Matriptase-2 is a transmembrane serine protease that negatively regulates hepcidin expression by cleaving membrane-bound hemojuvelin. Matriptase-2 has a complex ectodomain, including a C-terminal ...serine protease domain and its activation requires an autocatalytic cleavage. Matriptase-2 mutations have been reported in several patients with iron-refractory iron deficiency anemia. Here we describe a patient with 2 missense mutations in the second class A low-density lipoprotein receptor (LDLRA) domain. Functional studies of these 2 mutations and of a previously reported mutation in the second C1r/C1s, urchin embryonic growth factor and bone morphogenetic protein 1 (CUB) domain were performed. Transfection of mutant cDNAs showed that membrane targeting of the 2 LDLRA mutants was impaired, with Golgi retention of the variants. The activating cleavage was absent for the LDLRA mutants and reduced for the CUB mutant. All 3 mutated proteins were still able to physically interact with hemojuvelin but only partially repressed hepcidin expression compared with wild-type matriptase-2. Our results underline the importance of LDLRA and CUB domains of matriptase-2.
Objectives. To investigate the prevalence of the microsatellite instability related to mismatch repair (MMR) gene defects using a panel of six microsatellite markers, as recommended by a recent ...workshop on microsatellite instability in colon cancer, because it is still unclear whether abnormalities in DNA MMR genes are involved in transitional cell carcinoma (TCC) of the bladder.
Methods. Three mononucleotide repeats (BAT26, TGFβRII, and BAX) were studied in 33 TCC samples and in four bladder cancer cell lines. Three dinucleotide repeats (D2S123, D5S346, and D17S250) were studied in 21 of these 33 TCC samples.
Results. No alteration was detected either in the 33 TCC samples analyzed or in the four bladder cancer cell lines (T24, J82, 647V, and 1207) studied. A difference between normal and tumor DNA was observed in only 1 of 21 tumor samples for D17S250.
Conclusions. These data indicate that microsatellite instability is very uncommon in TCC of the bladder.
ABSTRACT
Iron‐refractory iron‐deficiency anemia (IRIDA) is a rare autosomal‐recessive disorder characterized by hypochromic microcytic anemia, low transferrin saturation, and inappropriate high ...levels of the iron hormone hepcidin. The disease is caused by variants in the transmembrane protease serine 6 (TMPRSS6) gene that encodes the type II serine protease matriptase‐2, a negative regulator of hepcidin transcription. Sequencing analysis of the TMPRSS6 gene in 21 new IRIDA patients from 16 families with different ethnic origin reveal 17 novel mutations, including the most frequent mutation in Southern Italy (p.W590R). Eight missense mutations were analyzed in vitro. All but the p.T287N variant impair matriptase‐2 autoproteotylic activation, decrease the ability to cleave membrane HJV and inhibit the HJV‐dependent hepcidin activation. Genotype–phenotype studies in IRIDA patients have been so far limited due to the relatively low number of described patients. Our genotype–phenotype correlation analysis demonstrates that patients carrying two nonsense mutations present a more severe anemia and microcytosis and higher hepcidin levels than the other patients. We confirm that TMPRSS6 mutations are spread along the gene and that mechanistically they fully or partially abrogate hepcidin inhibition. Genotyping IRIDA patients help in predicting IRIDA severity and may be useful for predicting response to iron treatment.
Iron‐refractory iron‐deficiency anemia (IRIDA) is a rare autosomal‐recessive disorder caused by TMPRSS6 mutations and characterized by hypochromic microcytic anemia, low transferrin saturation, and inappropriate high levels of the iron hormone hepcidin. We report 17 novel mutations in 21 new IRIDA patients. Functional studies indicate that TMPRSS6 mutations fully or partially abrogate hepcidin inhibition. Genotyping IRIDA patients help in predicting IRIDA severity and may be useful for predicting response to iron treatment.
DMT1 mediates the pH-dependent uptake of Fe2+ from the diet in duodenal enterocytes and in most other cells. It transfers iron from the endosomes to the cytosol following the uptake of the ...transferrintransferrin receptor complex. DMT1 mutations are responsible for severe hypochromic microcytic anemia in rodents and in 2 human patients described recently. We report a compound heterozygote for 2 new DMT1 mutations, associated with microcytic anemia from birth and progressive liver iron overload. The first mutation is a GTG deletion in exon 5, leading to the V114 in-frame deletion in transmembrane domain 2, and the second is a G → T substitution in exon 8 leading to the G212V replacement in transmembrane domain 5. Together with the 2 previously reported cases, this patient defines a new syndrome of congenital microcytic hypochromic anemia, poorly responsive to oral iron treatment, with liver iron overload associated paradoxically with normal to moderately elevated serum ferritin levels.
OBJECTIVE:--The aim of the present work was to determine, in a cohort of men and women, whether ferritin and transferrin were associated with glucose metabolism and whether they were predictive of ...the onset of hyperglycemia (impaired fasting glycemia or type 2 diabetes) after 3 years of follow-up. RESEARCH DESIGN AND METHODS--Among 4,501 subjects from the French Data from an Epidemiological Study on the Insulin Resistance Syndrome (DESIR) cohort, 1,277 subjects (644 men and 633 women) were randomly selected for the analysis of iron biomarkers at baseline and at 3 years. In addition, to determine whether these parameters were relevant to pathological changes, all 231 subjects normoglycemic at baseline and hyperglycemic 3 years later were analyzed for iron biomarkers. RESULTS:--At baseline, plasma ferritin concentrations were positively correlated with fasting insulin and fasting glucose in the 1,277 subjects. Although transferrin and ferritin were negatively correlated, transferrin was also positively correlated with fasting insulinemia. Baseline ferritin concentration was an independent predictor of an increase in insulin concentration over a 3-year period (P = 0.002). Further, baseline ferritin and transferrin were independently associated with the onset of hyperglycemia over a 3-year period in the whole population (P < 0.001 for both) and in each sex. CONCLUSIONS:--Although negatively correlated, both transferrin and ferritin were positively associated with the onset of abnormalities in glucose metabolism in a prospective study. These results further support the hypothesis of a causative role of iron metabolism in the onset of insulin resistance and type 2 diabetes.
STEAP3/TSAP6 encodes a ferrireductase that is involved in the acquisition of iron by developing erythroblasts and steap3/tsap6 null-mice display severe microcytic anemia. We report a family in which ...3 siblings born to healthy parents display transfusion-dependent hypochromic anemia. A nonsense STEAP3/TSAP6 was identified in the siblings at the heterozygous state. This mutation was inherited from their father while no mutation was found in their mother. A large variability of expression was found between normal alleles in a control population, confirming a previous report that STEAP3/TSAPS6 is an expressed quantitative trait locus (e-QTL). Determination of the relative allele expression showed that the “normal” allele was expressed at a significantly higher level in the father than in the affected siblings relative to the shared mutated allele. The blood level of STEAP3/TSAP6 mRNA was severely reduced in the siblings, while both parents were in the lower range of normal controls. The STEAP3/TSAP6 protein was also reduced in lymphocytic cell lines from the patients. Collectively, our data support the hypothesis that STEAP3/TSAP6 deficiency leads to severe anemia in the affected siblings and results from the combination of a mutated allele inherited from their father and a weakly expressed allele inherited from their mother.
Unexplained hyperferritinemia is a common clinical finding, even in asymptomatic persons. When early onset bilateral cataracts are also present, the hereditary hyperferritinemia-cataract syndrome ...(HHCS), because of heterozygous point mutation in the L ferritin iron-responsive element (IRE) sequence, can be suspected. We sequenced the L ferritin exon 1 in 52 DNA samples from patients referred to us for molecular diagnosis of HHCS. We identified 24 samples with a point mutation/deletion in the IRE. For the 28 samples in which no IRE mutation was present, we also genotyped HFE mutations and sequenced both H ferritin and ferroportin genes. We found an increased frequency of His63Asp heterozygotes (12 of 28) but no H ferritin mutations. We identified 3 new ferroportin mutations, producing, respectively, Asp157Gly, Gln182His, and Gly323Val amino acid replacements, suggesting that these patients have dominant type 4 hemochromatosis. This study demonstrates that both L ferritin IRE and ferroportin mutations can account for isolated hyperferritinemia. The presence of cataract does not permit the unambiguous identification of patients with HHCS, although the existence of a family history of cataract was only encountered in these patients. This raises the intriguing possibility that lens ferritin accumulation might be a factor contributing to age-related cataract in the general population. Additional causes of isolated hyperferritinemia remain to be identified.
Objective To assess the diagnostic and prognostic performance of a noninvasive FGFR3 mutation analysis. After transurethral resection (TUR) of noninvasive bladder transitional cell carcinoma (B-TCC), ...recurrence occurs in 70% of patients, thus justifying cystoscopic surveillance. Materials and Methods A prospective multicenter study was carried out with a 2-year follow-up of patients with superficial B-TCC. Urine samples were collected before TUR and then before each cystoscopy during follow-up. Screening for the most prevalent FGFR3 mutations was done using urinary cells. The prognostic significance of an FGFR3 mutation at the time of the initial diagnosis was determined. The performance of the test in diagnosing and/or predicting recurrence during follow-up was assessed by calculating sensitivity and specificity. Results Of 191 patients studied, 74 (39%) had a positive analysis before TUR ( FGFR3 mutation group). The presence of an FGFR3 mutation at the time of diagnosis was associated with a shorter time to recurrence ( P = .02). During follow-up, 68 patients from the FGFR3 mutation group were evaluated. FGFR3 mutation analysis showed a sensitivity of 0.73 and a specificity of 0.87 when compared with the results of cystoscopy. A positive urine test was predictive of recurrence either at the time of the positive result or later during the 2-year follow-up, with a sensitivity of 0.70 and a specificity of 0.87. Conclusion Among patients with an FGFR3 mutation in the initial tumor, a noninvasive urine test during follow-up can be valuable in diagnosing or predicting subsequent recurrence.
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