A novel SLC40A1 p.Y333H mutation with gain of function of ferroportin: A recurrent cause of haemochromatosis in China

Abstract

Background & Aims Hemochromatosis type 4, also known as ferroportin disease, is an autosomal dominant genetic disorder caused by pathogenic mutations in the SLC40A1 gene, which encodes ferroportin 1 (FPN1). We have identified a novel SCL40A1 p.Y333H mutation in our previous study. In the present study, we tried to investigate the frequency and pathogenicity of the SCL40A1 p.Y333H mutation in hemochromatosis in China. Methods Patients were analyzed for SCL40A1 p.Y333H as well as mutations in the other classic hemochromatosis‐related genes by Sanger sequencing. To analyze iron export capacity of the SLC40A1 p.Y333H mutant, the 293T cells were transfected with the SLC40A1 p.Y333H construct, and then treated with hepcidin after exposure to ferric ammonium citrate. Cellular localization of mutant FPN1, expression of FPN1 and intracellular ferritin were analyzed by immunofluorescence and Western‐blotting. Results Of 22 unrelated cases with primary iron overload, three cases (3/22, 13.6%) harbored the SLC40A1 p.Y333H, with no missense mutations identified in any other classical hemochromatosis‐related genes including HFE, HJV, HAMP, and TFR2. Pedigree analysis showed that three probands and the son of one proband had hemochromatosis of stage 3, while the son of another proband with age of 16 showed elevated transferrin saturation but normal serum ferritin level. In vitro studies showed the mutant p.Y333H ferroportin was resistant to hepcidin, affecting the subsequent internalization and degradation of FPN1, and was associated with ferroportin gain‐of‐function. Conclusions The SLC40A1 p.Y333H mutation is associated with gain‐of‐function of ferroportin, representing one of the major etiological factors of hemochromatosis in China.