Pathophysiology of hereditary hemochromatosis

Hereditary hemochromatosis (HH) encompasses several inherited disorders of iron homeostasis characterized by increased gastrointestinal iron absorption and tissue iron deposition. The most common form of this disorder is HFE-related HH, nearly always caused by homozygosity for the C282Y mutation. A substantial proportion of C282Y homozygotes do not develop clinically significant iron overload, suggesting roles for environmental factors and modifier genes in determining the phenotype. Recent studies have demonstrated that the pathogenesis of nearly all forms of HH involves inappropriately decreased expression of the iron-regulatory hormone hepcidin. Hepcidin serves to decrease the export of iron from reticuloendothelial cells and absorptive enterocytes. Thus, HH patients demonstrate increased iron release from these cell types, elevated circulating iron, and iron deposition in vulnerable tissues. The mechanism by which HFE influences hepcidin expression is an area of current investigation and may offer insights into the phenotypic variability observed in persons with mutations in HFE.     

Pathogenesis of hereditary hemochromatosis

Hereditary hemochromatosis comprises several inherited disorders of iron homeostasis characterized by increased gastrointestinal iron absorpstion and resultant tissue iron deposition. The identification of HFE and other genes involved in iron metabolism has greatly expanded our understanding of hereditary hemochromatosis. Two major hypotheses have been proposed to explain the pathogenesis of HFE-related hereditary hemochromatosis: the hepcidin hypothesis and the duodenal crypt cell programming hypothesis.     

Management of hereditary hemochromatosis

Hereditary hemochromatosis is a common disorder of iron metabolism with a prevalence as high as 8 per 1000. Affected individuals absorb excessive amounts of dietary iron and over time, tissue iron deposition results in skin discoloration, arthropathy, hepatic cirrhosis, heart failure, diabetes mellitus and impotence. Early diagnosis and institution of phlebotomy treatments will prevent these manifestations and normalize life expectancy. Once organ damage is established many of the manifestations are irreversible. Since the early manifestations of the disease are subtle, a case can be made for routine screening. This conclusion is supported by cost-effectiveness analysis based on available data. A reasonable screening strategy would start with a serum transferrin saturation. A value ≥ 55% should trigger a repeat transferrin saturation in a fasting state and a serum ferritin level. If both these tests are abnormal, a liver biopsy with quantitative iron determination is the currently accepted confirmatory test.     

Arthropathy in hereditary hemochromatosis

Arthropathy is one of the leading clinical manifestations of hereditary hemochromatosis (HH). Although cirrhosis of the liver is crucial for mortality in patients with HH, arthropathy has the greatest impact on the quality of life.Several mutations in the HFE and other genes have recently been identified, and the prevalence of some of these mutations has already been investigated in population studies in greater detail. Even though cofactors other than genetic predisposition may play a role in the establishment of the disease, the new understanding of the genetic background of this iron storage disorder may help in identifying patients before the onset of clinical symptoms. Early initiation of iron depletion therapy, not effective in established arthropathy of HH, might prevent the manifestation of arthropathy or reduce its severity.     

Hypogonadism in hereditary hemochromatosis

Hypogonadism, usually hypogonadotropic in origin, is the most common nondiabetic endocrinopathy in hereditary hemochromatosis (HH). Early studies, usually evaluating small numbers of patients with advanced HH, report prevalence rates of 10-100%. The clinical presentation of HH has changed in recent years as a result of increased awareness and screening. We assessed the prevalence of hypogonadism in a large group of patients with HH diagnosed in a single center over the past 20 yr, the period of follow-up spanning the time before and after widespread screening was introduced and the HFE gene was recognized. Abnormally low plasma testosterone levels, with low LH and FSH levels, were found in nine of 141 (6.4%) male patients tested. Eight of nine (89%) had associated hepatic cirrhosis; three of nine (33%) had diabetes. Inappropriately low LH and FSH levels were found in two of 38 females (5.2%) in whom the pituitary-gonadal axis could be assessed. This is the largest detailed study of hypogonadism reported in HH. The lower prevalence of hypogonadism compared with other reported series reflects the earlier diagnosis of HH in an unselected group of patients attending a single center. Patients with lesser degrees of hepatic siderosis at diagnosis are unlikely to develop hypogonadism.     

非HFE相关遗传性血色病

遗传性血色病(HH)多为常染色体隐性遗传病,其特征是肠道铁吸收过多导致肝、胰、心及其它脏器铁过量沉积,引发肝硬化、内分泌疾病、心力衰竭、心律失常、关节病和皮肤色素沉着等临床表现.Ⅰ型HH最常见,由6号染色体HFE基因突变所致.非HFE相关HH是指无HFE致病性突变的几种表型相近但遗传学形式独特的HH,由于受累基因在铁代谢作用中的不同,较典型HH临床发病可能更早,表型表现度更严重.     

Advances in hereditary hemochromatosis

Hereditary hemocromatosis (HH) is a genetic disease with a recessive autosomic pattern, in which inadequate iron (Fe) absorption is made by the intestinal cell. As consequence of that process, takes place a progressive accumulation of metal in different organs, predominantly in the liver. This leads to an alteration of liver structure and function: cirrhosis and hepatocarcinoma (1). The gene implied in this pathology was identified (HFE) in 1996. This codes a similar molecule to the mayor histocompatibility complex type 1(MHC-T1 like) that can modulate the transport of PE binding the transferrin receptor. This progress allows a deep understanding of the molecular and cellular biology of the homeostasis of the Fe and its alterations in the NH. The diagnosis of disease by means of a genetic test let to carry out a familiar screening and to detect asymptomatic carriers. This makes possible to begin the appropriate treatment at early stages of the disease in order to avoid its consequences and offering a better quality of life to these patients.     

HFE-associated hereditary hemochromatosis.

Hereditary hemochromatosis is a common inherited disorder of the iron metabolism. Screening studies indicate that it has a prevalence of one in 200 to 400, depending on the population studied, and a carrier rate of about one in seven to one in 10. Feder et al identified the hereditary hemochromatosis gene (HFE) in 1996 and two candidate mutations; the C282Y mutation has been shown to be responsible for the majority of the hereditary hemochromatosis cases worldwide. The gene discovery has led to rapid advances in the field of iron metabolism. Although the basic defect is still not fully understood, much is known about the sequence of events leading to iron overload. Hereditary hemochromatosis is a major candidate for population screening and meets the screening criteria of the World Health Organization, and Wilson and Jungner. It is one of the most prevalent genetic diseases in white populations, and, importantly, early diagnosis and simple effective treatment allow normal life expectancy. The discovery of the HFE gene and the frequency of the single C282Y mutation as a cause of most cases of hereditary hemochromatosis allow the possibility of widespread genetic testing. However, the logistics, and the psychological and social consequence of this, coupled with incomplete expression of the genotype, necessitate further studies before population screening can be justified.     

Arthritis in hereditary hemochromatosis

Seven pedigrees with 45 members were evaluated for arthropathy associated with hereditary hemochromatosis (HC). Patients with symptomatic extraarticular disease were compared with asymptomatic patients who had evidence of HC on laboratory findings, and with normal subjects. Patients who were homozygous for HC were compared with heterozygous patients and normal subjects. HC arthritis does not appear to be an early predictor of disease, and chondrocalcinosis is a late manifestation of HC arthropathy.     

遗传性血色病分子机制的研究进展

遗传性血色病是由于基因变异引起铁代谢异常,进而造成多器官铁沉积.目前认为铁代谢转运主要由hepcidin-转铁蛋白(FPN)轴控制,血色病蛋白编码基因(HFE)、FPN受体2(TfR2)、血幼素(HJV)、HAMP(hepcidin的编码基因)基因突变都可以影响hepcidin水平.FPN突变也可引起铁超负荷,但机制有所不同.各调节蛋白的基因突变可引起不同的疾病表型.     

The immunogenetics of hereditary hemochromatosis

Hereditary hemochromatosis (HH), an iron overload disease caused by unregulated intestinal iron absorption, is a recessive HLA-linked disease. HH is the most common inherited metabolic disorder with one of every 400 to 500 individuals having both genes and being likely to develop the disease. Thus, although the product of the hemochromatosis gene is unknown, its mode of inheritance allows HLA-genotyping of the proband and his/her siblings to be highly predictive of the genetic propensity to develop the clinical features of HH. In view of the known immunoregulatory properties of iron and its binding proteins, it is important to determine if the high levels of storage iron in HH influence the immunosurveillance network in HH patients and whether that has any clinical relevance. We have defined certain alterations of the effector cells of the cellular arm of the immune system and have studied a patient with HH who had specific immune alterations, including delayed cutaneous-type hypersensitivity anergy, and was diagnosed with poorly differentiated adenocarcinoma of the stomach four years after his HH diagnosis. Those findings are consistent with the interpretation that in certain clinical situations of elevated body iron stores, the immunoregulatory balance or environment may be tipped in favor of growth and development of cancer cells.     

Risk of disease in siblings of patients with hereditary hemochromatosis.

BACKGROUND: Parents of hereditary hemochromatosis (HH) homozygote patients, who are predominantly HH heterozygotes, have been found to have an increased risk of colonic neoplasia, diabetes, stroke death, stomach cancer and leukemia. The health histories of siblings of HH patients are reported. METHODS: Individuals homozygous for HH were mailed questionnaires concerning the health histories of their siblings. Spouses of the HH homozygotes were asked to complete accompanying questionnaires concerning their siblings. The frequencies of serious illness and, when specified, each reported disease were determined by zygosity, odds ratios and 95% confidence intervals estimated. RESULTS: Data were available for 279 siblings known to be HH homozygotes (HHs), and 1,265 other siblings of HH patients, who are predominantly hemochromatosis heterozygotes (HHhet). Controls consisted of 1,338 spouse siblings in whom only the general population prevalence of HH homozygosity and heterozygosity existed. Odds ratios comparing HH strata to controls were elevated for serious illness (1.12 in HHhet, 1.71 in HHs), diabetes (0.78, 2.45), arthritis (2.10, 1.69), and hepatoma (1.06, 11.96). CONCLUSIONS: There was a significant trend for increased risk of serious illness among siblings of HH patients with increasing exposure to the HH gene, especially for diabetes, arthritis and hepatoma.     

Intrafamilial variation in hereditary hemochromatosis

A review of 57 families with hereditary hemochromatosis revealed three pairs of HLA-identical, sex-matched siblings in which the younger sibling demonstrated considerably more iron loading than the older sibling. Liver biopsy, chemical hepatic iron determination, iron absorption studies, and number of venesections required were used to support these observations. Nineteen pairs of HLA identical, sex-matched siblings homozygous for hemochromatosis were found in which the iron loading was more marked in the older sibling. There was no evidence of blood loss, difference in alcohol consumption, or dietary iron loading to explain the increased iron loading in the younger sibling. These three families demonstrate that the rate of iron accumulation may vary within a family and that the extent of iron loading in hereditary hemochromatosis is not solely dependent on the duration of iron accumulation.     

Recent advances in hereditary hemochromatosis

Hereditary hemochromatosis, a very common genetic defect in the Caucasian population, is characterized by progressive tissue iron overload which leads to irreversible organ damage if it is not treated in a timely manner. Recent developments in the field of molecular medicine have radically improved the understanding of the physiopathology and diagnosis of this disease. However, transferrin saturation and serum ferritin are still the most reliable tests for identifying subjects with hereditary hemochromatosis. Therapeutic phlebotomy is the mainstay of the treatment of this disease and the life expectancy of these patients is similar to that of the normal population if phlebotomy is started before the onset of irreversible organ damage. In this review we discuss the genetics, pathophysiology, diagnosis, clinical features, and management of hereditary hemochromatosis.