Reduced phenotypic expression in genetic hemochromatosis with time: Role of exposure to non-genetic modifiers

Incidence of liver complications with hemochromatosis-associated HFE p.C282Y homozygosity: The role of central adiposity

BACKGROUND AND AIMS

The HFE p.C282Y+/+ (homozygous) genotype and central adiposity both increase liver disease and diabetes risks, but the combined effects are unclear. We estimated waist-to-hip ratio (WHR) associations with incident clinical outcomes in routine care in p.C282Y+/+ participants in the UK Biobank community cohort.

APPROACH AND RESULTS

Baseline WHR data available in 1297 male and 1602 female p.C282Y+/+ with 13.3-year mean follow-up for diagnoses. Spline regressions and Cox proportional hazard models were adjusted for age and genetic principal components. Cumulative incidence was from age 40 to 80 years. In p.C282Y+/+ males, there were positive linear WHR relationships for hospital inpatient-diagnosed liver fibrosis/cirrhosis ( p = 2.4 × 10 -5 ), liver cancer ( p = 0.007), non-alcoholic fatty liver disease ( p = 7.7 × 10 -11 ), and type 2 diabetes ( p = 5.1 × 10 -16 ). The hazard ratio for high WHR in p.C282Y+/+ males (≥0.96; 33.9%) was 4.13 for liver fibrosis/cirrhosis (95% CI: 2.04-8.39, p = 8.4 × 10 -5 vs. normal WHR); cumulative age 80 incidence 15.0% (95% CI: 9.8%-22.6%) versus 3.9% (95% CI: 1.9%-7.6%); for liver cancer, cumulative incidence was 9.2% (95% CI: 5.7%-14.6%) versus 3.6% (95% CI: 1.9%-6.6%). Hemochromatosis was diagnosed in 23 (96%) of the 24 high WHR p.C282Y+/+ males with incident fibrosis/cirrhosis. High WHR (≥0.85; 30.0%) p.C282Y+/+ females had raised hazards for liver fibrosis/cirrhosis (hazard ratio = 9.17, 95% CI: 2.51-33.50, p = 3.8 × 10 -7 ) and Non-alcoholic fatty liver disease (hazard ratio = 5.17, 95% CI: 2.48-10.78, p = 1.2 × 10 -5 ). Fibrosis/cirrhosis associations were similar in the subset with additional primary care diagnoses.

CONCLUSIONS

In p.C282Y+/+ males and females, increasing WHR is associated with substantially higher risks of liver complications. Interventions to reduce central adiposity to improve these outcomes should be tested.

Diagnosis and management of hereditary hemochromatosis: lifestyle modification, phlebotomy, and blood donation

The term hemochromatosis refers to a group of genetic disorders characterized by hepcidin insufficiency in the context of normal erythropoiesis, iron hyperabsorption, and expansion of the plasma iron pool with increased transferrin saturation, the diagnostic hallmark of the disease. This results in the formation of toxic non-transferrin-bound iron, which ultimately accumulates in multiple organs, including the liver, heart, endocrine glands, and joints. The most common form is HFE-hemochromatosis (HFE-H) due to p.Cys282Tyr (C282Y) homozygosity, present in nearly 1 in 200 people of Northern European descent but characterized by low penetrance, particularly in females. Genetic and lifestyle cofactors (especially alcohol and dysmetabolic features) significantly modulate clinical expression so that HFE-H can be considered a multifactorial disease. Nowadays, HFE-H is mostly diagnosed before organ damage and is easily treated by phlebotomy, with an excellent prognosis. After iron depletion, maintenance phlebotomy can be usefully transformed into a blood donation program. Lifestyle changes are important for management. Non-HFE-H, much rarer but highly penetrant, may lead to early and severe heart, liver, and endocrine complications. Managing severe hemochromatosis requires a comprehensive approach optimally provided by consultation with specialized centers. In clinical practice, a proper diagnostic approach is paramount for patients referred for hyperferritinemia, a frequent finding that reflects hemochromatosis only in a minority of cases.

Clinical characteristics of HFE C282Y/H63D compound heterozygotes identified in a specialty practice: key differences from HFE C282Y homozygotes

BACKGROUND

Patients with p.C282Y homozygous (p.C282Y) HFE mutations are more likely to develop hemochromatosis (HC) than p.C282Y/p.H63D compound heterozygotes (p.C282Y/H63D).

RESEARCH DESIGN AND METHODS

We conducted a retrospective chart review of 90 p.C282Y and 31 p.C282Y/H63D patients at a referral practice to illustrate the differences in the natural history of the disease in these two HC cohorts.

RESULTS

Over a median follow-up of 17 years, p.C282Y had higher mean serum ferritin (1105 mg/dL vs. 534 mg/dL, p = 0.001) and transferrin saturations (75.3% vs. 49.5%, p = 0.001) at diagnosis. p.C282Y underwent more therapeutic phlebotomies (TP) till de-ironing (mean 24 vs. 10), had higher mean mobilized iron stores (4759 mg vs. 1932 mg), and required more annual maintenance TP (1.9/year vs. 1.1/year, p = 0.039). p.C282Y/H63D were more likely to have obesity (45.2% vs. 20.2%, p = 0.007) at diagnosis, with a non-significant trend toward consuming more alcohol. There was no significant difference in the development of HC-related complications between the two cohorts.

CONCLUSIONS

p.C282Y have a higher mobilizable iron and require more TP. p.C282Y/H63D likely require additional insults such as obesity or alcohol use to develop elevated ferritin. De-ironing may mitigate the risk of developing HC-related complications.

Haemochromatosis

Haemochromatosis is one of the most common genetic diseases affecting patients of northern European ancestry. It is overdiagnosed in patients without iron overload and is underdiagnosed in many patients. Early diagnosis by genetic testing and therapy by periodic phlebotomy can prevent the most serious complications, which include liver cirrhosis, liver cancer, and death. This Seminar includes an update on the origins of haemochromatosis; and an overview pathophysiology, genetics, natural history, signs and symptoms, differential diagnoses, treatment with phlebotomy, outcomes, and future directions.

Arthritis Prediction of Advanced Hepatic Fibrosis in HFE Hemochromatosis

OBJECTIVE

To evaluate whether arthritis predicts the likelihood of advanced hepatic fibrosis in HFE hemochromatosis.

PATIENTS AND METHODS

We conducted a retrospective, cross-sectional analysis of 112 well-characterized patients with HFE hemochromatosis and liver biopsy-validated fibrosis staging recruited between January 1, 1983, and December 31, 2013. Complete clinical, biochemical, hematologic, and noninvasive serum biochemical indices (aspartate aminotransferase to platelet ratio index [APRI] and fibrosis 4 index [FIB4]) were available. Scheuer fibrosis stages 3 and 4, APRI greater than 0.44, or FIB4 greater than 1.1 were used to define advanced hepatic fibrosis. Comparisons between groups were performed using categorical analysis, unpaired or paired t test.

RESULTS

Male (n=76) and female (n=36) patients were similar in age. Nineteen patients had advanced hepatic fibrosis, and 47 had hemochromatosis arthritis. Arthritis was significantly associated with the presence of advanced hepatic fibrosis as determined by liver biopsy (sensitivity, 84%, [95% CI, 62% to 95%]; negative predictive value, 95% [95% CI, 87% to 99%]; relative risk, 7.4 [95% CI, 2.5 to 23]; P<.001), APRI (sensitivity, 75% [95% CI, 55% to 88%]; negative predictive value, 91% [95% CI, 81% to 96%]; relative risk, 4.5 [95% CI, 2.0 to 10.2]; P<.001), or FIB4 (sensitivity, 61% [95% CI, 41% to 78%]; negative predictive value, 67% [95% CI, 68% to 90%]; relative risk, 2.2 [95% CI, 1.1 to 4.6]; P=.03). Mean cell volume values were significantly higher pretreatment in patients with F3-4 fibrosis (96.7±1.1 fL) compared with F0-2 fibrosis (93.4±0.5 fL; P=.004) and declined following treatment (F3-4, 93.2±0.9 fL, P=.01; F0-2, 91.7±0.6 fL, P=.01).

CONCLUSION

Advanced hepatic fibrosis is strongly associated with arthritis in HFE hemochromatosis. The absence of arthritis predicts a low likelihood of advanced hepatic fibrosis, supporting its use as a clinical marker for advanced hepatic fibrosis in HFE hemochromatosis.

Hemochromatosis classification: update and recommendations by the BIOIRON Society

Hemochromatosis (HC) is a genetically heterogeneous disorder in which uncontrolled intestinal iron absorption may lead to progressive iron overload (IO) responsible for disabling and life-threatening complications such as arthritis, diabetes, heart failure, hepatic cirrhosis, and hepatocellular carcinoma. The recent advances in the knowledge of pathophysiology and molecular basis of iron metabolism have highlighted that HC is caused by mutations in at least 5 genes, resulting in insufficient hepcidin production or, rarely, resistance to hepcidin action. This has led to an HC classification based on different molecular subtypes, mainly reflecting successive gene discovery. This scheme was difficult to adopt in clinical practice and therefore needs revision. Here we present recommendations for unambiguous HC classification developed by a working group of the International Society for the Study of Iron in Biology and Medicine (BIOIRON Society), including both clinicians and basic scientists during a meeting in Heidelberg, Germany. We propose to deemphasize the use of the molecular subtype criteria in favor of a classification addressing both clinical issues and molecular complexity. Ferroportin disease (former type 4a) has been excluded because of its distinct phenotype. The novel classification aims to be of practical help whenever a detailed molecular characterization of HC is not readily available.

Dietary Iron Overload and Hfe-/- Related Hemochromatosis Alter Hepatic Mitochondrial Function

Iron is an essential co-factor for many cellular metabolic processes, and mitochondria are main sites of utilization. Iron accumulation promotes production of reactive oxygen species (ROS) via the catalytic activity of iron species. Herein, we investigated the consequences of dietary and genetic iron overload on mitochondrial function. C57BL/6N wildtype and Hfe^-/- mice, the latter a genetic hemochromatosis model, received either normal diet (ND) or high iron diet (HI) for two weeks. Liver mitochondrial respiration was measured using high-resolution respirometry along with analysis of expression of specific proteins and ROS production. HI promoted tissue iron accumulation and slightly affected mitochondrial function in wildtype mice. Hepatic mitochondrial function was impaired in Hfe^-/- mice on ND and HI. Compared to wildtype mice, Hfe^-/- mice on ND showed increased mitochondrial respiratory capacity. Hfe^-/- mice on HI showed very high liver iron levels, decreased mitochondrial respiratory capacity and increased ROS production associated with reduced mitochondrial aconitase activity. Although Hfe^-/- resulted in increased mitochondrial iron loading, the concentration of metabolically reactive cytoplasmic iron and mitochondrial density remained unchanged. Our data show multiple effects of dietary and genetic iron loading on mitochondrial function and linked metabolic pathways, providing an explanation for fatigue in iron-overloaded hemochromatosis patients, and suggests iron reduction therapy for improvement of mitochondrial function.

Genetic Diagnosis in Hereditary Hemochromatosis: Discovering and Understanding the Biological Relevance of Variants

BACKGROUND

Hereditary hemochromatosis (HH) is a genetic disease, leading to iron accumulation and possible organ damage. Patients are usually homozygous for p. Cys282Tyr in the homeostatic iron regulator gene but may have mutations in other genes involved in the regulation of iron. Next-generation sequencing is increasingly being utilized for the diagnosis of patients, leading to the discovery of novel genetic variants. The clinical significance of these variants is often unknown.

CONTENT

Determining the pathogenicity of such variants of unknown significance is important for diagnostics and genetic counseling. Predictions can be made using in silico computational tools and population data, but additional evidence is required for a conclusive pathogenicity classification. Genetic disease models, such as in vitro models using cellular overexpression, induced pluripotent stem cells or organoids, and in vivo models using mice or zebrafish all have their own challenges and opportunities when used to model HH and other iron disorders. Recent developments in gene-editing technologies are transforming the field of genetic disease modeling.

SUMMARY

In summary, this review addresses methods and developments regarding the discovery and classification of genetic variants, from in silico tools to in vitro and in vivo models, and presents them in the context of HH. It also explores recent gene-editing developments and how they can be applied to the discussed models of genetic disease.

Utility and Diversity: Challenges for Genomic Medicine

Genomic information is poised to play an increasing role in clinical care, extending beyond highly penetrant genetic conditions to less penetrant genotypes and common disorders. But with this shift, the question of clinical utility becomes a major challenge. A collaborative effort is necessary to determine the information needed to evaluate different uses of genomic information and then acquire that information. Another challenge must also be addressed if that process is to provide equitable benefits: the lack of diversity of genomic data. Current genomic knowledge comes primarily from populations of European descent, which poses the risk that most of the human population will be shortchanged when health benefits of genomics emerge. These two challenges have defined my career as a geneticist and have taught me that solutions must start with dialogue across disciplinary and social divides.

HFE Related Hemochromatosis: Uncovering the Inextricable Link between Iron Homeostasis and the Immunological System

The HFE gene (OMIM 235200), most commonly associated with the genetic iron overload disorder Hemochromatosis, was identified by Feder et al. in 1996, as a major histocompatibilty complex (MHC) class I like gene, first designated human leukocyte antigen-H (HLA-H). This discovery was thus accomplished 20 years after the realization of the first link between the then "idiopathic" hemochromatosis and the human leukocyte antigens (HLA). The availability of a good genetic marker in subjects homozygous for the C282Y variant in HFE (hereditary Fe), the reliability in serum markers such as transferrin saturation and serum ferritin, plus the establishment of noninvasive methods for the estimation of hepatic iron overload, all transformed hemochromatosis into a unique age related disease where prevention became the major goal. We were challenged by the finding of iron overload in a 9-year-old boy homozygous for the C282Y HFE variant, with two brothers aged 11 and 5 also homozygous for the mutation. We report a 20 year follow-up during which the three boys were seen yearly with serial determinations of iron parameters and lymphocyte counts. This paper is divided in three sections: Learning, applying, and questioning. The result is the illustration of hemochromatosis as an age related disease in the transition from childhood to adult life and the confirmation of the inextricable link between iron overload and the cells of the immune system.

Dietary and Sentinel Factors Leading to Hemochromatosis

Although hereditary hemochromatosis is associated with the mutation of genes involved in iron transport and metabolism, secondary hemochromatosis is due to external factors, such as intended or unintended iron overload, hemolysis-linked iron exposure or other stress-impaired iron metabolism. The present review addresses diet-linked etiologies of hemochromatosis and their pathogenesis in the network of genes and nutrients. Although the mechanistic association to diet-linked etiologies can be complicated, the stress sentinels are pivotally involved in the pathological processes of secondary hemochromatosis in response to iron excess and other external stresses. Moreover, the mutations in these sentineling pathway-linked genes increase susceptibility to secondary hemochromatosis. Thus, the crosstalk between nutrients and genes would verify the complex procedures in the clinical outcomes of secondary hemochromatosis and chronic complications, such as malignancy. All of this evidence provides crucial insights into comprehensive clinical or nutritional interventions for hemochromatosis.

Hereditary Hemochromatosis Associations with Frailty, Sarcopenia and Chronic Pain: Evidence from 200,975 Older UK Biobank Participants

BACKGROUND

Iron is essential for life but contributes to oxidative damage. In Northern-European ancestry populations, HFE gene C282Y mutations are relatively common (0.3%-0.6% rare homozygote prevalence) and associated with excessive iron absorption, fatigue, diabetes, arthritis, and liver disease, especially in men. Iron excess can be prevented or treated but diagnosis is often delayed or missed. Data on sarcopenia, pain, and frailty are scarce.

METHODS

Using 200,975 UK Biobank volunteers aged 60-70 years, we tested associations between C282Y homozygosity with Fried frailty, sarcopenia, and chronic pain using logistic regression adjusted for age and technical genetic covariates. As iron overload is progressive (with menstruation protective), we included specific analyses of older (65-70 years) females and males.

RESULTS

One thousand three hundred and twelve (0.65%) participants were C282Y homozygotes; 593 were men (0.62%) and 719 were women (0.68%). C282Y homozygote men had increased likelihoods of reporting chronic pain (odds ratio [OR] 1.23: 95% confidence interval [CI] 1.05-1.45, p = .01) and diagnoses of polymyalgia rheumatica, compared to common "wild-type" genotype. They were also more likely to have sarcopenia (OR 2.38: 1.80-3.13, p = 9.70 × 10-10) and frailty (OR 2.01: 1.45-2.80, p = 3.41 × 10-05). C282Y homozygote women (n = 312, 0.7%) aged 65-70 were more likely to be frail (OR 1.73: 1.05-2.84, p = .032) and have chronic knee, hip, and back pain. Overall, 1.50% of frail men and 1.51% of frail women in the 65-70 age group were C282Y homozygous.

CONCLUSIONS

HFE C282Y homozygosity is associated with substantial excess sarcopenia, frailty, and chronic pain at older ages. Given the availability of treatment, hereditary hemochromatosis is a strong candidate for precision medicine approaches to improve outcomes in late life.