Ferroportin (FPN1), encoded by the SLC40A1 gene, is the unique cellular iron exporter identified in mammals. FPN1 transfers iron from the intestine and macrophages into the bloodstream. This function is negatively regulated by hepcidin. Mutations in SLC40A1 may affect FPN1 function, originating distinct autosomal dominant diseases: (i) the Ferroportin Disease (FD), due to loss-of-function mutations, is characterized by decreased iron export from enterocytes and severely affected iron transfer in macrophages, giving rise to a marked iron accumulation in spleen and liver; and (ii) the Type 4 Hereditary Hemochromatosis (HH), resulting from gain-of-function mutations conferring resistance to hepcidin-mediated FPN1 degradation and consequently high cellular iron export.
In this study, 335 individuals suspected of having non-classic HH were enrolled. Six genes related with iron metabolism were analysed by SSCP, dHPLC or NGS. The latter used TruSeq or Nextera XT libraries and a MiSeq platform (Illumina). Genetic variants found were validated by Sanger sequencing. Predictive consequences at protein level were evaluated using Polyphen-2 and SIFT softwares.
From all patients analysed, three SLC40A1 pathogenic variants were detected in heterozygosity in three women: two missense, c.238G>A, p.Gly80Ser and c.610G>A, p.Gly204Ser; and one deletion, c.485_487delTTG; p.Val162del. These variants had been reported in public databases, but they were not known to be present in the Portuguese population. The p.Gly80Ser and the p.Val162del are FPN1 loss-of-function mutations and were found associated with hyperferritinemia and low transferrin saturation (FD). In contrast, the p.Gly204Ser induced a gain of FPN1 function with a full iron export capacity giving the patient a type 4-HH phenotype, which includes iron overload, hyperferritinemia and high transferrin saturation.
Detailed clinical evaluation of the suspected patients are useful to unravel the effect of different mutations in FPN1 function, expression and regulation.This work was partially supported by INSA_2013DGH910 and GenomePT (POCI-01-0145-FEDER-022184).info:eu-repo/semantics/publishedVersio
