Clinical Description
HFE hemochromatosis comprises three phenotypes:
Clinical HFE hemochromatosis (individuals with end-organ damage [e.g., cirrhosis, diabetes, cardiac failure, skin hyperpigmentation] secondary to iron storage)
Biochemical HFE hemochromatosis (individuals with elevated transferrin saturation [TS], not otherwise explained) with evidence of iron overload (elevated serum ferritin concentration)
Some individuals with HFE hemochromatosis may be identified because they have signs and symptoms related to iron overload (i.e., clinical HFE hemochromatosis). Other individuals are diagnosed with HFE hemochromatosis before symptoms develop, either through detection of abnormal iron-related studies (i.e., biochemical HFE hemochromatosis) or by molecular genetic testing used in their evaluation as family members at risk for HFE hemochromatosis (expressing or non-expressing p.Cys282Tyr homozygotes).
The difference between clinical and biochemical HFE hemochromatosis must be understood in the interpretation of population studies evaluating morbidity related to HFE hemochromatosis. Several large-scale screening studies in the general population have demonstrated that most individuals homozygous for p.Cys282Tyr do not have clinical HFE hemochromatosis. A significant proportion of individuals with homozygosity for p.Cys282Tyr (especially men) have biochemical HFE hemochromatosis.
Factors influencing disease manifestation
Clinical HFE Hemochromatosis
Individuals with clinical HFE hemochromatosis have inappropriately high absorption of iron from a normal diet by the mucosa of the small intestine, resulting in excessive parenchymal storage of iron, which may result in damage to target organs and, potentially, organ failure.
Age of onset. Symptoms related to iron overload usually appear between age 40 and 60 years in men and after menopause in women. Occasionally, HFE hemochromatosis manifests at an earlier age, but hepatic fibrosis or cirrhosis is rare before age 40 years.
Early signs. Often the first signs of clinical HFE hemochromatosis are arthropathy (joint stiffness and pain) involving the metacarpophalangeal joints, progressive increase in skin pigmentation resulting from deposits of melanin and iron, diabetes mellitus resulting from pancreatic iron deposits, and cardiomyopathy resulting from cardiac parenchymal iron stores. Hepatomegaly may or may not be present early in HFE hemochromatosis. Some asymptomatic individuals have hepatomegaly on physical examination. Some men, typically those with severe iron overload, have erectile dysfunction, hypotestosteronemia, loss of muscle mass, and osteoporosis due to hypogonadotropic hypogonadism. In women, hypogonadism leads to diminished libido, amenorrhea, and infertility in some individuals. Abdominal pain, weakness, lethargy, and weight loss are common nonspecific findings [Edwards & Barton 2018].
The HEIRS Study found an odds ratio of 3.3 for liver disease among men homozygous for p.Cys282Tyr [Adams et al 2005]. With progressive iron overload, cirrhosis may develop and be complicated by portal hypertension, primary liver cancer, and end-stage liver disease [Kowdley et al 2005]. Alcohol consumption worsens the symptoms in HFE hemochromatosis [Scotet et al 2003]. Approximately 50% of individuals with cirrhosis or liver failure also have diabetes mellitus and approximately 15% have congestive heart failure or cardiac arrhythmias. Cirrhosis is more common among p.Cys282Tyr homozygotes who consume more than 60 g of alcohol per day [Fletcher et al 2002]. Age, diabetes, alcohol consumption, and severity of iron overload increase the risk of cirrhosis, after adjusting for other factors [Barton et al 2018].
Life expectancy. Individuals diagnosed and treated prior to the development of cirrhosis have normal life expectancy. Those diagnosed after the development of cirrhosis have a decreased life expectancy even with iron depletion therapy [Adams et al 2005], primarily due to the development of hepatocellular cancer.
Prognosis. Individuals with cirrhosis who are treated have a better outcome than those who are not treated. Treatment of patients with cirrhosis to achieve iron depletion does not eliminate the 10%-30% risk of primary liver cancer (e.g., hepatocellular carcinoma, cholangiocarcinoma).
Failure to deplete iron stores after 18 months of treatment is a poor prognostic sign that reflects iron overload severity in most individuals and insufficient phlebotomy therapy in other individuals. With iron depletion, dysfunction of some organs (liver and heart) can improve. Endocrine abnormalities and arthropathy improve in 20% of treated individuals.
Death in individuals with clinical HFE hemochromatosis is often caused by liver failure, primary liver cancer, extrahepatic cancers, congestive heart failure, or arrhythmia.
Biochemical HFE Hemochromatosis
It is controversial whether individuals who have biochemical HFE hemochromatosis in the absence of clinical HFE hemochromatosis are at increased risk of developing complications of iron overload and are therefore candidates for phlebotomy treatment (see Management).
Ferritin levels at diagnosis. Bardou-Jacquet and colleagues concluded that HFE
p.Cys282Tyr homozygotes with a serum ferritin at diagnosis between the upper limit of normal and 1,000 μg/L have lower mortality than the general population due to phlebotomy therapy [Bardou-Jacquet et al 2015a, Bardou-Jacquet et al 2015b, Bardou-Jacquet et al 2015c]. Conversely, an Australian consortium concluded that the benefits of phlebotomy for p.Cys282Tyr homozygotes with mildly elevated serum ferritin remain unproven without a randomized study with long-term follow-up [Delatycki et al 2015].
Prospective follow-up study of a few HFE Cys282Tyr homozygotes found that iron overload is not progressive in all individuals. Although serum ferritin concentration may rise in these individuals over time, end-organ damage is uncommon and is more frequently observed in men than women [Allen et al 2008, Gurrin et al 2008].
Modifying factors. It has been assumed for many years that additional modifying factors or pathogenic variants in non-HFE genes are required for expression of hemochromatosis in some p.Cys282Tyr homozygotes. An international consortium identified a modifying variant p.Asp519Gly in GNPAT in p.Cys282Tyr homozygotes, which occurs with greater frequency in men and women with severe iron overload in the absence of heavy alcohol consumption than in those without severe iron overload [McLaren et al 2015, Barton et al 2017]. GNPAT p.Asp519Gly was not an independent risk factor for cirrhosis in men and women with p.Cys282Tyr homozygosity who underwent liver biopsy [Barton et al 2018].
Non-Expressing p.Cys282Tyr Homozygotes
Non-expressing homozygotes are unlikely to develop end-organ damage. Women represent a higher proportion of non-expressing homozygotes than men [Allen et al 2010, Gan et al 2011].
Three longitudinal population-based screening studies showed that 38%-50% of p.Cys282Tyr homozygotes develop iron overload (i.e., elevated serum ferritin concentration) and 10%-33% eventually develop hemochromatosis-related symptoms [Whitlock et al 2006] (i.e., nonspecific symptoms such as fatigue and arthralgia) or end-organ damage (e.g., cirrhosis, diabetes mellitus, and/or cardiomyopathy). The majority of HFE p.Cys282Tyr homozygotes who develop end-organ damage and corresponding manifestations are men [Allen et al 2010, European Association for the Study of the Liver 2010, Gan et al 2011].
Heterozygotes
Some individuals who are heterozygous for either HFE p.Cys282Tyr or p.His63Asp have elevated serum TS and serum ferritin concentrations, but they do not develop complications of iron overload [Bulaj et al 1996, Allen et al 2008].
Although a threshold TS of 45% may be more sensitive than higher values for detecting HFE hemochromatosis, TS of 45% may also identify heterozygotes who are not at risk of developing other clinical abnormalities [McLaren et al 1998].
In a large study of Danish men, Pedersen & Milman [2009] showed that:
Among p.Cys282Tyr heterozygotes, 9% had elevated serum TS (≥50%), 9% had elevated ferritin (≥300 ng/mL), and 1.2% had elevation of both serum TS and ferritin.
Among p.His63Asp heterozygotes, 8% had elevated serum TS, 12% had elevated ferritin, and 2% had elevation of both TS and ferritin.
Nomenclature
HFE hemochromatosis has been variably described in the past as hereditary hemochromatosis, primary hemochromatosis, genetic hemochromatosis, and bronze diabetes with cirrhosis.
After the description of other types of iron overload associated with pathogenic variants in non-HFE iron-related genes, HFE hemochromatosis was described as either HFE hemochromatosis or type 1 hemochromatosis. It is preferred to specify hemochromatosis according to gene or genotype. Using the term "hereditary" for hemochromatosis of known pathogenic genotype is redundant.
Prevalence
Among most populations of northern European ancestry, the prevalence of individuals homozygous for HFE
p.Cys282Tyr is 2:1,000 to 5:1,000 [Barton et al 2015]. In non-Hispanic whites in North America, the prevalence of p.Cys282Tyr homozygotes is 1:200 to 1:400 [Adams et al 2005].
Among African Americans, p.Cys282Tyr homozygotes are rare (1:6,781). The prevalence of heterozygotes is 1:775.
Among Asians, p.Cys282Tyr homozygotes are very rare (1:25,000). The prevalence of heterozygotes is 1:1,000.
Among Hispanics, the prevalence of p.Cys282Tyr homozygotes and heterozygotes is 0.027% and 3.0%, respectively.
Heterozygosity for p.His63Asp is common in most populations (northern Europeans: 25%; Hispanics: 18%; African Americans: 6%; Asians: 8.5%).
Approximately one third of northern European whites are heterozygous for either p.Cys282Tyr or p.His63Asp.