Hepcidin levels in hereditary hyperferritinemia: Insights into the iron-sensing mechanism in hepatocytes

Hereditary Hyperferritinemia-Cataract Syndrome in a Family With HFE-H63D Mutation

Hereditary hyperferritinemia-cataract syndrome (HHCS) is a rare genetic condition characterized by persistent hyperferritinemia (usually ferritin >1,000 ng/mL) without tissue iron overload, with or without early-onset slow-progressing bilateral nuclear cataract. It was first identified as a new genetic disorder in 1995, and since then genetic sequencing studies have been carried out to identify associated mutations in affected families. New mutations around the world are still being reported in the iron-responsive element (IRE) of the L-ferritin gene (FTL) to this day. Many clinicians remain unaware of this rare condition. The co-occurrence of FTL mutations and hereditary hemochromatosis (HH) mutations, especially H63D, on the HFE gene has been reported in the literature, which often leads to a diagnosis of HH, missed diagnosis of HHCS, incorrect treatment with phlebotomies and the occurrence of associated iatrogenic iron deficiency anemia. We herein report the case of a 40-year-old woman with spontaneous facial freckling, bilateral cataracts, homozygosity for HFE H63D mutation, iron deficiency anemia, and hyperferritinemia, who has been treated with phlebotomy and iron chelation therapy to no avail. Eleven years after being diagnosed and treated for HH, a reevaluation of her clinical presentation, laboratory results, medical imaging, and family history led to the recognition that her case is explained not by HH, but by an alternative diagnosis, HHCS. Our main objective in this report is to increase clinical awareness about HHCS, an often-unknown differential diagnosis of hyperferritinemia without iron overload, and to prevent adverse medical interventions in HHCS patients.

Unexplained isolated hyperferritinemia without iron overload

Although hyperferritinemia may be reflective of elevated total body iron stores, there are conditions in which ferritin levels are disproportionately elevated relative to iron status. Autosomal dominant forms of hyperferritinemia due to mutations in the L-ferritin IRE or in A helix of L-ferritin gene have been described, however cases of isolated hyperferritinemia still remain unsolved. We describe 12 Italian subjects with unexplained isolated hyperferritinemia (UIH). Four probands have affected siblings, but no affected parents or offspring. Sequencing analyses did not identify casual mutations in ferritin gene or IRE regions. These patients had normal levels of intracellular ferritin protein and mRNA in peripheral blood cells excluding pathological ferritin production at transcriptional and post-transcriptional level. In contrast with individuals with benign hyperferritinemia caused by mutations affecting the ferritin A helix, low rather than high glycosylation of serum ferritin was observed in our UIH subjects compared with controls. These findings suggest that subjects with UIH have a previously undescribed form of hyperferritinemia possibly attributable to increased cellular ferritin secretion and/or decreased serum ferritin clearance. The cause remains to be defined and we can only speculate the existence of mutations in gene/s not directly implicated in iron metabolism that could affect ferritin turnover including ferritin secretion.

Hereditary hemochromatosis: laboratory evaluation

The condition of hereditary hemochromatosis (HH) is caused by gene-dependent protein abnormalities involved in iron absorption, storage, or modulation of iron; these abnormalities result in iron overload. The clinical laboratory plays a significant role in case finding, diagnostic validation, and monitoring HH therapy. Elevated serum iron, transferrin saturation, and ferritin suggest HH, but results can also indicate other forms of hepatocyte injury such as alcoholic or viral hepatitis, or other inflammatory disorders involving the liver. In the context of elevated serum iron, transferrin saturation, and ferritin, and after ruling out secondary causes of iron overload, HFE gene evaluation is the preferred test to confirm the diagnosis of HH. However, 5% to 15% of patients with phenotypic HH do not have HFE gene mutations. In these cases, MRI evaluation or liver biopsy with iron quantification is indicated. The clinical role of hepcidin, the iron modulating protein, is undetermined at this time. Because hepcidin also plays a key role in antimicrobial and inflammatory activities, interpretation of hepcidin serum or urine concentration will require thorough understanding of its complex role in iron regulation.

Inherited disorders of iron metabolism

PURPOSE OF REVIEW

To discuss inherited iron disorders, their pathophysiology and clinical implications in the light of the recent advances in our knowledge of iron metabolism and its regulation.

RECENT FINDINGS

In previous years the molecular mechanisms of cellular iron uptake and release and the cellular and systemic iron homeostasis have been substantially clarified. New proteins (hepcidin, hemojuvelin, HFE, TFR2 and ferroportin), mutated in hereditary hemochromatosis, have been identified with a crucial role in iron regulation. These advances have modified our understanding of the pathophysiology of hemochromatosis, now considered a disorder either due to hepcidin deficiency or (rarely) due to hepcidin resistance. Novel genetic forms of iron-related microcytic anemia have been identified, due to defects of iron transport/utilization or to TMPRSS6 deficiency and hepcidin hyperproduction, as occurs in iron-refractory iron deficiency anemia (IRIDA). A role for hepcidin has been identified also in acquired conditions, as in iron-loading anemias and in anemia of chronic diseases and inflammation.

SUMMARY

Advances in basic research have improved the classification and diagnosis of genetic anemias and iron overload and are paving the way towards the development of drugs that target the molecular lesions.