Henoch Schonlein Purpura (HSP), vasculitis of small vessels with deposits of IgA, is considered by many authors as the systemic form of Berger's disease (IgA-N). IgA-N is characterized by IgA1 deposits in mesangial areas associated with mesangial proliferation. These two diseases remain the leading cause of ESRD by primitive glomerulopathy in Western countries. In recent years, considerable progress has been made in understanding the pathophysiological mechanisms of IgA-N. However, only a high rate of proteinuria at one year or the presence of severe glomerular inflammation on renal biopsy remain predictors of long term renal function. Moreover, the high variability of HSP clinical expression, from few purpura skin lesions that evolve favourably spontaneously, to rapidly progressive renal failure, remains so far unexplained but suggests the existence of individual genetic susceptibility.

In the first part of the study, we will study key factors based on physiopathological data obtained by our laboratory as well as by other groups. The second part of the study concerns genetic factors. Although the candidate genes that may confer a particular susceptibility to the disease, to progress to ESRD or respond to treatment are many, the genes involved in inflammation or controlling renin-angiotensin system are of particular interest.

We will apply these results by studying patients with HSP showing three distinct phenotypes (HSP with isolated cutaneous purpura or associated with minimal or severe renal disease) at diagnosis and after clinical remission.

The purpose of this study is to assess whether the phenotype at diagnosis is associated with the physiological markers and if one of them predicts a pejorative evolution of renal disease at 1 year. Meanwhile, study of polymorphism of selected genes of interest could allow identification of patients with specific genetic susceptibility or with bad prognosis factors who would be thus eligible for specific treatment.

Inclusion Criteria:

• Patients with HSP whose diagnosis was confirmed by histology of an active skin lesion, who signed the informed consent form or for minors, signature of the holders of parental authority.

Exclusion Criteria:

• Patients who do not have skin lesions; Patients receiving immunosuppressive drugs or steroids for more than 2 weeks; Patients with another diagnosis (platelets<100,000/mm3, bacterial purpura, other systemic disease);
• Patients unable to understand the protocol, refusing to sign the information form or unable to comply with regular follow-up consultation.

Children or adults, suffering from biopsy-proven HSP.2 groups:

1. Skin involvement +/- an extra renal disease (arthritis, digestive and/or other), without renal disease. Absence of renal disease is defined by: absence of hypertension (BP <95th percentile for height in children, BP <140/90 mmHg in adults), absence of hematuria (<5 RBCs /mm3 or < 5000 RBCs/ ml), absence of proteinuria (proteinuria <0.1 g/d) and absence of renal dysfunction (MDRD> 80 ml / min)
2. Renal impairment, defined by the presence of renal dysfunction (calculated clearance <60 ml/min) and/or proteinuria (daily proteinuria greater than 0.3 g) and/or hematuria.