = = 3 A 2= 2 f), like B, is odd. A further physical similarity between the two models is that one expects transport to be dominated by the longest streamlines [1(b)] [8,9]; for the random-flux (passive scalar) model with vanishing mean magnetic field (vorticity), these rare streamlines run along the interfaces of opposi...

Platelet-type von Willebrand disease (PTvWD) is an autosomal dominant bleeding disorder characterized by abnormally enhanced binding of von Willebrand factor (vWF) by patient platelets. Although the platelet glycoprotein (GP) Ib/IX complex is known to constitute the platelet's ristocetia-dependent receptor for vWF, a unique structural abnormality within this complex has not previously been identified in PT-vWD. Using the polymerase chain reaction to amplify genomic DNA coding for the a chain of GP lb (GP Ibta) and then sequencing the amplified DNA following cloning into M13mpl8 and M13mpl9 phage vectors, we have found a single point mutation in the GP Iba coding region of PT-vWD DNA resulting in the substitution of valine for glycine at residue 233. This substitution within the vWF-binding region of GP Iba is likely to exert a significant influence on the conformation of the resulting protein. Competitive oligonucleotide primer assay for this mutation showed a homozygous wild-type pattern in genomic DNA from the 161 normal volunteers studied and from 6 phenotypically normal members of a PT-vWD family. All 7 affected members of this family studied were heterozygous for the mutant allele. Platelet GP Iba mRNA reverse-transcribed and studied by competitive oligonucleotide primer assay showed similar expression of the mutant and wild-tpe alleles in the affected PT-vWD patients. Absence in the normal population, tight linkage with phenotypic expression of disease, and absence of any additional abnormality of GP Iba in these patients identify the glycine-to-valine substitution as a point mutation underlying functional abnormality of the vWF receptor in PT-vWD.Platelet-type von Willebrand disease (PT-vWD) is an autosomal dominant bleeding disorder in which patients characteristically show prolonged bleeding times, borderline thrombocytopenia, and decreased von Willebrand factor (vWF) high molecular weight multimers and functional activity (1-5). PT-vWD appears to result from an abnormality of the platelet receptor for vWF, whereby patient platelets show an abnormally increased binding of circulating vWF. In the laboratory, this platelet hyperresponsiveness may be demonstrated with the use of low concentrations of ristocetin. Whereas normal platelets show little or no aggregation at ristocetin concentrations as low as 0.5 mg/ml, patient platelets typically show significant binding of vWF, together with strong aggregation, following stimulation by 0.5 mg/ml, or even lower, concentrations of ristocetin (1-3). The unique ability of desialylated vWF (asialo-vWF) to agglutinate patient platelets in the presence of the divalent-cation chelator EDTA has additionally been demonstrated (6). Platelets from patients with PT-vWD also show a characteristically increased binding of the monoclonal antibody C-34, which is directed against an epitope within the platelet glycoprotein (GP) lb/IX complex (7). Although this complex is known to constitute the platelet's ristocetin-dependent receptor for vWF (8), identification of a u...

The primary sequences of the three individual glycoprotein (GP) chains, GPIb alpha, GPIb beta, and GPIX, comprising the normal platelet GPIb/IX receptor for von Willebrand factor (vWF) have recently been determined, opening the possibility for characterization of disorders of this receptor at the molecular level. The presence of a leucine tandem repeat in each of these chains is of particular interest, because such repeats may be involved in associations between polypeptide segments. We now report an autosomal dominant variant of Bernard-Soulier disease associated with the heterozygous substitution of phenylalanine for a highly conserved leucine residue within the GPIb alpha leucine tandem repeat. Affected individuals experienced a moderate bleeding tendency, thrombocytopenia, and an increased mean platelet volume. Platelet aggregation was decreased only in response to ristocetin or to asialo- vWF. The kd for 125I-vWF binding to patients platelets was significantly increased over control values at 0.5 mg/mL ristocetin, but was normal at 1.0 or 1.5 mg/mL ristocetin. While sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed an essentially normal complement of all components of the GPIb/IX complex, a minor amount of a putative proteolytic fragment was identified that migrated faster than GPIb and was immunoreactive with polyclonal anti-GPIb alpha antibody, but not with a monoclonal antibody directed against the 45-Kd amino-terminal region of GPIb alpha. However, because the great majority of patient GPIb alpha comigrates with normal GPIb alpha, the major functional abnormalities of the patient platelets are most likely a consequence of the altered structure of the nonproteolyzed protein. Full concordance within the studied family between phenotypic expression and a heterozygous single nucleotide substitution in genomic DNA coding for a phenylalanine in place of the wild-type leucine at residue 57 of the mature GPIb alpha, absence of this substitution in 266 alleles from the normal population, and the lack of any other abnormality of patient DNA throughout the entire coding sequence for GPIb alpha provide strong support that this substitution may constitute a pathologic point mutation responsible for the observed phenotypic abnormalities. While the roles that leucine tandem repeats may normally play within the GPIb/IX complex are not yet known, the perturbation of such a repeat in GPIb alpha may impair interaction with other components of the complex and/or with the binding of vWF.

Platelet-type von Willebrand disease (PT-VWD