Phenotypic expression of hereditary hemochromatosis: what have we learned from the population studies?

Profound advances in our knowledge of hereditary hemochromatosis (HH) during the past 150 years have resulted in two distinct "iron ages": the pre-HFE gene era and the post-HFE gene era. During these periods, family studies, HLA association studies, and ultimately HFE gene studies in various populations informed us of the genotypic prevalence as well as the clinical and biochemical penetrance of HH. We learned that HH has a highly variable clinical penetrance in susceptible individuals of Northern European ancestry. Further, we now recognize that the natural history of HH is not as discrete as previously believed, because genetic and environmental modifiers of disease penetrance are increasingly identified as influencing the clinical expression of HH.