Variant-specific quantification of factor H in plasma identifies null alleles associated with atypical Hemolytic Uremic Syndrome

7 páginas, 6 figuras -- PAGS nros. 782-788Atypical hemolytic uremic syndrome (aHUS) is associated with complement alternative pathway defects in over half the cases. Point mutations that affect complement surface regulation are common in factor H (CFH); however, sometimes individuals have null mutations in heterozygosis. The latter are difficult to identify, although a consistently low plasma factor H (fH) concentration is suggestive; definitive proof requires demonstration that the mutant sequence is not expressed in vitro. Here, novel reagents and assays that distinguish and individually quantify the common factor H-Y402H polymorphic variants were used to identify alleles of the CFH gene, resulting in low or null expression of full-length fH and also normal or increased expression of the alternative splice product factor H-like-1 (FHL-1). Our assay identified three Y402H heterozygotes with low or absent fH-H402 but normal or increased FHL-1-H402 levels in a cohort of affected patients. Novel mutations explained the null phenotype in two cases, which was confirmed by family studies in one. In the third case, family studies showed that a known mutation was present on the Y allele. The cause of reduced expression of the H allele was not found, although the data suggested altered splicing. In each family, inheritance of low expression or null alleles for fH strongly associated with aHUS. Thus, our assays provide a rapid means to identify fH expression defects without resorting to gene sequencing or expression analysisThis work was supported by the UK Multiple Sclerosis Society no 884/08 (to BPM), MRC Project Grant no. 84908 (to CLH and BPM), and Ministerio de Ciencia e Innovación SAF 2005-00913, the CIBER de Enfermedades Raras and Fundación Renal Iñigo Alvarez de Toledo (to SRdeC)Peer reviewe