Haemochromatosis and Secondary Iron Overload, HFE mutations, iron burden assessment and chelation therapy

Overview

• Iron overload occurs when body iron accumulates beyond physiological capacity, leading to deposition in parenchymal cells of the liver, endocrine organs, and heart with resultant end-organ injury.
• There is no regulated physiological pathway for iron excretion; iron homeostasis depends entirely on controlled intestinal absorption and macrophage recycling.
• When genetic or acquired disease disrupts this balance, progressive iron accumulation follows over years to decades.
• Hereditary haemochromatosis (HH) is the most common autosomal recessive disorder in Northern European populations, predominantly caused by HFE gene mutations.
• Secondary iron overload arises principally from transfusion-dependent anaemias or from ineffective erythropoiesis, which drives inappropriately high intestinal iron absorption independent of body iron stores.

Classification and Aetiology

Hereditary Haemochromatosis

• Non-HFE forms collectively account for fewer than 5% of all HH cases.
• Aceruloplasminaemia, congenital atransferrinaemia, and DMT1 (SLC11A2) mutations are additional rare genetic causes of iron overload not classified within the HH types above.

Secondary Iron Overload

• Each unit of transfused packed red cells delivers approximately 200-250 mg of iron.
• A transfusion-dependent patient receiving 2-4 units monthly accumulates 5-10 g of iron annually with no mechanism for physiological elimination.

Pathophysiology

The Hepcidin-Ferroportin Axis

• Hepcidin, a peptide hormone synthesised predominantly by hepatocytes, is the master regulator of systemic iron homeostasis.
• It binds to ferroportin (SLC40A1) on duodenal enterocytes, hepatocytes, and macrophages, triggering ferroportin internalisation and degradation, thereby reducing intestinal iron absorption and macrophage iron release.
• In HFE-related haemochromatosis, the C282Y mutation disrupts HFE protein association with transferrin receptor 1, impairing the BMP-SMAD signalling cascade that normally upregulates hepatic hepcidin synthesis.
• The result is inappropriately low serum hepcidin, sustained high ferroportin expression, and unregulated intestinal iron absorption.
• Mutations in HJV and HAMP cause more severe hepcidin deficiency, explaining the aggressive phenotype of juvenile haemochromatosis.
• TFR2 mutations similarly impair hepcidin upregulation.
• In type 4A (ferroportin loss-of-function), the mutant ferroportin has impaired iron-export function while remaining normally responsive to hepcidin; reduced efflux preferentially traps iron in macrophages.
• In type 4B (gain-of-function at hepcidin-binding site), ferroportin cannot be downregulated by hepcidin, producing parenchymal loading similar to classical HH.
• In secondary iron overload from ineffective erythropoiesis, erythroblast-derived erythroferrone suppresses hepcidin, disinhibiting ferroportin and driving excess iron absorption even when body stores are replete.
• Transfusional iron overload bypasses intestinal regulation entirely, depositing iron initially in the reticuloendothelial system before redistributing to parenchymal organs.
• Key distinction: In HFE-related HH, iron accumulates predominantly in parenchymal cells with relative macrophage sparing.
• In transfusional overload, iron initially loads reticuloendothelial macrophages before spilling into parenchymal compartments.

Cellular Iron Toxicity

Iron exceeding transferrin-binding capacity circulates as non-transferrin-bound iron (NTBI) and its more reactive subfraction, labile plasma iron (LPI). These species participate in Fenton chemistry, generating hydroxyl radicals that cause lipid peroxidation, mitochondrial dysfunction, and DNA damage:

• Liver: Hepatocyte injury → fibrosis → cirrhosis → hepatocellular carcinoma
• Pancreas: Direct beta-cell toxicity → diabetes mellitus; hepatic insulin resistance
• Anterior pituitary: Iron deposition → hypogonadotropic hypogonadism; rarely adrenal insufficiency
• Thyroid: Direct iron toxicity → hypothyroidism
• Heart: Myocardial siderosis → dilated cardiomyopathy and arrhythmia (most common cause of death in undertreated thalassaemia major)
• Joints: Calcium pyrophosphate crystal deposition, particularly at the second and third metacarpophalangeal joints → arthropathy, chondrocalcinosis, subchondral cysts, osteopenia

Laboratory and Imaging Diagnosis

Biochemical Assessment

Serum ferritin >1000 µg/L in HFE haemochromatosis is associated with clinically significant overload and is a threshold above which hepatic fibrosis staging is warranted; MRI-based assessment has largely supplanted liver biopsy for this purpose.

HFE Genotyping

• C282Y homozygosity: Accounts for 85-90% of classical HH in Northern European populations. The C282Y allele frequency is approximately 1 in 10 in this population; homozygosity in approximately 1 in 200-300. Penetrance is incomplete, iron-overload-related disease develops in approximately 28-50% of male and 1-5% of female homozygotes.
• C282Y/H63D compound heterozygosity: Present in approximately 5% of HH patients. Usually produces mild to moderate iron loading; clinical disease typically requires cofactors such as heavy alcohol use, hepatic steatosis, or coexisting ineffective erythropoiesis.
• H63D homozygosity: Not associated with clinically significant iron overload in isolation.
• S65C: Considered a polymorphism; not independently causative of iron overload.

Non-HFE gene sequencing (HJV, HAMP, TFR2, SLC40A1) is indicated when HFE testing is negative but an iron overload phenotype is confirmed, particularly in younger patients or those with disease severity disproportionate to HFE genotype.

MRI-Based Iron Quantification

MRI is the cornerstone of non-invasive iron burden assessment.

Cardiac T2 is the most clinically critical measurement in transfusion-dependent patients. T2 <10 ms mandates immediate chelation intensification.

Annual transfusion iron loading can be estimated:

$$\text{Annual iron load (mg/kg/year)} = \frac{\text{Units transfused per year} \times 225\ \text{mg Fe/unit}}{\text{body weight (kg)}}$$

Bone Marrow and Liver Biopsy

• Bone marrow biopsy (Perls'/Prussian blue stain): Assesses reticuloendothelial iron stores; sideroblast enumeration relevant in secondary causes. Not routinely performed for HH assessment.
• Liver biopsy: Permits histological fibrosis staging and direct hepatic iron concentration (HIC) measurement. The hepatic iron index (HII), HIC (µmol/g dry weight) divided by age, with HII >1.9 historically suggesting HH, is largely superseded by genotyping and MRI but may still be used in specific diagnostic uncertainty.

Comprehensive Assessment Framework

Diagnostic Algorithm

Differential Diagnosis

Management

Venesection in Hereditary Haemochromatosis

Therapeutic venesection is the primary treatment for HFE-related and most non-HFE hereditary haemochromatosis.

Induction (depletion) phase:

• Remove 450-500 mL (approximately 200-250 mg iron) weekly or fortnightly
• Continue until serum ferritin 50-100 µg/L and Tsat normalises
• Monitor FBC and ferritin every 2-4 venesections
• Withhold if haemoglobin falls below approximately 110 g/L

Maintenance phase:

• 2-6 venesections per year to maintain ferritin 50-100 µg/L
• Lifelong in most patients
• Symptoms of fatigue, elevated transaminases, mild fibrosis, and skin pigmentation typically resolve with iron depletion.
• Diabetes and hypogonadism may partially improve if treatment precedes irreversible glandular destruction.
• Cirrhosis and destructive arthropathy are irreversible.
• Hepatocellular carcinoma risk is substantially reduced but not eliminated; 6-monthly liver ultrasound and AFP surveillance is mandatory in patients with established cirrhosis.

Venesection alternatives:

• Subcutaneous desferrioxamine when anaemia coexists or phlebotomy is not tolerated
• Oral deferasirox at low dose for selected HH patients who cannot undergo venesection (not yet standard practice)
• High-dose IV desferrioxamine ± oral chelator for life-threatening cardiac failure in the rare HH patient with severe cardiomyopathy

Iron Chelation in Transfusion-Dependent Iron Overload

Chelation is the mainstay of treatment when venesection is not possible.

Initiation Thresholds

Chelation is generally initiated when any of the following are present:

• Serum ferritin consistently >1000 µg/L after ≥20 lifetime transfusion episodes, or
• LIC >7 mg/g dry weight on MRI, or
• Cardiac T2* <20 ms

Desferrioxamine (DFO)

The therapeutic index (TI) for DFO should not be exceeded:

$$\text{TI} = \frac{\text{mean daily dose (mg/kg)}}{\text{serum ferritin}\ (\mu\text{g/L})} < 0.025$$

Exceeding this ratio significantly increases toxicity risk.

Deferasirox (DFX)

• Dose should be reduced or suspended if creatinine rises >33% above baseline on two consecutive measurements.
• Deferasirox is the preferred first-line oral chelator globally due to once-daily dosing and adherence advantage.

Deferiprone (DFP)

Deferiprone must be immediately discontinued if absolute neutrophil count (ANC) falls below 1.5 × 10⁹/L; permanently discontinued if agranulocytosis (ANC <0.5 × 10⁹/L) occurs. Deferiprone has superior efficacy for cardiac iron removal compared with DFO alone and is preferentially used or combined when cardiac T2* is reduced.

Combination Chelation

DFO + deferiprone is used for severe cardiac iron overload (T2 <10 ms): DFO administered on alternate nights or during the day, deferiprone continuously. This combination provides additive/synergistic chelation with demonstrated improvement in cardiac T2 and reduction in cardiac events in thalassaemia major. DFO + deferasirox combination may also be used in refractory overload, though evidence is less established than for DFO + deferiprone.

Monitoring for Chelation-Related Adverse Effects and End-Organ Assessment

Prognosis and Special Considerations

HFE Haemochromatosis

• Life expectancy is normal in C282Y homozygotes diagnosed and treated before the development of cirrhosis or diabetes mellitus.
• Cirrhosis confers a markedly elevated hepatocellular carcinoma risk; this persists after iron depletion and mandates ongoing HCC surveillance.
• Penetrance is significantly lower in women than men, largely due to iron losses through menstruation and pregnancy; women typically present 10-20 years later than men.
• No dietary restriction is necessary beyond limiting alcohol; patients should avoid raw shellfish due to risk of severe Vibrio vulnificus infection in the iron-loaded state.

Transfusional Iron Overload

• Cardiac siderosis (T2* <10 ms) is the most common cause of death in undertreated thalassaemia major; introduction of effective chelation has transformed survival, and chelation can reverse cardiac and hepatic iron accumulation.
• Endocrine damage (hypogonadism, diabetes, hypothyroidism) may be irreversible once established, emphasising the importance of early chelation initiation.
• Patients with T2* <10 ms require intensive dual chelation and cardiac specialist co-management.
• Siderophilic infections, particularly Yersinia enterocolitica and Mucor species, complicate both iron overload and high-dose DFO therapy; fever in a chelated patient should prompt consideration of these pathogens.

Juvenile Haemochromatosis (Types 2A and 2B)

• Presents in the second and third decades with severe hypogonadotropic hypogonadism, cardiac failure, and cirrhosis before age 30.
• Requires urgent and intensive iron removal; venesection is first-line if haemoglobin permits, supplemented by chelation for cardiac overload.
• HJV mutations (type 2A) are the more common cause; HAMP mutations (type 2B) are rarer but phenotypically equivalent.

Ferroportin Disease (Type 4A)

• Loss-of-function variant presents with high ferritin but normal or low transferrin saturation and predominantly macrophage (RE) iron loading.
• Venesection often poorly tolerated due to anaemia tendency; chelation may be required.

Emerging Therapies

• Strategies targeting the hepcidin pathway, including minihepcidins, anti-erythroferrone agents, and transferrin supplementation, show efficacy in preclinical models and early clinical trials of non-transfusion-dependent thalassaemia and HH.
• None is yet in routine clinical practice.