Comparing the types of haemochromatosis- from genetics to clinics

Haemochromatosis is a genetic disorder of iron homeostasis. It can be caused by mutations in genes encoding the iron-regulatory hormone hepcidin (HAMP), and/or genes that regulate hepcidin expression (HFE, HJV, TFR2), or a gain-of-function mutation in the gene encoding hepcidin receptor ferroportin (FPN1/SLC40A1). HFE-related haemochromatosis is prevalent predominantly in individuals of northern European descent. These mutations result in dysregulated levels or activity of hepcidin, leading to high iron-saturation of transferrin followed by progressive liver iron accumulation in the absence of anaemia. To enable and enhance the understanding of haemochromatosis in both researchers and prospective medics, this review collates and discusses the genetic basis and consequent pathophysiology of the different types of haemochromatosis within a single, comparative review. The discussion is supported by figures and a summary table that compares the haemochromatosis types for prevalence, clinical manifestations, primary organs affected, iron-related biochemical parameters and mechanisms of iron loading. Also, gain-of-function ferroportin mutation is compared to ferroportin disease, which is a loss-of-function ferroportin mutation, and shows a tendency to anaemia. Essentially, HFE-related haemochromatosis (common type) and TFR2-related haemochromatosis (rare type) show late-onset, milder and gradual iron loading, and often involve liver and joint damage. In contrast, HJV- and HAMP-related haemochromatosis (rare types) show severe and rapid iron loading in the first three decades of life, with notable cardiac and endocrine complications. Hepcidin levels are more markedly decreased in HJV-related haemochromatosis compared to HFE and TFR2 types. There are minimal to absent levels of hepcidin in HAMP-related haemochromatosis.