ESPN 50th Annual Meeting

ESPN 2017


 
Genetic predisposition to infection in a case of atypical hemolytic uremic syndrome (aHUS)
LAMBERTUS VAN DEN HEUVEL VAN DEN HEUVEL 1 KRISTIAN RIESBECK 2 OMAIMA EL TAHIR 3 VALENTINA GRACCHI 4 MARIANN KREMLITZKA 2 SERVAAS MORRE 3 MARCELINE VAN FURTH 3 BIRENDRA SINGH 2 MARCIN OKROJ 5 NICOLE VAN DE KAR 1 ANNA BLOM 2 ELENA VOLOKHINA 1

1- RADBOUDUMC
2- LUND UNIVERSITY
3- VU UNIVERSITY MEDICAL CENTER
4- UNIVERSITY MEDICAL CENTRE GRONINGEN
5- MEDICAL UNIVERSITY OF GDANSK
 
Introduction:

Hemolytic uremic syndrome (HUS) is a major cause of renal failure in childhood. Most cases are caused by infection with Shiga-toxin producing Escherichia coli (STEC). In 5-10% of cases, HUS is not preceded by the STEC infection and is considered atypical (aHUS). These cases are strongly associated with genetic defects leading to dysregulation of the complement system. Often aHUS is triggered by a non-STEC infection, however, genetic predisposition to such infections in aHUS has not yet been studied. Here we present thorough complement analysis of a 2 months old patient in whom aHUS episode coincided with Bordetella pertussis infection (whooping cough), Klebsiella oxytoca sepsis and Moraxella catarrhalis pneumonia.

Material and methods:

In vitro kinetics of complement activation products (C3bc and TCC) in serum were quantified using ELISA. DNA analysis was performed by Sanger sequencing. Recombinant vitronectin variants were produced in HEK293T cells, purified and used in hemolytic assay with sheep erythrocytes and purified C5b-6, C7, C8 and C9 complement proteins.

Results:

The in vitro complement activation kinetics were compared in patient serum and normal human serum (NHS). In patient serum C3 activation rate (expressed as generation of C3bc) was comparable to the rate in NHS, but the rate of TCC generation was slower. Genetic analysis of TCC components and TCC inhibitors revealed a rare heterozygous variant p.Arg229Cys in vitronectin. Prediction software (SIFT, PolyPhen-2) indicated this change as pathogenic. In vitro experiments using recombinant vitronectin variants have shown that this mutation enhances complement inhibition at TCC level.

Conclusions:

Our work indicates that not only genetic changes leading to uncontrolled complement activation but also these increasing vulnerability to infections contribute to aHUS.