July 2019
Volume 60, Issue 9
Open Access
ARVO Annual Meeting Abstract  |   July 2019
Expression levels of rare missense variants in CFI found in age-related macular degeneration, atypical uremic syndrome or both diseases
Author Affiliations & Notes
  • Sarah de Jong
    Ophthalmology, Donders Institute for Brain, Cognition and Behaviour, Radboudumc, Netherlands
  • Elena Volokhina
    Pediatric Nephrology, Radboudumc, Netherlands
    Laboratory Medicine, Radboudumc, Netherlands
  • Sara Nilsson
    Translational Medicine, Lund University, Sweden
  • Bjorn Bakker
    Ophthalmology, Donders Institute for Brain, Cognition and Behaviour, Radboudumc, Netherlands
  • Eiko de Jong
    Ophthalmology, Donders Institute for Brain, Cognition and Behaviour, Radboudumc, Netherlands
  • Lambert van den Heuvel
    Pediatric Nephrology, Radboudumc, Netherlands
    Laboratory Medicine, Radboudumc, Netherlands
  • Anna Blom
    Translational Medicine, Lund University, Sweden
  • Anneke I Den Hollander
    Ophthalmology, Donders Institute for Brain, Cognition and Behaviour, Radboudumc, Netherlands
  • Footnotes
    Commercial Relationships   Sarah de Jong, None; Elena Volokhina, None; Sara Nilsson, None; Bjorn Bakker, None; Eiko de Jong, None; Lambert van den Heuvel, None; Anna Blom, None; Anneke Den Hollander, Gyroscope (C), Ionis Pharmaceuticals (C)
  • Footnotes
    Support  European Research Council
Investigative Ophthalmology & Visual Science July 2019, Vol.60, 4914. doi:
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    • Get Citation

      Sarah de Jong, Elena Volokhina, Sara Nilsson, Bjorn Bakker, Eiko de Jong, Lambert van den Heuvel, Anna Blom, Anneke I Den Hollander; Expression levels of rare missense variants in CFI found in age-related macular degeneration, atypical uremic syndrome or both diseases. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4914.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : Genetic variation in complement factor I (CFI) is strongly implicated in both age-related macular degeneration (AMD) and atypical hemolytic uremic syndrome (aHUS). Factor I (FI) is one of the main regulators of complement activity, and up to date 126 rare missense variants (minor allele frequency <1%) have been identified in AMD or aHUS patients. Many of these variants are of unknown clinical significance. Therefore we aim to clarify their contribution to disease risk by performing comprehensive expression level analysis of all identified CFI variants.

Methods : We created CFI constructs for 124 rare missense variants; for two variants site-directed mutagenesis was not successful. Wild-type (WT) and mutant recombinant FI proteins of 124 different variants were expressed in HEK293T cells, and sandwich ELISA was used to measure FI concentration in cell lysates and supernatants. Each experiment was performed twice in duplicates and expression level changes were calculated as a ratio to WT.

Results : For 45 (36%) out of 124 mutant recombinant proteins the expression was <50% compared to WT; for 23 (19%) mutants the expression was <15% compared to WT. The distribution of variants leading to reduced expression was similar for AMD and aHUS (Table 1). For all variants a similar level of reduction was seen in lysates and supernatants, indicating that none of the tested mutant recombinant proteins accumulated within the cell lysates.

Conclusions : We show that a substantial number of rare missense variants in CFI lead to decreased expression levels of FI in vitro, potentially causing elevated complement activation in variant carriers and increasing disease risk for AMD and aHUS. Better functional understanding of rare CFI variants improves classification of variants and can be useful for patient stratification in clinical trials with complement inhibitors and/or CFI supplementation therapy.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.

 

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