Mutations of SLC40A1 encoding ferroportin (Fpn), the unique cellular iron exporter, severely affect iron homeostasis causing type 4 hereditary hemochromatosis, an autosomal dominant iron overload condition with variable phenotypic manifestations. This disease can be classified as type 4A, better known as âferroportin diseaseâ, which is due to âloss of functionâ mutations that lead to decreased iron export from cells, or as type 4B hemochromatosis, which is caused by âgain of functionâ mutations, conferring partial or complete resistance to hepcidin-mediated Fpn degradation. In this work, we discuss clinical and molecular findings on a group of patients in whom a SLC40A1 single copy missense variant was identified. Three novel variants, p.D181N, p.G204R and p.R296Q were functionally characterized. Fpn D181N and R296Q mutants can be classified as full or partial loss of function, respectively. Replacement of G204 with arginine appears to cause a more complex defect with impact both on iron export function and hepcidin sensitivity. This finding confirms the difficulty of predicting the effect of a mutation on the molecular properties of Fpn in order to provide an exhaustive explanation to the wide variability of the phenotype in type 4 hereditary hemochromatosis.
Majore, S., Bonaccorsi di Patti, M.C., Valiante, M., Polticelli, F., Cortese, A., Di Bartolomeo, S., et al. (2018). Characterization of three novel pathogenic SLC40A1 mutations and genotype/phenotype correlations in 7 Italian families with type 4 hereditary hemochromatosis. BIOCHIMICA ET BIOPHYSICA ACTA. MOLECULAR BASIS OF DISEASE, 1864(2), 464-470 [10.1016/j.bbadis.2017.11.006].