BACKGROUND & AIMS: Haemochromatosis 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 
SLC40A1 p.Y333H mutation in our previous study. In the present study, we tried 
to investigate the frequency and pathogenicity of the SLC40A1 p.Y333H mutation 
in haemochromatosis in China.
METHODS: Patients were analysed for SLC40A1 p.Y333H as well as mutations in the 
other classic haemochromatosis-related genes by Sanger sequencing. To analyse 
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 analysed by 
immunofluorescence and Western blotting.
RESULTS: Of 22 unrelated cases with primary iron overload, three cases (3/22, 
13.6%) harboured the SLC40A1 p.Y333H, with no missense mutations identified in 
any other classical haemochromatosis-related genes including HFE, HJV, HAMP and 
TFR2. Pedigree analysis showed that three probands and the son of one proband 
had haemochromatosis 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 aetiological factors of 
haemochromatosis in China.