Predictors of mortality in infants with sclerema presenting to the Centre for Diarrhoeal Disease, Dhaka.

BACKGROUND: Sclerema is an uncommon, life-threatening condition, usually of newborns, with a case-fatality rate ranging from 50 to 100%. Very little is known about factors influencing outcome. AIM: To identify clinical and biochemical predictors associated with fatal outcome of sclerema in infants with diarrhoea. METHODS: Thirty infants with sclerema admitted to the Special Care Unit of the Dhaka Hospital of ICDDR,B with diarrhoea from May 2005 to end April 2006 were studied prospectively. Nine infants who died (30%) were considered to be cases while the 21 who survived constituted the comparison group. Hypothermia, severe malnutrition, septic shock, serum ammonia and CRP levels were considered to be predictors of death. Differences in proportions were compared by the chi(2) test and mean differences were compared using Student's t-test or the Mann-Whitney test, as appropriate. RESULTS: The mean age of the 30 infants was 2.1 months (range 12 d to 8 m). Fatal cases were more likely than survivors to be associated with severe underweight, a positive blood culture and higher serum ammonia and serum CRP levels. After adjusting for possible confounders in logistic regression analysis, the likelihood of death was higher in infants admitted with septic shock or who developed it soon after admission (OR 17.96, 95% CI 1.5-0220.4, p=0.024). CONCLUSIONS: Sclerema is associated with a high fatality rate and scleremic infants with diarrhoea who present with septic shock are at a greater risk of death.

Recent advances in disorders of iron metabolism: mutations, mechanisms and modifiers.

The spectrum of known disorders of iron metabolism has expanded dramatically over the past few years. Identification of HFE, the gene most commonly mutated in patients with hereditary hemochromatosis, has allowed molecular diagnosis and paved the way for identification of other genes, such as TFR2, that are important in non-HFE-associated iron overload. There are clearly several other, unidentified, iron overload disease genes yet to be found. In parallel, our understanding of iron transport has expanded through identification of Fpn1/Ireg1/MTP1, Sfxn1 and DCYTB: Ongoing studies of Friedreich's ataxia, sideroblastic anemia, aceruloplasminemia and neurodegeneration with brain-iron accumulation are clarifying the role for iron in the nervous system. Finally, as the number of known iron metabolic genes increases and their respective functions are ascertained, new opportunities have arisen to identify genetic modifiers of iron homeostasis.

Iron homeostasis: new tales from the crypt.

The enterocyte is a highly specialized cell of the duodenal epithelium that coordinates iron uptake and transport into the body. Until recently, the molecular mechanisms underlying iron absorption and iron homeostasis have remained a mystery. This review focuses on the proteins and regulatory mechanisms known to be present in the enterocyte precursor cell and in the mature enterocyte. The recent cloning of a basolateral iron transporter and investigations into its regulation provide new insights into possible mechanisms for iron transport and homeostasis. The roles of proteins such as iron regulatory proteins, the hereditary hemochromatosis protein (HFE)-transferrin receptor complex, and hephaestin in regulating this transporter and in regulating iron transport across the intestinal epithelium are discussed. A speculative, but testable, model for the maintenance of iron homeostasis, which incorporates the changes in the iron-related proteins associated with the life cycle of the enterocyte as it journeys from the crypt to the tip of the villous is proposed.

Interactions of the ectodomain of HFE with the transferrin receptor are critical for iron homeostasis in cells.

Expression of wild type HFE reduces the ferritin levels of cells in culture. In this report we demonstrate that the predominant hereditary hemochromatosis mutation, C282Y(2) HFE, does not reduce ferritin expression. However, the second mutation, H63D HFE, reduces ferritin expression to a level indistinguishable from cells expressing wild type HFE. Further, two HFE cytoplasmic domain mutations engineered to disrupt potential signal transduction, S335M and Y342C, were functionally indistinguishable from wild type HFE in this assay, as was soluble HFE. These results implicate a role for the interaction of HFE with the transferrin receptor in lowering cellular ferritin levels.

The hereditary hemochromatosis protein, HFE, specifically regulates transferrin-mediated iron uptake in HeLa cells.

HFE is the protein product of the gene mutated in the autosomal recessive disease hereditary hemochromatosis (Feder, J. N., Gnirke, A., Thomas, W., Tsuchihashi, Z., Ruddy, D. A., Basava, A., Dormishian, F., Domingo, R. J., Ellis, M. C., Fullan, A., Hinton, L. M., Jones, N. L., Kimmel, B. E., Kronmal, G. S., Lauer, P., Lee, V. K., Loeb, D. B., Mapa, F. A., McClelland, E., Meyer, N. C., Mintier, G. A., Moeller, N., Moore, T., Morikang, E., Prasss, C. E., Quintana, L., Starnes, S. M., Schatzman, R. C., Brunke, K. J., Drayna, D. T., Risch, N. J., Bacon, B. R., and Wolff, R. R. (1996) Nat. Genet. 13, 399-408). At the cell surface, HFE complexes with transferrin receptor (TfR), increasing the dissociation constant of transferrin (Tf) for its receptor 10-fold (Gross, C. N., Irrinki, A., Feder, J. N., and Enns, C. A. (1998) J. Biol. Chem. 273, 22068-22074; Feder, J. N., Penny, D. M., Irrinki, A., Lee, V. K., Lebron, J. A., Watson, N. , Tsuchihashi, Z., Sigal, E., Bjorkman, P. J., and Schatzman, R. C. (1998) Proc. Natl. Acad. Sci. U S A 95, 1472-1477). HFE does not remain at the cell surface, but traffics with TfR to Tf-positive internal compartments (Gross et al., 1998). Using a HeLa cell line in which the expression of HFE is controlled by tetracycline, we show that the expression of HFE reduces 55Fe uptake from Tf by 33% but does not affect the endocytic or exocytic rates of TfR cycling. Therefore, HFE appears to reduce cellular acquisition of iron from Tf within endocytic compartments. HFE specifically reduces iron uptake from Tf, as non-Tf-mediated iron uptake from Fe-nitrilotriacetic acid is not altered. These results explain the decreased ferritin levels seen in our HeLa cell system and demonstrate the specific control of HFE over the Tf-mediated pathway of iron uptake. These results also have implications for the understanding of cellular iron homeostasis in organs such as the liver, pancreas, heart, and spleen that are iron loaded in hereditary hemochromatotic individuals lacking functional HFE.