Altered Erythropoiesis in Mouse Models of Type 3 Hemochromatosis.

Type 3 haemochromatosis (HFE3) is a rare genetic iron overload disease which ultimately lead to compromised organs functioning. HFE3 is caused by mutations in transferrin receptor 2 (TFR2) gene that codes for two main isoforms (Tfr2α and Tfr2ß). Tfr2α is one of the hepatic regulators of iron inhibitor hepcidin. Tfr2ß is an intracellular isoform of the protein involved in the regulation of iron levels in reticuloendothelial cells. It has been recently demonstrated that Tfr2 is also involved in erythropoiesis. This study aims to further investigate Tfr2 erythropoietic role by evaluating the erythropoiesis of two Tfr2 murine models wherein either one or both of Tfr2 isoforms have been selectively silenced (Tfr2 KI and Tfr2 KO). The evaluations were performed in bone marrow and spleen, in 14 days' and 10 weeks' old mice, to assess erythropoiesis in young versus adult animals. The lack of Tfr2α leads to macrocytosis with low reticulocyte number and increased hemoglobin values, together with an anticipation of adult BM erythropoiesis and an increased splenic erythropoiesis. On the other hand, lack of Tfr2ß (Tfr2 KI mice) causes an increased and immature splenic erythropoiesis. Taken together, these data confirm the role of Tfr2α in modulation of erythropoiesis and of Tfr2ß in favoring iron availability for erythropoiesis.

Deferasirox treatment improved the hemoglobin level and decreased transfusion requirements in four patients with the myelodysplastic syndrome and primary myelofibrosis.

Transfusion-induced iron overload is a frequent problem that clinicians have to face in the treatment of patients affected by both myelodysplastic syndrome (MDS) and primary myelofibrosis (PMF). Different options are currently available for chelation therapy, e.g. oral once-daily administration of the iron chelator deferasirox. In 3 patients with MDS and 1 patient with PMF, deferasirox therapy resulted in an improvement in the hemoglobin level and a reduction in transfusion dependence. Our data open new insights regarding the benefit of iron chelation therapy not only for transfusional iron overload of myelodysplastic and myelofibrotic patients but also for the increase in hemoglobin levels. The biological mechanism of action of deferasirox, an effect which is not shared by other iron chelators, is still obscure and requires further investigations.

Juvenile hemochromatosis due to G320V/Q116X compound heterozygosity of hemojuvelin in an Irish patient.

Hemojuvelin (HJV) is a recently discovered gene responsible for 1q-linked juvenile hemochromatosis. The majority of mutations characterized in this gene are rare and private, except G320V, identified in patients from different countries. Here, we report the clinical features and the molecular study of a young Irish patient presenting with severe cardiac disease related to iron overload. We sequenced the coding region and the exon-intron boundaries of genes associated with juvenile hemochromatosis, HAMP and HJV encoding hepcidin and hemojuvelin respectively. Two heterozygous HJV mutations were identified: the G320V mutation and the new Q116X mutation that cause a premature stop codon in the protein. This finding increases the number of mutations identified in HJV gene and underlines that the G320V is a recurrent mutation, even in Northern Europe.

New mutations inactivating transferrin receptor 2 in hemochromatosis type 3.

Hereditary hemochromatosis usually results from C282Y homozygosity in the HFE gene on chromosome 6p. Recently, a new type of hemochromatosis (HFE3) has been characterized in 2 unrelated Italian families with a disorder linked to 7q. Patients with HFE3 have transferrin receptor 2 (TFR2) inactivated by a homozygous nonsense mutation (Y250X). Here the identification of 2 new TFR2 mutations is reported. In a large inbred family from Campania, a frameshift mutation (84-88 insC) in exon 2 that causes a premature stop codon (E60X) is identified. In a single patient with nonfamilial hemochromatosis, a T-->A transversion (T515A), which causes a Methionine-->Lysine substitution at position 172 of the protein (M172K), has been characterized. TFR2 gene gives origin to 2 alternatively spliced transcripts-the alpha-transcript, which may encode a transmembrane protein, and the beta-transcript, a shorter, possibly intracellular variant. Based on their positions, the effects of the identified mutations on the 2 TFR2 forms are expected to differ. Y250X inactivates both transcripts, whereas E60X inactivates only the alpha-form. M172K has a complex effect: it causes a missense in the alpha-form, but it may also prevent the beta-form production because it affects its putative initiation codon. Analysis of the clinical phenotype of 13 HFE3 homozygotes characterized at the molecular level has shown a variable severity, from nonexpressing patients to severe clinical complications. The identification of new mutations of TFR2 confirms that this gene is associated with iron overload and offers a tool for molecular diagnosis in patients without HFE mutations.

Linkage to chromosome 1q in Greek families with juvenile hemochromatosis.

Hereditary hemochromatosis (HH) is a genetically heterogeneous disease. The HFE gene resides on chromosome 6 and its mutations account for the majority of HH cases in populations of northern European ancestry. Recently, two new types of hemochromatosis have been identified: Juvenile hemochromatosis (JH or HFE2), which maps to chromosome 1q21, and an adult form defined as HFE 3, which results from mutations of the TFR 2 gene, located at 7q22. We have performed a linkage study in five unrelated families of Greek origin with non-HFE hemochromatosis. Linkage at the chromosome 1q21 JH locus was detected in affected members with the use of polymorphic markers. Comparison of haplotypes between Greek and Italian JH patients revealed the presence of a common haplotype. However, the fact that many other haplotypes carrying the JH defect were observed in the two populations indicates that the respective mutations may have occurred in different genetic backgrounds. We suggest that hemochromatosis patients without HFE mutations should be evaluated for other possible types of hemochromatosis since hemochromatosis type 3 (HFE3) has a clinical appearance similar to HFE 1, and JH may have a late onset in some cases.

Exclusion of ZIRTL as candidate gene of juvenile hemochromatosis and refinement of the critical interval on 1q21.

Hemochromatosis type 2 (HFE2) or juvenile hemochromatosis (JH) is a rare recessive disorder that causes iron overload, characterized by early onset and severe clinical course. The JH locus maps to chromosome 1q, in a 4-cM region encompassing markers D1S442 and D1S2347. Recently a gene named ZIRTL has been characterized and mapped to 1q21. This gene belongs to a family of divalent metal ion-transporting genes that encode for proteins involved in transport of different metals, including iron. Thus, the ZIRTL gene represents a positional and functional candidate for JH. Here we further restrict the candidate region through segregation analysis of two new polymorphic markers and haplotype analysis in JH families. Furthermore, we exclude ZIRTL as a JH candidate gene showing that it maps outside the critical interval and that its genomic sequence is normal in three patients.

A pilot C282Y hemochromatosis screening in Italian newborns by TaqMan technology.

Hereditary hemochromatosis (HH) is a disorder of iron metabolism that leads to iron overload in middle age and can be caused by homozygosity for the C282Y mutation in the HFE gene. Preliminary studies have estimated the frequency of this mutation at 0.5-1% in Italy, but this has not been verified on a large sample. We analyzed 1,331 Italian newborns for the C282Y mutation in the HFE gene using dried blood spots (DBS) from the Neonatal Screening Center in Turin, Italy. The mutation was assessed using a semi-automatable 5'-nuclease assay (TaqMan technology). We detected 55 heterozygotes and no homozygotes in our sampling, resulting in an overall frequency of 2.1% +/- 0.6 for the C282Y allele. Differences in allele frequency were observed, and ranged from 2.7% +/- 1.3 in samples from Northern Italy, to 1.7% +/- 0.9 in samples from Central-Southern Italy. The low frequency of the at-risk genotype for iron overload suggests that genetic screening for HFE in Italy would not be cost effective. The present study, in addition to defining C282Y frequency, documents detection of the major HFE mutation on routine DBS samples from neonatal screening programs using a semi-automatable, rapid, reliable, and relatively inexpensive approach.

The gene TFR2 is mutated in a new type of haemochromatosis mapping to 7q22.

Haemochromatosis is a common recessive disorder characterized by progressive iron overload, which may lead to severe clinical complications. Most patients are homozygous for the C282Y mutation in HFE on 6p (refs 1-5). A locus for juvenile haemochromatosis (HFE2) maps to 1q (ref. 7). Here we report a new locus (HFE3) on 7q22 and show that a homozygous nonsense mutation in the gene encoding transferrin receptor-2 (TFR2) is found in people with haemochromatosis that maps to HFE3.

A new mutation (G51C) in the iron-responsive element (IRE) of L-ferritin associated with hyperferritinaemia-cataract syndrome decreases the binding affinity of the mutated IRE for iron-regulatory proteins.

Hereditary hyperferritinaemia-cataract syndrome is an autosomal dominant disorder characterized by a constitutively increased synthesis of L-ferritin in the absence of iron overload. The disorder is associated with point mutations in the iron-responsive element (IRE) of L-ferritin mRNA. We report a new mutation, G51C, identified in two members of a Canadian family, presenting a moderate increase in serum ferritin and a clinically silent bilateral cataract. Gel retardation assays showed that the binding of the mutated IRE to iron-regulatory proteins (IRPs) was reduced compared with the wild type. Structural modelling predicted that the G51C induces a rearrangement of base pairing at the lateral bulge of the IRE structure which is likely to modify IRE conformation.

Recurrent mutations in the iron regulatory element of L-ferritin in hereditary hyperferritinemia-cataract syndrome.

BACKGROUND AND OBJECTIVE: Hereditary hyperferritinemia-cataract syndrome (HHCS) is an autosomal dominant disorder characterized by bilateral cataracts and increased serum and tissue L-ferritin, in the absence of iron overload. The deregulation of ferritin production is caused by heterogeneous mutations in the iron regulatory element (IRE) of L-ferritin that interfere with the binding of iron regulatory proteins. DESIGN AND METHODS: We have identified several patients from three unrelated Italian families with HHCS. Iron parameters were assessed by standard methods. The IRE element of L-ferritin was amplified by PCR using appropriate primers and directly sequenced. RESULTS: Ferritin levels ranged from 918 microg/L to 2490 microg/L in the patients studied. In one family bilateral cataracts were diagnosed early in life, whereas in the others cataracts were diagnosed around 40-50 years. The female proband of family 3 presented with a severe iron deficiency anemia, which was unrecognized because of the increased ferritin values. Sequencing of the IRE element of L-ferritin in the probands of the three families identified three different nucleotide substitutions (+32 GAE A, +40 AAE G and +39 CT) in the IRE of L-ferritin. These mutations have already been reported in unrelated subjects of different ethnic origins. INTERPRETATION AND CONCLUSIONS: Our findings are consistent with recurrent mutations associated with HHCS and underline the importance of this syndrome in the differential diagnosis of unexplained hyperferritinemia. In addition, the findings highlight the role played by transferrin saturation in the diagnosis of iron deficiency in these patients.

Juvenile hemochromatosis locus maps to chromosome 1q.

Juvenile hemochromatosis (JH) is an autosomal recessive disorder that leads to severe iron loading in the 2d to 3d decade of life. Affected members in families with JH do not show linkage to chromosome 6p and do not have mutations in the HFE gene that lead to the common hereditary hemochromatosis. In this study we performed a genomewide search to map the JH locus in nine families: six consanguineous and three with multiple affected patients. This strategy allowed us to identify the JH locus on the long arm of chromosome 1. A maximum LOD score of 5.75 at a recombination fraction of 0 was detected with marker D1S498, and a LOD score of 5. 16 at a recombination fraction of 0 was detected for marker D1S2344. Homozygosity mapping in consanguineous families defined the limits of the candidate region in an approximately 4-cM interval between markers D1S442 and D1S2347. Analysis of genes mapped in this interval excluded obvious candidates. The JH locus does not correspond to the chromosomal localization of any known gene involved in iron metabolism. These findings provide a means to recognize, at an early age, patients in affected families. They also provide a starting point for the identification of the affected gene by positional cloning.

Inherited HFE-unrelated hemochromatosis in Italian families.

Hemochromatosis (HH) is usually caused by the homozygous state for C282Y mutation in the HFE gene. A minority of iron loaded patients have no mutations in this gene. An infrequent subset shows an early-onset aggressive disorder, denoted juvenile hemochromatosis (JH), which has no linkage to 6p. In this report we describe six patients from three unrelated Italian families, four men and two women, aged 21 to 44 with the typical hemochromatosis phenotype, who are homozygous for the wild type allele at the HFE gene. In two families the disorder is unlinked to 6p; in one family some features of the juvenile form are seen, but linkage to 6p is not excluded. Our results point to genetic forms of hemochromatosis not associated with HFE and raise the problem of whether non-HFE hemochromatosis in Italy is related to the "juvenile" form. They also emphasize the importance of phenotypic as well as genetic diagnosis of HH.

Generation of a transcription map of a 1 Mbase region containing the HFE gene (6p22).

A transcription map was generated of a 1 Mb interval including the HFE gene on 6p22. Thirty-seven unique cDNA fragments were characterised following their retrieval from hybridisation of immobilised YACs to primary pools of cDNAs prepared from RNA of foetal brain, human liver, foetal human liver, placenta, and CaCo2 cell line. All cDNA fragments were positioned on the physical map on the basis of presence in aligned and overlapping YACs and cosmid clones of the region. The isolated cDNAs together with established or published sequence tagged sites (STSs) and markers provided sufficient landmark density to cover approximately 90% of the 1 Mb interval with cosmid clones. The precise localisation of two known genes (NPT1 and RING finger protein) was established. A minimum of 14 additional transcription units has also been integrated. Twenty-eight cDNA fragments showed no similarity with known sequences, but 20 of these detected discrete mRNAs upon northern analysis. Their characterisation is still under investigation. Eleven new polymorphisms were also identified and localised, and the HFE genomic structure was better defined. This integrated transcription map considerably extends a recently published map of the HFE region. It will be useful for the identification of genetic defects mapping to this region and for providing template resources for genomic sequencing.

Cloning of a new gene (FB19) within HLA class I region.

A novel gene (named FB19) has been identified within the HLA class I region at human chromosome 6p21.3. A 4.5-kb cDNA containing a 2820-bp open reading frame for a predicted protein of 940 aa was identified. No homology with known gene was detected at the DNA level, while the predicted protein is characterized by a glycine-rich region followed by a domain of 35 residues that shows high homology with the CAT56 gene, another gene of MHC class I. A 4. 5-kb transcript was detected in several tissues and cell lines, clearly indicating a wide distribution of expression. Once its function is defined, it could be possible to investigate the relationship between the FB19 gene and the several diseases already mapped within the HLA class I region.

GABA (gamma-amino-butyric acid) neurotransmission: identification and fine mapping of the human GABAB receptor gene.

GABA (gamma-amino-butyric acid) receptors are a family of proteins involved in the GABAergic neurotransmission of the mammalian central nervous system (CNS). They have physiological importance and clinical relevance in several diseases. We report the identification, cloning, and fine mapping of the human cDNA for GABAB receptor. A 4.2-Kb cDNA containing an open reading frame for a predicted protein of 960 aa was isolated from a fetal brain cDNA library. It had a strong identity (91.5%) with the rat GABAB receptor (rGB1A) nucleotide sequence, that corresponded to 98.6% identity at the amino acid level. Expression of the GABAB at the transcription level was detected by Northern analysis in all brain areas examined. The GABAB receptor has been mapped to human chromosome 6p21.3 within the HLA class I region close to the HLA-F gene. Susceptibility loci for multiple sclerosis, epilepsy, and schizophrenia have been suggested to map in this region.

Heterogeneity of hemochromatosis in Italy.

BACKGROUND & AIMS: Patients with hemochromatosis show variable phenotype expression. We evaluated the frequency of hemochromatosis gene (HFE) mutations and the contribution of HFE genotype, ancestral haplotype, ethnic background, and additional factors (alcohol intake, hepatitis viruses, and beta-thalassemia trait) to the severity of iron overload in a large series of Italian patients with a hemochromatosis phenotype. METHODS: HFE genotype was studied in 188 patients. Phenotype evaluation was available in 153 men and 20 women and was based mainly on iron removed. HFE genotype was determined by a polymerase chain reaction restriction assay and ancestral haplotype through D6S265 and D6S105 microsatellite analysis. RESULTS: The frequency of C282Y homozygotes was 64%, with a decreasing gradient from north to south. C282Y homozygotes showed more severe iron overload than the other HFE genotypes. In the same group, ancestral haplotype was associated with a more severe phenotype. Additional factors may favor the development of a relatively mild hemochromatosis phenotype in patients nonhomozygous for the C282Y mutation. CONCLUSIONS: Hemochromatosis in Italy is a nonhomogenous disorder in which genetic and acquired factors are involved. In patients with a single or no HFE mutation, further studies will enable a differentiation between true genetic disorders and interactions between genetic and acquired factors.