Tumor necrosis factor-alpha promoter variants and iron phenotypes in 785 hemochromatosis and iron overload screening (HEIRS) study participants

HLA-A*03, the hemochromatosis ancestral haplotype, and phenotypes of referred hemochromatosis probands with HFE p.C282Y homozygosity

Background

Human leukocyte antigen (HLA)-A*03, hemochromatosis ancestral haplotype marker, was associated with greater iron overload in hemochromatosis cohorts reported before discovery of the HFE gene. We sought to learn whether an A*03-linked locus influences phenotypes in referred HFE p.C282Y homozygotes.

Methods

We tabulated these phenotypes in probands with p.C282Y homozygosity: age, transferrin saturation (TS), serum ferritin (SF), conditions related to iron overload, fibrosis-four variables (FIB-4) index and aspartate aminotransferase-to-platelet ratio index (APRI) predictors of severe hepatic fibrosis, and iron removed to achieve depletion (QFe/age). We analyzed phenotypes of men and women separately across three A*03 subgroups.

Results

There were 104 men (57.8%) and 76 women (42.2%). Mean age (SD) was 49 ± 13 y. Mean TS was 79 ± 17%. Median SF (range) was 715 µg/L (28, 6103). Related conditions included: hemochromatosis arthropathy (21.7%); type 2 diabetes (18.9%); hypogonadotropic hypogonadism (5.8% of men); cardiomyopathy (0%); and cirrhosis (10.0%). Median QFe/age was 61 mg/y (0, 714). A*03 homozygosity, heterozygosity, and no A*03 occurred in 37 (20.6%), 104 (57.8%), and 39 probands (21.7%), respectively. In men, mean TS and median SF were significantly higher in A*03 homozygotes than heterozygotes but not A*03-negative probands. In men, median APRI was significantly lower in A*03 heterozygotes than homozygotes and A*03-negative probands. No other phenotypes, including QFe/age, differed significantly across A*03 subgroups in either men or women.

Conclusions

Our results suggest that an A*03-linked locus does not influence phenotypes in referred HFE p.C282Y homozygotes. It is unlikely that heritable factors that modify phenotypes of p.C282Y homozygotes are linked to the hemochromatosis ancestral haplotype.

Diabetes in HFE Hemochromatosis

Diabetes in whites of European descent with hemochromatosis was first attributed to pancreatic siderosis. Later observations revealed that the pathogenesis of diabetes in HFE hemochromatosis is multifactorial and its clinical manifestations are heterogeneous. Increased type 2 diabetes risk in HFE hemochromatosis is associated with one or more factors, including abnormal iron homeostasis and iron overload, decreased insulin secretion, cirrhosis, diabetes in first-degree relatives, increased body mass index, insulin resistance, and metabolic syndrome. In p.C282Y homozygotes, serum ferritin, usually elevated at hemochromatosis diagnosis, largely reflects body iron stores but not diabetes risk. In persons with diabetes type 2 without hemochromatosis diagnoses, serum ferritin levels are higher than those of persons without diabetes, but most values are within the reference range. Phlebotomy therapy to achieve iron depletion does not improve diabetes control in all persons with HFE hemochromatosis. The prevalence of type 2 diabetes diagnosed today in whites of European descent with and without HFE hemochromatosis is similar. Routine iron phenotyping or HFE genotyping of patients with type 2 diabetes is not recommended. Herein, we review diabetes in HFE hemochromatosis and the role of iron in diabetes pathogenesis in whites of European descent with and without HFE hemochromatosis.

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.