Comprehensive functional annotation of 18 missense mutations found in suspected hemochromatosis type 4 patients.
Hemochromatosis type 4 is a rare form of primary iron overload transmitted as an autosomal dominant trait caused by mutations in the gene encoding the iron transport protein ferroportin 1 (SLC40A1). SLC40A1 mutations fall into two functional categories (loss- versus gain-of-function) underlying two distinct clinical entities (hemochromatosis type 4A versus type 4B). However, the vast majority of SLC40A1 mutations are rare missense variations, with only a few showing strong evidence of causality. The present study reports the results of an integrated approach collecting genetic and phenotypic data from 44 suspected hemochromatosis type 4 patients, with comprehensive structural and functional annotations. Causality was demonstrated for 10 missense variants, showing a clear dichotomy between the two hemochromatosis type 4 subtypes. Two subgroups of loss-of-function mutations were distinguished: one impairing cell-surface expression and one altering only iron egress. Additionally, a new gain-of-function mutation was identified, and the degradation of ferroportin on hepcidin binding was shown to probably depend on the integrity of a large extracellular loop outside of the hepcidin-binding domain. Eight further missense variations, on the other hand, were shown to have no discernible effects at either protein or RNA level; these were found in apparently isolated patients and were associated with a less severe phenotype. The present findings illustrate the importance of combining in silico and biochemical approaches to fully distinguish pathogenic SLC40A1 mutations from benign variants. This has profound implications for patient management.
IMPMC, Sorbonne Universités - UMR CNRS 7590, UPMC Univ Paris 06, Muséum d'Histoire Naturelle, IRD UMR 206, Paris, France.
Isabelle
I
Callebaut
Laboratoire de Génétique Moléculaire et d'Histocompatibilité, Inserm U1078, Université de Brest, SFR SnInBioS, CHRU de Brest, Etablissement Français du Sang - Bretagne, Brest, France.
Rozenn
R
Joubrel
Laboratoire de Génétique, UPEC (Université Paris Est Creteil), GHU Henri Mondor, Créteil, France.
Serge
S
Pissard
Hôpital Bichat, Département de Génétique, Inserm U1149 - Center for Research on Inflammation, Université Paris Diderot, AP-HP, Paris, France.
Caroline
C
Kannengiesser
Biologie Moléculaire, CHU de Marseille, Hôpital Conception.
Victoria
V
Gérolami
Inserm U1035, Biothérapies des Maladies Génétiques et Cancers, Université de Bordeaux, CHU de Bordeaux, Pôle de Biologie et Pathologie, Bordeaux, France.
Cécile
C
Ged
Laboratoire de Génétique Moléculaire, UPJV EA4666, CHU d'Amiens, Amiens, France.
Estelle
E
Cadet
Service de Génétique, CHU de la Réunion, Saint-Denis, France and.
François
F
Cartault
Laboratoire de Génétique Moléculaire et d'Histocompatibilité, Inserm U1078, Université de Brest, SFR SnInBioS, CHRU de Brest, Etablissement Français du Sang - Bretagne, Brest, France.
Chandran
C
Ka
Laboratoire de Génétique Moléculaire et d'Histocompatibilité, Inserm U1078, Université de Brest, SFR SnInBioS, CHRU de Brest, Etablissement Français du Sang - Bretagne, Brest, France.
Isabelle
I
Gourlaouen
CHRU de Brest, Inserm CIC0502, Brest, France.
Lénaick
L
Gourhant
Hôpital Bichat, Département de Génétique, Inserm U1149 - Center for Research on Inflammation, Université Paris Diderot, AP-HP, Paris, France.
Claire
C
Oudin
Laboratoire de Génétique, UPEC (Université Paris Est Creteil), GHU Henri Mondor, Créteil, France.
Michel
M
Goossens
Hôpital Bichat, Département de Génétique, Inserm U1149 - Center for Research on Inflammation, Université Paris Diderot, AP-HP, Paris, France.
Bernard
B
Grandchamp
Inserm U1035, Biothérapies des Maladies Génétiques et Cancers, Université de Bordeaux, CHU de Bordeaux, Pôle de Biologie et Pathologie, Bordeaux, France.
Hubert
H
De Verneuil
Laboratoire de Génétique Moléculaire, UPJV EA4666, CHU d'Amiens, Amiens, France.
Jacques
J
Rochette
Laboratoire de Génétique Moléculaire et d'Histocompatibilité, Inserm U1078, Université de Brest, SFR SnInBioS, CHRU de Brest, Etablissement Français du Sang - Bretagne, Brest, France.
Claude
C
Férec
Laboratoire de Génétique Moléculaire et d'Histocompatibilité, Inserm U1078, Université de Brest, SFR SnInBioS, CHRU de Brest, Etablissement Français du Sang - Bretagne, Brest, France CHRU de Brest, Inserm CIC0502, Brest, France gerald.legac@univ-brest.fr.
Gérald
G
Le Gac
D000328:Adult; D000368:Aged; D019943:Amino Acid Substitution / Q000235:genetics; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000097:blood / Q000172:deficiency* / Q000235:genetics; D003198:Computer Simulation; D005260:Female; D005293:Ferritins / Q000097:blood; D005787:Gene Frequency / Q000235:genetics; D056726:Genetic Association Studies; D057809:HEK293 Cells; D006432:Hemochromatosis / Q000097:blood / Q000235:genetics*; D064451:Hepcidins / Q000494:pharmacology; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D007501:Iron / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D008958:Models, Molecular; D058977:Molecular Sequence Annotation; D020125:Mutation, Missense / Q000235:genetics*; D012326:RNA Splicing / Q000235:genetics; D013329:Structure-Activity Relationship; D044465:White People / Q000235:genetics; D055815:Young Adult; D000098742:Ferroportin
D027682:Cation Transport Proteins; D064451:Hepcidins; D000098742:Ferroportin; D005293:Ferritins; D007501:Iron