Regional review of patients with psoriatic arthritis in secondary care in the West Midlands: prevalence, disease activity and eligibility for anti-tumour necrosis factor therapy.

OBJECTIVES: Tumour necrosis factor alpha-blockers (TNF-alpha) are licensed for the treatment of psoriatic arthritis (PsA) and their use has been approved by the National Institute for Health and Clinical Excellence (NICE) for use in the United Kingdom under a set of defined clinical criteria. METHODS: In this out-patient study we evaluated PsA in rheumatology secondary care clinics in units across the West Midlands over a 2-week period, assessing prevalence, disease activity and eligibility for anti TNF-alpha treatment as defined by the NICE criteria. RESULTS: Of the 1718 forms returned from the 2000 sent (86% response rate), 175 patients had PsA (10.2%). Of those, 22 (12.6%) were already on anti TNF-alpha treatment. 12 patients were noted to have purely axial disease and as per the NICE guidelines should not be assessed under the PsA criteria. A further 5 patients fulfilled the criteria for treatment with anti TNF-alpha with no contraindications. In the region 22 out of 27 patients (81%) with active disease were correctly on Anti TNF therapy. In total 27 (15.4%) patients with PsA met the NICE criteria for treatment of PsA with anti TNF-alpha therapy. 3 patients had previously failed anti TNF-alpha treatment. No patient fulfilling criteria for treatment were found to have any contraindications to treatment. CONCLUSION: We note the relatively high proportion of PsA patients eligible for treatment with anti TNF-alpha blockers in the region (15.4%) compared to the NICE estimate (2.4%). This may be in part explained by a selection bias. However, the results may have significant implications for healthcare provision given the relatively high cost of anti-TNF-alpha agents. We comment on the limitations of such criteria and the effective use of regional collaboration for both training and audit purposes.

Metal ion dependency of microfibrils supports a rod-like conformation for fibrillin-1 calcium-binding epidermal growth factor-like domains.

The effects of the removal and replacement of divalent cations on the ultrastructure of 10 to 12 nm fibrillin-1-containing microfibrils have been studied, in order to investigate the conformation of fibrillin-1 calcium-binding epidermal growth factor-like (cbEGF-like) domains within the microfibril. The NMR structure of a covalently linked pair of cbEGF-like domains from fibrillin-1 recently identified a rigid rod-like conformation for the domain pair stabilised by interdomain calcium binding. This suggested that tandem arrays of fibrillin-1 cbEGF-like domains may adopt an extended conformation within a microfibril. If correct, then removal of bound calcium from fibrillin-1 would be expected to increase the flexibility of each cbEGF-like interdomain linkage, resulting in a decrease in the length of the interbead region of the microfibril (and thus a decrease in bead to bead periodicity), a concomitant increase in its diameter, and an overall increase in the flexibility of the microfibril. Our results show that removal of calcium by treatment with EGTA causes a large alteration of the microfibril structure, resulting in microfibrils with a reduced beaded periodicity, a disrupted interbead region and an increased overall flexibility. These effects are readily reversible by the re-addition of calcium (in the form of CaCl2), but not by the addition of magnesium (MgCl2). This is consistent with conformational changes in cbEGF-like domains causing the major structural effects on the microfibril. These results provide the first direct experimental evidence to support an extended rod-like conformation for multiple tandem repeats of fibrillin-1 cbEGF-like domains within the microfibril, as predicted by the NMR structure of an isolated fibrillin-1 cbEGF-like domain pair.

Calcium binding properties of an epidermal growth factor-like domain pair from human fibrillin-1.

Ca2+ binding epidermal growth factor-like (EGF-like) domains are found in a large number of extracellular proteins with diverse functions, including those involved in blood coagulation, determination of cell fate, cell adhesion and connective tissue architecture. Their importance is emphasised by the identification of mutations in these domains in patients with haemophilia B (defective in coagulation factor IX) and the Marfan syndrome (defective in the connective tissue protein fibrillin-1). The X-ray crystal structure of a single Ca2+ binding EGF-like domain from human coagulation factor IX has recently been solved. It shows that the Ca2+ ligands form a pentagonal bipyramid, where one ligand is provided by an adjacent (N-terminal) EGF-like domain in the crystal. The N and C termini of the neighbouring domains are only approximately 4 angstrum apart, hence the crystal packing has been proposed as a model for the association of contiguous EGF-like domains in proteins. Since the adjacent EGF-like domain in the crystal, although close, is not covalently linked to its neighbour, this model requires verification. In this study we have expressed and purified a Ca2+ binding EGF-like domain pair from human fibrillin-1 and used an in vitro refolding system to obtain protein with the correct EGF fold. The Ca2+ binding properties of the protein have been investigated by two-dimensional NMR. The affinity of the C-terminal domain for Ca2+ is approximately 25-fold higher than that of the N-terminal domain, consistent with the two Ca2+ binding sites having different local environments. In addition, these data provide the first direct experimental evidence that Ca2+ plays a major role in defining the interdomain linkage in multiple repeats of Ca2+ binding EGF-like domains.

Solution structure of a pair of calcium-binding epidermal growth factor-like domains: implications for the Marfan syndrome and other genetic disorders.

The nuclear magnetic resonance structure of a covalently linked pair of calcium-binding (cb) epidermal growth factor-like (EGF) domains from human fibrillin-1, the protein defective in the Marfan syndrome, is described. The two domains are in a rigid, rod-like arrangement, stabilized by interdomain calcium binding and hydrophobic interactions. We propose a model for the arrangement of fibrillin monomers in microfibrils that reconciles structural and antibody binding data, and we describe a set of disease-causing mutations that provide the first clues to the specificity of cbEFG interactions. The residues involved in stabilizing the domain linkage are highly conserved in fibrillin, fibulin, thrombomodulin, and the low density lipoprotein receptor. We propose that the relative orientation of tandem cbEGF domains in these proteins is similar, but that in others, including Notch, pairs adopt a completely different conformation.