Iron overload in an African American woman with SS hemoglobinopathy and a promoter mutation in the X-linked erythroid-specific 5-aminolevulinate synthase (ALAS2) gene

Sideroblastic anemia: functional study of two novel missense mutations in ALAS2

BACKGROUND

X-linked sideroblastic anemia (XLSA) is a disorder characterized by decreased heme synthesis and mitochondrial iron overload with ringed sideroblasts in bone marrow. XLSA is caused by mutations in the erythroid-specific gene coding 5-aminolevulinate synthase (ALAS2). Anemia in XLSA is extremely variable, characteristically microcytic and hypochromic with poikilocytosis, and the red blood cell distribution width is increased and prominent dimorphism of the red cell population. Anemia in XLSA patients responds variably to supplementation with pyridoxine.

METHODS AND RESULTS

We report four patients with XLSA and three mutations in ALAS2: c.611G>A (p.Arg204Gln), c.1218G>T (p.Leu406Phe) and c.1499A>G (p.Tyr500Cys). The in silico predictions of three ALAS2 mutations and the functional consequences of two ALAS2 mutations were assessed. We performed in silico analysis of these mutations using ten different softwares, and all of them predicted that the p.Tyr500Cys mutation was deleterious. The in vitro prokaryotic expression showed that the p.Leu406Phe and p.Tyr500Cys mutations reduced the ALAS2 specific activity (SA) to 14% and 7% of the control value, respectively.

CONCLUSION

In view of the results obtained in this study, a clear relationship between genotype and phenotype cannot be established; clinical variability or severity of anemia may be influenced by allelic variants in other genes or transcription factors and environmental conditions.

A comparison between whites and blacks with severe multi-organ iron overload identified in 16,152 autopsies

BACKGROUND & AIMS

Little is known about differences in the prevalence of severe iron overload at death in whites and blacks. We evaluated data and samples from 16,152 autopsies (8484 whites, 7668 blacks) performed at a single university hospital.

METHODS

Cases of severe multi-organ iron overload were identified by review of autopsy protocols and Perls-stained tissue specimens, analysis of hepatocyte and Kupffer cell iron levels, and measurement of liver tissue iron concentrations.

RESULTS

We analyzed autopsy data from 10,345 adults (age > or =21 years), 1337 children (1-20 years), and 4470 infants (<1 year). Iron overload without reports of excessive exogenous iron was observed in 18 adults; the prevalence in whites and blacks was 0.0019 and 0.0015, respectively (P = .6494). Twenty-nine adults and 2 children had iron overload with reports of excessive exogenous iron. In adults, the prevalences of iron overload with reports of excessive exogenous iron in whites and blacks were 0.0040 and 0.0013, respectively (P = .0107). Among adults, the prevalence of cirrhosis was 6-fold greater in those with iron overload. In adults with severe iron overload, 67% without reports of excessive exogenous iron and 14% with reports of excessive exogenous iron died of hepatic failure or cardiomyopathy caused by siderosis. The overall prevalence of deaths caused by severe iron overload in whites and blacks was 0.0021 and 0.0009, respectively (P = .0842).

CONCLUSIONS

The prevalence of severe iron overload without reports of excessive exogenous iron did not differ significantly between whites and blacks. The prevalence of iron overload with reports of excessive exogenous iron was greater in whites. Hepatic failure and cardiomyopathy were common causes of death in severe iron overload cases.

SLC40A1 Q248H allele frequencies and Q248H-associated risk of non-HFE iron overload in persons of sub-Saharan African descent

The ferroportin polymorphism SLC40A1 Q248H (exon 6, cDNA 744G-->T; Gln248His) occurs in persons of sub-Saharan African descent with and without iron overload, and is associated with elevated serum ferritin concentrations (SF). However, the risk of iron overload associated with Q248H has not been defined. We tabulated previously reported Q248H allele frequency estimates in African-Americans and Native Africans, and computed the risk of iron overload associated with Q248H in subjects who lacked HFE C282Y. The aggregate Q248H allele frequency in 1038 African-Americans in two cohorts from Alabama and one cohort each from Washington, DC and California was 0.0525 (95% CI: 0.0451, 0.0652); there was no significant difference in frequencies across these cohorts. The aggregate frequency in 259 Natives from southeast Africa in two cohorts was 0.0946 (95% CI: 0.0694, 0.1198); the difference between the frequencies of these cohorts was not significant. The aggregate Q248H frequencies in African-Americans and Native Africans differed significantly (0.0525 vs. 0.0946, respectively; p=0.0021). There were reports of 24 unrelated African-Americans and 15 unrelated Native Africans without HFE C282Y who had iron overload. In African-Americans, the odds ratio (OR) of Q248H-associated risk of iron overload using 610 C282Y-negative control subjects unselected for SF was 1.57 (95% CI: 0.52, 4.72; p=0.29). In Native Africans, the OR using 208 control subjects unselected for SF was 1.05 (95% CI: 0.28, 3.90; p=0.58). We conclude that the frequency of SLC40A1 Q248H is significantly lower in African-Americans than in Native Africans. Although OR estimates of iron overload in African-Americans and Native Africans with Q248H were greater than unity, the increased OR were not statistically significant.

Optimal management strategies for chronic iron overload

Iron overload is characterised by excessive iron deposition and consequent injury and dysfunction of target organs, especially the heart, liver, anterior pituitary, pancreas and joints. Iron overload disorders are common worldwide and occur in most major race/ethnicity groups. Physiological mechanisms to excrete iron are very limited. Thus, all patients with iron overload need safe and effective treatment that is compatible with their co-existing medical conditions. Treatments for iron overload include phlebotomy and erythrocytapheresis that remove iron predominantly as haemoglobin, and chelation therapy with drugs that bind excess iron selectively and increase its excretion. The most important potential benefits of therapy are preventing deaths due to cardiac siderosis and hepatic cirrhosis. Preventing iron-related injury to endocrine organs is critical in children. Successful treatment or prevention of iron overload increases quality of life and survival in many patients. This article characterises the major categories of iron overload disorders, tabulates methods to evaluate and treat iron overload, and describes treatment options for iron overload disorders. Research needed to advance knowledge about treatment of iron overload is proposed.

Chelation therapy for iron overload

Iron overload is characterized by excessive iron deposition and consequent injury and dysfunction of the heart, liver, anterior pituitary, pancreas, and joints. Because physiologic mechanisms to excrete iron are very limited, patients with iron overload and its complications need safe, effective therapy that is compatible with their coexisting medical conditions. The availability of three licensed iron chelation drugs (one parenteral, two oral) and the development and clinical investigation of other oral chelators represent new opportunities to prevent or manage iron overload in patients with heritable types of severe anemia, such as beta-thalassemia major and sickle cell disease, and for the formulation of alternatives to phlebotomy therapy for patients with iron overload associated with the HFE gene and other adult age-of-onset types of hemochromatosis, African iron overload, and African-American iron overload.

Iron overload and prolonged ingestion of iron supplements: clinical features and mutation analysis of hemochromatosis-associated genes in four cases

We evaluated and treated four white adults (one man, three women) who had iron overload associated with daily ingestion of iron supplements for 7, 15, 35, and 61 years, respectively. We performed HFE mutation analysis to detect C282Y, H63D, and S65C in each patient; in two patients, HFE exons were sequenced. In two patients, direct sequencing was performed to detect coding region mutations of TFR2, HAMP, FPN1, HJV, and ALAS2. Patients 1-4 ingested 153, 547, 1,341, and 4,898 g of inorganic iron as supplements. Patient 1 had hemochromatosis, HFE C282Y homozygosity, and beta-thalassemia minor. Patient 2 had spherocytosis and no HFE coding region mutations. Patient 3 had no anemia, a normal HFE genotype, and no coding region mutations in HAMP, FPN1, HJV, or ALAS2; she was heterozygous for the TFR2 coding region mutation V583I (nt 1,747 G-->A, exon 15). Patient 4 had no anemia and no coding region mutations in HFE, TFR2, HAMP, FPN1, HJV, or ALAS2. Iron removed by phlebotomy was 32.4, 10.4, 15.2, and 4.0 g, respectively. There was a positive correlation of log(10) serum ferritin and the quantity of iron removed by phlebotomy (P = 0.0371). Estimated absorption of iron from supplements in patients 1-4 was 20.9%, 1.9%, 1.1%, and 0.08%. We conclude that the clinical phenotypes and hemochromatosis genotypes of adults who develop iron overload after ingesting iron supplements over long periods are heterogeneous. Therapeutic phlebotomy is feasible and effective, and would prevent complications of iron overload.

Disparate phenotypic expression of ALAS2 R452H (nt 1407 G → A) in two brothers, one with severe sideroblastic anemia and iron overload, hepatic cirrhosis, and hepatocellular carcinoma

We report the case of a man with severe X-linked sideroblastic anemia, severe iron overload, and hepatic cirrhosis who died of hepatocellular carcinoma. Evaluation of family members using DNA sequencing revealed that he was hemizygous for the novel ALAS2 mutation R452H (exon 9; nt 1407 G --> A). The proband's brother, an ALAS2 R452H hemizygote, had mild anemia and mild iron overload. Four female relatives were ALAS2 R452H heterozygotes, but they had mild or no anemia and no iron overload. Sequencing of TFR2, HFE, FPN1 (SLC40A1), HAMP, HJV, and the erythrocyte pyruvate kinase genes of family members was also performed. We thus detected the novel TFR2 missense mutation I449V (exon 10; nt 1345 A --> G) in the proband's wife and daughter, neither of whom had anemia or iron overload. Possible explanations for the disparate red blood cell and iron phenotypes of the proband and his family members are discussed.

Three kinships with ALAS2 P520L (c. 1559 C → T) mutation, two in association with severe iron overload, and one with sideroblastic anemia and severe iron overload

Mutations in aminolevulinate synthase 2 (ALAS2) are usually associated with sideroblastic anemia and iron overload. The objective of this study was to determine if "mild" mutations in ALAS2 might increase the severity of primary iron overload. Direct sequencing of the ALAS2 gene was performed on 24 subjects with primary hemochromatosis and one subject with sideroblastic anemia with severe iron overload. We identified a novel mutation P520L (c. 1559 C --> T) in ALAS2 in three subjects. Two had severe iron overload and no anemia: one also had HFE C282Y homozygosity, and the other was wildtype for HFE and other iron-related genes. The third subject had sideroblastic anemia with iron overload, and was hemizygous for both P520L and R560H (c. 1679 G --> A) mutations in ALAS2. The P520L mutation was found at a frequency of 0.0013 (741 alleles) in white control subjects, but was not found in 158 alleles from black control subjects. The proline in this position is highly conserved across species from humans to zebrafish. However, genotype/phenotype studies of the families demonstrate that the P520L mutation alone has no iron-associated phenotype, but it may act as a modifier of iron overload in the presence of mutations in HFE or other uncharacterized hemochromatosis genes. Thus, ALAS2 mutations might contribute to more severe iron loading in persons with primary hemochromatosis.

A juvenile hemochromatosis patient homozygous for a novel deletion of cDNA nucleotide 81 of hemojuvelin

BACKGROUND

A 25-year-old woman of English/Irish background was diagnosed with hemochromatosis. She manifested hypogonadotrophic hypogonadism and congestive heart failure. Although there were abnormal liver function tests, no cirrhosis was present. The patient has been treated intermittently by phlebotomy for 24 years. The aim of this study was to investigate the genetic basis of the patient's iron overload disease.

METHODS

Genetic analysis was performed by direct sequencing of the genes for hemojuvelin, HFE, hepcidin, ferroportin and transferrin receptor 2.

RESULTS AND CONCLUSIONS

Molecular analysis showed that the patient was homozygous for a previously undescribed mutation of HJV, the gene encoding hemojuvelin. This mutation, nt 81G deletion, causes a frameshift encoding 23 additional irrelevant amino acids and premature termination. No mutations were found in the other hemochromatosis genes, hepcidin, HFE, ferroportin or transferrin receptor 2, which might have contributed to her iron overload.

Genetic background of primary iron overload syndromes in Japan

The different prevalences of iron overload syndromes between Caucasians and Asians may be accounted for by the differences in genetic background. The major mutation of hemochromatosis in Celtic ancestry, C282Y of HFE, was reported in a Japanese patient. Five patients of 3 families with the hepatic transferrin receptor gene (TFR2)-linked hemochromatosis were found in different areas of Japan, suggesting that TFR2 is a major gene in Japanese people. Three patients with mutations in the hemojuvelin gene, HJV, showed also middle-age-onset hemochromatosis. A heterozygous mutation in the H ferritin gene, FTH1, was found in a family of 3 affected patients. Another autosomal dominant SLC40A1-linked hyperferritinemia (ferroportin disease) was found in 3 patients of 2 families. Two patients with hemochromatosis were free from any mutations in the genes investigated. In conclusion, the genetic backgrounds of Japanese patients with primary iron overload syndromes were partially clarified, showing some phenotype-genotype correlations.

Stainable hepatic iron in 341 African American adults at coroner/medical examiner autopsy

Background

Results of previous autopsy studies indicate that increased hepatic iron stores or hepatic iron overload is common in African Americans dying in hospitals, but there are no reports of hepatic iron content in other cohorts of African Americans.

Methods

We investigated the prevalence of heavy liver iron deposition in African American adults. Using established histochemical criteria, we graded Perls' acid ferrocyanide-reactive iron in the hepatocytes and Kupffer cells of 341 consecutive African American adults who were autopsied in the coroner/medical examiner office. Heavy staining was defined as grade 3 or 4 hepatocyte iron or grade 3 Kupffer cell iron.

Results

There were 254 men and 85 women (mean age ± 1 SD: 44 ± 13 y vs. 48 ± 14 y, respectively; p = 0.0255); gender was unstated or unknown in two subjects. Approximately one-third of subjects died of natural causes. Heavy staining was observed in 10.2% of men and 4.7% of women. 23 subjects had heavy hepatocyte staining only, six had heavy Kupffer cell staining only, and one had a mixed pattern of heavy staining. 15 subjects had histories of chronic alcoholism; three had heavy staining confined to hepatocytes. We analyzed the relationships of three continuous variables (age at death in years, hepatocyte iron grade, Kupffer cell iron grade) and two categorical variables (sex, cause of death (natural and non-natural causes)) in all 341 subjects using a correlation matrix with Bonferroni correction. This revealed two positive correlations: hepatocyte with Kupffer cell iron grades (p < 0.01), and male sex with hepatocyte iron grade (p < 0.05). We also analyzed the relationship of steatosis, inflammation, and fibrosis/cirrhosis in 30 subjects with heavy iron staining using a correlation matrix with Bonferroni correction. There were significant positive correlations of steatosis with inflammation (r = 0.5641; p < 0.01), and of inflammation with fibrosis/cirrhosis (r = 0.6124; p < 0.01).

Conclusions

The present results confirm and extend previous observations that heavy liver iron staining is relatively common in African Americans. The pertinence of these observations to genetic and acquired causes of iron overload in African Americans is discussed.