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| ==Pathophysiology== | | ==Pathophysiology== |
| HSP can develop after infections with [[streptococcus|streptococci]] ([[Streptococcus pyogenes|β-haemolytic, Lancefield group A]]), [[hepatitis B]], [[herpes simplex virus]], [[parvovirus B19]], [[Coxsackievirus]], [[adenovirus]], ''[[Helicobacter pylori]]'', [[measles]], [[mumps]], [[rubella]], [[mycoplasma]] and numerous others. Drugs linked to HSP, usually as an idiosyncratic reaction, include [[vancomycin]], [[ranitidine]], [[streptokinase]], [[cefuroxime]], [[diclofenac]], [[enalapril]] and [[captopril]]. Several diseases have been reported to be associated with HSP, often without a causative link. Only in about 35% of cases can HSP be traced to any of these causes.
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| The exact cause of HSP is unknown, but most of its features are due to the deposition of abnormal antibodies in the wall of blood vessels, leading to [[vasculitis]]. These antibodies are of the subclass IgA<sub>1</sub> in [[polymer]]s; it is uncertain whether the main cause is overproduction (in the digestive tract or the [[bone marrow]]) or decreased removal of abnormal IgA from the circulation. It is suspected that abnormalities in the IgA<sub>1</sub> molecule may provide an explanation for its abnormal behaviour in both HSP and the related condition [[IgA nephropathy]]. One of the characteristics of IgA<sub>1</sub> (and [[IgD]]) is the presence of an 18 [[amino acid]]-long ''hinge region'' between [[complement system|complement]]-fixating region 1 and 2. Of the amino acids, half is [[proline]], while the other ones are mainly [[serine]] and [[threonine]]. The majority of the serines and the threonines have elaborate sugar chains, connected through [[oxygen]] atoms ([[glycosylation#O-linked glycosylation|O-glycosylation]]). This process is thought to stabilise the IgA molecule and make it less prone to [[proteolysis]]. The first sugar is always [[N-acetyl-galactosamine]] (GalNAc), followed by other [[galactose]]s and [[sialic acid]]. In HSP and IgAN, it appears that these sugar chains are deficient. The exact reason for these abnormalities are not known.
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| ==References== | | ==References== |
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| {{reflist|2}} | | {{reflist|2}} |
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| [[Category:Disease]] | | [[Category:Disease]] |