Mechanisms of HFE-induced regulation of iron homeostasis: Insights from the W81A HFE mutation

The mechanisms by which the hereditary hemochromatosis protein, HFE, decreases transferrin-mediated iron uptake were examined. Coimmunoprecipitation studies using solubilized cell extracts demonstrated that transferrin (Tf) competed with HFE for binding to the transferrin receptor (TfR) similar to previous in vitro studies using soluble truncated forms of HFE and the TfR. At concentrations of Tf approaching those found in the blood, no differences in Tf binding to cells were detected, which is consistent with the lower binding constant of HFE for TfR versus Tf. However, cells expressing HFE still showed a decrease in Tf-mediated iron uptake at concentrations of Tf sufficient to dissociate HFE from the TfR. These results indicate that the association of HFE with TfR is not essential for its ability to lower intracellular iron stores. To test the effect of HFE on lowering intracellular iron levels independently of its association with TfR, a mutated HFE (fW81AHFE) that shows greatly reduced affinity for the TfR was transfected into tetracycline-controlled transactivator HeLa cells. HeLa cells expressing fW81AHFE behaved in a similar manner to cells expressing wild-type HFE with respect to decreased intracellular iron levels measured by iron regulatory protein gel-shift assays and ferritin levels. The results indicate that HFE can lower intracellular iron levels independently of its interaction with the TfR.     

Cantú Syndrome Resulting from Activating Mutation in the KCNJ8 Gene

ATP‐sensitive potassium (K_ATP) channels, composed of inward‐rectifying potassium channel subunits (Kir6.1 and Kir6.2, encoded by KCNJ8 and KCNJ11, respectively) and regulatory sulfonylurea receptor (SUR1 and SUR2, encoded by ABCC8 and ABCC9, respectively), couple metabolism to excitability in multiple tissues. Mutations in ABCC9 cause Cantú syndrome (CS), a distinct multiorgan disease, potentially via enhanced K_ATP channel activity. We screened KCNJ8 in an ABCC9 mutation‐negative patient who also exhibited clinical hallmarks of CS (hypertrichosis, macrosomia, macrocephaly, coarse facial appearance, cardiomegaly, and skeletal abnormalities). We identified a de novo missense mutation encoding Kir6.1[p.Cys176Ser] in the patient. Kir6.1[p.Cys176Ser] channels exhibited markedly higher activity than wild‐type channels, as a result of reduced ATP sensitivity, whether coexpressed with SUR1 or SUR2A subunits. Our results identify a novel causal gene in CS, but also demonstrate that the cardinal features of the disease result from gain of K_ATP channel function, not from a Kir6‐independent SUR2 function.     

Common variation at 6p21.31 (BAK1) influences the risk of chronic lymphocytic leukemia

We performed a meta-analysis of 3 genome-wide association studies to identify additional common variants influencing chronic lymphocytic leukemia (CLL) risk. The discovery phase was composed of genome-wide association study data from 1121 cases and 3745 controls. Replication analysis was performed in 861 cases and 2033 controls. We identified a novel CLL risk locus at 6p21.33 (rs210142; intronic to the BAK1 gene, BCL2 antagonist killer 1; P = 9.47 × 10(-16)). A strong relationship between risk genotype and reduced BAK1 expression was shown in lymphoblastoid cell lines. This finding provides additional support for polygenic inheritance to CLL and provides further insight into the biologic basis of disease development.     

Genetic Variants in Toll-Like Receptor 2 (TLR2), TLR4, TLR9, and FCγ Receptor II Are Associated with Antibody Response to Quadrivalent Meningococcal Conjugate Vaccine in HIV-Infected Youth

This study examined the association of host genetic variants with the antibody response to the quadrivalent meningococcal conjugate vaccine (MCV4) in HIV-infected youth. Genetic variants associated with severity of meningococcal disease, including the IgG Fc receptor (FCγRII)-A484T, interleukin-10 (IL-10)-A1082G, -C819T, and -C627A, IL-4-C589T, mannose binding lectin-2 (MBL2)-A/O, -H/L, -P/Q, and -X/Y, toll-like receptor 2 (TLR2)-G2408A, TLR4-A12874G and -C13174T, and TLR9-T1237C and -T1486C were determined by real-time PCR (RT-PCR) for 271 HIV-infected subjects (median, 17 years). Response was defined as a ≥4-fold increase from entry in bactericidal antibody titers to each serogroup. Generalized estimating equation (GEE) models were used to evaluate the association of allelic variants with the immunologic response to all serogroups within each subject with and without adjusting for CD4 percentage and HIV viral load. At week 4, but not after, subjects with TLR2-2408-G/A versus -G/G genotypes and the TLR4-12874-A/A genotype were more likely to achieve a ≥4-fold increase overall in the four serogroups (unadjusted P of 0.006 and adjusted P of 0.008 and unadjusted P of 0.008 and adjusted P of 0.019, respectively). At week 28, the TLR9-1237 T allele was associated with enhanced antibody response (T allele versus C/C, unadjusted P of 0.014 and adjusted P of 0.009), which was maintained at week 72 (unadjusted and adjusted P of 0.008). At week 72, the FcγRII-131Arg allotype was associated with a ≥4-fold increase in antibody titer versus those with His/His (unadjusted P of 0.009; adjusted P of <0.001). These findings suggest that for HIV-infected youth, the initial antibody response to MCV4 is associated with variants in TLR2 and TLR4 while the long-term response is associated with genetic polymorphisms in TLR9 and FcγRIIa.     

Atypical glomerulopathy associated with the cblE inborn error of vitamin B12 metabolism

Background

The cblE disorder is an inherited disorder of vitamin B₁₂ metabolism that results in elevated levels of homocysteine and decreased methionine in body fluids. Renal complications have been reported in patients with cblC disease, but not in those with cblE disease. The renal complications of cblC disease include thrombotic microangiopathy (TMA), neonatal hemolytic uremic syndrome, chronic renal failure, tubulointerstitial nephritis and proximal renal tubular acidosis. Previously, we reported a patient with cblC disease who had an atypical glomerulopathy that manifested with proteinuria and progressive renal insufficiency.

Case-Diagnosis/Treatment

Studies were done on cultured fibroblasts. Renal biopsy tissue was examined by light and electron microscopy. There was decreased incorporation of labeled methyltetrahydrofolate and decreased synthesis of methylcobalamin. Complementation analysis placed the patient into the cblE complementation group. The findings from the histological and ultrastructural studies of renal biopsy were similar, but not identical, to those of idiopathic membranoproliferative glomerulonephritis (MPGN) and overlapped with those of TMA.

Conclusions

We describe a patient with cblE disease who had an atypical glomerulopathy similar to MPGN. Additional findings included migraine headaches, hypothyroidism and livedo reticularis.     

Outpatient burn data: An untapped resource

Introduction

The National Burn Repository (NBR) currently only contains inpatient data from participating United States burn centres. However, the majority of the patients treated in burn centres are managed as outpatients. Unfortunately, this significant demographic is not represented in the NBR annual report. The purpose of this study is to compare the difference in aetiology and demographics between inpatient and outpatient burn patients. In addition, the workload demands for data entry of inpatient and outpatient records in the burn registry will be compared.

Methods

Outpatient and inpatient burn data at an American Burn Association-Verified Burn Center were prospectively collected during fiscal year 2008. Data collected included age, burn size and aetiology of burn. Aetiology was also stratified by age group. Inpatient data were compared with outpatient data with Fisher's exact test. The amount of time taken to enter inpatients’ and outpatients’ data parameters in the TRACS v5.0 database was also recorded.

Results

Data were collected for 241 inpatients and for 543 outpatients during fiscal year 2008. No significant differences in gender or race were found between the two groups. When comparing demographics, outpatients tended to be younger (26 ± 19 years vs. 32 ± 22 years, p = 0.01) with a smaller burn size (2.5 ± 7% vs. 6.8 ± 12%, p < 0.001) and a lower frequency of full-thickness burns (17% vs. 41%, p < 0.001).Of the patients managed as an outpatient, a total 29.7% were eventually admitted to the hospital. Just over half of those (16.7%) initially managed in the outpatient setting were admitted for a planned surgical procedure. The other 13% were admitted for pain control and wound-care issues.Injury was more likely to be caused by flame in inpatients (p < 0.001). Scald injuries were more common in the outpatient setting (34% vs. 27%), but this difference did not reach statistical significance (p = 0.079). Outpatients were more likely to be injured with a contact burn (p < 0.0001). Outpatient injury was more likely to be work-related than inpatient injury (p = 0.0497), but less likely to be related to recreational activity (p = 0.006) or arson/abuse/assault (p = 0.0158). An experienced TRACSv5.0 user required 11 ± 0.6 min to enter an inpatient record and 6 ± 0.6 min to enter an outpatient record in the system (p = 0.002).

Conclusions

Inpatient injury is more likely to be caused by flame, whereas outpatient injury is more likely to be caused by scald and contact burns. Work-related burn is more likely to be treated in the outpatient setting. Outpatient burn data also take less time to enter. Since significant differences in aetiology exist, outpatient data should be reported separately from inpatient data in order to understand the full spectrum of burn aetiology. The NBR and other registries should be modified to track outpatient burn data and outcomes.