Novel mutations in the ferritin-L iron-responsive element that only mildly impair IRP binding cause hereditary hyperferritinaemia cataract syndrome

Sara Luscieti,Martina U Muckenthaler,Gabriele Tolle,Jessica Aranda,Carmen Benet Campos,Frank Risse,Érica Morán,Mayka Sánchez

doi:10.1186/1750-1172-8-30

Abstract

BackgroundHereditary Hyperferritinaemia Cataract Syndrome (HHCS) is a rare autosomal dominant disease characterized by increased serum ferritin levels and early onset of bilateral cataract. The disease is caused by mutations in the Iron-Responsive Element (IRE) located in the 5′ untranslated region of L-Ferritin (FTL) mRNA, which post-transcriptionally regulates ferritin expression.MethodsWe describe two families presenting high serum ferritin levels and juvenile cataract with novel mutations in the L-ferritin IRE. The mutations were further characterized by in vitro functional studies.ResultsWe have identified two novel mutations in the IRE of L-Ferritin causing HHCS: the Badalona +36C > U and the Heidelberg +52 G > C mutation. Both mutations conferred reduced binding affinity on recombinant Iron Regulatory Proteins (IPRs) in EMSA experiments. Interestingly, the Badalona +36C > U mutation was found not only in heterozygosity, as expected for an autosomal dominant disease, but also in the homozygous state in some affected subjects. Additionally we report an update of all mutations identified so far to cause HHCS.ConclusionsThe Badalona +36C > U and Heidelberg +52 G > C mutations within the L-ferritin IRE only mildly alter the binding capacity of the Iron Regulatory Proteins but are still causative for the disease.

Highlights

Hereditary Hyperferritinaemia Cataract Syndrome (HHCS) is a rare autosomal dominant disease characterized by increased serum ferritin levels and early onset of bilateral cataract
* Correspondence: msanchez@imppc.org 1Institute of Predictive and Personalized Medicine of Cancer (IMPPC), Ctra. de Can Ruti, Camí de les Escoles s/n, 08916, Badalona, Barcelona, Spain Full list of author information is available at the end of the article (FTL) mRNA cause reduced Iron regulatory protein (IRP) binding with concomitant up-regulation of Ferritin L (FTL) synthesis in the Hereditary Hyperferritinaemia Cataract Syndrome (HHCS)
For this mutation we performed folding prediction analysis of the wild-type (WT) and the mutated sequences, using the SIREs and RNAfold Web Servers and the result shows that the Badalona +36C > U substitution increases the folding free energy and opens the structure of the mutated FTL-Iron-Responsive Element (IRE), when compared to the wild-type IRE (Additional file 1: Figure S1). For both mutations we examined the ability of the mutated IRE to bind recombinant IRP1 or IRP2 by electrophoretic mobility shift assays (EMSAs)

Summary

Introduction

Hereditary Hyperferritinaemia Cataract Syndrome (HHCS) is a rare autosomal dominant disease characterized by increased serum ferritin levels and early onset of bilateral cataract. The disease is caused by mutations in the Iron-Responsive Element (IRE) located in the 50 untranslated region of L-Ferritin (FTL) mRNA, which post-transcriptionally regulates ferritin expression. The H subunit generates ferroxidase activity to incorporate iron into the protein shell and the L subunit facilitates iron-core formation The synthesis of these two proteins is controlled post-transcriptionally by the Iron Regulatory Proteins (IRPs) that bind to the Iron Responsive Element (IRE), a conserved hairpin-like motif, located in the 50 untranslated region (UTR) of ferritin mRNAs [2]. Mutations in the IRE of Ferritin L (FTL) mRNA cause reduced IRP binding with concomitant up-regulation of FTL synthesis in the Hereditary Hyperferritinaemia Cataract Syndrome (HHCS). In vitro studies indicate a minor disturbance of the IRP-IRE binding by these mutations

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Conclusion