Iron overload in Sub-Saharan Africa: to what extent is it a public health problem?

Excessive deposition of Fe in the organs and tissues of Sub-Saharan Africans was first described in South Africa in 1929. Fe overload, or siderosis, was initially attributed to infections and to metallic poisoning (Cu, Sn, Zn), and then to malnutrition. In 1953 it was hypothesized that it was due primarily to excessive Fe intake derived from foods and drinks prepared in Fe vessels. Recently, in 1992 it was advanced that a gene distinct from any HLA-linked locus may also play a role. As to sequelae, in early research on series of hospital patients, the condition was linked to scurvy, osteoporosis, diabetes, cirrhosis, and latterly, to hepatocellular cancer and tuberculosis. Accordingly, many have concluded that Fe overload is responsible for considerable morbidity and mortality, that adventitious Fe intake should be reduced, and that phlebotomy be recommended for those severely affected. However, there are numerous limitations in the evidence. There are also problems in interpretation, since levels of Fe in the serum are affected additionally by a variety of factors: infection, inflammation, certain cancers and alcohol intake. These considerations complicate attempts to assess to what extent the associations described denote causation, and whether Fe overload has significant ramifications for ill in the general African population. While the adverse sequelae of overload may be less of significance than many believe, the precise pathogenicity of the phenomenon will remain uncertain until further investigations, including prospective studies, are undertaken.

Iron overload in porphyria cutanea tarda

BACKGROUND AND OBJECTIVE

Porphyria cutanea tarda (PCT) is a disorder of porphyrin metabolism associated with decreased activity of uroporphyrinogen decarboxylase (URO-D) in the liver. The relevance of iron in the pathogenesis of PCT is well established: iron overload is one of the factors that trigger the clinical manifestations of the disease and iron depletion remains the cornerstone of therapy for PCT. A role for genetic hemochromatosis in the pathogenesis of iron overload in PCT has been hypothesized in the past but only after the recent identification of the genetic defect causing hemochromatosis has the nature of this association been partially elucidated. This review will outline current concepts of the pathophysiology of iron overload in PCT as well as recent contributions to the molecular epidemiology of hemochromatosis defects in PCT.

EVIDENCE AND INFORMATION SOURCES

The authors of the present review have a long-standing interest in the pathogenesis, etiology and epidemiology of iron overload syndromes. Evidence from journal articles covered by the Science Citation Index(R) and Medline(R) has been reviewed and collated with personal data and experience.

STATE OF THE ART AND PERPECTIVES

Mild to moderate iron overload plays a key role in the pathogenesis of PCT. The recent identification of genetic mutations of the hemochromatosis gene (HFE) in the majority of patients with PCT confirms previous hypotheses on the association between PCT and hemochromatosis, allows a step forward in the understanding of the pathophysiology of the disturbance of iron metabolism in the liver of PCT patients, and provides an easily detectable genetic marker which could have a useful clinical application. Besides the epidemiological relevance of the association between PCT and hemochromatosis, however, it remains to be fully understood how iron overload, and in particular the cellular modifications of the iron status secondary to hemochromatosis mutations, affect the activity of URO-D, and how the altered iron metabolism interacts with the other two common triggers for PCT and etiological agents for the associated liver disease: alcohol and hepatitis viruses. The availability of a genetic marker for hemochromatosis will allow some of these issues to be addressed by studying aspects of porphyrins and iron metabolism in liver samples obtained from patients with PCT, liver disease of different etiology and different HFE genotypes, and by in vitro studies on genotyped cells and tissues.

Iron loading and disease surveillance

Iron is an oxidant as well as a nutrient for invading microbial and neoplastic cells. Excessive iron in specific tissues and cells (iron loading) promotes development of infection, neoplasia, cardiomyopathy, arthropathy, and various endocrine and possibly neurodegenerative disorders. To contain and detoxify the metal, hosts have evolved an iron withholding defense system, but the system can be compromised by numerous factors. An array of behavioral, medical, and immunologic methods are in place or in development to strengthen iron withholding. Routine screening for iron loading could provide valuable information in epidemiologic, diagnostic, prophylactic, and therapeutic studies of emerging infectious diseases.

Research priorities in hereditary hemochromatosis

The Working Group on Research Priorities used a formal nominal group technique to identify and prioritize the specific aims of applied research needed to provide the scientific basis for population screening for iron overload disorders. The most important applied research goal was characterization of the natural history of the relation between genotype and phenotype in hereditary hemochromatosis and other iron overload disorders. Three other important research objectives were development of an optimal approach to screening for iron overload; analyses of the cost-effectiveness of screening; and assessment of the ethical, legal, and social implications of screening. To achieve these specific aims, two research studies were recommended as being of the highest priority: a multicenter, cross-sectional, population-based study of the natural history of iron overload and a multicenter, case-control study of patients with disease manifestations potentially attributable to hereditary hemochromatosis in primary care and subspecialty clinics.

Evaluation of iron status in patients with chronic hepatitis C

AIM

To evaluate the prevalence of iron overload in chronic hepatitis C and its relationship with liver histology.

PATIENTS AND METHODS

Serum iron, unsaturated iron binding capacity and ferritin levels were determined in 204 consecutive anti-hepatitis C virus positive subjects, whereas hepatic iron concentration, hepatic histological grading and staging, hepatitis C virus genotypes were further assessed in a subgroup of 50 patients who underwent liver biopsy for chronic hepatitis.

RESULTS

An increase in the serum markers of iron metabolism was more frequently found in subjects with aminotransferase activities above the normal range, whereas hepatic iron overload, established by direct hepatic iron determination, was found only in 9/50 (18%) patients with chronic hepatitis C. No serum iron marker could reliably predict hepatic iron stores. Patients with mild iron overload usually showed active hepatitis and fibrosis, whereas iron overload was not present in patients without fibrosis or with very mild fibrosis. Two out of nine patients with iron overload were shown to be beta thalassaemia heterozygous, and two were heterozygous carriers of a putative haemochromatosis gene mutation (His63Asp).

CONCLUSIONS

Many anti-hepatitis C virus positive patients with elevated aminotransferase activities have serum ferritin levels above the normal range, but only a minority of patients with chronic hepatitis C have a mild iron overload. In chronic hepatitis C, a relationship does exist between hepatic iron content and liver fibrosis.

Distribution of transferrin saturations in the African-American population

To determine if transferrin saturations in African Americans may reflect the presence of a gene that influences iron metabolism, we analyzed the distribution of these values in 808 African Americans from the second National Health and Nutrition Survey. We tested for a mixture of three normal distributions consistent with population genetics for a major locus effect in which the proportion of normal homozygotes is p2; of heterozygotes, 2pq; of affected homozygotes, q2; and in which p+q = 1. Three subpopulations based on transferrin saturation were present (P < .0001) and the fit to a mixture of three normal distributions was good (P = .2). A proportion of .009 was included in a subpopulation with a mean +/- standard deviation transferrin saturation of 63.4% +/- 5.7% (postulated homozygotes for a gene that influences iron metabolism), while a proportion of .136 had an intermediate saturation of 38.0% +/- 5.7% (postulated heterozygotes) and .856 a saturation of 24.6% +/- 5.7% (postulated normal homozygotes). These proportions were consistent with population genetics because the sum of the square roots of the proportions with the lowest mean transferrin saturation (P = .925) and the highest (q = 0.093) was approximately 1 (1.018). The results are consistent with the presence in African Americans of a common locus that influences iron metabolism.

Iron-overload disease in infants involving fetal growth retardation, lactic acidosis, liver haemosiderosis, and aminoaciduria

BACKGROUND

Several cases of a distinctive lethal neonatal disorder have been found in the Children's Hospital, Helsinki, Finland. However, the combination of presenting features is not typical of any known metabolic disease. We have analysed all known cases of this disorder in the hospital since 1965 and in Finland since 1990 to define clinical features of the disease.

METHODS

We studied 17 newborn infants with severe growth retardation from 12 Finnish families and traced their genealogy. In addition to routine clinical studies, diagnostic workup included analysis of respiratory-chain function in isolated muscle mitochondria and necropsy specimens, pyruvate dehydrogenase complex activities in fibroblasts, analysis of aminoacids and organic acids in urine, staining of tissue samples for iron, and assay of liver iron content.

FINDINGS

The infants were born near term (mean 37.8 [SD 3] gestational weeks) but were severely growth retarded (birthweight 1690 [460] g--ie, -3.8 [SD 0.6] SD score for gestational age). By age 24 h, mean pH was 7.00 (0.12), lactate 12.2 (7.5) mmol/L, and pyruvate 121 (57) micromol/L. All had aminoaciduria and failed to thrive; nine died neonatally (age 2-12 days), and eight died in infancy (1-4 months). The liver of four infants showed microscopic haemosiderosis and increased iron content (2.8-5.5 mg iron/g dry weight). In those four infants serum ferritin concentration (1260-2700 microg/L) and transferrin saturation (61-100%) were high, transferrin concentration (0.54-0.76 g/L) was low.

INTERPRETATION

We describe a previously unrecognised clinical picture of a genetic disease, which presents with fetal growth retardation and lactic acidosis after birth. Genealogical studies indicate an autosomal-recessive mode of inheritance for this disease, which is distinct from other lactic acidoses, neonatal haemochromatosis, and hepatitis. The diagnostic criteria are: fetal growth retardation; severe lactic acidosis; aminoaciduria; iron overload with haemosiderosis of the liver, increased serum ferritin concentration, hypotransferrinaemia, and increased transferrin iron saturation. Organ dysfunction may be partly due to the toxic effects of free iron.

African iron overload and hepatocellular carcinoma (HA-7-0-080)

Although HLA-linked hemochromatosis greatly increases the risk for hepatocellular carcinoma in people of European ancestry, iron overload in Africa is not thought to be etiologically related to this malignancy. To determine if African iron overload may be associated with hepatocellular carcinoma, we reviewed 320 consecutive diagnostic liver biopsies processed at the University of Zimbabwe from 1992 to 1994 and we selected for analysis 215 biopsies from adults that were suitable for the histological assessment of hepatocellular iron. Subjects were stratified according to hepatocellular iron grades of 0-2+ (normal levels to mild siderosis; n = 183) and grades of 3+ and 4+ (distinctly elevated levels consistent with iron overload; n = 32). Thirty-six subjects had hepatocellular carcinoma. Logistic regression modeling revealed a significant association between iron overload and hepatocellular carcinoma after adjustment for age, sex and and the presence of portal fibrosis or cirrhosis (p = 0.041). The odds of hepatocellular carcinoma in subjects with iron overload was 3.1 (95% confidence interval of 1.05-9.4) times that of subjects without iron overload. While we could not test for exposure to viral hepatitis or to aflatoxins in this study, our findings suggest that iron overload may be a risk factor for hepatocellular carcinoma in Africa.

High prevalence of hepatitis C virus type 1b in Italian patients with Porphyria cutanea tarda

BACKGROUND

A strong association between sporadic porphyria cutanea tarda and chronic hepatitis C virus infection was recently described in Italy, France and Spain.

AIMS

To explore whether hepatitis C virus genotype plays a role in porphyria cutanea tarda complicating chronic hepatitis C.

PATIENTS

Forty-seven hepatitis C virus-positive porphyria cutanea tarda patients and a control group of 45 patients of similar age with hepatitis C virus-associated chronic liver disease.

METHODS

Comparison of frequency of hepatitis C virus genotypes in the two groups and in relation to the age of patients, hepatic histopathology and with the presence of other factors potentially able to trigger porphyria cutanea tarda.

RESULTS

A single genotype, hepatitis C virus 1b, was found to be present in nearly 90% of porphyria cutanea tarda-associated chronic liver disease, significantly exceeding the frequency of the same genotype in the control group (p = 0.0001). The presence of hepatitis C virus 1b was not related to the age of patients or disease severity as evaluated by hepatic histopathology.

CONCLUSIONS

Hepatitis C virus-associated chronic hepatitis found in the majority of Italian patients with porphyria cutanea tarda is usually sustained by hepatitis C virus genotype 1b. This viral strain might have a direct pathogenic role in inducing porphyria cutanea tarda or could increase the susceptibility of patients of other triggering factors such as iron overload or alcohol abuse.

Iron overload in patients with chronic viral hepatitis: how common is it?

OBJECTIVES

To establish the prevalence of increased hepatic iron content in patients with hepatitis C virus-related chronic hepatitis and to assess the accuracy of serum iron and ferritin in detecting tissue iron overload.

METHODS

Serum iron, serum ferritin, and hepatic iron content were determined in 81 consecutive patients undergoing liver biopsy for chronic ALT elevation and hepatitis C virus infection. Moreover, in a subgroup of 28 patients, outcome of a 6-month course of interferon (IFN) treatment (6 million U of recombinant IFN, three times weekly) was determined after a mean follow-up of 24 +/- 6 months and the outcome was compared with the pretreatment values of hepatic iron content.

RESULTS

Elevated serum iron or ferritin levels were detected in approximately 40% of patients, but elevated hepatic iron content was observed in only eight patients (10%). One of these patients had a hepatic iron index > 1.9, indicating hemochromatosis. Liver iron content and serum iron levels were not correlated. No differences in hepatic iron content were observed among patients with a sustained response to IFN (seven patients), short-term responders (seven patients), or nonresponders (14 patients).

CONCLUSIONS

Ten percent of patients with chronic hepatitis C have elevated hepatic iron content. These patients cannot be identified using serum markers of iron status. The relationship between liver iron and response to IFN treatment requires further prospective investigations.

Spontaneous iron overload in Sprague-Dawley rats

In a review of the toxicological studies performed in our laboratory during the period 1986-1995, we occasionally observed significant iron overloading in the liver. Liver tissue was examined by light and electron microscopy, and the results were analyzed by sex and age (7, 9, 11, 19, 31, 59, and 111 wk). The intensity of iron overload increased with age: the accumulation began in pericanalicular siderosomes of periportal hepatocytes and extended progressively to the entire lobule and also to nonhepatocytic cells (Kupffer cells in sinusoids and macrophages around bile ducts in portal tracts) and occasionally with distortion of sinusoids by sideroblastic nodules and moderate enlargement of portal tracts in the oldest animals. No significant inflammatory infiltrates, degeneration, necrosis or fibrosis were noted. Hepatocyte pigmentation alone was prominent at 9 and 11 wk. The frequency of pigmentation of parenchymal and nonhepatocytic cells increased from 9 wk for females; in males, this was seen only at 111 wk. The intensity of pigmentation of nonhepatocytic cells versus parenchymal cells increased with aging. The frequency of those different types of iron overloading was higher for females up to 111 wk. The pathology of spontaneous iron overloading in the Sprague-Dawley rat, described here in spite of differences, has some similarities to that of human hereditary hemochromatosis.

Iron overload among a psychiatric outpatient population

BACKGROUND

Iron overload has been suggested to be an unrecognized cause of psychiatric morbidity. This study sought to estimate the prevalence of iron overload in a large outpatient psychiatric clinic.

METHOD

A retrospective review of screening blood chemistries was conducted on 661 active outpatients at a large, university outpatient psychiatric clinic to identify elevated iron status results (plasma iron, percentage of iron saturation) suggestive of iron overload. Patients with positive profiles were asked to undergo a subsequent blood chemistry to confirm positive results (plasma iron, percentage of iron saturation, plus plasma ferritin). Patients with positive repeated iron chemistry results were considered likely candidates for iron overload.

RESULTS

Twenty-one patients (3.2%) were identified as meeting one of the criteria suggestive of iron overload on initial screening reports. Thirty-one percent of those who underwent subsequent, confirmatory testing (5/16) continued to meet one of the criteria. On the basis of these results, we estimated a 1% (3.2 x 0.31) prevalence rate of likely candidates for iron overload. A review of these patients' charts indicated that they carried an unexpectedly high rate of bipolar affective disorder (80%) as a diagnosis and were, without exception, atypical in that they were resistant to conventional psychiatric treatment and lacked a family history for this disorder. The prevalence of positive iron overload profiles on a routine blood chemistry was similar to the prevalence of positive thyroid abnormalities based on TSH results in this population.

CONCLUSION

Blood chemistry profiles suggestive of iron overload may be associated with a small portion of treatment-resistant psychiatric patients. Routine screening for iron abnormalities, especially in treatment-resistant patients, should be considered. Further studies are required to determine the causal association, if any, between iron excess and primary psychiatric illnesses.

Iron overload in patients with chronic hepatitis C: a clinicopathologic study

Recent studies suggest that increased hepatic iron may impair the response to interferon therapy in patients with chronic hepatitis C. We reviewed the records and liver biopsies of 72 patients with chronic hepatitis C to determine the prevalence of iron overload and to evaluate whether there is a correlation between serum and hepatic iron concentrations and activity of liver disease. Patients with other causes of liver disease or iron overload were excluded. Necroinflammatory activity and fibrosis were evaluated using modified Knodell score. Hepatic iron was assessed using Brissot's grading system. Increased serum iron and ferritin levels were found in 29% and 43% patients, respectively. Hepatic iron grades 0, I, II, III, and IV were present in 37%, 35%, 25%, 3%, and 0% of patients, respectively. A significant correlation was found between hepatic iron grade and serum ferritin (P = .0001). There was no correlation between hepatic iron grade and histological activity index or fibrosis score. In summary, we found a high proportion of patients with chronic hepatitis C had mild to moderate increase in hepatic iron content even when patients with alcoholism and recurrent transfusions were excluded. However, very few patients had severely increased iron load.

Lack of association between porphyria cutanea tarda and alpha 1-antitrypsin deficiency

OBJECTIVE

To determine whether alpha 1-antitrypsin deficiency is involved in the pathogenesis of chronic liver disease in patients with porphyria cutanea tarda and in their recently described high prevalence of hepatitis C virus infection.

DESIGN

Consecutive patients diagnosed as having porphyria cutanea tarda and chronic liver disease.

SETTING

A northern Italian hospital.

METHODS

alpha 1-antitrypsin phenotypes were characterized by isoelectric focusing and the results confirmed by DNA analysis in 63 Italian patients with porphyria cutanea tarda.

RESULTS

alpha 1-antitrypsin phenotypes different from the normal one were found in 13% of the patients. This prevalence did not differ from that in control subjects (9%). Clinical characteristics of patients with porphyria cutanea tarda with normal or altered alpha 1-antitrypsin phenotype, including age of presentation of the disease, prevalence of hepatitis C virus infection, liver histology, prevalence of iron overload and hepatocellular carcinoma occurrence, did not differ significantly.

CONCLUSION

alpha 1-antitrypsin does not seem to play a role in the pathogenesis of chronic liver disease and hepatitis C virus infection in patients with porphyria cutanea tarda. Patients in whom the two defects coexist do not have a more severe disease.

Relationship between serum ferritin, alcohol intake, and social status in 2235 Danish men and women

The objective was to examine the relationships between serum ferritin, alcohol intake, and socioeconomic factors (school education, occupational education, occupation, income, marital status, cohabitation status, housing, social class) in a population survey performed in Copenhagen County during 1982-1984. The participants were selected at random from the census register and comprised 2235 healthy Danish individuals, non-blood donors (1044 men, 1191 women) in cohorts being 30, 40, 50, and 60 years old. The participants gave a detailed social and medical history and had a clinical examination including blood samples. In all age-groups, men had significantly higher serum ferritin and alcohol intake than women. In men, there was no relationship between serum ferritin and social class. Significant relationships were observed between ferritin and occupation (unemployed and self-employed men had higher ferritin than those with other occupations) and ferritin and income (in younger men, ferritin displayed a steady increase with income). None of the social variables were related to the prevalence of iron deficiency or iron overload. Alcohol intake was related to occupation and income, but not to social class. In women, none of the social variables showed any significant relationship to ferritin levels or iron overload. The prevalence of small iron stores (serum ferritin < or = 30 micrograms/l) was lower and the intake of alcohol was higher in women from high social classes. In both men and women, serum ferritin displayed highly significant positive correlations with alcohol intake. Likewise, the prevalence of iron overload (serum ferritin > 90th percentile) was closely correlated to alcohol intake. In conclusion, socioeconomic factors per se had a minor influence on serum ferritin levels and iron status in Danes. The distinct association between alcohol intake and serum ferritin levels should be considered in future iron status surveys.

New advances in iron metabolism, iron deficiency, and iron overload

Rapid advances were made in understanding the molecular and cellular bases of iron metabolism and its disorders. Molecular mechanisms for the cellular uptake, storage, and utilization of iron were clarified in investigations of the structure and functions of transferrin, transferrin receptor, ferritin, erythroid delta-aminolevulinic acid synthase, and the RNA-binding protein termed the iron responsive-element binding protein. Evidence was obtained that a nuclear DNA-binding protein, NF-E2, may be involved in the regulation of both hemoglobin synthesis in erythroid cells and of iron absorption in the intestine. Clinically, progress was made in improving the diagnosis and management of both iron deficiency and iron overload, with studies of the usefulness of serum transferrin receptor measurements, of a new therapeutic preparation of iron using a "gastric delivery system," and of the development of new orally active iron-chelating agents.