Mutations leading to abrogation of matriptase-2 proteolytic activity in humans are associated with an iron-refractory iron deficiency anemia (IRIDA) due to elevated hepcidin levels. Here we describe two novel heterozygous mutations within the matriptase-2 (TMPRSS6) gene of monozygotic twin girls exhibiting an IRIDA phenotype. The first is the frameshift mutation (P686fs) caused by the insertion of the four nucleotides CCCC in exon 16 (2172_2173insCCCC) that is predicted to terminate translation before the catalytic serine. The second mutation is the di-nucleotide substitution c.467C>A and c.468C>T in exon 3 that causes the missense mutation A118D in the SEA domain of the extracellular stem region of matriptase-2. Functional analysis of both variant matriptase-2 proteases has revealed that they lead to ineffective suppression of hepcidin transcription. We also demonstrate that the A118D SEA domain mutation causes an intra-molecular structural imbalance that impairs matriptase-2 activation. Collectively, these results extend the pattern of TMPRSS6 mutations associated with IRIDA and functionally demonstrate that mutations affecting protease regions other than the catalytic domain may have a profound impact in the regulatory role of matriptase-2 during iron deficiency.

This study aimed at assessing the relationship between thrombosis, hyperhomocysteinemia and vitamin B12 deficiency using a case-control study carried out in 326 patients with thrombosis (case group) and 351 patients from the same hospital (control group). Apart from the classic risk factors, a number of hematological variables were evaluated, including serum vitamin B12 (B12), red cell folate (RCF), and serum homocysteine (Hcy). An evaluation of serum methylmalonic acid (MMA) and a clinical study were carried out to investigate B12 pathology. Results of univariate analysis demonstrated decreased B12 levels in thrombosis (Student's t test, p < 0.0001). Vitamin B12 below 200 pmol/l (LB200) or below 150 pmol/l (LB150), and red cell folate below 600 nmol/l were found in 17.2, 8.6, and 2.2% of cases with thromboembolism, respectively. An increase in Hcy was detected in 86 cases with thrombosis (26.3%). An abnormality in vitamin B12 and/or renal function was found in 80% of cases with hyperHcy and thrombosis. The MMA increase demonstrated that vitamin B12 deficiency was present in these patients with low levels of vitamin B12 in serum, and the MMA levels were in concordance with Hcy levels. The clinical study revealed B12 malabsorption in most cases with LB200. Multivariate analysis showed that serum vitamin B12 (RR 0.998, CI 0.997-0.999) was moderately related to thromboembolism. The results indicated that vitamin B12 deficiency was common among patients with hyperhomocysteinemia and thrombosis. Moreover, HyperHcy was caused by vitamin B12 deficiency and/or chronic renal failure in most patients with thrombosis. As the main cause of vitamin B12 deficiency was vitamin malabsorption, parenteral vitamin B12 with or without folic acid should be administered for the treatment of this condition. However, it remains to be demonstrated whether this treatment approach prevents recurrent thromboses in patients with vitamin B12 deficiency and thrombosis, as suggested by some case reports.

Hydrops fetalis is rarely caused by congenital dyserythropoietic anemia (CDA). We report a patient with hydrops fetalis as a result of severe anemia. This patient needed intrauterine transfusions from 21 weeks of gestation until birth. The hematologic study showed an atypical CDA (hydrops fetalis-associated CDA) characterized by features resembling CDA type II, but negative acidified serum lysis test (HEMPAS negative). The patient was regularly transfused for a year, after which an allogeneic bone marrow transplantation (BMT) from an HLA-identical sibling was successfully carried out. His actual hemoglobin is 127 g/L, and he has not received transfusions for more than a year. In conclusion, intrauterine transfusions and BMT could cure an otherwise lethal atypical CDA. (Blood. 2002;100:356-358)

Plasma holotranscobalamin (holoTC) transports active cobalamin. Decreased levels of holoTC have been considered to be the earliest marker of cobalamin (Cbl) deficiency. In this work, holoTC was evaluated in low or borderline serum Cbl (LB12) and a concordance analysis was carried out with methylmalonic acid (MMA) and homocysteine (Hcy). Levels of Cbl, holoTC, MMA, and Hcy were investigated in a reference group in 106 patients with LB12 (≤200 pmol/l) and in 27 with folate deficiency (FOL). HoloTC levels were evaluated by an automated immunoassay (Active B12, Abbott Lab, Abbott Park, IL, USA). Lower levels of holoTC were observed in both LB12 and FOL groups (reference group vs LB12; p < 0.0001. Reference group vs FOL; p = 0.002). HoloTC levels were lower in LB12 than in FOL (p = 0.001). In LB12, concordance between Hcy and MMA was 82.1 % (chi-square test, p < 0.001; Kappa Index, 0.64, p < 0.0001). Concordance between Hcy and holoTC was 62 % (chi-square test, p = 0.006; Kappa index, 0.245, p = 0.006). Concordance between holoTC and MMA was 55.6 % (p = 0.233). Some cases with LB12 and elevated MMA did not show decreased holoTC. By contrast, MMA and Hcy were not increased in some patients with low holoTC and LB12. In conclusion, levels of holoTC were decreased in LB12 and FOL. In LB12 patients, holoTC concordance with MMA was poor. MMA/Hcy levels were not increased in a significant number of subjects with LB12 and low holoTC. This profile was found in iron deficiency. The significance of these changes remains to be clarified.

In patients with repeatedly high B12 levels, ICs were detected in approximately 25% of samples. Precipitation with PEG is an easy method to confirm the presence of ICs and to evaluate serum vitamin B12 levels in these patients.