No abstract

Acquired thrombotic thrombocytopenic purpura (TTP) has been linked to severe deficiency of ADAMTS-13 activity caused by autoantibodies inhibitory to ADAMTS-13. We report data on a patient with confirmed TTP who had severely reduced ADAMTS-13 activity but showed no ADAMTS-13 inhibition in a widely used fluid phase activity assay. With a newly developed enzyme-linked immunosorbent assay, using immobilized recombinant ADAMTS-13, we found high titers of IgM and IgG antibodies that bound to ADAMTS-13, but did not neutralize protease activity. These autoantibodies probably influenced the half-life of ADAMTS-13 or its binding to the endothelial cell surface, thereby compromising ADAMTS-13 activity in vivo. Given that ADAMTS-13 may interact physiologically with various receptors or ligands, the occurrence, distribution, and the epitope mapping of nonneutralizing antibodies will be an important area for future research. (Blood. 2003;102:3241-3243)

In recent decades, global temperature has increased at an unprecedented rate. This has been causing rapid environmental shifts that have altered the selective regimes determining the annual organization of birds. In order to assess the potential for adaptive evolution in the timing of autumn migration, we estimated heritabilities of the onset of migratory activity in a southern German blackcap (Sylvia atricapilla) population. Heritabilities (h2=0.34-0.45) and coefficients of additive genetic variation (CV(A)=4.7-5.7) were significant and consistent when estimated by different methods, irrespective of whether they were derived from birds hatched in the wild or bred in captivity. In an artificial selection experiment, we selected for later onset of migratory activity, simulating expected natural selection on this trait. We obtained a significant delay in the mean onset of migratory activity by more than one week after two generations of selection. Realized heritability (h2=0.55) was in agreement with expected heritability in the cohort that the selection line was derived from. Our results suggest that evolutionary changes in the timing of autumn migration may take place over a very short time period and will most probably be unconstrained by the lack of additive genetic variation.

Sequence analysis of the ADAMTS13 locus of 2 patients with hereditary thrombotic thrombocytopenic purpura (TTP) revealed the homozygous presence of 4 single nucleotide polymorphisms (SNPs) (R7W, Q448E, P618A, A732V) and a rare missense mutation (R1336W). Analysis of the individual effect of any amino acid exchanges showed that several sequence variations can interact with each other, thereby altering the phenotype of ADAMTS13 deficiency. Introduction of polymorphisms R7W, Q448E, and A732V had no or only minor effects on ADAMTS13 secretion. In contrast, P618A, R1336W, and the A732V-P618A combination strongly reduced ADAMTS13-specific activity and antigen levels. Surprisingly, R7W and Q448E were positive modifiers of ADAMTS13 secretion in the context of P618A and A732V but neither could rescue the severely reduced specific activity conferred by P618A. However, in the context of R1336W, polymorphisms R7W and Q448E enhanced the detrimental effect of the missense mutation and led to undetectable enzyme activity. We show that dependent on the sequence context, the same polymorphisms might be either positive or negative modifiers of gene expression. Our results might therefore be widely relevant to understanding the influence of polymorphisms on the phenotypic expression of complex diseases. Introductionvon Willebrand factor (VWF) is crucial for primary hemostasis by mediating extracellular matrix-platelet interactions and delivering factor VIII to the site of vascular injury. The large and heterogeneous glycoprotein circulates as a multimer composed of identical units, ranging in molecular weight from 500 kDa to more than 20 000 kDa. 1 Plasma VWF is predominately secreted as high molecular weight, "unusually large," VWF (ULVWF) multimers. Because ULVWF binds more avidly to components of the extracellular matrix 2 and to various platelet receptors 3,4 than low molecular weight VWF, the hemostatic activity of VWF is size dependent and much more pronounced for high molecular weight VWF than for smaller multimers. This intrinsic property of ULVWF allows for platelet attachment to sites of vascular injury under high shear stress conditions of fastflowing blood. 5 However, immediately downstream from the site of injury, the multimeric size of VWF needs to be physiologically regulated to prevent the formation of platelet and VWF-rich thrombi.A VWF-cleaving protease, now called ADAMTS13 (a disintegrin and metalloprotease with thrombospondin type-1 motifs) has been identified. [6][7][8][9][10][11][12][13] ADAMTS13 cleaves VWF between Tyr1605 and Met1606 in the A2 domain of the VWF monomer, 6,7,14,15 yielding typical fragments of 176 kDa and 140 kDa and smaller VWF multimers. Severe deficiency of ADAMTS13 may result in ULVWF spontaneously interacting with platelet receptors 5 and cause the life-threatening disorder thrombotic thrombocytopenic purpura (TTP). 16,17 Acquired TTP has been associated with the inhibition of ADAMTS13 activity by autoimmune antibodies, [18][19][20][21] whereas mutations in the ADAMTS13 gene have been ...